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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.
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The aggregate crosstalk from a large number of communications channels.
Babinet point
One of the three commonly detectable points of zero polarization of diffuse sky radiation, neutral points, lying along the vertical circle through the sun; the other two are the Arago point and Brewster point.
The Babinet point typically lies only 15° to 20° above the sun, and hence is difficult to observe because of solar glare. The existence of this neutral point was discovered by Babinet in 1840.
Any effect in a sensor or other apparatus or system above which the phenomenon of interest must manifest itself before it can be observed. See background counts, background noise.
background counts
In radiation counters, responses of the counting system caused by radiation coming from sources other than that to be measured.
background luminance
In visual-range theory, the luminance (brightness) of the background against which a target is viewed. Compare adaptation luminance.
background noise
1. In recording and reproducing, the total system noise independent of whether or not a signal is present. The signal is not to be included as part of the noise.
2. In receivers, the noise in the absence of signal modulation on the carrier.
Ambient noise detected, measured, or recorded with the signal part of the background noise. Included in this definition is the interference resulting from primary power supplies, that separately is commonly described as hum.
background return
See clutter.
Dead space or unwanted movement in a control system.
An undoing of things already done during a countdown, usually in reverse order.
back pressure
Pressure exerted backward; in a field of fluid flow, a pressure exerted contrary to the pressure producing the main flow.
back radiation = counterradiation.
back scatter = backward scatter.
back scattering = backward scatter.
back-scattering cross section
See scattering cross section.
back-to-chest acceleration
See physiological acceleration, table.
1. An item kept available to replace an item which fails to perform satisfactorily.
2. A redundant component in a system which is not the normally active (or prime, primary) component. Also known as second-string.
backward scatter
The scattering of radiant energy into the hemisphere of space bounded by a plane normal to the direction of the incident radiation and lying on the same side as the incident ray; the opposite of forward scatter. Also called back scattering .
Atmospheric backward scatter depletes 6 to 9 percent of the incident solar beam before it reaches the earth's surface.
In radar usage,
backward scatter refers only to that radiation scattered at 180° to the direction of the incident wave.
backward wave
In traveling-wave tubes, a wave whose group velocity is opposite to the direction of electron-stream motion.
A plate, grating, or the like used especially to block, hinder, or divert a flow or to hinder the passage of something, as: (a) A plate used to conduct, or help to conduct, a flow of cooling air around an engine cylinder. (b) A plate, wall, or the like in a fuel tank or other liquid container, used especially to prevent sloshing of the contents. (c) A ridge or wall on the top of a piston in a two-stroke-cycle engine, used to deflect the incoming mixture upward and divert it from the exhaust port. (d) A plate in the forward section of a pitot tube, used to reduce turbulence in the tube and to prevent dirt, moisture, etc., from entering the system.
bailout bottle
A personal supply of oxygen usually contained in a cylinder under pressure and utilized when the individual has left the central oxygen system as in a parachute jump.
The degassing of surfaces of a vacuum system by heating during the pumping process.
1. The equilibrium attained by an aircraft, rocket, or the like when forces and moments are acting upon it so as to produce steady flight, especially without rotation about its axes; also used with reference to equilibrium about any specified axis, as, an airplane in balance about its longitudinal axis .
2. A weight that counterbalances something, especially on an aircraft control surface, a weight installed forward of the hinge axis to counterbalance the surface aft of the hinge axis.
balanced amplifier
An amplifier circuit in which there are two identical signal branches connected so as to operate in phase opposition and with input and output connections each balanced to ground. Also called push-pull amplifier .
balanced circuit
A circuit, the two sides of which are electrically alike and symmetrical with respect to a common reference point, usually ground.
balanced detector
A demodulator for frequency-modulation systems. In one form the output consists of the rectified difference of the two voltages produced across two resonant circuits, one circuit being tuned slightly above the carrier frequency and the other slightly below.
balanced modulator
A device in which the carrier and modulating signal are so introduced that, after modulation takes place, the output contains the two sidebands without the carrier.
ballistic body
A body free to move, behave, and be modified in appearance, contour, or texture by ambient conditions, substances, or forces, as by the pressure of gases in a gun, by rifling in a barrel, by gravity, by temperature, or by air particles.
A rocket with a self-contained propulsion unit is not considered a ballistic body during the period of its guidance or propulsion.
ballistic camera
A ground-based camera using multiple exposures on the same plate to record the trajectory of a rocket.
ballistic condition
A condition affecting the behavior of a vehicle in flight.
Ballistic conditions include the velocity, weight, shape, and size of the vehicle; likewise the density and temperature of the ambient element, the magnetic field, etc.
ballistic density
A representation of the atmospheric density actually encountered by a projectile in flight, expressed as a percentage of the density according to the standard artillery atmosphere.
Thus, if the actual density distribution produced the same effect upon a projectile as the standard density distribution, the ballistic density would be 100 percent .
ballistic missile
A missile designed to operate primarily in accordance with the laws of ballistics.
A ballistic missile is guided during a portion of its flight, usually the upward portion, and is under no thrust from its propelling system during the latter portion of its flight; it describes a trajectory similar to that of an artillery shell.
ballistic recovery
Nonlifting reentry.
The science that deals with the motion, behavior, and effects of projectiles, especially bullets, aerial bombs, rockets, or the like; the science or art of designing and hurling projectiles so as to achieve a desired performance.
ballistic temperature
That temperature (in° F) which, when regarded as a surface temperature and used in conjunction with the lapse rate of the standard artillery atmosphere, would produce the same effect on a projectile as the actual temperature distribution encountered by the projectile in flight.
ballistic trajectory
The trajectory followed by a body being acted upon only be gravitational forces and the resistance of the medium through which it passes.
A rocket without lifting surfaces is in a ballistic trajectory after its engines cease operating.
ballistic vehicle
A nonlifting vehicle; a vehicle that follows a ballistic trajectory.
ballistic wind
That constant wind which would produce the same effect upon the trajectory of a projectile as the actual wind encountered in flight. Ballistic winds can be regarded as made up of range wind and crosswind components. See zone wind.
ball lightning
A relatively rare form of lightning, consisting of a reddish, luminous ball, of the order of 1 foot in diameter, which may move rapidly along solid objects or remain floating in midair. Hissing noises emanate from such balls, and they sometimes explode nosily but may also disappear noiselessly. Also called globe lightning .
It has been suggested that ball lightning is a temporarily stable plasma.
balloon-type rocket
A liquid-fuel rocket, such as Atlas, that requires the pressure of its propellants (or other gases) within it to give it structural integrity.
A cross between a balloon and a parachute, used to brake the free fall of sounding rockets.
1. = frequency band.
2. = absorption band.
3. A group of tracks on a magnetic drum.
4. = auroral band. See aurora.
band-elimination filter
A wave filter that attenuates one frequency band, neither the critical nor cutoff frequencies being zero or infinite.
band of position
An area extending to either side of a line of position of imperfect accuracy, within which a craft is considered to be located.
band-pass filter
A wave filter that has a single transmission band extending from a lower cutoff frequency greater than zero to a finite upper cutoff frequency.
bands with ray structure (abbr R.B.)
See aurora.
1. In an antenna, the range of frequencies within which its performance, in respect to some characteristic, conforms to a specified standard.
2. In a wave, the least frequency interval outside of which the power spectrum of a time-varying quantity is everywhere less than some specified fraction of its value at a reference frequency.
3. The number of cycles per second between the limits of a frequency band.
Sense 2 permits the spectrum to be less than the specified fraction within the interval. Unless otherwise stated, the reference frequency is that at which the spectrum has its maximum value.
4. In information theory, the information-carrying capacity of a communications channel.
bang-bang control
Flicker control, especially as applied to rockets.
Bang-bang in this term is imitative, arising from the noise made by control mechanisms slamming first to one side, then to the other, in this sort of control.
A unit of pressure equal to 106 dyne per square centimeter (106 barye), 1000 millibars, 29.53 inches of mercury. See torr.
Some writers have used bar as equivalent to barye (1 dyne per square centimeter).
A commercial trade name for a type of carbon dioxide absorber, a mixture of calcium hydroxide and barium hydroxide.
Bárány chair
(After Robert Bárány, 1876-1936, Swedish physician). A kind of chair in which a person is revolved to test his susceptibility to vertigo.
bare core
A reactor core without a reflector.
barn (Abbr b)
A unit of area for measuring a nuclear cross section. One barn equals 10-24 square centimeter.
barocline = baroclinic.
Of, pertaining to, or characterized by baroclinity. Sometimes called barocline.
baroclinicity = baroclinity.
The state of stratification in a fluid in which surfaces of constant pressure (isobaric) intersect surfaces of constant density (isosteric). The number, per unit area, of isobaric-isosteric solenoids intersecting a given surface is a measure of the baroclinity. Also called baroclinicity, barocliny .
Barotropy is the state of zero baroclinity. Since the presence of solenoids (baroclinity) complicates the dynamics of the fluid, there has been much investigation of the extent to which an atmosphere, though obviously a baroclinic fluid, can be dynamically treated as barotropic. See equivalent-barotropic model.
barocliny = baroclinity.
An instrument used to measure atmospheric pressure.
barometric altimeter = pressure altimeter.
barometric pressure = atmospheric pressure.
barometric wave
Any wave in the atmospheric pressure field. The term is usually reserved for short-period variations not associated wit cyclonic-scale motions or with atmospheric tides. See pressure wave, sense 2.
The atmosphere below the critical level of escape.
(From barometric switch). 1. Specifically, a pressure-operated switching device used in a radiosonde. In operation, the expansion of an aneroid capsule causes an electrical contact to scan a radiosonde commutator composed of conductors separated by insulators. Each switching operation corresponds to a particular pressure level. The contact of an insulator or a conductor determines whether temperature, humidity, or reference signals will be transmitted. 2. Any switch operated by a change in atmospheric pressure.
Of, pertaining to, or characterized by a condition of barotropy.
barotropic disturbance
1. An atmospheric wave in a two-dimensional nondivergent flow, the driving mechanism for which lies in the variation of vorticity of the basic current and/or in the variation of the vorticity of the earth about the local vertical. When the basic current is uniform, the wave is a Rossby wave . Also called barotropic wave .
2. An atmospheric wave of cyclonic scale in which troughs and ridges are approximately vertical.
barotropic model
Any of a number of model atmospheres in which some of the following conditions exist throughout the motion: coincidence of pressure and temperature surfaces; absence of vertical wind shear; absence of vertical motions; absence of horizontal velocity divergence; and conservation of the vertical component of absolute vorticity.
barotropic vorticity equation
The vorticity equation in the absence of horizontal divergence and vertical motion, so that the absolute vorticity of a parcel is conserved:
where is the relative vorticity and f is the coriolis parameter.
This equation may also be interpreted as governing vertically averaged flow in which divergence is present but wind direction is constant with height. See equivalent barotropic model.
barotropic wave = barotropic disturbance.
The state of a fluid in which surfaces of constant density (or temperature) are coincident with surfaces of constant pressure; it is the state of zero baroclinity. Mathematically, the equation of barotropy states that the gradients of the density and pressure fields are proportional:
where is the density; p is the pressure; and B is a function of thermodynamic variables, called the coefficient of barotropy.
With the equation of state, this relation determines the spatial distribution of all state parameters once these are specified on any surface. For a homogeneous atmosphere, B=0; for an adiabatic atmosphere,
B = c v / cp RT
cv and cp are the specific heats at constant volume and pressure, respectively; R is the gas constant; and T is the Kelvin temperature; for an isothermal atmosphere, B = 1/RT.
The center of mass of a system of masses, as the barycenter of the earth-moon system .
barycentric elements
Orbital elements referred to the center of mass of the solar system.
The pressure unit of the centimeter-gram-second system of physical units; equal to one dyne per square centimeter (0.001 millibar). Sometimes called bar or microbar.
A quantity, the powers of which are assigned as the unit value of columns in a numeric system; for example, two is the base in binary notation, and ten in decimal notation. Also called radix . See logarithm, binary notation.
base drag
Drag owing to a base pressure lower than the ambient pressure. It is a part of the pressure drag.
base line
1. Any line which serves as the basis for measurement of other lines, as in a surveying triangulation, measurement of auroral heights, etc.
2. The geodesic line between two stations operating in conjunction for the determination of a line of position, as the two stations constituting a loran rate.
3. In radar, the line traced on amplitude-modulated indicators which corresponds to the power level of the weakest echo detected by the radar. It is retraced with every pulse transmitted by the radar, but appears as a nearly continuos display on the scope.
Target signals show up as perpendicular deviations from the base line; range is measured along the base line; signal strength is indicated by the magnitude of the deviations; and the type of target usually can be determined by the appearance of the deviations.
base point
In computer terminology, the character, or the location of an implied symbol, which separates the integral part of an expression in positional notation from the fractional part; the point which marks the place between the zero and negative powers of the base. Also called radix point . See binary point, decimal point, fixed point, floating point.
base pressure
In aerodynamics, the pressure exerted on the base, or extreme aft end, of a body, as of a cylindrical or boattailed body or of a blunt-trailing-edge wing, in a fluid flow.
base-timing sequencing
(abbr BT sequencing)
The control of the time sharing of a single transponder between several ground transmitters through the use of suitable coded timing signals.
basic thermal radiation
Thermal radiation from a quiet sun.
A unit of signaling speed. The speed in bauds is the number of code elements per second.
Baumé scale (abbr Be)
Either of two scales sometimes used to graduate hydrometers; one scale is for liquids heavier than water, the other for liquids lighter than water.
Bayard-Alpert ionization gage
A type of ionization vacuum gage using a tube with an electrode structure designed to minimize X-ray induced electron emission from the ion collector.
Bayer letter
The Greek (or Roman) letter used in a Bayer name.
Bayer name
The Greek (or Roman) letter and the possessive form of the Latin name of a constellation, used as a star name. Examples are Cygni (Deneb), Orionis (Rigel), and Ursae Majoris (Alkaid). See navigational stars, table.
In radar, a rectangular display in which targets appear as blips with bearing indicated by the horizontal coordinate and distance by the vertical coordinate. Also called B-scan or B-scope .
1. A light, group of lights, electronic apparatus, or other device that guides, orients, or warns aircraft, spacecraft, etc. in flight.
2. A structure, building, or station where such a device is mounted or located. See radar beacon, radio beacon.
beacon delay
The amount of inherent delay within a beacon, i.e., the time between the arrival of a signal and the response of the beacon.
beacon skipping
A condition where transponder return pulses from a beacon are missing at the interrogating radar.
Beacon skipping can be caused by interference, overinterrogation of beacon, antenna nulls, or pattern minimums.
beacon stealing
Loss of beacon tracking by one radar due to (interfering) interrogation signals from another radar.
beacon tracking
The tracking of a moving object by means of signals emitted from a transmitter or transponder within or attached to the object.
See lunar crater, note.
1. A ray or collection of focused rays of radiated energy. See beam width, radiation pattern.
2. A beam (sense 1) of radio waves used as a navigation aid.
3. =electron beam.
4. A body, one of whose dimensions is large compared with the others, whose function is to carry lateral loads (perpendicular to the long dimension) and bending movements.
beam angle= beam width.
beam-climber guidance= beam-rider guidance.
beam rider
A craft following a beam, particularly one which does so automatically, the beam providing the guidance.
beam-rider guidance
A system for guiding aircraft or spacecraft in which a craft follows a radar beam, light beam, or other kind of beam along the desired path. Also called beam-climber guidance . See guidance.
beam splitter
A partially reflecting mirror which permits some incident light to pass through and reflects the remainder.
beam-switching tube
A trochotron in which an electron beam can be formed and switched to any one of several (usually 10) positions.
beam width
A measure of the concentration of power of a directional antenna. It is the angle in degrees subtended at the antenna by arbitrary power-level points across the axis of the beam. This power level is usually the point where the power density is one-half that which is present in the axis of the beam at the same distance from the antenna (half-power points). Also called beam angle .
The beam width of a radar determines the minimum angular separation which two targets can have and still be resolved. Roughly speaking, two targets at the same range whose angular separations at the radar antenna exceeds one-half of the beam width between half-power points will be resolved or distinguishable as two individual targets. The smaller the beam width, the greater the annular resolving power. Beam width may be at different locations through the axis depending upon the shape of the antenna reflector.
The horizontal direction of an object or point, usually measured clockwise from a reference line or direction through 360°.
A bearing is often designated as true, magnetic, compass, grid, or relative as the reference direction is true, magnetic, compass, or grid north, or heading, respectively.
At one time
bearing was restricted to reference to the direction of a terrestrial object or point as distinguished from azimuth which referred to the direction of a celestial body. This distinction has been blurred by usage.
bearing angle
Horizontal direction measured from 0° at the reference direction clockwise or counterclockwise through 90° or 180°. Compare bearing.
Bearing angle is labeled with the reference direction as a prefix and the direction of measurement from the reference direction as a suffix. Thus, bearing angle N 37° W is 37° west of north, or bearing 323°.
1. One complete cycle of the variations in the amplitude of two or more periodic phenomena of different frequency which mutually react. See beat frequency. 2. To produce beating.
beat-beat Dovap = Dovap elsse.
beat frequency
The frequency obtained when two simple harmonic quantities of different frequencies f1 and f2 are superimposed. The beat frequency equals f1- f2 .
A wave phenomenon in which two or more periodic quantities of different frequencies produce a resultant having pulsations of amplitude.
This process may be controlled to produce a desired beat frequency. See heterodyne .
beavertail antenna
A type of radar antenna which forms a beam having a greater beam width in azimuth than in elevation, or vice versa. In physical dimensions, its long axis lies in the plane of smaller beam width.
See tektite.
Beer law = Bouguer law.
The way in which an organism, organ, body, or substance acts in an environment or responds to excitation, as the behavior of steel under stress , or the behavior of an animal in a test .
The fundamental division of a logarithmic scale for expressing the ratio of two amounts of power, the number of bels denoting such a ratio being the logarithm to the base 10 of this ratio.
With P1 and P2 designating two amounts of power and N the number of bels denoting their ratio, N = log10 (P1/P2) bels.
Bemporad formula
A formula for the optical air mass m in terms of the zenith distance z of the sun or other celestial body:
m = R/58.36 sec sin z
where R is astronomical refraction, seconds of arc.
For values of z less than about 70°, the Bemporad formula can be replaced by the simpler approximate formula,
m = sec z
1. Pains in the extremities, abdomen, and chest caused by aeroemphysema and in some instances by aeroembolism resulting from the reduction of ambient air pressure.
2. Popularly used as synonymous with aeroembolism (sense 2).
Bernoulli law or Bernoulli theorem
(After Daniel Bernoulli, 1700-1782, Swiss scientist).
1. In aeronautics, a law or theorem stating that in a flow of incompressible fluid the sum of the static pressure and the dynamic pressure along a streamline is constant if gravity and frictional effects are disregarded.
From this law it follows that where there is a velocity increase in a fluid flow there must be a corresponding pressure decrease. Thus an airfoil, by increasing the velocity of the flow over its upper surface, derives lift from the decreased pressure.
2. As originally formulated, a statement of the conservation of energy (per unit mass) for a nonviscous fluid in steady motion. The specific energy is composed of the kinetic energy u2/2, where u is the speed of the fluid; the potential energy gz, where g is the acceleration of gravity and z is the height above an arbitrary reference level; and the work done by the pressure forces of a compressible fluid v dp, where p is the pressure, v is the specific volume, and the integration is always with respect to values of p and v on the same parcel. Thus, the relationship
= Constant along a streamline

is valid for a compressible fluid in steady motion, since the streamline is also the path. If the motion is also irrotational, the same constant holds for the entire fluid.
Besselian star numbers
Constants used in the reduction of a mean position of a star to an apparent position (used to account for short-term variations in the precession, nutation, aberration, and parallax).
Besselian year = fictitious year.
Bessel fictitious year = fictitious year.
beta decay
Radioactive transformation of a nuclide in which the atomic number changes by ±1 with the emission of a beta particle and the mass number remains unchanged. Also called beta disintegration .
Increase of atomic number occurs with negative beta particle emission, decrease with positive beta particle (positron) emission or upon electron capture.
beta disintegration = beta decay.
beta factor, -factor
In plasma physics, the ratio of the plasma kinetic pressure to the magnetic pressure.
If is less than 1, the magnetic field has a chance to contain the plasma providing there are no instabilities. If is larger than 1, there is no possible chance of containment.
beta particles
See betatron, note.
beta ray, -ray
A stream of beta particles.
A particle accelerator in which magnetic induction is used to accelerate electrons.
Betatron refers to the accelerated particles, electrons, which are identical with beta particles.
bias error
A measurement error that remains constant in magnitude for all observations. A kind of systematic error.
An example is an incorrectly set zero adjustment.
bidirectional transducer
A transducer device capable of measuring input in both a positive and a negative direction from a reference zero or rest position.
bilateral transducer
A transducer capable of transmission simultaneously in both directions.
billiard-ball collision = elastic collision.
See tektite.
bimetallic strip gage
A thermal conductivity vacuum gage in which deflection of a bimetallic strip with changing temperature indicates the changes in pressure.
1. Involving the integer two (2). See binary notation.
2. =binary cell.
3. =binary star.
binary cell
Any device or circuit that can be placed in either of two stable states to store a bit of binary information. Often called a binary .
binary chain
A cascaded series of binary cells.
binary code
A code composed of a combination of entities each of which can assume one of two possible states. Each entity must be identifiable in time or space.
binary counter
A counter with two distinguishable states.
binary device = binary cell.
binary digit
A digit (0 or 1) in binary notation. See bit.
binary magnetic core
A ferromagnetic material which can be caused to assume either of two stable magnetic states and thus can be used in a binary cell.
binary notation
A system of positional notation in which the digits are coefficients of power of the base 2 in same way as the digits in the conventional decimal system are coefficients of power of the base 10.
Binary notation employs only two digits, 1 and 0, therefore is used extensively in computers where the on and off positions of a switch or storage device can represent the two digits. In decimal notation 111 = (1 X 102) + (1 X 101) + (1 x 100) = 100 + 10 + 1 = one hundred and eleven. In binary notation 111 = (1 x 22) + (1 x 21) + (1 x 20) = 4 + 2 + 1 = seven.
binary number system
See binary notation.
binary point
The base point in binary notation.
binary star
A system of two stars revolving about their barycenter.
The smaller star of the system is referred to as the companion or comes.
Visible binaries are those which can be resolved into two stars by a telescope.
Spectroscopic binaries are those which cannot be resolved by a telescope by show temporary displacement and doubling of the lines in their spectra.
binding energy
1. The force which holds molecules, atoms, or atomic particles together; specifically, the force which holds an atomic nucleus together.
2. The energy required to break chemical, atomic, or molecular bonds.
The study of biological, behavioral, and medical problems pertaining to astronautics. This includes systems functioning in the environments expected to be found in space, vehicles designed to travel in space, and the conditions on celestial bodies other than on earth.
Chemistry dealing with the chemical processes and compounds of living organisms.
The study of the relations of climate and life, especially the effects of climate on the health and activity of human beings (human bioclimatology) and on animals and plants.
The study of the effects of dynamic processes (motion, acceleration, weightlessness, etc.) on living organisms.
The study of systems, particularly electronic systems, which function after the manner of, or in a manner characteristic of, or resembling, living systems.
A container for housing a living organism in a habitable environment and for recording biological functions during space flight.
An artificial satellite which is specifically designed to contain and support man, animals, or other living material in a reasonably normal manner for an adequate period of time and which, particularly for man and animals, possesses the proper means for safe return to the earth. See ecological system.
A sensor used to provide information about a life process.
That transition zone between earth and atmosphere within which most forms of terrestrial life are commonly found; the outer portion of the geosphere and inner or lower portion of the atmosphere. See hydrosphere.
The application of engineering and technological principles to the life sciences.
The remote measuring and evaluation of life functions, as, e.g. in spacecraft and artificial satellites.
A test chamber used for biological research within which the environmental conditions can be completely controlled, thus allowing observations of the effect of variations in environment on living organisms.
A rocket propellant consisting of two unmixed or uncombined chemicals (fuel and oxidizer) fed to the combustion chamber separately.
bipropellant rocket
A rocket using two separate propellants which are kept separate until mixing in the combustion chamber.
biquinary notation
A numerical system in which each decimal digit is represented by a pair of digits consisting of a coefficient of five followed by a coefficient of one.
For example, the decimal digit 7 is represented in biquinary notation by 12 [(1 x 5) + (2 x 1)], and the decimal quantity 3648 is represented by 03 11 04 13.
The abacus is based on biquinary notation.
A colloquial term for a rocket, satellite, or spacecraft.
bistable elements
In computer terminology, a device which can remain indefinitely in either of two stable states.
bistable multivibrator
A multivibrator which can exist indefinitely in either of two stable states. Also called flip-flop .
bistatic reflectivity
The characteristic of a reflector which reflects energy along a line, or lines, different from, or in addition to, that of the incident ray.
For example, any reflector that scatters the incident energy.
1. An abbreviation of binary digit.
2. A single character of a language employing only two distinct kinds of characters.
3. A quantity of intelligence which is carried by an identifiable entity and which can exist in either of two states.
4. A unit of storage capacity; the capacity in bits of a storage device is the logarithm to the base two of the number of possible states of the device.
5. A quantum of information.
6. Loosely, a mark.
bit rate
The frequency derived from the period of time required to transmit one bit.
black body, blackbody (symbol b used as a subscript)
1. An ideal emitter which radiates energy at the maximum possible rate per unit area at each wavelength for any given temperature. A black body also absorbs all the radiant energy in the near visible spectrum incident upon it.
No actual substance behaves as a true black body, although platinum black and other soots rather closely approximate this ideal. However, one does speak of a black body with respect to a particular wavelength interval. This concept is fundamental to all the radiation laws, and is to be compared with the similarly idealized concepts of the white body and the gray body. In accordance with the Kirchhoff law, a black body not only absorbs all wavelengths, but emits at all wavelengths and does so with maximum possible intensity for any given temperature.
2. A laboratory device which simulates the characteristics of a black body (sense 1). See hohlraum.
black-body emission= black-body radiation.
black-body radiation
The electromagnetic radiation emitted by an ideal black body; it is the theoretical maximum amount of radiant energy of all wavelengths which can be emitted by a body at a given temperature.
The spectral distribution of black-body radiation is described by Planck law and the related radiation laws. If a very tiny opening is made into an otherwise completely enclosed space (hohlraum), the radiation passing out through this hole when the walls of the enclosure have come to thermal equilibrium at some temperature will closely approximate ideal black-body radiation for that temperature.
black box
1. In engineering design, a unit whose output is a specified function of the input, but for which the method of converting input to output is not necessarily specified.
2. Colloquially, any unit, usually an electronic device such as an amplifier, which can be mounted in, or removed from, a rocket, spacecraft, or the like as a single package.
1. A fadeout of radio communications due to ionospheric disturbances.
Blackouts are most common in, but are not restricted to, the arctic. An arctic blackout may last for days or even weeks during periods of intense auroral activity. Past experiments with high-altitude nuclear detonations have produced blackouts and artificial auroras over the subtropics .
2. A fadeout of radio and telemetry transmission between ground stations and vehicles traveling at high speeds in the atmosphere caused by signal attenuation in passing through ionized boundary layer (plasma sheath) and shock wave regions generated by the vehicle.
3. A vacuum tube characteristic which results from the formation of a dielectric film on the surface of the control grid.
A negative charge, accumulated on the film when the grid is driven positive with respect to the cathode, affects the operating characteristics of the tube.
4. A condition in which vision is temporarily obscured by a blackness, accompanied by a dullness of certain of the other senses, brought on by decreased blood pressure in the eye and a consequent lack of oxygen, as may occur, e.g., in pulling out of a high-speed dive in an airplane. Compare grayout, redout.
1. (a) An arm of a propeller; a rotating wing. (b) Specifically, restrictive, that part of a propeller arm or of a rotating wing from the shank outward, i.e., that part having an efficient airfoil shape and that cleaves the air. See blade shank.
2. A vane (in sense 2), such as a rotating vane or stationary vane in a rotary air compressor, or a vane of a turbine wheel.
To blank out or obscure weak radio signals by a stronger signal.
blank-off pressure
See ultimate pressure.
1. The brief and rapid movement of air or other fluid away from a center of outward pressure, as in an explosion.
2. The characteristic instantaneous rise in pressure, followed by a sudden decrease, that results from this movement, differentiated from less rapid pressure changes.
3. To take off from a launching pad or stand. Said of a rocket in reference to the blast effects caused by rapid combustion of fuel as the rocket starts to move upward. (Popular).
This term is commonly used for explosion, but the two terms should be distinguished. In space, an explosion could take place, but no blast would follow.
blast chamber
A combustion chamber, especially a combustion chamber in a gas-turbine engine, jet engine, or rocket engine.
blast deflector
A device used to divert the exhaust of a rocket fired from a vertical position.
A missile launch (Slang).
blast vane = jet vane.
Blaton formula
In meteorology, an expression relating the curvature of the trajectory Ki of a fluid parcel to the streamline Ks
where v is the parcel speed, is the local change of wind direction, is the wind angle, and t is time. The curvatures and change of wind direction are positive for cyclonic flow.
To let a fluid, such as air or liquid oxygen, escape from a pipe, tank, or the like.
bleed off
To take off a part or all of a fluid from a tank or line, normally through an escape valve or outlet, as in to bleed off excess oxygen from a tank .
A spot of light or deflection of the trace on a radarscope, loran indicator, or the like, caused by the received signal, as from a reflecting object. Also called a pip or echo .
A fairly small-scale temperature and moisture inhomogeneity produced by turbulence within the atmosphere.
The abnormal gradient of the index of refraction resulting from a blob can produce a radar echo of the type known as angels.
In computer operations, a group of machine words considered as a unit.
blockhouse, block house
1. A reinforced concrete structure, often built underground or half underground, and sometimes dome shaped, to provide protection against blast, heat, or explosion during rocket launchings or related activities; specifically, such a structure at a launch site that houses electronic control instruments used in launching a rocket.
2. The activity that works in such a structure.
blocking oscillator
A regenerative circuit which generates pulses of short duration.
Blocking oscillators are used in digital computers.
blowdown tunnel
A type of wind tunnel in which stored compressed gas is allowed to expand through a test section to provide a stream of gas or air for model testing.
The downstream side may or may not be reduced in pressure to provide greater expansion potential.
blowdown turbine
A turbine attached to a reciprocating engine which receives exhaust gases separately from each cylinder, utilizing the kinetic energy of the gases.
The action of applying an explosive force and separating a package section away from the remaining part of a rocket vehicle or reentry body, usually to retrieve an instrument or to obtain a record made during early flight. See fallaway section.
blue-sky scale = Linke scale.
bluff body
A body having a broad, flattened front, as in some reentry vehicles.
bluntness (symbol B)
A parameter of a conic related to the eccentricity, e, of the conic in the following way:
B = 1- e2
B = 1/(1-e2)
The rear portion of an elongated body, as a rocket, having decreasing cross-sectional area toward the rear.
Fluctuation of the strength of a radar echo, or its indication on a radarscope, due to alternate interference and reinforcement of returning reflected waves.
1. The main part or main central portion of an airplane, airship, rocket, or the like; a fuselage or hull.
2. In a general sense, any fabrication, structure, or other material form, especially one aerodynamically or ballistically designed, as, an airfoil is a body designed to produce an aerodynamic reaction.
body angle
The angle which the longitudinal axis of the airframe makes with some selected line.
body axis
Any one of a system of mutually perpendicular reference axes fixed in an aircraft or similar body and moving with it. See axis.
body of revolution
A symmetrical body having the form described by rotating a plane curve about an axis in its plane.
1. A supporting and aligning wheel or roller on the inside of an endless track, used, e.g., in certain types of landing gear.
2. A type of landing-gear unit consisting of two sets of wheels in tandem with a central strut.
Bohr magneton, electronic Bohr magneton (symbol µB)
A constant equivalent to the magnetic moment of an electron, 9.27372 x 10-21 erg/gauss. See physical constants, tables.
Bohr magneton is sometimes used as a synonym for nuclear magneton.
Bohr radius (symbol a0)
The smallest possible radius of an electron orbit in the Bohr model of the atom, 5.29167 x 10-9 centimeters.
boilerplate model
A metal copy of a flight vehicle, the structure or components of which are heavier than the flight model.
boiling point (abbr bp)
The temperature at which the equilibrium vapor pressure between a liquid and its vapor is equal to the external pressure on the liquid. Compare ice point.
The vaporization of a liquid, such as liquid oxygen or liquid hydrogen, as its temperature reaches its boiling point under conditions of exposure, as in the tank of rocket being readied for launch.
A brilliant meteor, especially one which explodes; a detonating fireball.
The record obtained from a bolometer.
An instrument which measures the intensity of radiant energy by employing a thermally sensitive electrical resistor; a type of actinometer. Also called actinic balance . Compare radiometer.
Two identical, blackened, thermally sensitive electrical resistors are used in a Wheatstone bridge circuit. Radiation is allowed to fall on one of the elements, causing a change in its resistance. The change is a measure of the intensity of the radiation.
bolometric magnitude
1. The magnitude of a star for the entire electromagnetic spectrum without atmospheric absorption.
The magnitude measured within the earth's atmosphere by a bolometer is the radiometric magnitude.
2. Loosely = radiometric magnitude.
Boltzmann constant (symbol k)
The ratio of the universal gas constant to Avogadro number; equal to 1.38054 x 10-16 erg/°K. Sometimes called gas constant per molecule, Boltzmann universal conversion factor .
Boltzmann universal conversion factor = Boltzmann constant.
Bond albedo
The ratio of the amount of light reflected from a sphere exposed to parallel light to the amount of light incident upon it. Sometimes shortened to albedo.
The Bond albedo is used in planetary astronomy.
1. Specifically, a system of connections between all metal parts of an aircraft or other structure forming a continuos electrical unit and preventing jumping or arcing of static electricity.
2. Gluing or cementing together for structural strength.
Boo, Boot
International Astronomical Union abbreviation for Bootes. See constellation.
Boolean algebra
The study of the manipulation of symbols representing operations according to the rules of logic.
Boolean algebra corresponds to an algebra using only the numbers 0 and 1, therefore can be used in programming digital computers which operate on the binary principle.
1. Additional power, pressure, or force supplied by a booster, as, hydraulic boost, or extra propulsion given a flying vehicle during lift-off, climb, or other part of its flight as with a booster engine.
2. Boost pressure.
3. To supercharge.
4. To launch or to push along during a portion of flight, as to boost a ramjet to flight speed by means of a rocket, or a rocket boosted to altitude with another rocket .
1. Short for booster engine or booster rocket.
2. = launch vehicle.
booster engine
An engine, especially a booster rocket, that adds its thrust to the thrust of the sustainer engine.
booster pump
A pump in a fuel system, oil system, or the like, used to provide additional or auxiliary pressure when needed or to provide an initial pressure differential before entering a main pump, as in pumping hydrogen near the boiling point.
booster rocket
1. A rocket motor, either solid or liquid, that assists the normal propulsive system or sustainer engine of a rocket or aeronautical vehicle in some phase of its flight.
2. A rocket used to set a vehicle in motion before another engine takes over.
In sense 2 the term launch vehicle is preferred.
booster vehicle = launch vehicle.
boostglide vehicle
A vehicle designed to glide in the atmosphere following a rocket-powered phase. Portions of the flight may be ballistic, out of the atmosphere.
boost pressure
Manifold pressure greater than the ambient atmospheric pressure, obtained by supercharging. Often called boost.
Bootes (abbr Boo, Boot)
See constellation.
1. Referring to a self-generating or self-sustaining process; specifically, the operation of liquid-propellant rocket engines in which, during main-stage operation, the gas generator is fed by the main propellants pumped by the turbopump, and the turbopump in turn is driven by hot gases from the gas generator system.
Such a system must be started in its operation by outside power or propellants. When its operation is no longer dependent on outside power or propellant the system is said to be in bootstrap operation.
2. In computer operations, the coded instructions at the beginning of an input tape which together with manually inserted instructions, initiate a routine.
3. = leap-frog. See, leapfrog test.
boresight camera
A camera mounted in the optical axis of a tracking radar to photograph rockets being tracked while in camera range and thus provide a correction for the alignment of the radar.
boresight error
The linear displacement between two parallel lines of sight.
In radio the process of aligning a directional antenna system by an optical procedure.
Bose-Einstein statistics
Formulas relating to equations of state and partition of kinetic energy when the wave functions are symmetric.
Bouguer law
A relationship describing the rate of decrease of flux density of a plane-parallel beam of monochromatic radiation as it penetrates a medium which both scatters and absorbs at that wavelength. This law may be expressed
where I is the flux density of the radiation; alpha sub lambda is the attenuation coefficient (or extinction coefficient) of the medium at wavelength lambda; I sub lambda 0 is the flux density at the source; and x is the distance from the source. Sometimes called Beer law, Lambert law of absorption . See absorption coefficient, scattering coefficient.
bounce table
A testing device which subjects devices and components to impacts such as might be encountered in accidental dropping.
boundary conditions
A set of mathematical conditions to be satisfied, in the solution of a differential equation, at the edges or physical boundaries (including fluid boundaries) of the region in which the solution is sought. The nature of these conditions usually is determined by the physical nature of the problem. See boundary-value problem.
boundary layer
The layer of fluid in the immediate vicinity of a bounding surface; in fluid mechanics, the layer affected by viscosity of the fluid, referring ambiguously to the laminar boundary layer, turbulent boundary layer, planetary boundary layer, or surface boundary layer .
In aerodynamics the boundary-layer thickness is measured from the surface to an arbitrarily chosen point, e.g., where the velocity is 99 percent of the stream velocity. Thus, in aerodynamics, boundary layer by selection of the reference point, can include only the laminar boundary layer or the laminar boundary layer plus all, or a portion of, the turbulent boundary layer.
boundary-value problem
A physical problem completely specified by a differential equation in an unknown, valid in a certain region of space, and certain information (boundary condition) about the unknown, given on the boundaries of that region. The information required to determine the solution depends completely and uniquely on the particular problem. See initial-value problem.
Boussinesq approximation
The assumption (frequently used in the theory of convection) that the fluid is incompressible except insofar as the thermal expansion produces a buoyancy, represented by a term gaT (a is equivalent to alpha), where g is the acceleration of gravity; a is the coefficient of thermal expansion; and T is the perturbationtemperature.
bow wave
A shock wave in front of a body, such as an airfoil, or apparently attached to the forward tip of the body.
Boyle law = Boyle-Mariotte law.
Boyle-Mariotte law
The empirical generalization that for many so-called perfect gases, the product of pressure p and volume V is constant in an isothermal process: pV = F(T) where the function F the temperature T cannot be specified without reference to other laws (e.g., Charles-Gay-Lussac law). Also called Boyle law, Mariotte law .
brake parachute = deceleration parachute.
braking ellipses
A series of ellipses, decreasing in size due to aerodynamic drag, followed by a spacecraft in entering a planetary atmosphere.
In theory, this maneuver will allow a spacecraft to dissipate the heat generated in entry without burning up.
braking rocket = retrorocket.
1. In an electrical circuit, a portion of a network consisting of one or more two-terminal elements in series.
2. The point in a computer program at which the machine will proceed with one of two or more possible routines according to existing conditions and instructions.
branch point = node.
Brayton cycle
(After George B. Brayton, American engineer). Same as Joule cycle.
Joining metals by flowing a thin-layer capillary thickness of nonferrous filler metal into the space between them.
Bonding results from the intimate contact produced by the dissolution of a small amount of base metal in the molten filler metal, without fusion of the base metal. Sometimes, the filler metal is put in place as a thin solid sheet or as cladding and the composite is heated as in furnace brazing.
The term
brazing is used where the temperature exceeds some arbitrary value, such as 800°F; the term soldering is used for temperatures lower than the arbitrary value.
1. An assembly of preliminary circuits or parts used to prove the feasibility of a device, circuit, system, or principle without regard to the final configuration or packaging of the parts.
2. To prepare a breadboard , sense 1.
The action of a boundary layer separating from a surface.
breakaway phenomenon
See breakoff phenomenon.
breakdown potential = dielectric strength.
breakoff = breakoff phenomenon.
breakoff phenomenon
The feeling which sometimes occurs during high-altitude flight of being totally separated and detached from the earth and human society. Also called the breakaway phonomonon.
break point
In computer operations, a point at which a break-point instruction inserted in the routine will cause the machine to stop, upon a command from the operator, for a check of progress.
break-point instruction
In computer operations, an instruction which, in conjunction with a manually operated control, causes the machine to stop.
bremsstrahlung (German, braking radiation).
Electromagnetic radiation produced by the rapid change in the velocity of an electron or another fast, charged particle as it approaches an atomic nucleus and is deflected by it. See bremsstrahlung effect.
bremsstrahlung effect
The emission of electromagnetic radiation as a consequence of the acceleration of charged elementary particles, such as electrons, under the influence of the attractive or repulsive force fields of atomic nuclei near which the charged particle moves.
In cosmic-ray shower production, bremsstrahlung effects give rise to emission of gamma rays as electrons encounter atmospheric nuclei. The emission of radiation in the bremsstrahlung effect is merely one instance of the general rule that electromagnetic radiation is emitted only when electric charges undergo acceleration.
brennschluss (German, combustion termination ).
The cessation of burning in a rocket, resulting from consumption of the propellants, from deliberate shutoff, or from other cause; the time at which this cessation occurs. See burnout, cutoff.
Brewster point
One of the three commonly detectable points of zero polarization of diffuse sky radiation, neutral points, along the vertical circle through the sun; the other two are the Arago point and Babinet point.
This neutral point, discovered by Brewster in 1840, is located about 15° to 20° directly below the sun; hence it is difficult to observe because of the glare of the sun.
1. The attribute of visual perception in accordance with which an area appears to emit more or less light.
2. = luminance.
In sense 2 luminance is preferred.
brightness level = adaptation luminance.
brightness temperature
1. In astrophysics, the temperature of a black body radiating the same amount of energy per unit area at the wavelengths under consideration as the observed body. Compare effective temperature, antenna temperature.
2. The temperature of a nonblack body determined by measurement with an optical pyrometer.
Brinell hardness number (abbr Bhn)
A parameter describing the hardness of a material as the ratio of pressure on a standard sphere used to indent the material to be tested to the area of the indentation produced.
British candle = international candle.
British thermal unit (abbr Btu)
The amount of heat required to raise 1 pound of water at 60 degrees F, 1° F.
This unit is defined for various temperatures, but the general usage seems to be to take the Btu as equal to 252 15° gram-calories or 1055 joules.
broadside array
An antenna array whose direction of maximum radiation is perpendicular to the line or plane of the array according as the elements lie on a line or plane. A uniform broadside array is a linear array whose elements contribute fields of equal amplitude and phase.
brush discharge = corona discharge.
B-scan = B-display.
A cathode-ray indicator in which a signal appears as a spot with bearing as the horizontal coordinate and distance as the vertical coordinate. Also called B-display .
In loran, the designation applied to the transmitting station of a pair, the signal of which always occurs more than half a repetition period after the next succeeding signal and less than half a repetition period before the next preceding signal from the other station of the pair, designated an A- station.
The second trace of an oscilloscope having more than one, as the lower trace of a loran indicator.
Btu (abbr)
British thermal unit.
1. An unstable state of equilibrium of a thin-walled body stemming from compressive stresses in the walls.
2. The lateral deflection of a thin-walled body resulting from such instability.
In computers: 1. An isolating circuit used to avoid reaction of a driven circuit on the corresponding driving circuit.
2. A storage device used to compensate for a difference in rate of flow of information or time or occurrence of events when transmitting information from one device to another.
buffer storage
In computer operations, storage used to compensate for a difference in rate of flow or time of occurrence when transferring information from one device to another.
The beating of an aerodynamic structure or surfaces by unsteady flow, gusts, etc.; the irregular shaking or oscillation of a vehicle component owing to turbulent air or separated flow.
Of a radiant energy signal, to increase, often temporarily, in received signal strength without a change of receiver controls.
The opposite is fade.
A wall, partition, or similar member in a rocket, spacecraft, airplane fuselage, or similar structure, at right angles to the longitudinal axis of the structure, and serving to strengthen, divide, or help give shape to the structure.
bulk modulus
The reciprocal of the coefficient of compressibility.
See potential index of refraction.
A separation or breakdown of the laminar flow past a body; the eddying or turbulent flow resulting from this.
Burble occurs over an airfoil operating at an angle of attack greater than the angle of maximum lift, resulting in a loss of lift and an increase of drag. See compressibility burble.
burble angle = burble point.
burble point
A point reached in an increasing angle of attack at which burble begins. Also called burble angle.
burner = combustion chamber.
burn-in = debug.
burning rate (symbol r)
The velocity at which a solid propellant in a rocket is consumed.
Burning rate is measured in a direction normal to the propellant surface and is usually expressed in inches per second.
burning rate constant (symbol a )
A constant, related to initial grain temperature, used in calculating the burning rate of a rocket propellant grain.
burning-rate exponent (symbol n)
The exponent n in the equation
r = ap cn
where r is burning rate, pc is chamber pressure; and a and n are constants.
The value of n varies with the propellant.
1. An act or instance of fuel or oxidant depletion or, ideally, the simultaneous depletion of both; the time at which this occurs. Compare cutoff.
In the United Kingdom all burnt is preferred to burnout.
2. An act or instance of something burning out or of overheating; specifically, an act or instance of a rocket combustion chamber, nozzle, or other part overheating so as to result in damage or destruction.
burnout velocity
The velocity of a rocket, rocket-powered aircraft, or the like at the time the fuel or oxidant or both are depleted. Also called burnt velocity.
burnt velocity = burnout velocity.
1. In a reactor, the percentage of fissionable atoms that have been fissioned. 2. Depletion of reactor fuel by fission.
1. A single pulse of radio energy; specifically such a pulse at radar frequencies.
2. = solar radio burst.
3. = cosmic ray burst.
burst disk
A diaphragm designed to burst at a predetermined pressure differential; sometimes used as a valve, e.g., in a liquid-propellant line in a rocket. Also called a rupture disk .
In computer operations, a main circuit, channel, or part for the transfer of information. Also called trunk .
Busch lemniscate
The locus in the sky, of all points at which the plane of polarization of diffuse sky radiation is inclined 45° to the vertical. Also called neutral line .
1. In supersonic diffuser aerodynamics, a nonsteady shock motion and airflow associated with the shock system ahead of the inlet, very rapid pressure pulsations are produced which can affect downstream operation in the burner, nozzle, etc.
2. Sustained oscillation of an aerodynamic control surface caused by intermittent flow separation on the surface, or by a motion of shock waves across the surface, or by a combination of flow separation and shock-wave motion on the surface.
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