S

Source edition 1965. Please read the Introduction to find out about this dictionary and our plans for it. Caution many entries have not been updated since the 1965 edition.
Greek symbols may not appear correctly in some browsers. For example a gamma may appear as γ.

sabot: A device fitted around or in back of a projectile in a gun barrel or launching tube to support or protect the projectile or to prevent the escape of gas ahead of it.; The sabot separates from the projectile after launching.
Sagitta (abbr Sge, Sgte): See constellation.
Sagittarius (abbr Sgr, Sgtr): See constellation.
salvo launch: Act of launching two or more rockets simultaneously.
sample: In statistics, a group of observations selected from a statistical population by a set procedure. See random sample.; Samples may be taken at random or systematically. The sample is taken in an attempt to estimate the population.
sandwich: Of sandwich construction, as in sandwich panel, sandwich skin , etc.
sandwich construction: A type of construction in which two sheets, sides, or plates are separated by a core of stiffening material, generally lightweight. See honeycomb core.
Sarah: (From search and rescue and homing). A radio homing device originally designed for personnel rescue and now used in spacecraft recovery operations at sea.
saros: The eclipse cycle of about 18 years, almost the same length as 223 synodical months. See lunar cycle.; At the end of each saros the sun, moon, and line of nodes return to approximately the same relative positions and another series of eclipses begins, closely resembling the series just completed.
satellite: 1. An attendant body that revolves about another body, the primary; especially in the solar system, a secondary body, or moon, that revolves about a planet. See table XIII for a list of satellites of the solar system.; 2. A manmade object that revolves about a spatial body, such as Explorer I orbiting about the earth. See spacecraft, Table XIV.; 3. Such a body intended and designed for orbiting, as distinguished from a companion body that may incidentally also orbit, as in the observer actually saw the orbiting rocket rather than the satellite.; 4. An object not yet placed in orbit, but designed or expected to be launched into an orbit.
satelloid: A vehicle that revolves about the earth or other body, but at such altitudes as to require sustaining thrust to balance drag.
saturation-adiabatic lapse rate: A special case of process lapse rate, defined as the rate of decrease of temperature with height of an air parcel lifted in a saturation-adiabatic process through an atmosphere in hydrostatic equilibrium. Also called moist-adiabatic lapse rate.; Owing to the release of latent heat, this lapse rate is less than the dry-adiabatic lapse rate, and the differential equation representing the process must be integrated numerically. Wet-bulb potential temperature is constant with height in an atmosphere with this lapse rate.
saturation vapor pressure: 1. The vapor pressure of a system, at a given temperature, wherein the vapor of a substance is in equilibrium with a plane surface of the pure liquid or solid phase of that substance; that is, the vapor pressure of a system that has attained saturation but not supersaturation. Compare equilibrium vapor pressure, vapor tension.; The saturation vapor pressure of any pure substance, with respect to a specified parent phase, is an intrinsic property of that substance and is a function of temperature alone (see Clapeyron-Clausius equation).; 2. = equilibrium vapor pressure.
Saturn: See planet, table.
saturnographic: Referring to positions on Saturn measured in latitude from Saturn's equator and in longitude from a reference meridian.
S-band: A frequency band used in radar extending approximately from 1.55 to 5.2 kilomegacycles per second.
scalar: Any physical quantity whose field can be described by a single numerical value at each point in space.; A scalar quantity is distinguished from a vector quantity by the fact that a scalar quantity possesses only magnitude, whereas a vector quantity possesses both magnitude and direction.
scalar acceleration: The square root of the sum of the squares of three orthogonal components of an acceleration.
scalar product: A scalar equal to the product of the magnitudes of any two vectors and the cosine of the angle θ between their positive directions. Also called dot product, direct product, inner product. See vector product.; For two vectors A and B, the scalar product is most commonly written A ^. B, read A dot B, and occasionally as (AB). If the vectors A and B have the components A_x, B_x, A_y, B_y, and A_z, B_z along rectangular Cartesian, x, y, and z axes, respectively, then A ^. B = A_xB_x + A_yB_y + A_zB_z = |A||B|cosθ = AB cosθ If a scalar product is zero, one of the vectors is zero or else the two are perpendicular.
scalar velocity: The square root of the sum of the squares of three orthogonal components of a velocity.
scale effect: Any variation in the nature of the flow and in the force coefficients associated with a change in value of the Reynolds number, i.e., caused by change is size without change in shape.
scale height (symbol h, h_s): A measure of the relationship between density and temperature of any point in an atmosphere; the thickness of a homogeneous atmosphere which would give the observed temperature: h = kT/mg = R*T/Mg where k is the Boltzmann constant; T is the absolute temperature; m and M are the mean molecular mass and weight, respectively, of the layer; g is the acceleration of gravity; and R* is the universal gas constant. Compare virtual height.
scale model: A model of a different size from its prototype and having dimensions in some constant ratio to the dimensions of the prototype, especially such a model of smaller size than its prototype.
scale of 10 counter = decade counter.
scaler: A device that produces an output pulse whenever a prescribed number of input pulses have been received. Also called scaling circuit.; The number of input pulses per output pulse of a scaler is termed the scaling factor. A binary scaler is a scaler whose scaling factor is 2. A decade scaler is a scaler whose scaling factor is 10.
scaling circuit = scaler.
scaling factor: See scalar, note.
scanner: A radar mechanism incorporating a rotatable antenna, or radiator, motor drives, mounting, etc., for directing a searching radar beam through space and imparting target information to an indicator. See parabolic reflector.
scanning: In radar, the motion of the radar antenna assembly when searching for targets.; Scanning usually follows a systematic pattern involving one or more of the following: (1) In horizontal scanning (or searchlighting), the antenna is continuously rotated in azimuth around the horizon or in a sector (sector scanning); used to generate plan-position-indicator-scope displays. (b) Vertical scanning is accomplished by holding the azimuth constant but varying the elevation angle of the antenna; used in height-finding radars to generate the relative-height-indicator-scope display. (c) For conical scanning, a somewhat offcenter radiating element is rotated while its parabolic reflectors fixed in position so that the radiated beam generates a concially shaped volume with the antenna at the apex; used to determine accurate bearing and elevation angle of targets and employed in automatic tracking radars. (d) In helical scanning (or spiral scanning) the azimuth and elevation angle of the antenna are constantly varied so that at a given distance from the radar the radiated beam generates the surface of a hemisphere; used for radio direction finding, in certain types of search radars, and in tracking radars to search areas for targets.
scaphandre = full pressure suit.
scatter: 1. = scattering.; 2. The relative dispersion of points on a graph, especially with respect to a mean value, or any curve used to represent the points. See dispersion.; 3. To accomplish scattering.
scatter angle: The angle between any given ray of scattered radiation and the incident ray. See relative scatter intensity, scattering.; Convention varies as to whether this angle is measured with respect to the direction in which the incident radiation was advancing or with respect to the direction from scatterer to radiation source.
scatter communication: See scatter propagation, note.
scattered power = received power.
scatterer = scattering particle.
scattering: The process by which small particles suspended in a medium of a different index of refraction diffuse a portion of the incident radiation in all directions. In scattering, no energy transformation results, only a change in the spatial distribution of the radiation. Also called scatter.; Along with absorption, scattering is a major cause of the attenuation of radiation by the atmosphere. Scattering varies as a function of the ratio of the particle diameter to the wavelength of the radiation. When this ratio is less than about one-tenth, Rayleigh scattering occurs in which the scattering coefficient varies inversely as the fourth power of the wavelength. At larger values of the ratio of particle diameter to wavelength, the scattering varies in a complex fashion described by the Mie theory; at a ratio of the order of 10, the laws of geometric optics begin to apply.
scattering area coefficient: The dimensionless ratio of the scattering cross section to the geometric cross section of a scattering particle. Also called scattering area ratio.
scattering area ratio = scattering area coefficient.
scattering coefficient: A measure of the attenuation due to scattering of radiation as it traverses a medium containing scattering particles. Also called total scattering coefficient.
scattering cross section: The hypothetical area normal to the incident radiation that would geometrically intercept the total amount of radiation actually scattered by a scattering particle. It is also defined, equivalently, as the cross-section area of an isotropic scatterer (a sphere) which would scatter the same amount of radiation as the actual amount. Also called extinction cross section, effective area.
scattering function: The intensity of scattered radiation in a given direction per lumen of flux incident upon the scattering material.
scattering gage = scattering-type pressure gage.
scattering loss: That part of the transmission loss which is due to scattering within the medium or due to roughness of the reflecting surface.
scattering particle: The small particles responsible for scattering.
scattering power: In radar terminology, the ratio of the total power scattered by a target to the power in the incident wave, independent of the direction of scattering. The scattering power measures the loss of energy by absorption in the scatterers. Also called total scattering cross section. Compare radar reflectivity.
scattering-type pressure gage: An ionization gage in which measurement is made of the electrons scattered by collision of the gas molecules with the electrons from a p-particle emitter.
scatter propagation: Specifically, the long-range propagation of radio signals by scattering due to index of refraction inhomogeneities in the lower atmosphere. Also called tropospheric propagation.; Recognition of this process and the development of specialized equipment (basically, more powerful transmitters and sensitive receivers) has greatly increased the range of VHF and UHF communication. The over-all technique is known as scatter communication.
schlieren: (German, streaks, striae).; 1. Regions of different density in a fluid, especially as shown by special apparatus.; 2. Pertaining to a method or apparatus for visualizing or photographing regions of varying density in a field of flow. See schlieren photography, scintillation.; Used in compounds, such as schlieren lens, schlieren method, schlieren photograph, etc.
schlieren method: See schlieren.
schlieren photography: A method of photography for flow patterns that take advantage of the fact that light passing through a density gradient in a gas is refracted as though it were passing through a prism. Compare shadowgraph.
Schneider index: A composite weighted index of pulse and blood-pressure response to exercise, utilized as a test of physical efficiency.
Schuler pendulum: A hypothetical pendulum with a period of 84 minutes.; A simulated Schuler pendulum carried in a vehicle moving in the earth's gravitational field would always indicate the true vertical.
Schuler tuning: Adjusting a system performing the function of a pendulum so that is has a period of 84 minutes. See Schuler pendulum.
Schumann-Runge bands: See absorption band.
Schumann-Runge continuum: See absorption band.
scintillating counter = scintillation counter.
scintillation: 1. Generic term for rapid variations in apparent position, brightness, or color of a distant luminous object viewed through the atmosphere.; If the object lies outside the earth's atmosphere, as in the case of stars and planets, the phenomenon is termed astronomical scintillation; if the luminous source lies within the atmosphere, the phenomenon is termed terrestrial scintillation. As one of the three principal factors governing astronomical seeing, scintillation is defined as variations in luminance only. It is clearly established that almost all scintillation effects are caused by anomalous refraction occurring in rather small parcels or strata of air, schlieren, whose temperatures and hence densities differ slightly from those of their surroundings. Normal wind motions transporting such schlieren across the observer's line of sight produce the irregular fluctuations characteristic of scintillation. Scintillation effects are always much more pronounced near the horizon than near the zenith. Parcels of the order of only centimeters to decimeters are believed to produce most of the scintillatory irregularities in the atmosphere.; 2. A flash of light produced in a phosphor by an ionizing event. See scintillation counter. 3. On a radar display, a rapid apparent displacement of the target from its mean position. Also called target glint or wander.; This includes but is not limited to shift of effective reflection point on the target.
scintillation counter: The combination of phosphor, photomultiplier tube, and associated circuits for counting scintillations, sense 2. Also called scintillating counter.
scintillation meter = scintillometer.
scintillometer: A type of photoelectric photometer used in a method of determining high altitude winds on the assumption that stellar scintillation is caused by atmospheric inhomogeneities ( schlieren) being carried along by the wind near tropopause level. Also called scintillation meter.
Scl, Scul: International Astronomical Union abbreviations for Sculptor. See constellation.
Sco, Scor: International Astronomical Union abbreviations for Scorpius. See constellation.
scope: The general abbreviation for an instrument of viewing, such as telescope, microscope, and oscilloscope. In radar installations, the cathode-ray oscilloscope indicators are commonly referred to as scopes or radarscopes.; Because of possible ambiguity this term should be avoided in formal reports.
Scor: International Astronomical Union abbreviation for Scorpius. See constellation.
Scorpius (abbr Sco, Scor): See constellation.
scotopic vision: Vision associated with levels of illumination below approximately 0.01 foot-lambert, effective primarily in the detection of movement and low luminous intensities. Compare photopic vision. Also called parafoveal vision.; Scotopic vision is associated with rod function.
screaming: A form of combustion instability, especially in a liquid-propellant rocket engine, of relatively high frequency and characterized by a high-pitched noise.
screeching: A form of combustion instability, especially in an afterburner, of relatively high frequency and characterized by a harsh, shrill noise.
screen: 1. A device to shield or separate one part of an apparatus from other parts, or to separate the effects of one part on others.; 2. A surface on which images are displayed, as the face of a cathode-ray tube.
scrub: To cancel a scheduled firing, either before or during countdown.
Sct, Scut: International Astronomical Union abbreviations for Scutum. See constellation.
Scul: International Astronomical Union abbreviations for Sculptor. See constellation.
Sculptor (abbr Scl, Scul): See constellation.
Scutum (abbr Sct, Scut): See constellation.
sea clutter: See ground return.
sealed cabin: The occupied space of an aircraft or spacecraft characterized by walls which do not allow any gaseous exchange between the inner atmosphere and its surrounding atmosphere and containing its own mechanisms for maintenance of the inside atmosphere.
sea level = mean sea level.
sea-level pressure: The atmospheric pressure at mean sea level, either directly measured or, most commonly, empirically determined from the observed station pressure.
searchlighting: Horizontal scanning, in which the antenna beam is continuously rotated in azimuth.
search radar: A radar designed for the approximate location of (usually airborne) objects. Search radar beams are usually wide, wider in the vertical than in the horizontal, making it possible to scan large volumes of space quickly. Compare tracking radar.
sea return: See ground return.
seat belt = lap belt.
seat-to-head acceleration: See physiological acceleration.
second (abbr s): See; The unit of time, the second, was defined originally as the fraction 1/86 400 of the mean solar day. The exact definition of the "mean solar day" was left to astronomers, but their measurements have shown that on account of irregularities in the rotation of the Earth, the mean solar day does not guarantee the desired accuracy. In order to define the unit of time more precisely, the 11th CGPM (1960) adopted a definition given by the International Astronomical Union which was based on the tropical year [see ephemeris second]. Experimental work had, however, already shown that an atomic standard of time-interval, based on a transition between two energy levels of an atom or a molecule, could be realized and reproduced much more accurately. Considering that a very precise definition of the unit of time of the International System, the second, is indispensable for the needs of advanced metrology, the 13th CGPM (1967) decided to replaced the definition of the second by the following:; The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom (13th CGPM (1967), Resolution 1).; The previous is an excerpt (with the exception of the reference to "ephemeris second") from WWW version of the National Institute of Standards and Technology: Physics Laboratory's International System of Units (SI)
secondary: 1. = secondary great circle.; 2. A celestial body revolving around another body, its primary.; 3. A particle emitted in secondary emission.
secondary circle = secondary great circle.
secondary cosmic radiation = secondary cosmic ray.
secondary cosmic rays: Secondary emission in the atmosphere stimulated by primary cosmic rays. See air shower.
secondary electron emission: The release of electrons from a surface which is bombarded by energetic electrons.; The yield or ratio of secondary to primary electrons is a function of the primary electron energy.
secondary emission: Emission of subatomic particles or photons stimulated by primary radiation; for example, cosmic rays impinging on other particles and causing them, by disruption of their electron configurations or even of their nuclei, to emit particles and photons or both in turn.
secondary great circle: A great circle perpendicular to a primary great circle, as a meridian. Also called secondary circle, secondary.
secondary instrument: An instrument whose calibration is determined by comparison with an absolute instrument.
secondary radar: See radar, note.
secondary radiation: Electromagnetic or particulate radiation resulting from absorption of other radiation in matter.
secondary scattering: See multiple scattering, scattering.
second law of thermodynamics: An inequality asserting that it is impossible to transfer heat from a colder to a warmer system without the occurrence of other simultaneous changes in the two systems or in the environment.; It follows from this law that during an adiabatic process, entropy cannot decrease. For reversible adiabatic processes entropy remains constant, and for irreversible adiabatic processes it increases. Another equivalent formulation of the law is that it is impossible to convert the heat of a system into work without the occurrence of other simultaneous changes in the system or its environment. This version, which requires an engine to have a cold source as well as a heat source, is particularly useful in engineering applications. See first law of thermodynamics.
Secor (abbr) = sequential collation of range.
Secor/DME: (Sequential collation of range/distance measuring equipment). A distance measuring system used in rocket tracking.
section: One of the cross-section parts that a rocket vehicle is divided into, each adjoining another at one or both of its end. Usually described by a designating word, as in nose section, aft section, center section, tail section, thrust section, tank section , etc.
sectionalized vertical antenna: A vertical antenna which is insulated at one or more points along its length. The insertion of suitable reactances or applications of a driving voltage across the insulated points results in a modified current distribution giving a more desired radiation pattern in the vertical plane.
sector scanning: See scanning.
secular: Pertaining to long periods of time on the order of a century, as secular perturbations, secular terms.
secular perturbations: Changes in the orbit of a planet or satellite that operate in extremely long cycles; long term perturbations.
secular terms: In the mathematical expression of an orbit, terms for very long period perturbations, in contrast to periodic terms , terms of short period.
Seebeck effect: The establishment of an electric potential difference tending to produce a flow of current in a circuit of two dissimilar metals the junctions of which are at different temperatures.
seeding: 1. The introduction of atoms, such as sodium, with a low ionization potential into a hot gas for the purpose of increasing the electrical conductivity.; 2. = cloud seeding.
seeing: A blanket term long used by astronomers for the disturbing effects produced by the atmosphere upon the image quality of an observed celestial body. Also called astronomical seeing.; Recent studies show that seeing is a combination of three principal and distinct effects that the human eye is not capable of distinguishing: (a) scintillation, i.e., fluctuations in brightness; (b) transverse displacements of the image; and (c) variations of the radius of curvature of the wavefront rendering the image in an out of focus.
seismic mass: The element in an accelerometer which is intended to serve as the force-summing member for applied accelerations, gravitational forces, or both.
selective absorption: Absorption which varies with the wavelength of radiation incident upon the absorbing substance. See absorption spectrum.; A substance which absorbs in such fashion is called a selective absorber and is to be contrasted with an ideal black body, white body, or gray body. In reality, all substances are selective absorbers when due regard is paid to their interaction with all wavelengths of the complete electromagnetic spectrum.
selective scattering: Scattering which varies with the wavelengths of radiation incident upon the scattering particles.; In general, the largest and most complex degree of selectivity is found for wavelengths nearly equal to the diameter of the scattering particles.
selectivity: The degree of falling off in response of a resonant device with departure from resonance.
selenocentric: Relating to the center of the moon; referring to the moon as a center.
selenographic: 1. Of or pertaining to the physical geography of the moon.; 2. Specifically, referring to positions on the moon measured in latitude from the moon's equator and in longitude from a reference meridian.
selenoid: A satellite of the earth's moon. (No such satellites are known).
selenology: That branch of astronomy that treats of the moon, its magnitude, motion, constitution, and the like. Selene is Greek for moon.
self-adaptive control system: A particular type of stability augmentation system which changes the response of a given control input by constantly sampling response and adjusting its gain, rather than having a fixed or selective gain system.
self-balancing potentiometer: See potentiometer.
self-excited vibration = self-induced vibration.
self-induced vibration: Vibration of a mechanical system resulting from conversion, within the system, of nonoscillatory excitation to oscillatory excitation. Also called self-excited vibration.
self-information = information content.
selsyn: (A trade name, from self-synchronous; often capitalized). An electrical remote indicating instrument operating on direct current, in which the angular position of the transmitter shaft, carrying a contact arm moving on a resistance strip, controls the pointer on the indicator dial.
semiactive homing guidance: Guidance in which a craft or vehicle is directed toward a destination by means of information received from the destination in response to transmissions from a source other than the craft.; In active homing guidance the information received is in response to transmissions from the craft. In passive homing guidance natural radiations from the destination are utilized.
semiactive tracking system: A trajectory measuring system which tracks a signal source normally aboard the target for other purposes, or a system that illuminates the target by use of a ground transmitter but requires no special electronics on board the missile, e.g., telemetry elsse, Dovap elsse, Cotat, Cotar, VHF/ ADF, pulse radar (skin track).
semicircular canals: Structures of the inner ear, the primary function of which is to register movement of the body in space. They respond to change in the rate of movement.
semiconductor: An electronic conductor, with resistivity in the range between metals and insulators, in which the electrical charge carrier concentration increases with increasing temperature over some temperature range. Certain semiconductors possess two types of carriers, namely, negative electrons and positive holes.
semiconductor device: An electron device in which the characteristic distinguishing electronic conduction takes place within a semiconductor.
semidiameter: 1. The radius of a closed figure.; 2. Half the angle at the observer subtended by the visible disk of a celestial body.
semidiameter correction: A correction due to semidiamter, particularly that sextant altitude correction resulting from observation of the upper or lower limb of a celestial body, rather than the center of that body.
semidiurnal: Having a period of, occurring in, or related to approximately half a day.
semimajor axis (symbol a ): One-half the longest diameter of an ellipse.
semiminor axis (symbol b ): One-half the shortest diameter of an ellipse.
semimonocoque: A structural concept in which longitudinal members as well as formers reinforce the skin and help carry the stresses. Compare with monocoque.
semitransparent photocathode: A photocathode in which radiant flux incident on one side produces photoelectric emission from the opposite side. See phototube.
sensation level: The level of psychophysiologic stimulation above the threshold.
sense antenna: An antenna used to resolve a 180 degrees ambiguity in a directional antenna.
sense-reversing reflectivity: The characteristic of a reflector that reverses the sense of a circularly polarized incident ray. See polarization.; For example, a perfect corner reflector is invisible to a circularly polarized radar because it reverses the sense.
sensibility: In measurements, the smallest change that is reliably detectable.
sensible atmosphere: That part of the atmosphere that offers resistance to a body passing through it.
sensible horizon: See horizon, note.
sensible temperature: The temperature at which average indoor air of moderate humidity would induce, in a lightly clothed person, the same sensation of comfort as that induced by the actual environment. Compare effective temperature.; Sensible temperature depends on the air temperature; radiation from the sun, sky, and surrounding objects; relative humidity; and air motion. The wet-bulb temperature is often taken as an approximate measure.
sensing element = sensor.
sensitivity: 1. The ability of electronic equipment to amplify a signal, measured by the minimum strength of signal input capable of causing a desired value of output. The lower the input signal for a given output, the higher the sensitivity.; 2. In measurements, the derivative representing the change in instrument indication produced by a change in the variable being measured.
sensitometry: The measurement of the light response characteristics of photographic film under specified conditions of exposure and development.
sensor: 1. The component of an instrument that converts an input signal into a quantity which is measured by another part of the instrument. Also called sensing element.; 2. The nerve endings or sense organs which receive information from the environment, from the organism, or from both.
separation: 1. The action of a fallaway section or companion body as it casts off from the remaining body of a vehicle, or the action of the remaining body as it leaves a fallaway section behind it.; 2. The moment of this action.
separation velocity: The velocity at which a space vehicle is moving when some part or section is separated from it; specifically, the velocity of a space probe or satellite at the time of separation from the launch vehicle.
September equinox = autumnal equinox.
sequencer: A mechanical or electronic device that may be set to initiate a series of events and to make the events follow in a given sequence. See program.
sequential collation of range: (abbr Secor) A spherical, long-baseline, phase-comparison trajectory measuring system utilizing three or more ground stations, time sharing a single transponder, to provide nonambiguous range measurements to determine the instantaneous position of a vehicle in flight.
sequential control: Control by completion of a series of one or more events.
Ser, Serp: International Astronomical Union abbreviations for Serpens (Cap. and Caud.). See constellation.
Serpens (Cap. and Caud.) (abbr Ser, Serp): See constellation.
servo: 1. = servomechanism.; 2 Pertaining to or incorporating a servomechanism.
servomechanism: A control system incorporating feedback in which one or more of the system signals represent mechanical motion.; It should be noted that servomechanism and regulator are not mutually exclusive terms; their application to a particular system will depend on the method of operation of that system.
set: 1. To place a storage device in a prescribed state.; 2. To place a binary cell in the one state.
Sex, Sext: International Astronomical Union abbreviations for Sextans. See constellation.
sexidemical notation: A positional notation based on the integer sixteen.
Sext: International Astronomical Union abbreviation for Sextans. See constellation.
Sextans (abbr Sex, Sext): See constellation.
sextant: A double-reflecting instrument for measuring angles, primarily altitudes of celestial bodies.; As originally used, the term applied only to instruments having an arc of 60 degrees, a sixth of a circle, from which the instrument derived its name. Such an instrument had a range of 120 degrees. In modern practice the term applies to a similar instrument, regardless of its range, very few modern instruments being sextants in the original sense.
sextant altitude: The altitude of a celestial body as actually measured by a sextant. See altitude difference.
sferics: 1. (Also spelled spherics ). The study of atmospherics, especially from a meteorological point of view. This involves techniques of locating and tracking atmospherics sources and evaluating received signals (waveform, frequency, etc.) in terms of source.; 2. = atmospherics.
sferics fix: The estimated location of a source of atmospherics, presumably a lightning discharge.
sferics observation: An evaluation, from one or more sferics receivers, of the location of weather conditions with which lightning is associated.; Such observations are more commonly obtained from networks of two or three widely spaced stations. Simultaneous observations of the azimuth of the discharge are made at all stations and the location of the storm is determined by triangulation.
sferics receiver: An instrument which measures, electronically, the direction of arrival, intensity, and rate of occurrence of atmospherics. In its simplest form the instrument consists of two orthogonally crossed antennas. Their output signals are connected to an oscillograph so that one loop measures the north-south component whereas the other measures the east-west component. These are combined vertically to give the azimuth. Also called lightning recorder.
Sge, Sgte: International Astronomical Union abbreviation for Sagitta. See constellation.
Sgr, Sgtr: International Astronomical Union abbreviation for Sagittarius. See constellation.
Sgte: International Astronomical Union abbreviation for Sagitta. See constellation.
Sgtr: International Astronomical Union abbreviation for Sagittarius. See constellation.
shadow: Darkness in a region, caused by an obstruction between the source of light and the region.; By extension, the term is applied to a similar condition when any form of radiant energy is cut off by an obstruction, as a radar shadow. The darkest part of a shadow in which light is completely cut off is called the umbra; a lighter part surrounding the umbra, in which the light is only partly cut off, is called the penumbra.
shadowgraph: 1. A picture or image in which steep density gradients in the flow about a body are made visible, the body itself being presented in silhouette.; 2. The optical method or technique by which this is done. A shadowgraph differs from a schlieren photograph in that the schlieren method depends on the first derivative of the refractive index while the shadow method depends on the second derivative. Interference measurements give the refractive index directly.
shadow shield: A shield that is interposed between a radiation source and a specific area to be protected.; Useful in space, a shadow shield is less effective in the earth's atmosphere because air scattering deflects radiation around it.
shaker: An electromagnetic device capable of imparting known vibratory acceleration to a given object.
shake-table test: A laboratory test for vibration tolerance, in which the device to be tested is place in a vibrator.
shaped-beam antenna: A unidirectional antenna whose major lobe differs materially from that obtainable from an aperture of uniform phase. Also called phase-shaped antenna.
shear strength: In materials, the stress required to produce fracture in the plane of cross section, the conditions of loading being such that the directions of force and of resistance are parallel and opposite although their paths are offset a specified minimum amount.
shear wave: A wave in an elastic medium which causes an element of the medium to change its shape without a change of volume. Mathematically, a shear wave is one whose velocity field has zero divergence. Also called rotational wave.; A shear plane wave in an isotropic medium is called a transverse wave.
sheath = plasma sheath.
shell: A body one of whose dimensions is small compared with the others.
shield: A body of material used to prevent or reduce the passage of particles or radiation.; A shield may be designated according to what it is intended to absorb, as a gamma-ray shield or neutron shield, or according to the kind of protection it is intended to give, as a background, biological, or thermal shield. The shield of a nuclear reactor is a body of material designed to prevent the escape of neutrons and radiation into a protected area, which frequently is the entire space external to the reactor. It may be required for the safety of personnel or to reduce radiation sufficiently to allow use of counting instruments.
shielding: The arrangement of shields used for any particular circumstances; the use of shields.
shimmer = terrestrial scintillation.
shock: 1. = shock wave.; 2. A blow, impact, collision, or violent jar.; 3. A sudden agitation of the mental or emotional state or an event causing it.; 4. The sudden stimulation caused by an electrical discharge on the animal or human organism (e.g., electric shock).
shock absorber: A device for the dissipation of energy used to modify the response of a mechanical system to applied shock.
shock front: 1. A shock wave regarded as the forward surface of a fluid region having characteristics different from those of the region ahead of the wave.; 2. The front side of a shock wave.
shock isolator: A resilient support that tends to isolate a system from applied shock. Also called shock mount.
shock mount = shock isolator.
shock spectrum: A plot of the maximum acceleration experienced by a single-degree-of-freedom system as a function of its own natural frequency in response to an applied shock.
shock tube: A relatively long tube or pipe in which very brief high-speed gas flows are produced by the sudden release of gas at very high pressure into a low-pressure portion of the tube; the high-speed flow moves into the region of low pressure behind a shock wave.
shock tunnel: A shock tube used as a wind tunnel.
shock wave: A surface or sheet of discontinuity (i.e., of abrupt changes in conditions) set up in a supersonic field or flow, through which the fluid undergoes a finite decrease in velocity accompanied by a marked increase in pressure, density, temperature, and entropy, as occurs, e.g., in a supersonic flow about a body. Sometimes called a shock. See attached shock wave, bow wave, condensation shock wave, detached shock wave, Mach wave, normal shock wave, oblique shock wave.
Shodop (abbr) = short-range Doppler.
shooting star = meteor.
shoran: (From short-range navigation). A precision electronic position fixing system using a pulse transmitter and receiver and two transponder beacons at fixed points. High- precision shoran is called hiran.
short-baseline system: A trajectory measuring system using a baseline the length of which is very small compared with the distance of the object being tracked.
short-period error = random error.
short-range Doppler (abbr Shodop): A short range trajectory measuring system using the intersections of the ellipsoids of Dovap and the hyperboloids of Dovap elsse or telemetry elsse during a rocket launch.
short-range navigation = shoran.
short-wave radiation: In meteorology, a term used loosely to distinguish radiation in the visible and near-visible portions of the electromagnetic spectrum (roughly 0.4 to 1.0 micron in wavelength) from long-wave radiation ( infrared radiation).
shot: 1. An act or instance of firing a rocket, especially from the earth's surface, as, the shot carried the rocket 200 miles.; 2. The flight of a rocket, as, the rocket made a 200-mile shot.
shoulder harness: A harness that fastens over a person's shoulders to prevent his being thrown forward in his seat. See lap belt.
shower = air shower (cosmic rays).
shutdown: The process of decreasing engine thrust to zero.
shutoff = fuel shutoff.
SI (abbr) = International System of Units.
SID (abbr) = sudden ionospheric disturbance.
sideband: 1. Either of the two frequency bands on both sides of the carrier frequency within which fall the frequencies of the wave produced by the process of modulation.; 2. The wave components lying within such a band.
side lobe: See lobe.
sidereal: Of or pertaining to the stars.; Although sidereal generally refers to the stars and tropical to the vernal equinox, sidereal time and the sidereal day are based upon the position of the vernal equinox relative to the meridian. The sidereal year is based upon the stars.
sidereal day: The duration of one rotation of the earth on its axis, with respect to the vernal equinox. It is measured by successive transits of the vernal equinox over the upper branch of a meridian.; Because of the precession of the equinoxes, the sidereal day thus defined is slightly less than the period of rotation with respect to the stars, but the difference is less than 0.01 second. The length of the mean sidereal day is 24 hours of sidereal time or 23 hours 56 minutes 4.09054 seconds of mean solar time.
sidereal hour angle: (abbr SHA). Angular distance west of the vernal equinox; the arc of the celestial equator, or the angle at the celestial pole, between the hour circle of the vernal equinox and the hour circle of a point on the celestial sphere, measured westward from the hour circle of the vernal equinox through 360 degrees.; Angular distance east of the vernal equinox, through 24 hours, is right ascension.
sidereal month: The average period of revolution of the moon with respect to the stars, a period of 27 days 7 hours 43 minutes 11.5 seconds, or approximately 27 1/3 days.
sidereal period: 1. The time taken by a planet or satellite to complete one revolution about its primary as seen from the primary and as referred to a fixed star.; 2. Specifically, the interval between two successive returns of an earth satellite in orbit to the same geocentric right ascension.
sidereal time: Time based upon the rotation of the earth relative to the vernal equinox.; Sidereal time may be designated as local or Greenwich as the local or Greenwich meridian is used as the reference. When adjusted for nutation, to eliminate slight irregularities in the rate, it is called mean sidereal time.
sidereal year: The period of one apparent revolution of the earth around the sun, with respect to the stars, averaging 365 days 6 hours 9 minutes 9.55 seconds in 1955, and increasing at the rate of 0.000095 second annually.; Because of the precession of the equinoxes this is about 20 minutes longer than a tropical year.
sight = celestial observation.
sigma = standard deviation.
signal: 1. A visible, audible, or other, indication used to convey information.; 2. The information to be conveyed over a communication system.; 3. Any carrier of information; opposed to noise.
signal strength: In radio, a measure of the received radiofrequency power, generally expressed in decibels relative to some standard value, normally either 1 milliwatt or that power which would have resulted at the same distance under free-space transmission. Also called field strength.
signal-to-noise ratio: (abbr SNR or S/N). A ratio which measures the comprehensibility of a data source or transmission link, usually expressed as the root-mean-square signal amplitude divided by the root-mean-square noise amplitude.; The higher the S/N ratio, the less the interference with reception.
signal transmission level: In a transmission system, the signal level, of a kind to be specified, at a designated position in the system.; The signal level at some specified position near the source may be taken as the zero reference level. In an acoustic system the signal level is often in the form of a sound pressure level; either the reference sound pressure or the reference sound pressure level must be specified.
signal velocity: See velocity of propagation, note.
signs: See zodiac.
silver-cell battery: A type of short-duration, high-power-density battery of light weight used for single-time, high-power applications in vehicles where weight is critical.
silver-disk pyrheliometer: An instrument used for the measurement of direct solar radiation. See pyrheliometer.; It is constructed in the following manner. A silver disk located at the lower end of a diaphragmed tube serves as the radiation receiver for a calorimeter. Radiation falling on the silver disk is periodically intercepted by means of a shutter located in the tube, causing temperature fluctuations of the calorimeter which are proportional to the intensity of the radiation. The instrument is normally used as a secondary instrument and is calibrated against the water-flow pyrheliometer. It is used by the U.S. Weather Bureau as a standard instrument.
simple average: See arithmetic mean, sense 2.
simple harmonic motion: A motion such that the displacement is a sinusoidal function of time.
simple harmonic quantity: A periodic quantity that is a sinusoidal function of the independent variable. Thus, γ = A sin ( ωx + φ) where y is the simple harmonic quantity; A is the amplitude; ω is the angular frequency; x is the independent variable; and φ is the phase of the oscillation.; The maximum value of the simple harmonic quantity is the amplitude A; it is sometimes called, for emphasis, the single amplitude to distinguish it from double amplitude which for a simple harmonic quantity is the same as the total excursion or peak-to-peak value. When a simple harmonic quantity is expressed as a complex quantity, the term amplitude must be used with caution in view of possible confusion with the alternate meaning of amplitude as the angle or argument of a complex quantity.
simple reflection = specular reflection.
simple reflector = specular reflector.
simple standard deviation: See standard deviation.
sine wave: A wave which can be expressed as the sine of a linear function of time, or space, or both.
single-degree-of-freedom system: A mechanical system for which only one coordinate is required to define completely the configuration of the system at any instant. See degree of freedom.
single-entry compressor: A centrifugal compressor that takes in air or fluid on only one side of the impeller, the impeller being faced with vanes only on that side.
single sheath: See plasma sheath, note.
single-sideband modulation: Modulation whereby the spectrum of the modulating wave is translated in frequency by a specified amount either with or without inversion.
single-sideband transmission: That method of operation in which one sideband is transmitted and the other sideband is suppressed. The carrier wave may be either transmitted or suppressed.
single-stage compressor: A centrifugal compressor having a single impeller wheel, with vanes either on one or on both sides of the wheel; also, an axial flow compressor with one row of rotor blades and one row of stator blades. Axial-flow compressors are normally multistage.
single-stage rocket: A rocket vehicle provided with a single rocket propulsion system. See stage.
sink: 1. In the mathematical representation of fluid flow, a hypothetical point or place at which the fluid is absorbed.; 2. A heat sink. See source.
sinking: In atmospheric optics, a refraction phenomenon, the opposite of looming, in which an object on or slightly above the geographic horizon apparently sinks below it. Compare inferior mirage, stooping.; Sinking occurs whenever the rate of density decreases with height through the atmosphere is of smaller magnitude than normal or, in extreme cases, where the density actually increases with height.
sintered ceramic: A ceramic body or coating prepared by heating a ceramic powder below its melting point but at a sufficiently high temperature to cause interdiffusion of ions between contacting particles and subsequent adherence at the points of contact.
sintering: The bonding of adjacent surfaces of particles in a mass of powders, usually metal, by heating.
sinus: A hollow or cavity; a recess or pocket. Specifically, sinuses: air cavities lined by mucous membrane which communicate with the nasal cavity; the ethmoidal, frontal, sphenoidal, and maxillary sinuses.
sinus barotrauma = aerosinusitis.
sinusoidal: Having the form of a sine wave.
skiatron: 1. A dark trace oscilloscope tube. See dark trace tube.; 2. A display employing an optical system with a dark trace tube.
skimmer basin = deluge collection pond.
skin: The covering of a body, of whatever material, such as the covering of a fuselage, of a wing, of a hull, of an entire aircraft, etc.; a body shell, as of a rocket; the surface of a body.
skin temperature: The outer surface temperature of a body.
skin tracking: The tracking of an object by means of radar without using a beacon or other signal device on board the object being tracked.
skip effect: A phenomenon in which sound or radio energy may be detected only at various distance intervals from the energy source as the result of the presence of an energy reflecting or refracting layer in the atmosphere. See radio duct.; For long radio waves, the ionosphere acts as the reflecting layer. For shorter wavelengths, the effect may be produced by strong superstandard propagation in elevated layers of the troposphere. Skip effects make it possible on occasion to detect targets at distances far greater than the normal radio horizon, while closer targets remain undetected.
skirt: The lower outer part of a rocket vehicle; specifically, the half-stage of an Atlas.
skirt fog: The cloud of steam and water that surrounds the engines of a rocket being launched from a wet emplacement.
skyhook balloon: (Originally a code name for a U.S. Navy Project.) A large free balloon having a plastic envelope, used especially for constant-level meteorological observations at very high altitudes.
sky light = diffuse sky radiation.
sky radiation = diffuse sky radiation.
sky screen: An optical device used to detect the departure of a rocket from its intended trajectory.
sky wave: In radio, radio energy that is received after having been reflected by the ionosphere. Compare wave.
slant range: The line-of-sight range of a radar or radio. See range.
slave: 1. = slave station.; 2. Device that follows an order given by a master through remote control.
slave antenna: A directional antenna that is positioned in azimuth and elevation by a servo system. The information controlling the servosystem is supplied by a tracking or positioning system.
slave station: In a hyperbolic navigation system, a station whose transmissions are controlled by a master station. Often shortened to slave. See hyperbolic navigation.
slaving: Of a gyro, the use of a torquer to maintain the orientation of the spin axis relative to an external reference such as a pendulum or magnetic compass.
sleeve-dipole antenna: A dipole antenna surrounded in its central portion by a coaxial sleeve.
slenderness ratio: A dimensionless number expressing the ratio of a rocket vehicle length to its diameter.
slew: To change the position of an antenna or range gear assembly by injecting a synthetic error signal into the positioning servo amplifier.
slewing: 1. Of a gyro, the rotation of the spin axis caused by applying torque about the axis of rotation.; 2. In radar, changing the scale on the display.
slip: A sprayable slurry comprising a frit suspended in a liquid carrier (sometimes also used for dip and brush coating).
slip flow: See rarefied gas dynamics, note.
slope angle: The angle in the vertical plane between the flightpath and the horizontal.
sloshing: The back-and-forth movement of a liquid fuel in its tank, creating problems of stability and control in the vehicle.
slow ion = large ion.
slug: A unit of mass; the mass of a free body which if acted upon by a force of 1 pound would experience an acceleration of 1 foot per square second; thus approximately 32.16 pounds.
slurry: A suspension of fine solid particles in a liquid.
slurry fuel: A fuel consisting of a suspension of fine solid particles in a liquid.
small calorie (abbr cal): See calorie.
small circle: The intersection of a sphere and a plane which does not pass through the center of the sphere, as a parallel of latitude.
small ion: An atmospheric ion, apparently a singly charged atmospheric molecule (or, rarely, an atom) about which a few other neutral molecules are held by the electrical attraction of the central ionized molecule. Estimates of the number of satellite molecules range as high as 12. Also called light ion, fast ion.; Small ions may disappear either by direct recombination with oppositely charged small ions or by combination with neutral Aitken nuclei to form new large ions, or by combination with large ions of opposite sign. The small ion, collectively, is the principal agent of atmospheric conduction.
small perturbation: A disturbance imposed on a system in steady state, with amplitude assumed small, i.e., the square of the amplitude is negligible in comparison with the amplitude, and the derivatives of the perturbation are assumed to be of the same order of magnitude as the perturbation. See perturbation, method of small perturbations.
Snell law: See refraction, index of refraction.
Snort track: A rail track on which a supersonic rocket sled is driven, located at the Naval Ordnance Test Station.
snow = grass.
snubber: A device used to increase the stiffness of an elastic system, usually by a large factor, whenever the displacement becomes larger than a specified amount.
sofar: (From sound fixing and ranging). A system of navigation providing hyperbolic lines of position determined by shore listening stations which receive sound signals produced by depth charges dropped at sea and exploding in a sound channel which is at a considerable depth in most areas.; This system is used in Project Mercury for locating spacecraft down at sea.
softening range: An arbitrarily defined temperature range below the crystal melting point where a ceramic becomes soft and noticeably viscous; a softening range rather than a sharp melting point occurs in ceramics containing a glass base.
soft landing: The act of landing on the surface of a planet without damage to any portion of the vehicle or payload except possibly the landing gear.
soft radiation: Radiation absorbable by an absorber equivalent to 10 centimeters of lead or less.; Radiation which can penetrate more than 10 centimeters of lead is termed hard radiation.
solar: 1. Of or pertaining to the sun or caused by the sun, as solar radiation, solar atmospheric tide.; 2. Relative to the sun as a datum or reference , as solar time.
solar activity: Any type of variation in the appearance or energy output of the sun. See faculae, flare, flocculi, granules, prominence, spicules, sunspot.
solar air mass: The optical air mass penetrated by light from the sun for any given position of the sun in the sky.
solar antapex: See solar apex.
solar apex: The point on the celestial sphere toward which the sun is traveling. Also called apex of the sun's way.; The solar apex is at approximately right ascension 270 degrees declination 34 degrees N. The point diametrically opposite the solar apex on the celestial sphere is the solar antapex, right ascension 90 degrees declination 34 degrees S.
solar atmospheric tide: An atmospheric tide due to the thermal or gravitational action of the sun.; Six and eight hour components of small amplitude have been observed. They are primarily thermal in origin. The 12-hour component has by many times the greatest amplitude of any atmospheric tidal component, about 1.5 millibars at the equator and 0.5 millibar in middle latitudes. This relatively large amplitude is often explained as a resonance effect. The 24-component is a thermal tide with great local variability.
solar cell: A photovoltaic cell that converts sunlight into electrical energy.
solar constant: The rate at which solar radiation is received outside the earth's atmosphere on a surface normal to the incident radiation and at the earth's mean distance from the sun.; Measurements of solar radiation at the earth's surface by the Smithsonian Institution for several decades give a best value for the solar constant of 1.934 calories per square centimeter per minute. Measurements from rockets of the intensity of the ultraviolet end of the spectrum have corrected this value to 2.00 calories per square centimeter per minute with a probable error of +/- 2 percent.
solar corona: See corona.
solar corpuscular rays: Cosmic radiation supposedly originating in the sun. See corpuscular cosmic ray.
solar cosmic rays: Cosmic rays supposedly originating in the sun.
solar cycle: The periodic increase and decrease in the number of sunspots. The cycle has a period of about 11 years.
solar day: 1. The duration of one rotation of the earth on its axis, with respect to the sun.; This may be either a mean solar day, or an apparent solar day, as the reference is the mean or apparent sun, respectively.; 2. The duration of one rotation of the sun on its axis.
solar eclipse: The obscuration of the light of the sun by the moon.; A solar eclipse is partial if the sun is partly obscured, total if the entire surface is obscured, or annular if a thin ring of the sun's surface appears around the obscuring body.
solar flare: See flare.
solarimeter: 1. = pyranometer.; 2. Specifically, a pyranometer consisting of a Moll thermopile covered by a bell glass.
solar parallax: The angle at the sun subtended by the equatorial diameter of the earth. See parallax.; The adopted value of the solar parallax in the system of astronomical constants is 8.80 seconds of arc.
solar prominence = prominence.
solar protons: Protons emitted by the sun, especially during solar flares.
solar radiation: The total electromagnetic radiation emitted by the sun. See insolation, direct solar radiation, diffuse sky radiation, global radiation, extraterrestrial radiation, solar constant.; To a first approximation, the sun radiates as a black body at a temperature of about 5700 degrees K; hence about 99.9 percent of its energy output falls within the wavelength interval from 0.15 micron to 4.0 microns, with peak intensity near 0.47 micron. About one-half of the total energy in the solar beam is contained within the visible spectrum from 0.4 to 0.7 micron, and most of the other half lies in the near infrared, a small additional portion lying in the ultraviolet.
solar-radiation observation: An evaluation of the radiation from the sun that reaches the observation point. The observing instrument is usually a pyrheliometer or pyranometer.; Two types of such observation are taken. The more common consists of measurements of the radiation reaching a horizontal surface, consisting of both radiation from the sun (direct solar radiation) and that reaching the instrument indirectly by scattering in the atmosphere (diffuse sky radiation). The other type of observation involves the use of an equatorial mount that keeps the instrument pointed directly at the sun at all times. The sensitive surface of the instrument is normal to the path of the radiation and is shielded from indirect radiation from the sky.
solar radio burst: A sudden increase in the flux from the sun at radio frequencies.
solar radio waves: Radiation at radio frequencies originating in the sun or its corona.
solar simulator: A device which produces thermal energy, equivalent in intensity and spectral distribution to that from the sun, used in testing materials and space vehicles.
solar system: The sun and other celestial bodies within its gravitational influence, including planets, asteroids, satellites, comets, and meteors.
solar tide: See solar atmospheric tide.
solar time: Time based upon the rotation of the earth relative to the sun.; Solar time may be designated as mean or astronomical if the mean sun is the reference, or apparent if the apparent sun is the reference. The difference between mean and apparent time is called equation of time. Solar time may be further designated according to the reference meridian, either the local or Greenwich meridian or additionally in the case of mean time, a designated zone meridian. Standard or daylight-saving are variations of zone time. Time may also be designated according to the timepiece, as chronometer time or watch time, the time indicated by these instruments.
solar wind: Streams of plasma flowing approximately radially outward from the sun.
solar year = tropical year.
solenoid: A tube formed in space by the intersection of unit-interval isotimic surfaces of two scalar quantities.; Solenoids formed by the intersection of surfaces of equal pressure and density are frequently referred to in meteorology. A barotropic atmosphere implies the absence of solenoids of this type, since surfaces of equal pressure and density coincide.
solid angle (symbol ω): A portion of the whole of space about a given point, bounded by a conical surface with its vertex at that point and measured by the area cut by the bounding surface from the surface of a sphere of unit radius centered at that point. See steradian.
solid propellant: Specifically, a rocket propellant in solid form, usually containing both fuel and oxidizer combined or mixed, and formed into a monolithic (not powered or granulated) grain.
solid-propellant engine = solid-propellant rocket engine.
solid-propellant rocket engine: A rocket engine fueled with a solid propellant. Such motors consist essentially of a combustion chamber containing the propellant, and a nozzle for the exhaust jet, although they often contain other components, as grids, liners, etc.
solid rocket: A rocket that uses a solid propellant.
solid rocket fuel: A solid propellant.
solid rotation: The rotation of a system as though is were a solid or rigid body rotating about a fixed axis, all points within the body having the same angular velocity.
solid-state devices: Devices which utilize the electric, magnetic, and photic properties of solid materials, e.g., binary magnetic cores, transistors, etc.
solstice: 1. One of the two points of the ecliptic farthest from the celestial equator; one of the two points on the celestial sphere occupied by the sun at maximum declination.; That in the northern hemisphere is called the summer solstice and that in the southern hemisphere the winter solstice. Also called solstitial point.; 2. That instant at which the sun reaches one of the solstices, about June 21 (summer solstice) or December 22 (winter solstice).
solstitial colure: That great circle of the celestial sphere through the celestial poles and the solstices.
solstitial point = solstice.
sonar: (From sound, navigation, and ranging.) A method or system, analogous to radar used under water, in which high-frequency sound waves are emitted so as to be reflected back from objects, and used to detect the objects of interest. Called asdic by the British.
sonar capsule: A device designed to reflect high-frequency sound waves. See sonar.; The sonar capsule, if attached to a reentry body, may be used to locate the reentry body in case of a water landing.
sone: A unit of loudness. A simple tone of frequency 1000 cycles per second, 40 decibels above a listener's threshold, produces a loudness of 1 sone.; The loudness of any sound that is judged by the listener to be n times that of the 1-sone tone is n sones. A millisone is equal to 0.001 sone. The loudness scale is a relation between loudness and level above threshold for a particular listener. In presenting data relating loudness in sones to sound pressure level, or in averaging the loudness scales of several listeners, the thresholds (measured or assumed) should be specified.
sonic: 1. In aerodynamics, of or pertaining to the speed of sound; that which moves at acoustic velocity as in sonic flow ; designed to operate or perform at the speed of sound, as in sonic leading edge.; 2. Of or pertaining to sound, as in sonic amplifier.; In sense 2, acoustic is preferred to sonic.
sonic agglomeration: The union of small particles suspended in a fluid medium into larger aggregates by the action of sound waves.
sonic barrier: A popular term for the large increase in drag that acts upon an aircraft approaching acoustic velocity; the point at which the speed of sound is attained and existing subsonic and supersonic flow theories are rather indefinite. Also called sound barrier.
sonic boom: A noise caused by a shock wave that emanates from an aircraft or other object traveling at or above sonic velocity .; A shock wave is a pressure disturbance and is received by the ear as a noise or clap.
sonic delay line = acoustic delay line.
sonic drilling: The process of cutting or shaping materials with an abrasive slurry driven by a reciprocating tool attached to an electromechanical transducer operating at ultrasonic frequencies.
sonic frequency = audiofrequency.
sonics: The technology of sound in processing and analysis. Sonics includes the use of sound in any noncommunication process.
sonic soldering: The method of joining metals by metallic bonding alloys through the use of mechanical vibrations to break up the surface oxides.
sonic speed: Acoustic velocity; by extension, the speed of a body traveling at a Mach number of 1.
sonic wave = sound wave.
sophisticated: Complex and intricate; making use of advanced art; requiring special skills to operate.
sorb: To take up gas by sorption.
sorbate: Gas taken up by a sorbent.
sorbent: The material which takes up gas by sorption.
sorption: The taking up of gas by absorption, adsorption, chemisorption, or any combination of these process. See absorption.
sound: 1. An oscillation in pressure, stress, particle displacement, particle velocity, etc., in a medium with internal forces (e.g., elastic, viscous), or the superposition of such propagated oscillations.; 2. A sensation evoked by the oscillation described above in the human ear.; In case of possible confusion, the term sound wave or elastic wave may be used for concept 1 and the term sound sensation for concept 2. Not all sound wave can evoke an auditory sensation, e.g., ultrasound. The medium in which the sound exists is often indicated by an appropriate adjective, e.g., airborne, water borne, structure borne.
sound absorption: Sound absorption is the change of sound energy into some other form, usually heat, in passing through a medium oron striking a surface.
sound barrier = sonic barrier.
sound energy: The energy which sound waves contribute to a particular medium.
sound energy density: At a point in a sound field, the sound energy contained in a given infinitesimal part of the medium divided by the volume of that part of the medium.; The terms instantaneous energy density, maximum energy density, and peak energy density have meanings analogous to the related terms used for sound pressure. In speaking of average energy density in general, it is necessary to distinguish between the space average (at a given instant) and the time average (at a given point).
sound energy flux: The average rate of flow of sound energy for one period through any specified area.; In a medium of density ρ for a plane or spherical free wave having a velocity of propagation c, the sound energy flux through the area S corresponding to an effective sound pressure p is J = ( p²S / ρc ) cos θ where θ = the angle between the direction of propagation of the sound and the normal to the area S.
sound energy flux density = sound intensity.
sound field: A region containing sound waves. See near field, far field.
sounding: 1. In geophysics, any penetration of the natural environment for scientific observation.; 2. In meteorology, same as upper air observation. However, a common connotation is that of a single complete radiosonde observation.; 3. = air sounding.
sounding rocket: A rocket that carries aloft equipment for making observations of or from the upper atmosphere. See air sounding. Compare probe, sense 3.; Usually a sounding rocket has a near vertical trajectory.
sound intensity: In a specified direction at a point, the average rate of sound energy transmitted in the specified direction through a unit area normal to this direction at the point considered. Also called sound energy flux density, sound power density.
sound level: Specifically, a weighted sound pressure level, obtained by the use of metering characteristics and the weightings A, B, or C specified in American Standard Publication Z24.3-1944: Sound Level Meters for Measurement of Noise and Other Sounds. The weighting employed pressure is 0.0002 microbar.; A suitable method of stating the weighting is, for example, The A-sound level was 43 decibels.
sound power: Of a source, the total sound energy radiated by the source per unit of time.
sound power density = sound intensity.
sound pressure: At a point, the total instantaneous pressure at that point in the presence of a sound wave minus the static pressure at that point. See effective sound pressure.
sound pressure level: In decibels, 20 times the logarithm to the base 10 of the ratio of the sound pressure to the reference pressure. The reference pressure must be explicitly stated.; The following reference pressures are in common use: (a) 2 X 10E-4 microbar, (b) 1 microbar. Reference pressure (a) is in general use for measurements concerned with hearing and with sound in air and liquids, whereas (b) has gained widespread acceptance for calibration of transducers and various kinds of sound measurements in liquids. Unless otherwise explicitly stated, it is to be understood that the sound pressure is the effective (root-mean-square) sound pressure. It is to be noted that in many sound fields the sound pressure ratios are not the square roots of the corresponding power ratios.
sound probe: A device that responds to some characteristic of an acoustic wave (e.g., sound pressure, particle velocity) and that can be used to explore and determine this characteristic in a sound field without appreciably altering that field.
sound wave: A mechanical disturbance advancing with infinite velocity through an elastic medium and consisting of longitudinal displacements of the medium, i.e., consisting of compressional and rarefactional displacements parallel to the direction of advance of the disturbance; a longitudinal wave. Sound waves are small-amplitude adiabatic oscillations. The wave equation governing the motion of sound waves has the form ² = (1/c²)(²/t²) where ² is the Laplace operator, is the velocity potential, c is the speed of sound, and t is the time; the density variations and velocities are small. As so defined, this includes waves outside the frequency limits of human hearing, which limits customarily define sound. Also called acoustic wave, sonic wave. See ultrasonic, infrasonic, pressure wave.; Gases, liquids, and solids transmit sound waves, and the propagation velocity is characteristic of the nature and physical state of each of these media. In those cases where a steadily vibrating sound generator acts as a source of waves, one may speak of a uniform wave train; but in other cases (explosions, lightning discharges) a violent initial disturbance sends out a principal wave, followed by waves of more or less rapidly diminishing amplitude.
source: 1. The location or device from which energy emanates as a sound source, heat source , etc.; 2. Specifically, in the mathematical representation of fluid flow, a hypothetical point or place from which fluid emanates.; The strength of a source; the rate of mass flow of unit density across a curve enclosing the source is given by Q = 2π r v_r where r is the distance from the source and v_r is the radial speed.; 3. Specifically, the device which supplies signal power to a transducer.
southbound node = descending node.
South Tropical Disturbance: An elongated dark band in the cloud surface of Jupiter at about the latitude of the Great Red Spot. It was first seen in 1901 as a dark spot which then spread rapidly. It has at times exceeded 180 degrees of longitude in length and, like the Red Spot, appears and disappears intermittently.
SP (abbr) = solid propellant.
space: 1. Specifically, the part of the universe lying outside the limits of the earth's atmosphere.; 2. More generally, the volume in which all celestial bodies, including the earth, move.
space-air vehicle: A vehicle operable either within or above the sensible atmosphere. Also called aerospace vehicle.
space biology = bioastronautics.
space capsule: A container used for carrying out an experiment or operation in space.; A capsule is usually assumed to carry an organism or equipment.
space charge: 1. The electric charge carried by a cloud or stream of electrons or ions in a vacuum or a region of low gas pressure when the charge is sufficient to produce local changes in the potential distribution.; 2. The net electric charge within a given volume.
space coordinates: A three-dimensional system of Cartesian coordinates by which a point is located by three magnitudes indicating distance from three planes which intersect at a point.
spacecraft: Devices, manned and unmanned, which are designed to be placed into an orbit about the earth or into a trajectory to another celestial body.; From 1957 through 1962 spacecraft were designated by the year and a Greek letter assigned in the order of launching, as 1958α for the first satellite of 1958. When more than one object was put in orbit by a single launch vehicle, each object was numbered, as 1961o2. (Space probes were not included in this system until 1960). Beginning January 1, 1963, arabic numerals supplanted Greek letters in the scientific designations of all spacecraft with a lifetime of more than 90 minutes. Thus, the first satellite launched in 1963 was 1963-1, the last was 1963-55. When more than one component is put in orbit, alphabetical suffixes are added to the designations, as 1963-4A. The letter A usually designates the component carrying the principle scientific payload; B, C, etc., are used as needed for any subsidiary payloads and then for inert components in order of maximum brightness. The designation system was promulgated formally in the COSPAR Guide to Rocket and Satellite Information and Data Exchange. The Guide has been published in full in COSPAR Information Bulletin No. 9, July 1962, and in IGY Bulletin No. 61, July 1962. Table XIV is a listing of scientific satellites and space probes launched through 1964 and is reprinted from the IG Bulletin (International Geophysics Bulletin) published by the National Academy of Sciences.
space equivalent: A condition within the earth's atmosphere that is virtually identical, in terms of a particular function, with a condition in outer space.; For example, at 50,000 feet, the drop in air pressure and the scarcity of oxygen creates a condition, so far as respiration is concerned, that is equivalent to a condition in outer space where no appreciable oxygen is present; thus, a physiological space equivalent is present in the atmosphere.
space medicine: A branch of aerospace medicine concerned specifically with the health of persons who make, or expect to make, flights into space beyond the sensible atmosphere.
space modulation: The combining of signals outside of an electronic device or conductor to form a signal of desired characteristics. See modulation.
space motion: Motion of a celestial body through space.; That component perpendicular to the line of sight is termed proper motion and that component in the direction of the line of sight, radial motion.
space polar coordinates: A system of coordinates by which a point on the surface of a sphere is located in three dimensions by (a) its distance from a fixed point at the center, called the pole; (b) the colatitude or angle between the polar axis (a reference line through the pole) and the radius vector (a straight line connecting the pole and the point); and (c) the longitude or angle between a reference plane through the polar axis and a plane through the radius vector and polar axis. See polar coordinates, spherical coordinates, cylindrical coordinates.
space probe: See probe, note, and spacecraft, note and Table XIV.
space reddening: The observed reddening, or absorption of shorter wavelengths, of the light from distant celestial bodies due to scattering by small particles in interstellar space. Compare red shift.
space simulator: 1. Any device used to simulate one or more parameters of the space environment used for testing space systems or components.; 2. Specifically, a closed chamber capable of approximately the vacuum and normal environments of space.
space suit: A pressure suit for wear in space or at very low ambient pressures within the atmosphere, designed to permit the wearer to leave the protection of a pressurized cabin.
span: 1. The dimension of a craft measured between lateral extremities; the measure of this dimension.; 2. Specifically, the dimension of an airfoil from tip to tip measured in a straight line.; Span is not usually applied to vertical airfoils.
spark discharge: That type of gaseous electrical discharge in which the charge transfer occurs intermittently along a relatively constricted path of high ion density, resulting in high luminosity. It is of short duration and to be contrasted with the nonluminous point discharge, with the diffuse corona discharge, and also with the continuous arc discharge.; The exact meaning to be attached to the term spark discharge varies somewhat in the literature. It is frequently applied to just the transient phase of the establishment of any arc discharge. A lightning discharge is a large-scale spark discharge, though its very length introduces certain details not found in laboratory short-spark processes.
spark spectrum: The spectrum of an ion. The degree of ionization, or order of the spectrum, is indicated by a Roman numeral following the symbol for the element. The first spark spectrum is indicated by II, the second by III, and so on. Thus Fe IV indicates the spectrum of an iron atom which has lost three electrons. See arc spectrum.
spatial: Pertaining to space.
spatio: A combining form meaning space.
special perturbations: A method of orbit determination by numerical integration which takes into account the perturbing forces which are causing the orbit to depart from the orbit as calculated by Kepler laws.
specific: A modifier generally implying per unit mass.
specific heat: The ratio of the heat absorbed (or released) by unit mass of a system to the corresponding temperature rise (or fall). If this ratio varies with temperature, it must be defined as a differential quotient dQ/dT, where dQ is the infinitesimal increment of heat per unit mass and dT is the infinitesimal increment of temperature.; For gases the thermodynamic process must be specified; two specific heats are defined, one being the specific heat in a constant-pressure process c_p = (dQ / dT)_pand the other, the specific heat in a constant-volume process c_v = (dQ / dT)_v In a perfect gas these are, by definition, constants with respect to temperature, and the difference of the specific heat at constant pressure and the specific heat at constant volume is equal to the gas constant: R = c_p - c_v
specific humidity: In a system of moist air, the (dimensionless) ratio of the mass of water vapor to the total mass of the system. The specific humidity may be approximated by the mixing ratio for many purposes: q = w /(1 + w ) where q is the specific humidity and w is the mixing ratio. See absolute humidity, relative humidity, dew point.
specific impulse (symbol I_sp): A performance parameter of a rocket propellant, expressed in seconds, equal to the thrust F in pounds divided by the weight flow rate in pounds per second: I_sp = F /; Specific impulse is also equivalent to the effective exhaust velocity divided by the gravitational acceleration.
specific power: The energy delivered per pound of fuel in a reactor or in a radioisotope power source.
specific propellant consumption: The reciprocal of the specific impulse, i.e., the required propellant flow to produce one pound of thrust in an equivalent rocket.
specific speed: Of a pump, a parameter used to predict pump performance.
specific thrust = specific impulse.
specific volume (symbol v ): Volume per unit mass of a substance. The reciprocal of density.
spectra: Plural of spectrum.
spectral: 1. Of or pertaining to a spectrum.; 2. Referring to thermal radiation properties, for ratios such as emittance, reflectance, and transmittance, at a specified wavelength; for powers, such as emissive power, within a narrow wavelength band centered on a specified wavelength.
spectral absorptance: See absorptance, note.
spectral emissivity: See emissivity, note.
spectral function: The Fourier representation of a given function; that is, the Fourier transform if the given function is aperiodic or the set of coefficients of the Fourier series if the given function is periodic. Also called spectrum. See continuous spectrum, discrete spectrum.
spectral line: A bright, or dark, line found in the spectrum of some radiant source. See absorption line, emission line.; Bright lines indicate emission, dark lines indicate absorption.
spectrograph: See spectroscope.
spectroheliogram: See spectroheliograph.
spectroheliograph: An instrument for taking photographs (spectroheliograms) of the image of the sun monochromatic light. The wavelength of light chosen for this purpose corresponds to one of the Fraunhofer lines, usually the light of hydrogen or ionized calcium. A similar instrument used for visual, instead of photographic, observations in a spectrohelioscope.
spectrohelioscope: See spectroheliograph, note.
spectrophotometer: A photometer which measures the intensity of radiation as a function of the frequency (or wavelength) of the radiation. Also called spectroradiometer. See Dobson spectrophotometer.; In one design, radiation enters the spectrophotometer through a slit and is dispersed by means of a prism. A bolometer having a fixed aperture scans the dispersed radiation so that the intensity over a narrow wave band is obtained as a function of frequency.
spectropyrheliometer: An instrument which measures the spectral distribution of the intensity of direct solar radiation. See pyrheliometer, spectrophotometer.
spectroscope: An apparatus to effect dispersion of radiation and visual display of the spectrum obtained.; A spectroscope with a photographic recording device is called a spectrograph.
spectroscopic binaries: See binary star, note.
spectrum: 1. In physics, any series of energies arranged according to wavelength (or frequency).; 2. The series of images produced when a beam of radiant energy is subject to dispersion.; 3. Short for electromagnetic spectrum or for any part of it used for a specific purpose as the radio spectrum (10 kilocycles to 300,000 megacycles).; 4. In mathematics, = function.; 5. In acoustics, the distribution of effective sound pressures or intensities measured as a function of frequency in specified frequency bands.
specular reflection: Reflection in which the reflected radiation is not diffused; reflection as from a mirror. Also called regular reflection, simple reflection. Compare diffuse reflection.; The angle between the normal to the surface and the incident beam is equal to the angle between the normal to the surface and the reflected beam. Any surface irregularities on a specular reflector must be small compared to the wavelength of the incident radiation.
specular reflector: Any surface exhibiting specular reflection. Also called regular reflector, simple reflector.
specular transmission density: See photographic transmission density, note.
speed: Rate of motion.; Rate of motion in a straight line is called linear speed, whereas change of direction per unit time is called angular speed. Speed and velocity are often used interchangeably although some authorities maintain that velocity should be used only for the vector quantity.
speed of light (symbol c ): The speed of propagation of electromagnetic radiation through a perfect vacuum; a universal dimensional constant equal to 299,792.5 +/- 0.4 kilometers per second. Also called velocity of light.
speed of relative movement: Also called relative speed. See relative movement.
speed of sound (symbol c_s): The speed of propagation of sound waves. In the atmosphere c_s = [γ (R*/M₀)T_M]^1/2 where γ is the ratio of specific heat of air at constant pressure to that a constant volume, R* is the universal gas constant, M₀ is the mean molecular weight of air at sea level, and T_M is the molecular scale temperature.; At sea level in the standard atmosphere, the speed of sound is 340.294 meters per second (1116.45 feet per second). The concept of the speed of sound in the atmosphere loses its applicability at about 90 kilometers where the mean of free path of air molecules approaches the wavelengths of sound waves.
sphere of influence: The surface in space about a planet where the ratio of the force with which the sun perturbs the motion of a particle about the planet, to the force of attraction of the planet equals the ratio of the force with which the planet perturbs the motion of a particle about the sun, to the force of attraction of the sun on the particle.; The volume inside this surface defines the region where the attracting body exerts the primary influence on a particle.
sphere of position: See line of position, note.
spherical angle: The angle between two intersecting great circles.
spherical coordinates: 1. A system of coordinates defining a point on a sphere or spheroid by its angular distances from a primary great circle and from a reference secondary great circle, as latitude and longitude. See celestial coordinates.; 2. = space polar coordinates.
spherical excess: The amount by which the sum of the three angles of a spherical triangle exceeds 180 degrees.
spherical stratification: See horizontal stratification.
spherical system: A trajectory measuring system, whose locus of the measured range is a sphere with the ground equipment at the center.; A unique point in space is determined by the intersection of three or more spheres. The term spherical system has been applied to systems using three or more slant ranges to determine space position.
spherical triangle: A closed figure having arcs of three great circles as sides.
spherical wave: A wave whose phase front surfaces are spheres. Such waves propagate from a point source.
spherics: Variant spelling of sferics.
spheroid: An ellipsoid; a figure resembling a sphere. Also called ellipsoid or ellipsoid of revolution from the fact that it can be formed by revolving an ellipse about one of its axes. If the shorter axis is used as the axis of revolution, an oblate spheroid results, and if the longer axis is used, a prolate spheroid results. The earth is approximately an oblate spheroid.
spheroidal excess: The amount by which the sum of the three angles of a triangle on the surface of a spheroid exceeds 180 degrees.
spicules: Bright spikes extending into the chromosphere of the sun from below.; They are several hundred miles in diameter and extend outward 5000 to 10,000 miles. Spicules have a lifetime of several minutes and may be related to granules.
spin = angular momentum (in atomic and nuclear physics).
spin axis: The axis of rotation of the rotor of a gyro.
spineward acceleration: See physiological acceleration.
spinner: Rotating part of a radar antenna used to impact any subsidiary motion in addition to the primary slewing of the beam.
spin rocket: A small rocket that imparts spin to a larger rocket vehicle or spacecraft.
spin stabilization: Directional stability of a spacecraft obtained by the action of gyroscopic forces which result from spinning the body about its axis of symmetry.
spin table: A flat round platform on which human and animal subjects can be placed in various positions and rapidly rotated, much as on a phonograph record, in order to simulate and study the effects of prolonged tumbling at high rates.; Complex types of tumbling can be simulated by mounting the spin table on the arm of a centrifuge.
spiral layer = Ekman layer.
spiral scanning: Scanning in which the direction of maximum radiation describes a portion of a spiral. The rotation is always in one direction.
spoiler: A plate, series of plates, comb, tube, bar, or other device that projects into the airstream about a body to break up or spoil the smoothness of the flow, especially such a device that projects from the upper surface of an airfoil, giving an increased drag and a decreased lift. Compare deflector, sense (a).; Spoilers are normally movable and consist of two basic types: the flap spoiler, which is hinged along one edge and lies flush with the airfoil or body when not in use, and the retractable spoiler, which retracts edgewise into the body.
spontaneous emission: The decay of an atom or ion in an excited energy state E_j to a lower state E_i without the influence of any external perturbation. This process results in the emission of a photon of energy hv = E_j - E_iwhere h is the Planck constant and v is the frequency.
spontaneous-ignition temperature: In testing fuels, the lowest temperature of a plate or other solid surface adequate to cause ignition in air of a fuel upon the surface.
sporadic D: See ionosphere.
sporadic E: See ionosphere.
sporadic meteor: A meteor which is not associated with one of the regularly recurring meteor showers or streams.
spores: The reproductive element of the lower forms of living organism, usually unicellular.
spray electrification = Lenard effect.
spray region = fringe region.
spread reflection: Reflection from a rough surface with large irregularities. Also called mixed reflection.
spurious disk: The round image of perceptible diameter of a star as seen through a telescope, due to diffraction of light in the telescope.
spurious emission = spurious radiation.
spurious radiation: 1. Any undesired emission from a radio transmitter.; 2. Any electromagnetic radiation from a radio receiver. Also called spurious emission.
spurious response: Output from a receiver due to a signal or signals having frequencies other than that to which the receiver is tuned.
spurious transmitter output: Any part of the radio frequency output of a transmitter which is not a component of the theoretical output as determined by the type of modulation and specified bandwidth limitations.
spurious tube counts: In radiation-counter tubes, counts other than background counts and those caused directly by the radiation to be measured.; Spurious counts are caused by failure of the quenching process, electrical leakage, and the like. Spurious counts may seriously affect measurement of background counts.
sputtering: Dislocation of surface atoms of a material from bombardment by high-energy atomic particles.
square wave: 1. An oscillation, the amplitude of which shows periodic discontinuities between two values, remaining constant between jumps.; 2. Specifically, in radar a pulse initiated by a rapid rise to peak power, maintained at a constant peak power over the finite pulse length, and terminated by rapid decrease from peak power.
squib: 1. Any of various small explosive devices.; 2. An explosive device used in the ignition of a rocket. Usually called an igniter.
squitch: A squib -operated switched.
squitter: Random firing, intentional or otherwise, of a transponder transmitter in the absence of interrogation.
SSB (abbr) = single sideband.
SS loran: Sky-wave synchronized loran, or loran in which the sky wave rather than the ground wave from the master controls the slave. SS loran is used with unusually long baselines.
stability: 1. The property of a body, as an aircraft or rocket, to maintain its attitude or to resist displacement, and, if displaced, to develop forces and moments tending to restore the original condition.; 2. Of a fuel, the capability of a fuel to retain its characteristics in an adverse environment, e.g. extreme temperature.
stability augmentation system: An auxiliary system to the basic manual vehicle control system whereby response of the control surfaces to inputs by the pilot can be adjusted to give a preselected vehicle response by selection of certain fixed gains in a standard feedback loop on control-surface output.
stabilized data: Radar data output corrected for tilt or roll of an unstabilized radar antenna, such as shipboard installations, etc.
stable platforms: A gyroscopic device so designed as to maintain a plane of reference in space regardless of the movement of the vehicle carrying the stable platform.
stadimeter: An instrument for determining the distance to an object of know dimension by measuring the angle subtended at the observer by the object. The instrument is graduated directly in distance.
stadimetric: Pertaining to a navigational fix which involves a measure of distance.
stage: 1. A self-propelled separable element of a rocket vehicle. See multistage rocket.; 2. A step or process through which a fluid passes, especially in compression or expansion.; 3. A set of stator blades and a set of rotor blades in an axial-flow compressor or in a turbine; an impeller wheel in a radial-flow compressor. See multistage compressor, single-stage compressor, single-stage turbine.
stage-and-a-half: A liquid-propellant rocket of which only part of the propulsion unit falls away from the rocket vehicle during flight, as in the case of booster rockets falling away to leave the sustainer engine to consume remaining fuel.
staging: The process or operation during the flight of a rocket vehicle whereby a full stage or half stage is disengaged from the remaining body and made free to decelerate or be propelled along its own flightpath. See separation.
stagnation point: A point in a field of flow about a body where the fluid particles have zero velocity with respect to the body.
stagnation pressure: 1. The pressure at a stagnation point.; 2. In compressible flow, the pressure exhibited by a moving gas or liquid brought to zero velocity by an isentropic process.; 3. = total pressure.; 4. = impact pressure.; Because of the lack of a standard meaning, stagnation pressure should be defined when it is used.
stagnation region: Specifically, the region at the front of a body moving through a fluid where the fluid has negligible relative velocity.
standard: 1. An exact value, or a concept, that has been established by authority or agreement, to serve as a model or rule in the measurement of a quantity or in the establishment of a practice or procedure.; 2. A document that establishes engineering and technical limitations and applications for items, materials, processes, methods, design, or engineering practices.
standard artillery atmosphere: A set of values describing atmospheric conditions on which ballistic computations are based: namely, no wind, a surface temperature of 15 degrees C, a surface pressure of 1000 millibars, a surface relative humidity of 78 percent, and a lapse rate which yields a prescribed density-altitude relation.
standard artillery zone: A vertical subdivision of the standard artillery atmosphere. It may be considered a layer of air of prescribed thickness and density.
standard atmosphere: 1. A hypothetical vertical distribution of atmospheric temperature, pressure, and density which, by international agreement, is taken to be representative of the atmosphere (see Table XV ) for purposes of pressure altimeter calibrations, aircraft performance calculations, aircraft and rocket design, ballistic tables, etc. The air is assumed to be devoid of dust, moisture, and water vapor and to obey the perfect gas law and the hydrostatic equation (the air is static with respect to the earth).; Standard atmospheres, sense 1, which have been used are: (a) The NACA standard atmosphere, also called U.S. standard atmosphere, prepared in 1925, which was supplanted by (b) The ICAO standard atmosphere, adopted in 1952, which was extended to greater altitudes by (c) The ARDC model atmosphere, 1956, and (d) The U.S. extension to the ICAO standard atmosphere, adopted in 1956, which has been revised by (e) The ARDC model atmosphere, 1959, which incorporated some satellite data which has been supplanted by (f) The U.S. Standard Atmosphere-1962. (See Table XV ).; 2. (abbr atm). A standard unit of atmospheric pressure, defined as that pressure exerted by a 760-millimeter column of mercury at standard gravity (980.665 centimeters per second per second) at temperature 0 degrees C.; 1 standard atmosphere = 760 millimeters of mercury; = 29.9213 inches of mercury; = 1013.250 millibars.
standard conditions = standard temperature and pressure.
standard deviation (symbol σ): A measure of the dispersion of data points around their mean value. It is the positive square root of the arithmetic mean of the squares of the deviation from the arithmetic mean of the population: where m is arithmetic mean; d is deviation from the arithmetic mean; and n is number of points.
standard-deviation estimate: See standard deviation, note.
standard error of estimate (symbol S): A measure of the dispersion (scatter) of data points with respect to a curve of regression. S is the positive square root of the arithmetic mean of the squares of the deviations from a curve of regression: where d is deviation from R ; R is curve of regression; and n is number of points.; S is a measure of the variation to be expected in making predictions from the regression equation.
standard gravity: See gravity.
standardization: 1. The act or process of reducing something to, or comparing it with, a standard.; 2. A measure of uniformity.; 3. A special case of calibration whereby a known input is applied to a device or system for the purpose of verifying the output or adjusting the output to a desired level or scale factor.; Applied to transducers, standardization indicates adjustments of the output to a standard value within specified limits of error.
standardize = normalize.
standard pressure: 1. In meteorology, usually a pressure of 1000 millibars, but other pressures may be used as standard for specific purposes.; 2. In physics, a pressure of 1 standard atmosphere.
standard propagation: The propagation of radio energy over a smooth spherical earth of uniform dielectric constant and conductivity under conditions of standard refraction in the atmosphere, i.e., an atmosphere in which the index of refraction decreases uniformly with height at a rate of 12 N-units per 1000 feet. See superstandard propagation, substandard propagation, standard atmosphere.; Standard propagation results in a ray curvature due to refection which has a value approximately one-fourth that of the earth's curvature, giving a radio horizon which is about 15 percent greater than the distance to the geometrical horizon. This is equivalent to straight-line propagation over a fictitious earth whose radius is four-thirds the radius of the actual earth.
standard refraction: The refraction which would occur in an idealized atmosphere in which the index of refraction decreases uniformly with height at the rate of 39 X 10E-6 per kilometer. See standard propagation.; Standard refraction may be included in ground-wave calculations by use of an effective earth radius of 8.5 X 10E6 meters, or four-thirds the geometrical radius of the earth.
standard temperature: 1. A temperature that depends upon some characteristic of some substance, such as the melting, boiling, or freezing point, that is used as a reference standard of temperature.; 2. In physics, usually the ice point (0 degrees C); less frequently, the temperature of maximum water density (4 degrees C).; 3. In meteorology, this has no generally accepted meaning, except that it may refer to the temperature at zero altitude in the standard atmosphere (15 degrees C).
standard temperature and pressure: (abbr STP). Usually a temperature of 0 degrees C but also used to designate a temperature of 15 degrees C and 1 standard atmosphere (see standard pressure).
standard time: See time.
standard value of gravity: See acceleration of gravity.
standing wave: A periodic wave having a fixed distribution in space which is the result of interference of progressive waves of the same frequency and kind. Such waves are characterized by the existence of nodes or partial nodes and antinodes that are fixed in space.
stand talker: A person on a static test stand responsible for coordinating and timing the preparations for a static test.
Stanton number: (symbol N_St). A number expressing the ratio of the heat transmission perpendicular and parallel to the flow direction, defined as h/c_p ρv where h is the heat transfer coefficient, c_p is the specific heat, ρ is the density, and v is the flow velocity.
star: 1. A self-luminous celestial body exclusive of nebulas, comets, and meteors; any one of the suns seen in the heavens. Distinguished from planets or planet satellites that shine by reflected light. See navigational stars, table VII.; 2. Any luminous body seen in the heavens.; The star (sense 1) of our solar system is the sun. In sense 2, star sometimes excludes the sun, the moon, and manmade satellites from the category.
star catalogue: A listing of stars giving positions for a specified mean equinox and equator. Stars are often identified by catalogue numbers.
star classification: Stars are classified by their spectra, designated by letters, sometimes with numerical subdivisions, as the sun is a G1-type star. The seven main types with their principal spectral characteristics are, in order of decreasing temperature:
O - He II absorption;
B - He I absorption;
A - H absorption;
F - Ca II absorption;
G - strong metallic lines;
K -bands developing;
M - very red.
Also, the letters, P, W, Q, R, N, and S are used to designate comparatively rare types of stars which do not fall into the main series.
star cluster: A group of stars physically close together in space.
star grain = star perforated grain.
Stark effect: The broadening or splitting of a spectral line observed when a luminous gas is acted upon by a strong electric field.
star perforated grain: A hollow rocket propellant grain with the cross section of the hole having a multipointed shape.
starting pressure: In rocketry, the minimum chamber pressure required to establish shock-free flow in the exit plane of a supersonic nozzle.
star tracker: A telescopic instrument on a rocket or other flight borne vehicle that locks onto a celestial body and gives guidance reference to the vehicle during flight. See celestial guidance, sun tracker.
state of the art: The level to which technology and science have at any designated cutoff time been developed in a given industry or group of industries.
state parameter = thermodynamic function of state.
state variable: Any independent variable in a problem which must be specified to define a condition of state, as for example a component of position.
static: 1. Involving no variation with time.; 2. Involving no movement, as in static test.; 3. Any radio interference detectable as noise in the audio stage of a receiver.
static conversion: Energy conversion in which no moving parts or equipment are utilized.
static firing: The firing of a rocket engine in a hold-down position to measure thrust and accomplish other tests.
static pressure (symbol p): 1. The pressure with respect to a stationary surface tangent to the mass-flow velocity vector.; 2. The pressure with respect to a surface at rest in relation to the surrounding fluid.
static test: An instance of static testing.
static testing: The testing of a rocket or other device in a stationary or hold-down position, either to verify structural design criteria, structural integrity, and the effects of limit loads or to measure the thrust of a rocket engine.
station: A location where measurements are made, e.g., along an airfoil in a wind tunnel test.
stationary orbit: An orbit in which the satellite revolves about the primary at the angular rate at which the primary rotates on its axis. From the primary, the satellite thus appears to be stationary over a point on the primary.; A stationary orbit with respect to the earth is commonly called a 24-hour orbit.
stationary wave: A standing wave in which the net energy flux is zero at all points.; Stationary waves can only be approximated in practice.
station constants: In tracking and telemetry, constants usually associated with instrumentation sites, e.g., survey coordinates, zeroing correction, etc.
station error: In geodesy and surveying, the difference, usually negligible, between the astronomical and geodetic latitudes, due to local gravitational anomalies.
station keeping: The sequence of maneuvers that maintains a vehicle in a predetermined orbit.
station pressure: The atmospheric pressure computed for the level of the station elevation.; This may or may not be the same as either the climatological station pressure or the actual pressure, the difference being attributable to the difference in reference elevations. Station pressure usually is the base value from which sea-level pressure and altimeter setting are determined.
stator: In machinery, a part or assembly that remains stationary with respect to a rotating or moving part or assembly such as the field frame of an electric motor or generator, or the stationary casing and blades surrounding an axial-flow-compressor rotor or turbine wheel; a stator blade.
statute mile: 5280 feet = 1.6093 kilometers = 0.869 nautical mile. Also called land mile.
steady flight: Flight without accelerations or oscillations.
steady flow: A flow whose velocity vector components at any point in the fluid do not vary with time. See streamline flow.
steady state: 1. The condition of a substance or system whose local physical and chemical properties do not vary with time.; 2. Specifically, the stable operating condition of a reactor in which the neutron inventory remains constant; that is, the effective multiplication factor k_e is equal to 1.
steady-state problem: See initial-value problem.
steady-state vibration: A condition that exists in a system if the velocity of each particle is a continuing periodic quantity.
steerable antenna: A directional antenna whose major lobe can be readily shifted in direction.
steering function: An empirical relation based on the relative distance and velocity of the target, used in guidance of rockets and spacecraft.
Stefan-Boltzmann constant: (symbol σ). A universal constant of proportionality between the radiant emittance of a black body and the fourth power of the body's absolute temperature; 5.6697 X 10E-5 erg centimeter squared second degrees KE4.
Stefan-Boltzmann law: One of the radiation laws which states that the amount of energy radiated per unit time from a unit surface area of an ideal black body is proportional to the fourth power of the absolute temperature of the black body. The law is written: E = σT⁴where E is the emittance of the black body; σ is the Stefan-Boltzmann constant; and T is the absolute temperature of the black body. Also called Stefan law.; This law was established experimentally by Stefan and was given theoretical support by thermodynamic reasoning due to Boltzmann. This law may be deduced by integrating Planck law over the entire frequency spectrum.
Stefan law = Stefan-Boltzmann law.
stellar: Of or pertaining to stars.
stellarator machine: An experimental thermonuclear device where containment in a magnetic field is achieved by closing the field upon itself and thus allowing the particles to perform endless spiral motion.
stellar classification: See star classification.
stellar inertial guidance: The guidance of a flight-borne vehicle by a combination of celestial and inertial guidance; the equipment which accomplishes the guidance.
stellar magnitude = magnitude.
stellar map matching: A process during the flight of a vehicle by which a chart of the stars set into the guidance system is automatically matched with the position of the stars observed through telescopes so as to give guidance to the vehicle. See map-matching guidance.
stellar parallax = heliocentric parallax.
stellar scintillation = astronomical scintillation.
St. Elmo's fire = corona discharge.
step rocket = multistage rocket.
steradian: The unit solid angle which cuts unit area from the surface of a sphere of unit radius centered at the vertex of the solid angle. There are 4 steradians in a sphere.
stereochemistry: Chemistry dealing with the arrangement of atoms and molecules in three dimensions.
sternumward acceleration: See physiological acceleration.
stiction = static friction.
stiffness: The ratio of change of force (or torque) to the corresponding change in translational (or rotational) displacement of an elastic element.
stilb: A unit of luminance (or brightness) equal to 1 international candle per square centimeter. Compare apostilb.
stimulus: 1. = excitation.; 2. = measurand.
Stirling cycle: A theoretical heat engine cycle in which heat is added at constant volume, followed by isothermal expansion with heat addition. The heat is then rejected at constant volume, followed by isothermal compression with heat rejection.; If a regenerator is used so that heat rejected during the constant-volume process is recovered during heat addition at constant volume, the thermal efficiency of the Stirling cycle is the same as for the Carnot cycle, with less compressive work needed.
stochastic: Conjectural; in statistical analysis, = random.
stochastic process: An ordered set of observations in one or more dimensions, each being considered as a sample of one item from a probability distribution.
stoichiometric: Of a mixture of chemicals, having the exact proportions required for complete chemical combination, applied especially to combustible mixtures used as propellants.
stooping: An atmospheric refraction phenomenon, a mirage; a special case of sinking in which the curvature of light rays due to atmospheric refraction decreases with elevation so that the visual image of a distant object is foreshortened in the vertical.; The opposite of stooping is towering.
stopping point: The end of the highly luminous path of a visual meteor. Also called Hemmungspunkt.
storable: Of a liquid; subject to being placed and kept in a tank without benefit of special measures for temperature or pressure control, as in storable propellant.
storage: 1. The act of storing information. See store.; 2. Any device in which information can be stored. Also called a memory device.; 3. In a computer, a section used primarily for storing information. Such a section is sometimes called a memory or a store.; The physical means of storing information may be electrostatic, ferroelectric, magnetic, acoustic, optical, chemical, electronic, electrical, mechanical, etc., in nature.
storage capacity: The amount of information, usually expressed in bits (i.e., the log₂ of the number of distinguishable states in which the storage can exist), that can be retained in storage. Also called memory capacity.
store: 1. To retain information in a device from which it can later be withdrawn.; 2. To introduce information into such a device.; 3. A container, rocket, bomb, or vehicle carried externally in a craft.
straddle carrier: A ground vehicle that carries its load suspended between its wheels.
strain: The deformation produced by a stress divided by the original dimension.
strain gage: An instrument used to measure the strain or distortion in a member or test specimen (such as a structural part) subjected to a force.
stratosphere: See atmospheric shell.
stratosphere radiation: Any infrared radiation involved in the complex infrared exchange continually proceeding within the stratosphere.
stream: A group of meteoroids with nearly identical orbits, also called meteor stream.
streamline: A line whose tangent at any point in a fluid is parallel to the instantaneous velocity vector of the fluid at that point. The differential equations of the streamlines may be written dr X v = 0, where dr is an element of the streamline and v is the velocity vector; or in Cartesian coordinates, dx / u = dy /v = dz /w, where u, v, w, are the fluid velocities along the orthogonal X, Y, Z axes, respectively.; In steady-state flow the streamlines coincide with the trajectories of the fluid particles; otherwise, the streamline pattern changes with time. See free streamline. Compare trajectory.
streamline flow = laminar flow.
stress: 1. The force per unit area of a body that tends to produce a deformation.; 2. The effect of a physiological, psychological, or mental load on a biological organism which causes fatigue and tends to degrade proficiency.
stress concentration: In structures, a localized area of high stress. See stress raiser.
stress cycle: A variation of stress with time, repeated periodically and identically. See fatigue.
stress raisers: Changes in contour or discontinuities in a structure that cause local increases in stress.
stress ratio: The ratio of the minimum stress to the maximum stress occurring in one stress cycle.
stress tensor: The complete set of stress components in a solid or fluid medium, which are written as a tensor τ_ij. It has nine components, one for each of the coordinate faces of an imaginary element upon which the stress acts ( j = x, y, z ) and for each direction in which the stress is directed ( i = x, y, z ).; By definition, an inviscid fluid is one in which the six tangential stresses (i +/- j) are zero, and the three normal stresses (i = j) are equal to the negative of the pressure.
stretchout: An action whereby the time for completing an action, especially a contract, is extended beyond the time originally programmed or contracted for.
strewn field: See tektite.
stringer: A slender, lightweight, lengthwise fill-in structural member in a rocket body, or the like, serving to reinforce and give shape to the skin.
Strouhal number (symbol N_Str): A nondimensional number occurring in the study of periodic or quasiperiodic variations in the wake of objects immersed in a fluid stream: N_Str = nl / u where n is a frequency; l is a representative length, and u is a representative velocity of the stream.
structural weight = construction weight.
subassembly: An assembly that is a component part of a larger assembly.
subastral point = substellar point.
subatomic particle: Any particle of less than atomic mass, e.g., the electron, proton, and neutron, also called atomic particle.; Subatomic particles are classified by relative mass into four groups: leptons, mesons, nucleons, and hyperons, from lowest to highest masses, respectively.
subaudio frequency: A frequency below the audiofrequency range, below about 15 cycles per second.
subcarrier: A carrier which is applied as a modulating wave to modulate another carrier or an intermediate subcarrier.
subcarrier oscillator: In a telemetry system, the oscillator which is directly modulated by the measurand or by the equivalent of the measurand in terms of changes in the transfer elements of a transducer.
subchannel: In a telemetry system, the route required to convey the magnitude of a single subcommutated measurand.
subcommutation: In telemetry, commutation of additional channels with output applied to individual channels of the primary commutator.; Subcommutation is called synchronous if its rate is a submultiple of that of the primary commutator. Unique identification must be provided for the subcommutation frame pulse.
subframe: In telemetry, a complete sequence of frames during which all subchannels of a specific channel are sampled once.
subgravity: A condition in which the acceleration acting on a body is less than normal gravity, between 0 and 1 g.
subharmonic: A sinusoidal quantity having a frequency that is an integral submultiple of the fundamental frequency of a periodic quantity to which it is related.
sublimation: The transmission of a substance directly from the solid state to the vapor state, or vice versa, without passing through the intermediate liquid state. See condensation, evaporation.
subliming ablator: An ablation material characterized by sublimation of the material at the heated surface.
sublunar point: The geographical position of the moon; that point on the earth at which the moon is in the zenith at a specified time.
subpermanent magnetism = permanent magnetism.: The expression subpermanent magnetism is sometimes used because of the slow dissipation of such magnetism, but the expression permanent magnetism is considered preferable.
subrefraction: Less-than-normal refraction, particularly as related to atmospheric refraction.; Greater-than-normal refraction is called super refraction.
subroutine: A set of instructions necessary to direct a computer to carry out a well-defined mathematical or logical operation; a submit of a routine, usually coded in such a manner that it can be treated as a black box by the routine using it.
subsatellite point: Intersection of the local vertical passing through a satellite in orbit with the earth's surface.
subsolar point: The geographical position of the sun; that point on the earth at which the sun is in the zenith at a specified time.
subsonic: In aerodynamics, of or pertaining to, or dealing with speeds less than acoustic velocity as in subsonic aerodynamics.
subsonic flow: Flow of a fluid, as air over an airfoil, at speeds less than acoustic velocity.; Aerodynamic problems of subsonic flow are treated with the assumption that air acts as an incompressible fluid.
substandard propagation: The propagation of radio energy under conditions of substandard refraction in the atmosphere, that is, refraction by an atmosphere or section of the atmosphere in which the index of refraction decreases with height at a rate of less than 12 N-units per 1000 feet. See standard propagation, superstandard propagation.; Substandard propagation produces a less-than-normal downward bending or even an upward bending of radio waves as they travel through the atmosphere, giving closer radio horizons and decreased radar and radio coverage. It results primarily when propagation takes place through a layer in which moisture remains constant or increases with height.
substandard refraction: Also called subrefraction. See substandard propagation.
substantial derivative = individual derivative.
substellar point: The geographical position of a star; that point on the earth at which the star is in the zenith at a specified time. Also called subastral point.
substratosphere: Loosely and nontechnically, the very high troposphere.
subtend: To be opposite, as an arc of a circle subtends an angle at the center of the circle , the angle being formed by the radii joining the ends of the arc with the center.
sudden-commencement magnetic storm: A magnetic storm characterized by a world-wide sudden commencement which takes place in a matter of minutes and shows no recurrence after 27 days, the period of rotation of the sun.
sudden ionospheric disturbance: (abbr SID). A complex combination of sudden changes in the condition of the ionosphere and the effects of these changes.; The following are the most important effects accompanying a sudden ionospheric disturbance: (a) radio fadeout, a condition in which there is a marked and abrupt increase in absorption in the D-region for high frequency radio waves (2 to 3 megacycles) and a consequent loss of long-distance radio reception in this range of frequencies; (b) magnetic crotchet, a sudden change in the earth's magnetic field due to an increase in the conductivity of the lower ionosphere, the change being in the nature of an augmentation of the normal quiet-day magnetic change; (c) sudden enhancements of long-wave atmospherics recorded in the frequency range between 10 and 100 kilocycles due to the improved reflectivity at oblique incidence of the D-region for such low-frequency radio waves; (d) sudden phase anomalies of discrete low-frequency radio waves (10 to 100 kilocycles) due to descent of the D-layer; and (e) sudden field-strength anomalies of distant low-frequency radio signals (10 to 100 kilocycles) due to interference between the groundwave and the skywave. A sudden ionospheric disturbance usually occurs a few minutes after a solar flare and is noted only on the sunlit side of the earth. The return of the ionosphere to its normal condition following a pronounced sudden ionospheric disturbance usually takes from half an hour to an hour, sometimes longer.
summer solstice: 1. That point on the ecliptic occupied by the sun at maximum northerly declination. Sometimes called June solstice, first point of Cancer.; 2. That instant at which the sun reaches the point of maximum northerly declination, about June 21.
sun: The star at the center of the solar system, around which the planets, planetoids, and comets revolve. It is a G-type star.; The sun visible in the sky is called apparent or true sun. A fictitious sun conceived to move eastward along the celestial equator at a rate that provides a uniform measure of time equal to the average apparent time is called mean sun; a fictitious sun conceived to move eastward along the ecliptic at the average rate of the apparent sun is called dynamical mean sun.
sunrise: The crossing of the visible horizon by the upper limb of the ascending sun.
sunset: The crossing of the visible horizon by the upper limb of the descending sun.
sunspot: A relatively dark area on the surface of the sun consisting of a dark central umbra surrounded by a penumbra which is intermediate in brightness between the umbra and the surrounding photosphere. See relative sunspot number.; Sunspots usually occur in pairs with opposite magnetic polarities. They have a lifetime ranging from a few days to several months. Their occurrence exhibits approximately an 11-year period (the sunspot cycle).
sunspot cycle: A cycle with an average length of 11.1 years but varying between about 7 and 17 years in the number and area of sunspots, as given by the relative sunspot number. This number rises from a minimum of 0 to 10 to a maximum of 50 to 140 about 4 years later, and then declines more slowly.; An approximate 11-year cycle has been found or suggested in geomagnetism, frequency of aurora, and other ionospheric characteristics. The u-index of geomagnetic intensity variation shows one of the strongest known correlations to solar activity. Eleven-year cycles have been suggested for various tropospheric phenomena, but none of these has been substantiated.
sunspot number: See relative sunspot number.
sunspot relative number = relative sunspot number.
sun's way: The path of the solar system through space. See solar apex.
sun tracker: A species of star tracker designed to lock onto the sun to afford guidance to a rocket or other flight-borne object. See star tracker.
superadiabatic lapse rate: An environmental lapse rate greater than the dry-adiabatic lapse rate, such that potential temperature decreases with height.
superalloy: An alloy developed for very high temperature service where relatively high stresses (tensile, thermal, vibratory, and shock) are encountered and where oxidation resistance is frequently required.
supercommutation: Commutation by connection of single data input source to equally spaced contacts of the commutator (cross-patching).; Corresponding crosspatching is required at the decommutator.
super high frequency (abbr SHF).: See frequency bands.
superior conjunction: The conjunction of a planet and the sun when the sun is between the earth and the other planet.
superior mirage: A spurious image of an object formed above its true position by abnormal atmospheric refraction conditions; opposite to an inferior mirage. Compare towering, looming, inferior mirage.; Superior mirages occur when the temperature lapse rate near the earth's surface is less than its normal value or, especially, when the temperature actually increases with height. Under these conditions the velocity of light increases upward in such a way that light rays are bent downward as they propagate through the layer in quasi-horizontal directions. The downward curvature gives the impression that the position of the object viewed is well above its true position in space. The object also appears inverted. Complex combination of superior and inferior mirages may occur with unusual density stratifications.
superior planets: The planets with orbits larger than that of the earth: Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.
superior transit = upper transit.
superpressure balloon: See constant-level balloon, note.
superrefraction = superstandard refraction.
supersonic: Of or pertaining to, or dealing with, speeds greater than the acoustic velocity. Compare with ultrasonic.
supersonic compressor: A compressor in which a supersonic velocity is imparted to the fluid relative to the rotor blades, the stator blades, or to both the rotor and stator blades, producing oblique shock waves over the blades to obtain a high pressure rise.
supersonic diffuser: A diffuser designed to reduce the velocity and increase the pressure of fluid moving at supersonic velocities.
supersonic flow: In aerodynamics, flow of a fluid over a body at speeds greater than the acoustic velocity and in which the shock waves start at the surface of the body. Compare hypersonic flow.
supersonic nozzle: A converging-diverging nozzle designed to accelerate a fluid to supersonic speed.
supersonics: Specifically, the study of aerodynamics of supersonic speeds. See hypersonics.
superstandard propagation: The propagation of radio waves under conditions of superstandard refraction (superrefraction) in the atmosphere, that is, refraction by an atmosphere or section of the atmosphere in which the index of refraction decreases with height at a rate of greater than 12 N-units per 1000 feet. See standard propagation, substandard propagation.; Superstandard propagation produces a greater-than-normal downward bending of radio waves as they travel through the atmosphere, giving extended radio horizons and increased radar coverage. It results primarily from propagation through layers near the earth's surface in which the moisture lapse rate is greater than normal, or the temperature lapse rate less than normal, or both. A condition in which warn dry air moves out over a cool water surface is an example of superrefraction. A layer in which the downward bending is greater than the curvature of the earth is called a radio duct. Frequently, the general term, anomalous propagation, is used for superstandard propagation.
superstandard refraction: Refraction by an atmosphere or section of the atmosphere in which the index of refraction decreases with height at a rate greater than 12 N-units per 1000 feet. Also called superrefraction.
supplement: An angle equal to 180 degrees minus a given angle. Thus 110 degrees is the supplement of 70 degrees and the two are said to be supplementary. See complement, explement.
supplementary angles: Two angles whose sum is 180 degrees.
support equipment: See ground support equipment.
surface: 1. A two-dimensional extent; the outside or superficies of any body; especially, the surface of the earth, either land or water, used in combinations as surface-to-air, etc.; 2. A wing, rudder, propeller blade, vane, hydrofoil, or the like - applied in this sense to the entire structure or body.
surface boundary layer: That thin layer of air adjacent to the earth's surface, extending up to the so-called anamometer level (the base of the Ekman layer). Within this layer the wind distribution is determined largely by the vertical temperature gradient and the nature and contours of the underlying surface; shearing stresses are approximate constant. Also called surface layer, friction layer, atmospheric boundary layer, ground layer. See logarithmic velocity profile, planetary boundary layer, free atmosphere.
surface duct: An atmospheric duct for which the lower boundary is the surface of the earth.
surface layer = surface boundary layer.
surface of position: A surface on some point of which a craft is located. See line of position, fix.
surge: A transient rise in power, pressure, etc., such as a brief rise in the discharge pressure of a rotary compressor.
survey: The process of determining accurately the position, extent, contour, etc., of an area, usually for the purpose of preparing a chart.
suspended phase: See suspension.
suspension: In physical chemistry, a system composed of one substance (suspended phase, suspensoid) dispersed throughout another substance (suspending phase) in a moderately finely divided state, but not so finely divided as to acquire the stability of a colloidal system.; Given sufficient time, a suspension will, be definition, separate itself by gravitational action into two visibly distinct portions, whereas a colloidal system, by definition, is stable. Dust in the atmosphere is an example of a suspension of a solid in a gas.
suspensoid: See suspension.
sustainer: Anything that acts to sustain an action or movement already begun; specifically, a sustainer engine.
sustainer engine: A rocket engine that maintains the velocity of a rocket vehicle once it has achieved its programmed velocity by use of booster or other engine.; This term is applied, for example, to the remaining engine of the Atlas after the two booster engines have been jettisoned. The term is also applied to a rocket engine used on an orbital flider to provide the small amount of thrust now and then required to compensate for the drag imparted by air particles in the upper atmosphere.
sweat cooling = transpiration cooling.
sweep: The motion of the visible dot across the face of a cathode-ray tube, as a result of deflections of the electron beam.; A linear time-base sweep has a constant sweep speed before retrace. An expanded time-base sweep is produced if the sweep speeds is increased during a selected part of the cycle; a delayed time-base sweep if the start of the sweep is delayed, usually to provide an expanded scale for a particular part. A sweep intended primarily for measurement of range may be called a range sweep. See trace.
swing-around trajectory: A planetary round trip trajectory which requires no propulsion at the destination planet, but uses the planet's gravitational field to effect the necessary orbit change to return to earth.
synchrocyclotron: A cyclotron in which the frequency of the electric field is frequency modulated to permit the acceleration of particles to relativistic energies. Also called FM cyclotron.
synchronism: The relationship between two or more periodic quantities of the same frequency when the phase difference between them is zero or constant at a predetermined value.
synchronous: Coincident in time, phase, rate, etc.
synchronous computer: A computer in which the starting time of every ordinary operational cycle is controlled by signals which occur at regular intervals. Contrast with asynchronous computer.
synchronous satellite: An equatorial west-to-east satellite orbiting the earth at an altitude of approximately 35,900 kilometers at which altitude it makes one revolution in 24 hours, synchronous with the earth's rotation.
synchrotron: A device for accelerating particles, ordinarily electrons, in a circular orbit in an increasing magnetic field by means of an alternating electric field applied in synchronism with the orbital motion.
synergic ascent: The ascent of a rocket vehicle along a synergic curve.
synergic curve: A curve plotted for the ascent of a rocket vehicle calculated to give the vehicle an optimum economy in fuel with an optimum velocity.; This curve, plotted to minimize air resistance, starts off vertically, but bends towards the horizontal between 20 and 60 miles altitude to minimize the thrust required for vertical ascent.
synodical month: The average period of revolution of the moon about the earth with respect to the sun, a period of 29 days 12 hours 44 minutes 2.8 seconds.; This is sometimes called the month of the phases, since it extends from new moon to the next new moon. Also called lunation.
synodic period: The interval of time between and planetary configuration of a celestial body, with respect to the sun, and the next successive same configuration of that body, as from inferior conjunction to inferior conjunction.
synodic satellite: A hypothetical earth satellite, situated 0.84 of the distance to the moon on a line joining the centers of the earth and moon and having the same period of revolution as the moon.
synoptic: Pertaining to or affording an overall view.; In meteorology, this term refers to meteorological data obtained simultaneously over a wide area for the purpose of presenting a comprehensive and nearly instantaneous picture of the state of the atmosphere. Thus, to a meteorologist, synoptic takes on the additional connotation of simultaneity.
synoptic correlation = Eulerian correlation.
synoptic meteorology: The study and analysis of weather information gathered at the same time. See synoptic.
syntony: The situation of two or more oscillating circuits having the same resonance frequency.
system: 1. Any organized arrangement in which each component part acts, reacts, or interacts in accordance with an overall design inherent in the arrangement.; 2. Specifically, a major component of a given vehicle such as a propulsion system or a guidance system. Usually called a major system to distinguish it from the systems subordinate or auxiliary to it.; The system of sense 1 may become organized by a process of evolution, as in the solar system, or by deliberate action imposed by the designer, as in a missile system or an electrical system. In sense 2, the system embraces all its own subsystems including checkout equipment, servicing equipment, and associated technicians and attendants. When the term is preceded by such designating nouns as propulsion or guidance, it clearly refers to a major component of the missile. Without the designating noun, the term may become ambiguous. When modified by the word major, however, it loses its ambiguity and refers to a major component of the missile.
systematic error: An error that is always a function of the magnitude of the quantity observed.; When the error is constant it is called a bias error. Systematic errors are often caused by false elements in an instrument. An example is an eccentrically mounted azimuth circle or an azimuth circle with graduation errors.
system of astronomical constants: An interrelated group of values constituting a model of the earth and the motions which together with the theory of celestial mechanics serves for the calculations of ephemerides. See astronomical constants, note and tables II and III.
syzygy: A point of the orbit or a planet or satellite at which it is in conjunction or opposition.; The term is used chiefly in connection with the moon, when it refers to the points occupied by the moon at new and full phase.

Back to Table of Contents