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- Video display of a
beacon's replies to interrogations
from two or more nonsynchronized radars.
- racon (From radar
- A transponder
by a primary
- (From radio detection and ranging).
- 1. A method, system, or technique of using beamed, reflected, and timed radio waves
for detecting, locating, or tracking objects (such as rockets), for measuring
altitude, etc., in any of various activities, such as air traffic control or
- 2. The electronic equipment or apparatus used to generate, transmit,
receive, and, usually, to display radio scanning or locating waves; a radar
- The terms primary radar and secondary radar may be used when the return
signals are, respectively, by reflection and by the transmission of a second
signal as a result of triggering responder beacon by the incident signal.
- radar altimeter = radio
- radar altitude
- The altitude of an aircraft or spacecraft as determined by a radio
altimeter; thus, the actual distance from the nearest terrain feature.
- radar astronomy
- The study of celestial bodies within the solar system by means of radiation
originating on earth but reflected from the body under observation. See radio
- radar band
- See frequency
- radar beacon
- A beacon
transmitting a characteristic signal on radar frequency,
permitting a craft to determine the bearing and sometimes the range of the
- A racon returns a coded signal when triggered by the proper type of
radar pulse; a ramark continuously transmits a signal which appears as a
radial line on the plan position indicator.
- radar beam
- See beam.
- radar cross section
- The ratio of power returned in
a radar echo to power received by the target
reflecting the signal. Compare scattering
- radar duct
- See radio
- radar echo
- See echo.
- radar frequency
- See frequency
- radar horizon
- The angle of
elevation at which the beam from a radar antenna is
intercepted by the earth's horizon. Compare radio
- radar indicator = radarscope.
- radar mile
- A time unit of 10.75 microseconds duration; the time it takes for the signal emitted
by a radar to travel from the radar to a target one mile
distant and return to the radar.
- radar range
- 1. The distance from a radar to a target
as measured by the radar.
- 2. The maximum distance at which a radar set is effective in detecting
- Radar range depends upon variables such as weather conditions, type of
target, etc. Radar range, sense 2, is sometimes given a specific definition,
e.g., the range at which the set is effective one-half of the time.
- radar range equation
- The relation between the maximum range Rmax at which a point target is
detectable and the properties of the radar and the target
Rmax = [(PA2λ2σ)/(4π)3Smin)]1/4
where P is the transmitted power of the
radar; λ is its wavelength; σ is the scattering cross section of the target;
A is the antenna gain; and Smin is the threshold signal.
- radar reflectivity
- In general, the measure of the efficiency of a radar
target in intercepting and returning a radar signal. It
depends upon the size, shape, aspect, and the dielectric properties at the
surface of the target. It includes the effects of not only reflection (see reflectivity)
but also scattering
- radar reflector
- A device capable of or intended for reflecting radar signals.
- radar scan
- 1. The searching motion of a radar beam in any of various path
configurations; the pattern of the motion of a radar beam.
- 2. Radar
- radar scanning
- The action or process of moving or directing a searching radar beam. See
- The cathode-ray
tube or oscilloscope in a radar set,
which displays the received signal in such a manner as to indicate range,
bearing, etc. Sometimes called a radar indicator.
- radar screen
- 1. The face of a cathode-ray
oscilloscope used in a radar set.
- 2. A network of radar installations, or their emanations, serving, e.g.,
to detect strange aircraft.
- radar set
- An electronic apparatus consisting principally of a transmitter, antenna,
receiver, and indicator for sending out scanning beams and receiving and
displaying the reflected waves or the waves emitted by a radar beacon. See radar.
- radar shadow
- A condition in which radar
frequency signals do not reach a region because of an intervening
- radar target
- An object which reflects a sufficient amount of a radar signal to
produce an echo signal on the radar screen.
- radar volume
- The volume in space that is irradiated by a given radar. For a continuous-wave
radar it is equivalent to the antenna radiation pattern. For a pulse radar
it is a function of the cross-section area of the beam of the antenna and the
pulse length of the transmitted pulse.
- radar wave
- A transmitted or reflected radio wave
used in radar;
a radio wave in one of the frequency
bands used for radar.
- Motion along a radius.
- radial motion
- Motion along a radius, or a component in such a direction, particularly
that component of space motion of a celestial
body in the direction of the line of sight.
- radial velocity
- In radar,
that vector component of the velocity of a
that is directed away from or toward the ground station.
- The angle subtended at the center of a circle by an arc equal in length to
a radius of the circle. It is equal to 360°/2π or approximately 57 degrees 17
minutes 44.8 seconds.
- In radiometry, a measure of the intrinsic radiant intensity
emitted by a radiator in a given direction. It is the irradiance
(radiant flux density) produced by radiation from the source upon a unit
surface area oriented normal to the line between source and receiver, divided
by the solid angle subtended by the source at the receiving surface. It is
assumed that the medium between the radiator and receiver is perfectly
transparent; therefore, radiance is independent of attenuation
between source and receiver.
- If the radiant source is a perfectly diffuse radiator (that is, emits
exactly according to Lambert
law), then its radiance is equal to its emittance per
unit solid angle. The radiance of a light source is termed luminance
- radiancy (symbol R, , W)
- The rate of radiant-energy emission for a
unit area of a source in all the radial directions of the overspreading
- 1. Pertaining to the emission or
the measurement of electromagnetic
radiation. Compare luminous.
- 2. In astronomy, the apparent location on the celestial
sphere of the origin of the luminous trajectories
seen during a meteor
- For convenience, the common meteor showers are named for the
constellations of stars in which their radiants appear.
- 3. In describing auroras, a projected point of intersection of lines drawn
coincident with auroral streamers; that is, the point from which the aurora
seems to originate.
- radiant density = radiant energy density.
- radiant emittance
- See emittance,
- radiant energy (symbol U )
- 1. The energy of any
type of electromagnetic
radiation. Also called radiation.
- 2. Infrequently, any energy that may be radiated, as, for example,
- radiant energy density (symbol u )
- The instantaneous amount of radiant energy contained in a unit volume of
- radiant energy thermometer
- An instrument which determines the black body
temperature of a substance by measuring its thermal radiation.
- The substance need not be thermally black over the whole spectrum,
since it is possible to limit the measurement to those frequencies where it is
- radiant flux (symbol Φ)
- The rate of flow of radiant energy.
- radiant flux density = radiant flux per unit area
- When applied to a source, it is called radiancy or radiant emittance
(symbol W). When applied to a receiver, it is called irradiancy or irradiance
- radiant heat
- This term, still used in certain engineering fields, is to be avoided
since it confuses the distinct physical concepts of radiation and heat.
- radiant intensity
- Radiant flux per unit solid angle.
- radiant temperature
- The temperature
obtained by use of a total radiation pyrometer
when sighted upon a nonblack body.
- This is always less than the true temperature.
- radiating element
- A basic subdivision of an antenna which in itself is capable of radiating
or receiving radiofrequency
- 1. The process by which electromagnetic energy is propagated through free
space by virtue of joint undulatory variations in the electric and magnetic
fields in space. This concept is to be distinguished from conduction and
convection. A group of physical principles known as the radiation laws
comprise, to a large extent, the current state of practical knowledge of the
complex radiative processes.
- 2. The process by which energy is propagated through any medium by virtue
of the wave
motion of that medium, as in the propagation of sound wave through the
atmosphere, or ocean waves along the water surface.
- 3. = radiant
- 4. = electromagnetic
radiation, specifically, high-energy radiation such as gamma rays
- 5. Corpuscular emissions, such as α or β-radiation.
- 6. = nuclear
- 7. = radioactivity.
- radiation belt
- An envelope of charged particles trapped in the magnetic
field of a spatial body. See Van Allen
- radiation constants
- Values used in Planck law
and other radiation calculations. The first radiation constant (symbol
) = 3.7415 erg centimeters squared per second. The
second radiation constant (symbol ) = 1.43879
centimeters degrees K. See physical
- radiation cooled
- Of a structure, pertaining to the use of materials able to radiate heat at
a rate such that the rate of increase of the temperature of the material is
- radiation counter
- An instrument used for detecting or measuring moving subatomic particles
by a counting process.
- radiation dose
- The amount of radiation absorbed by a material, system, or tissue in a
given amount of time; usually measured in one of the commonly accepted units
as roentgen, roentgen-equivalent-man,
- radiation laws
- 1. The four physical laws which, together, fundamentally describe the
behavior of black-body radiation: (a) the Kirchhoff
law is essentially a thermodynamic relationship between emission and
absorption of any given wavelength at a given temperature; (b) the Planck law
describes the variation of intensity of black-body radiation at a given
temperature, as a function of wavelength; (c) the Stefan-Boltzmann
law relates the time rate of radiant energy emission from a black body to
its absolute temperature; (d) the Wien law
relates the wavelength of maximum intensity emitted by a black body to its
- 2. All the more inclusive assemblage of empirical and theoretical laws
describing all manifestations of radiative phenomena; e.g., Bouguer law
- radiation lobe
- A portion of the radiation
pattern bounded by one or two cones of nulls.
- radiation medicine
- That branch of medicine dealing with the effect of radiation,
specifically high-energy radiation such as X-rays, gamma rays, and energetic
particles on the body and with the prevention or cure of physiological
injuries resulting from such radiation.
- radiation pattern
- A graphical representation of the radiation of
as a function of direction. Cross sections in which radiation patterns are
frequently given are vertical planes and the horizontal plane, or the
principal electric and magnetic polarization planes. Also called antenna
pattern, lobe pattern, coverage diagram.
- Two types of radiation patterns should be distinguished. They are: (a)
the free-space radiation pattern which is the complete lobe pattern of the
antenna and is a function of the wavelength, feed system, and reflector
characteristics, and (b) the field radiation pattern which differs primarily
from the free-space pattern by the formation of interference lobes whenever
direct and reflected wave trains interfere with each other as is found in most
surface-based radars. The envelope of these interference lobes has the same
shape, but, for a perfectly reflecting surface, it has up to twice the
amplitude of the free-space radiation pattern.
- radiation pressure (symbol Pr)
exerted upon any material body by electromagnetic
radiation incident upon it. See Poynting-Robertson
- This pressure is manifested whenever the electromagnetic momentum is a
radiation field is changes, and is exactly twice as great when the radiation
is reflected at normal incidence as it is when the radiation is entirely
absorbed at normal incidence. The magnitude of any radiation-pressure effect
is directly proportional to the intensity of the radiation, and is very small
by most standards. On a perfectly reflecting surface Pr = u/3 where u is
radiation density, the amount of radiative energy per unit volume in the space
above the surface. Radiation pressure has a perceptible effect on the orbit of
earth satellites, especially those with a large reflecting surface such as
- radiation pyrometer
- See pyrometer,
- radiation shield
- 1. A device used on certain types of instruments to prevent unwanted radiation
from biasing the measurement of a quantity.
- 2. A device used to protect human beings from the harmful effects of nuclear
radiation, cosmic radiation, or the like.
- 3. = heat
- radiation sickness
- A syndrome following intense acute exposure to ionizing
radiations. It is characterized by nausea and vomiting a few hours after
exposure. Further symptoms include bloody diarrhea, hemorrhage under the skin
(and internally), epilation (hair falling), and a decrease in blood-cell
- 1. Any source of radiant
energy, especially electromagnetic
- 2. A device that dissipates the heat from something, as from water or oil,
not necessarily by radiation only.
- Generally, the application of the terms radiator (in sense 2) or heat
exchanger to a particular apparatus depends upon the point of view: If the
emphasis is upon merely getting rid of heat, radiator is most often used, or
sometimes cooler; if the emphasis is upon transferring heat, heat exchanger is
used -- but these distinctions do not always hold true.
- 1. Communication by electromagnetic
waves, without a connecting wire.
- 2. Pertaining to radiofrequency,
as in radio wave.
- Exhibiting or pertaining to radioactivity.
- radioactive gas
- 1. In atmospheric electricity, any one of the three radioactive inert
gases, radon, thoron, and actinon, which contribute to atmospheric ionization
by virtue of the ionizing effect of the alpha particles which each emits on
disintegration. These three gases are isotopic to each other, all having
atomic number 86.
- 2. Any gaseous material containing radioactive
- radioactive ionization gage
- An ionization
gage in which the ions are produced by radiations (usually alpha
particles) emitted from a radioactive source.
- 1. Spontaneous disintegration of atomic nuclei with emission of corpuscular
- The principal types of radioactivity are alpha decay, beta decay, and
isomeric transition. To be considered as radioactive a process must have a
measurable lifetime between approximately 10E-10 second and approximately
10E17 years. Radiations emitted within a time too short for measurement are
called prompt. Prompt radiations such as gamma rays and X-rays are often
associated with radioactive disintegrations.
- 2. The number of spontaneous disintegrations per unit mass and per unit
time of a given unstable (radioactive) element, usually measured in curies.
- radio altimeter
- A device that measures the altitude of a craft above the terrain by
measuring the elapsed time between transmission of radio waves
from the craft and the reception of the same waves reflected from the terrain.
Also called radar altimeter.
- radio astronomy
- 1. The study of celestial
objects through observation of radiofrequency
waves emitted or reflected by these objects.
- In this sense radio astronomy includes both the use of radiation
emitted by the celestial bodies and of radiation originating on earth and
reflected by celestial bodies (radar astronomy).
- 2. Specifically, the study of celestial objects by measurement of the
radiation emitted by them in the radiofrequency range of the electromagnetic
- Radio astronomy measurements are usually of the intensity of
the received signal but often include polarization
of the signal and angular size of the source.
- radio beacon
- Any radio transmitter,
together with its associated equipment, that emits signals enabling the
determination, by means of suitable receiving equipment, of direction,
distance, or position with respect to the beacon.
- radio beam
- See beam.
- The study of the effects produced on living organisms by radiation.
- radio blackout = blackout, sense 1.
- radio channel
- A frequency
band comprised of the emission bandwidth,
guard bands, and the frequency
- radio command
- A radio signal to which
a rocket, satellite, or the like responds.
- radio control
- 1. Remote control of a
pilotless airplane, a rocket, etc., by means of radio signals that
activate controlling devices.
- 2. Any radio apparatus used for this kind of control.
- radio direction finder
- A radio-receiving set, together with its associated equipment, used to
determine the direction from which a radio signal is
- radio duct
- A rather shallow, almost horizontal layer in the atmosphere
through which vertical temperature and moisture gradients are such as to
produce an index
of refraction lapse rate of greater than -48 N-units per 1000 feet. Strong
temperature, or moisture inversions, or both are necessary for the formation
of radio ducts. The resulting superstandard
propagation is such as to cause the curvature of rays traveling through it
to be greater than that of the earth. Radio energy which originates within the
duct and leaves the antenna at angles near the horizontal may thus be
trapped within the layer. See anomalous
- The effect is similar to that of a mirage (it is sometimes called radio
mirage), and radar targets may be detected at phenomenally long ranges if both
target and radar are in the duct. The greater the elevation angle between
radar and target, the less the possibility of serious distortion due to
transmission through ducts. Ducts may be surface based or elevated, with
thickness ranging from a few tens of feet up to a maximum of 1000 feet.
Elevated ducts are generally associated with subsidence or frontal inversions
and are seldom found above 15,000 to 20,000 feet.
- radio energy
radiation of greater wavelength (lower frequency) than infrared
radiation, that is, of wavelength
greater than about 1000 microns (0.01 centimeter). The high-frequency end of
the radio energy spectrum is known as microwave radiation. See frequency
- radio fadeout = fadeout.
- radiofrequency (abbr RF)
- 1. A frequency at
which coherent electromagnetic radiation of energy is useful for communication
- Roughly, the radiofrequency of the electromagnetic spectrum lies
between 10E4 and 10E12 cycles per second. See frequency
- 2. Specifically, the frequency of a given radio carrier
- radiofrequency band
- See frequency
- radio goniometer = radio direction finder.
- radio guidance system
- A guidance
system that uses radio signals to guide an aircraft or spacecraft in flight;
includes both the flight-borne equipment and the guidance station equipment on
- radio hole
- Strong fading of the
at some position in space along an air-to-air or air-to-ground radio path. The
effect is caused by the abnormal refraction
of radio waves.
- radio horizon
- The locus of points at which direct rays from a radio transmitter
become tangential to the earth's surface. Assuming a smooth surface, the
distance of the horizon is given approximately by the equation
where r is the distance, statute miles,
and h is the height, feet, of the antenna above
the surface. See effective
radius of the earth, scatter
propagation. Compare radar
- The horizon extends beyond (below) the geometrical and visible horizons
as the result of normal atmospheric refraction. It may be decreased or
increased in particular cases as standard propagation is replaced by substandard
propagation or superstandard
propagation, respectively. Beyond the radio horizon, surface targets
cannot be detected under normal atmospheric conditions although significant
amounts of radio power have been detected in the diffraction zone below the
horizon. It is now felt that this represents power scattered by
turbulence-produced atmospheric inhomogeneities.
- radio interferometer
- An interferometer
operating at radiofrequencies.
- Radio interferometers are used in radio astronomy and in satellite
- radio meteor
- A meteor
which has been detected by the reflection of a radio signal from the
meteor trail of relatively high ion density ( ion column).
meteor. Compare photographic
- Such an ion column is left behind a meteoroid when it reaches the
region of the upper atmosphere between about 80 and 120 kilometers, although
occasionally radio meteors are detect at higher altitudes. The maximum
reflection occurs when the column is perpendicular to the line to the
- An instrument for detecting and, usually, measuring radiant
energy. Compare bolometer.
- radiometer vacuum gage = Knudsen gage.
- radiometric magnitude (symbol mrad)
- The magnitude of
body measured with reference to the total radiation observable through the
- The science of measurement of radiant energy.
- In practice, there is no clear distinction between radiometry
although photometry usually refers to measurement in the visible and
- radio mirage
- See radio
- A radioactive nuclide; an
atom which emits corpuscular or electromagnetic radiation.
- radiophare = radio beacon.
- This term is commonly used in international terminology.
- An instrument, usually balloon-borne, for the simultaneous measurement and
transmission of meteorological data while moving vertically through the
atmosphere. See dropsonde.
- The instrument consists of transducers for the measurement of pressure,
temperature, and humidity; a modulator for the conversion of the output of the
transducers to a quantity which controls a property of the radiofrequency
signal; a selector switch which determines the sequence in which the
parameters are to be transmitted; and a transmitter which generates the
- The range of frequencies of electromagnetic
radiation usable for radio communication.
- The radiospectrum ranges from about 10 kilocycles per second to over
300,000 megacycles per second. Corresponding wavelengths are 30 kilometers to
1 millimeter. See frequency
- radio telescope
- A device for receiving, amplifying, and measuring the intensity of radio waves
originating outside the earth's atmosphere or reflected from a body outside
- A radio telescope usually includes a source of radiation of known power
for calibration of the received signal. The term radio telescope is not
restricted to devices incorporating a paraboloidal dish antenna. A radio
telescope can use any antenna or combination of antennas which will accept the
radiation being studied.
- radio theodolite = radio direction finder.
- radio waves
produced by oscillation
of an electric charge at a frequency
useful for radio communication. Formerly called Hertzian waves.
- radius vector
- A straight line connecting a fixed reference point or center with a second
point, which may be moving; specifically, in astronomy, the straight line
connecting the center of a celestial
body with the center of a body which revolves around it, as the radius
vector of the moon. See polar
- radix = base (of a number system).
- radix point
- The index which separates the digits
associated with negative powers from those associated with the zero and
positive powers of the base of the number
system in which a quantity is represented. For example, binary point,
- (From radar dome. Pronounced raydome ). A dielectric
housing for an antenna.
- ram air
- Air entering an airscoop or
air inlet as a
result of the high-speed forward movement of a vehicle.
- A fixed radar
frequency facility which continuously emits a signal so that a bearing
indication appears on a radar display. See radar
- ram drag
- The drag
produced by the momentum of
air entering an airscoop or an
air inlet of
an aeronautical vehicle in flight.
- ramjet = ramjet engine.
- ramjet engine
- A type of jet engine
with no mechanical compressor consisting of a specially shaped tube or duct
open at both ends, the air necessary for combustion being shoved into the duct
and compressed by the forward motion of the engine, where the air passes
through a diffuser and
is mixed with fuel and burned,
the exhaust gases issuing in a jet from the rear
opening. The ramjet engine cannot operate under static conditions. Often
called a ramjet. Also called Lorin tube.
- Eluding precise prediction, completely irregular. Compare stochastic.
- In connection with probability and statistics, the term random implies
collective or long-run regularity; thus, a long record of the behavior of a
random phenomenon presumably gives a fair indication of its general behavior
in another long record, although the individual observations have no
discernible system of progression.
- random error
- Errors that are not systematic, are not erratic, and are not mistakes.
- Such random errors are caused by disturbed elements in the measuring
instrument and usually are of an approximately normal or Gaussian
distribution. Such random errors are sometimes called short-period errors.
- random number
- An expression formed by a set of digits selected
from a sequence of digits in which each successive digit is equally likely to
be any of the digits.
- random noise
- An oscillation
whose instantaneous amplitude occur, as a function of time, according to a
normal (Gaussian) curve. Also called Gaussian noise, random Gaussian noise.
- random sample
- A sample
taken at random from a population.
- random variable
- A variable characterized by random behavior
in assuming its different possible values. Mathematically, it is described by
its probability distribution, which specifies the possible values of a random
variables together with the probability associated (in an appropriate sense)
with each value. A random variable is said to be continuous if its
possible values extend over a continuum and discrete if its possible
values are separated by finite intervals. Also called variate. See
- random vibration
- An oscillation
whose instantaneous magnitude is
not specified for any given instant of time. The instantaneous magnitudes of a
random oscillation are specified only by probability distribution functions
giving the fraction of the total time that the magnitude, or some sequence of
magnitudes, lies within a specified range.
- A random vibration whose instantaneous magnitudes occur according to
distribution is called Gaussian random vibration. Wide-band vibration
amplitude is usually expressed as root-mean-square acceleration in
gravitational units of acceleration g. The parameter used to specify the
frequency distribution of a random vibration is power spectral density (g2 per cycle per second), sometimes called
acceleration density or acceleration spectral density.
- 1. The difference between the maximum and minimum of a given set of
numbers; in a periodic
process it is twice the amplitude, i.e., the wave height.
- 2. The distance between two objects, usually an observation point and an
object under observation. See slant
- 3. A maximum distance attributable to some process, as in visual range
or the range of a rocket.
- 4. An area in and over which rockets are fired for testing, as Atlantic
- 5. = radar
- range attenuation
- In radar
terminology, the decrease in power
density (flux density) caused by the divergence of the flux lines with
distance, this decrease being in accordance with the inverse-square law.
- For one-way transmission, this attenuation is proportional to 1/RE2
where R is the range from the transmitter. For a radar and a point target, the
range attenuation is proportional to 1/RE4, the transmission being two way.
- range error
- The error in radar range
measurement due to the propagation
of radio energy through a nonhomogeneous atmosphere. This error is due to the
fact that the velocity of radio-wave propagation varies with the index
of refraction and that ray travel is not in straight lines through actual
atmospheres. The resulting range error is generally insignificant. Compare azimuth
- range gating
- The use of circuits in radar to suppress
all targets falling outside selected range limits.
- range-height-indicator scope
- (abbr RHI-scope). A type of radar indicator
(radar-scope); an intensity-modulated indicator on
which echoes are displayed in coordinates of slant range and elevation angle,
simulating, thereby, a vertical cross section of the atmosphere along some
azimuth from the radar.
- The power of the signal returned from the target is used to modulate
the intensity of the electron beam.
- range marker
- The index marks displayed on radar indicators to establish the scale or
facilitate determination of the distance of a target from the radar. On the plan
position indicator scope, for example, range markers take the form of
concentric circles with the position of the radar at the center. See azimuth
marker. Also called distance marker.
- range only measurement of trajectory and recording (abbr Romotar)
- A nonambiguous spherical and elliptical, long-baseline, range-only trajectory
measuring system utilizing phase comparison techniques with range
- The system consists of three of more receivers which track a transponder
interrogated by a signal transmitter. The reference signal from the ground
transmitter is also received by the ground receivers. Simultaneous range
measurements are made by the ground receivers, which are correlated with base
timing from which space position can be computed by triangulation. The system
operates on 387 and 417 megacycles.
- range rate
- The rate at which the distance from the measuring equipment to the target
or signal source being tracked is changing with respect to time. See radial
- range ring
- A circle on a plan
position indicator, particularly one with an adjustable diameter, to
indicate distance from the antenna. See distance
- range safety officer
- An official on a rocket test range whose
responsibility is to supervise the planning and execution of each test to
insure the maximum safety of all personnel and property within the range
- range strobe
- An index mark which may be displayed on some types of radar indicators
to assist in the determination of the exact range of a target.
- range sweep
- See sweep,
- range wind
- The component of a ballistic
wind which is parallel to the longitudinal axis of the range.
- ranging pulse
- In a radar system the pulse used to
measure the range of the
object being tracked.
- ranging system
- A radar
system which measures range (distance).
- Rankine cycle
- An idealized thermodynamic cycle consisting of two constant-pressure
processes and two isentropic processes.
- Rankine temperature scale
- (abbr degrees R). A temperature scale with the degree-interval of the Fahrenheit
temperature scale and the zero point at absolute
zero. The ice point is
thus 491.69 degrees Rankine and the boiling
point of water is 671.69 degrees Rankine.
- Rankine vortex
- A two-dimensional circular flow in which a
circular region about the origin is in solid rotation:
Constant where V is the tangential speed and R is the distance
from the origin; the region outside is free of vorticity, the speed being
inversely proportional to the distance from the origin (as in the V-R
VR = Constant.
- This vortex has occasionally been used as a model for the surface wind
distribution in a hurricane. It is characteristic of a cylindrical vortex in a
liquid with a free surface.
- (From radiosonde
observation). An observation of the vertical distribution of temperature,
pressure, and relative humidity, obtained by means of a radiosonde.
- rarefraction wave = expansion wave.
- rarefied gas dynamics
- The study of the phenomena related to the molecular or noncontinuum nature
of gas flow at
densities where λ / l > 0.01
where λ is molecular mean free path and l
is a characteristic dimension of the flow field.
Flow with λ / l > 0.01 is called molecular flow.
Flow with λ / l < 0.01 is called continuum flow.
Flow with λ / l of approximately 0.01 to 0.1 is called slip flow.
Flow with λ / l of approximately 0.1 to 10 is called transition flow.
Flow with λ / l > 10 is called free molecule flow.
Slip flow and transition flow
are not always distinguished from each other. The value 1 is sometimes used
instead of 10 as the boundary value for transition flow and free molecule
- rare gas = inert gas.
- The pattern followed by the electron
beam exploring element scanning the screen of a television transmitter or
- raster line
- One line of a raster, or scanning pattern.
- rate gyro
- A single-degree-of-freedom
gyro having primarily elastic restraint of its spin axis about the output
axis. In this gyro an output signal is produced by gimbal angular
displacement, relative to the base, which is proportional to the angular rate
of the base about the input axis.
- rate integrating gyro
- A single-degree-of-freedom
gyro having primarily viscous restraint of its spin axis about the output
axis. In this gyro an output signal is produced by gimbal angular
displacement, relative to the base, which is proportional to the integral of
the angular rate of the base about the input axis.
- rate of decay
- 1. Of a sound, the time rate at which the sound
pressure level (or other stated characteristic) decreases at a given point
and at a given time. A commonly used unit is the decibel per second.
- 2. Of a radioactive nuclide, the
number of nuclei of that nuclide changing (or disintegrating) per unit time.
It is usually expressed as the instantaneous rate of decay by - dN/dt
where N is the total number of the state nuclides present at the
given time t.
- rate of incidence = impingement rate.
- ratio deviation
- In a frequency
modulation system, the ratio of the maximum frequency
deviation to the maximum modulating frequency of
the system. Also called modulation index.
- rational horizon = celestial horizon.
- See horizon.
- RATO, Rato, or rato
- (From rocket-assisted
- 1. A take-off in
which a rocket or rockets, commonly of the solid-fuel type, are used to
provide additional thrust. Hence, RATO bottle, Rato bottle, rato unit ,
etc., a rocket so used.
- 2. A RATO bottle or unit; the complete apparatus on an aircraft,
comprising rockets, ignition system, etc., for assisted take-off. See JATO.
- A magic
tee modification for the acceptance of higher power; a circular loop of
coaxial line closed upon itself and having four branching connections.
- raw data
- Data that is in a form ready for processing.
- Different groups regard data in various forms as raw, dependent on
their function. A photographic processing group may regard the latent image as
raw data, a reading group may regard the photographic image as raw data, a
computing group may regard certain digits data as raw data, and so on.
- A measurement of wind direction and speed at altitude by radar tracking of
a balloon-borne target.
- A combination raob and rawin; an
observation of temperature, pressure, relative humidity, and winds-aloft by
means of radiosonde
and radio direction finding equipment or radar tracking.
- 1. An elemental path of radiated
the energy following this path. It is perpendicular to the phase
fronts of the radiation.
- 2. One of a series of lines diverging from a common point, as radii from
the center of a circle.
- 3. A long, narrow, light colored streak on the lunar surface originating
from a crater. Rays
range in length to over 150 kilometers and usually several radiate from the
same crater, like spokes of a wheel.
- Rayleigh atmosphere
- An idealized atmosphere
consisting of only those particles, such as molecules, that are smaller than
about one-tenth the wavelength
of all radiation incident upon that atmosphere. In such an atmosphere, simple
scattering would prevail.
- This model atmosphere is amenable to reasonably complete theoretical
treatment, and hence has often served as a useful starting point in
description of the optical properties of actual atmospheres. The polarization
of skylight, for example, exhibits almost none of the complexities found in
the real atmosphere.
- Rayleigh formula
- See aerodynamic
force, drag, drag
- Rayleigh law
- See Rayleigh
- Rayleigh limit
- See Rayleigh
- Rayleigh number
- The nondimensional ratio between the product of buoyancy forces and heat
advection and the product of viscous forces and heat conduction in a fluid. It
is written as
where g is the acceleration of gravity;
ΔzT is a characteristic vertical temperature
difference in the characteristic depth d ; α is the coefficient of expansion; v is the
kinematic viscosity; and k the thermometric conductivity.
- The Rayleigh number is equal to the product of the Grashof and Prandtl
numbers, and is the critical parameter in the theory of thermal
- Rayleigh scattering
- Any scattering
process produced by spherical particles whose radii are smaller than about
one-tenth the wavelength
of the scattered radiation.
- In Rayleigh scattering, the scattering coefficient varies inversely
with the fourth power of the wavelength, a relation known as the Rayleigh law.
The angular intensity polarization relationships for Rayleigh scattering are
conveniently simple. For particles not larger than the Rayleigh limit, there
is complete symmetry of scattering about a plane normal to the direction of
the incident radiation, so that the forward scatter equals the backward
scatter. The Rayleigh scattering coefficient ks is
where n is the number of scatters of diameter d;
m is the index of refraction; and λ is the wavelength of the radiation.
- Rayleigh wave
- 1. A two-dimensional barotropic
disturbance in a fluid having one
or more discontinuities in the vorticity profile.
- 2. A surface wave associated with the free boundary of a solid, such that
a surface particle describes an ellipse whose
major axis is normal to the surface and whose center is at the undisturbed
surface. At maximum particle displacement away from the solid surface the
motion of the particle is opposite to that of the wave.
- The propagation velocity of a Rayleigh wave is slightly less than that
of a shear wave in the solid; the wave amplitude of the Rayleigh wave
diminishes exponentially with depth.
- rays (abbr R)
- See aurora.
- ray tracing
- A procedure used in the graphical determination of the path followed by a
single ray of
radiant energy as it travels through media of varying index
- reaction balance
- A type of thrust meter using a balance to measure the static thrust of a rocket or jet
- reaction engine
- An engine that develops thrust by its
reaction to a substance ejected from it; specifically, such an engine that
elects a jet or stream of gases created by the burning of fuel within the
engine. Also called reaction
- A reaction engine operates in accordance with Newton third law of
motion, i.e., to every action (force) there is an equal and opposite reaction.
Both rocket engines and jet engines are reaction engines.
- reaction motor = reaction engine.
- reaction propulsion
by reaction to a jet or jets ejected from one or more reaction
- reaction time
- In human engineering, the interval between an input signal (physiological)
or a stimulus (psychophysiological) and the response elicited by the signal.
- reaction turbine
- A type of turbine having
rotor blades shaped so that they form a ring of nozzles, the
turbine being rotated by the reaction of the fluid ejected
from between the blades. Compare impulse
- reactor = nuclear reactor.
- reactor core
- In a nuclear
reactor the region containing the fissionable
- In computer
operations, to acquire information, usually from some form of storage. See write.
- read in
- In computer
operations, to introduce information into storage.
- 1. The action of a radio transmitter
transmitting data either instantaneously with the acquisition of the data or
by playing of a magnetic tape upon which the data have been recorded. See instantaneous
- 2. The data transmitted by the action described in sense 1.
- 3. In computer
operations, to extract information from storage.
- readout indicators
- Any type of indicating instrument from which meaningful information and
data can be directly obtained and used.
- readout station
- A recording or receiving radio station at which data are received from a
in a probe, satellite, or other spacecraft.
- real time
- Time in which reporting on events or recording of events is simultaneous
with the events.
- For example, the real time of a satellite is that time in which it
simultaneously reports its environment as it encounters it; the real time of a
computer is that time during which it is accepting data.
- real-time data
- Data presented in usable form at essentially the same time the event
- The delay in presenting the data must be small enough to allow a
corrective action to be taken if required.
- rearward acceleration
- See physiological
- Reamer temperature scale
- A temperature
scale in which, under a pressure of 1 atmosphere, the ice point is
0 degrees and the boiling
point of water is 80 degrees.
- An oxygen system with a circuit closed to the atmosphere, to which oxygen
is added to meet the user's needs; carbon dioxide and water vapor are removed
from the expired gas.
- received power
- In radar,
the power of a target
signal received at the antenna. This power is normally of the order of
microwatts as compared to the megawatts of transmitted power. Also called
- 1. The initial component or sensing element of a measuring system. For
example, the receiver of a thermoelectric thermometer is the measuring
- 2. An instrument used to detect the presence of and to determine the
information carried by electromagnetic
radiation. A receiver includes circuits designed to detect, amplify,
rectify, and shape the incoming radiofrequency
signals received at the antenna in such
a manner that the information- containing component of this received energy
can be delivered to the desired indicating or recording equipment.
- A sensory nerve ending or organ in a living organism that is sensitive to
physical or chemical stimuli.
- 1. A direction 180 degrees from a given direction.
- 2. The quotient of 1 divided by a given number.
- reciprocal centimeter
- See wave
- reciprocating engine
- An engine,
especially an internal-combustion engine, in which a piston or pistons moving
back and forth work upon a crankshaft or other device to create rotational
- See principle
- The psychological process in which an observer so interprets the visual
stimuli he receives from a distant object that he forms a correct conclusion
as to the exact nature of the object.
- Recognition is a more subtle phenomenon than the antecedent step of
detection, for the latter involves only the simpler process of interpreting
visual stimuli to the extend of concluding that an object is present at some
distance from the observer.
- The process by which a positive and a negative ion join to form a
neutral molecule or
other neutral particle, also process by which radicals or dissociations
species join to form molecules.
- Recombination is applied both to the simple case of capture of free
electrons by positive atomic or molecular ions, and also to the more complex
case of neutralization of a positive small ion by a negative small ion or a
similar (but much more rare) neutralization of large ions. Recombination is,
in general, a process accompanied by emission of radiation. The light emitted
from the channel of a lightning stroke is recombination radiation as is airglow. The
much less concentrated recombinations steadily occurring in all parts of the
atmosphere where ions are forming and disappearing does not yield observable
radiation. The rate at which electrons, small ions, and large ions recombine
is a function of their respective mobilities and of their concentration. The
former dependence is expressed in terms of the recombination coefficient of
the particular ion type.
- recombination coefficient
- A measure of the specific rate at which oppositely charged ions join to form
neutral particles (a measure of ion recombination).
- recombination energy
- The energy released as heat or light when two oppositely charged ions join to form
a neutral atom or molecule, or two dissociated atoms combine to form a stable
- Of a rocket vehicle
or one of its parts, so designed or equipped as to be located after flight and
recovered with or without damage.
- 1. The procedure or action that obtains when the whole of a satellite, or
a section, instrumentation package, or other part of a rocket vehicle is
retrieved after a launch, as in recovery was counted upon to give added
- 2. The conversion of kinetic
energy to potential
energy such as in the deceleration of air in the duct of a ramjet
engine. Also called ram recovery.
- 3. In flying, the action of a lifting vehicle returning to an equilibrium
attitude after a nonequilibrium maneuver.
- recovery capsule
- A capsule
designed to be recovered after reentry. See reentry
- recovery gear
- The devices and equipment used to mark and locate a nose cone or other
part of a rocket
vehicle after impact.
- recovery package
- A package attached to a reentry or other body designed for recovery,
containing devices intended to locate the body after impact.
- This package may, for example, release a balloon that will buoy up a
reentry body (if it impacts in water) and serve as a radio beacon or light.
- recovery temperature
- Short for adiabatic
- 1. In metals, the change from one crystal structure to another, as occurs
on heating or cooling through a critical temperature.
- 2. The formation of a new strain-free grain structure from that existing
in cold-worked metal, usually accomplished by heating.
- rectangular curvilinear coordinates
- See curvilinear
- A static device having an asymmetrical conduction characteristic which is
used to convert attending current into direct current.
- A rotating device for this purpose is called a converter. Compare inverter.
- 1. In a countdown to
stop the count and to return to an earlier point in the countdown, as in we
have recycled, now at T minus 80 and counting. Compare hold.
- 2. To give a completely new checkout to a
rocket or other object.
- The condition occurring under negative g
in which objects appear to have a red coloration due to uncertain causes,
possibly venous congestion of engorged eyelids. Compare blackout,
- red shift
- In astronomy, the displacement of observed spectral lines toward the
longer wavelengths of the red end of the spectrum. Compare space
- The term red shift is applied both to the Doppler
effect caused by the relative speed of recession of the observed body and
the gravitational or relativistic shift in which the frequency of light
emitted by atoms in stellar atmosphere is decreased by a factor proportional
to the mass-radius relationship of the star.
- Red Spot Hollow
- See Great Red
- reduced frequency (symbol k)
- The frequency of vibration of
a body, or of the variation of the flow behind the
body, expressed as the circular frequency times the representative length of
the body divided by the velocity of the flow.
- 1. In information theory: of a source, the amount by which the logarithm
of the number of symbols available at the source exceeds the average
information content per symbol of the source.
- The term redundancy has been used loosely in other senses. For example,
a source whose output is normally transmitted over a given channel has been
called redundant, if the channel utilization index is less than unity.
- 2. The existence of more than one means for accomplishing a given task,
where all means must fail before there is an overall failure to the system.
- Parallel redundancy applies to systems where both means are working at
the same time to accomplish the task, and either of the system is capable of
handling the job itself in case of failure of the other system. Standby
redundancy applies to a system where there is an alternative means of
accomplishing the task that is switched in by a malfunction sensing device
when the primary system fails.
- Reech number
- The reciprocal lg/V2 , of the Froude
number, where g is the acceleration of gravity; l is a
characteristic length; and V is a characteristic speed.
- The event occurring when a spacecraft
or other object comes back into the sensible
atmosphere after being rocketed to higher altitudes; the action involved
in this event.
- reentry body
- That part of a space vehicle that reenters the atmosphere after flight
above the sensible
- reentry nose cone
- A nose
cone designed especially for reentry,
consisting of one or more chambers protected by an outer shield. See heat sink.
- reentry trajectory
- That part of a rocket's
trajectory that begins at reentry and ends at target or at the surface.
- If the rocket is unguided at reentry, its reentry trajectory is
ballistic in character.
- reentry vehicle
- Any payload carrying vehicle
designed to leave the sensible
atmosphere and then return through it to earth.
- This term applies both to return vehicles from orbital or space
payloads and to boostglide
- reference ellipsoid
- An ellipsoid of revolution used as a datum for geodetic measurements. See
- reference frame = coordinate system.
- reference line = datum line.
- reference plane = datum plane.
- reference point = datum point.
- reference signal
- In telemetry,
against which data-carrying signals are compared to measure differences in
time, phase, frequency, etc.
- An assumed zero value of a quantity relative to which magnitudes of the
quality are measured, or a structure having this zero value of the quantity;
e.g., a voltage measured relative to the ground as a referent.
- reflectance (symbol ρ)
- The ratio of the radiant flux reflected by
a body to that incident upon it. Also called reflection factor.
- For an opaque body, the sum of the reflectance and the absorptance for
the incident radiation is unity ρ + α = 1.
- reflected code = cyclic code.
- reflected ray
- A ray
extending outward from a point of reflection.
- reflected wave
- 1. A shock wave,
wave, or compression
wave reflected by another wave incident upon a wall or other boundary.
- 2. In electronics, a radio wave reflected from a surface or object.
- reflecting telescope
- A telescope which collects light by means of a concave mirror.
- The process whereby a surface of discontinuity turns back a portion of the
incident radiation into the medium through which the radiation approached. See
- For true reflection to occur there must be a real discontinuity of the
of refraction or at least it must change over an interfacial layer of
thickness small compared to the wavelength of the radiation. If the change of
refractive index is gradual (as may occur in a stratified medium) radiation
may be returned by a process of continuous refraction, not to be confused with
reflection. In radar, the term reflection is often applied to the return of
radio energy from a volume of precipitation or cloud particles, where scattering
is the important process. When the scale of the irregularities on the
reflecting surface is small compared to the wavelength, regular or specular
reflection (also called mirror reflection, regual reflection) results; if the
irregularities are large compare of reflection is not affected by wavelength
except as the relative scale of the irregularities of the surface change with
wavelength. the fraction of the incident radiation reflected does depend on
wavelength because of the selective nature of the absorptivity and
transmissivity. The idealized white body is a total reflector; a black body
reflects none of the incident radiation. The laws of specular reflection are:
(first law) the reflected ray lies in the same plane as the incident ray and
the normal to the surface at the point of incidence; and (second law) the
angle of reflection equals the angle of incidence, both measured from the
normal to the surface.
- reflection coefficient
- A measure of the quality of specular
reflection produced by a given surface; defined as the ratio of the
radiant energy reflected along the geometrical reflection path to the total
that is incident upon the surface. By definition, a reflection coefficient of
1.0 implies perfect specular reflection. Compare reflectivity.
- Reflection coefficients of less than 1.0 occur either as a result of
energy loss by absorption at the reflection surface, or by scattering of the
energy out of the geometrical reflection path due to the diffuse or irregular
nature of the reflecting surface. Note that the reflection coefficient varies
with wavelength since a surface which might appear to be rough at very short
wavelengths is much smoother to longer wavelength radiation. It also varies
- 1. A measure of the fraction of radiation
reflected by a given surface; defined as the ratio of the radiant
energy reflected to the total that is incident upon that surface. Compare
coefficient. See radar
- The reflectivity of any given substance is, in general, a variable
strongly dependent upon the wavelength of the radiation in question. The
reflectivity of a given surface for a specified broad spectral range, such as
the visible spectrum or the solar spectrum, is referred to as the albedo.
- 2. In thermal radiation, a property of a material, measured as the reflectance
of a specimen of the material that is thick enough to be completely opaque and
has an optically smooth surface.
- 1. In general, any object that reflects incident energy; usually
it is a device designed for specific reflection characteristics. See retroreflector,
- 2. In an antenna, a parasitic
element located in a direction other than the general direction of the
major lobe of radiation.
- 3. A material of high scattering
cross section that surrounds a reactor core to reduce the escape of
neutrons, many of which are reflected back into the core.
- 4. A repeller.
- refracted ray
- A ray
extending onward from the point of refraction.
- refracted wave
- A wave that
has had its direction of motion changed by refraction.
- refracting telescope
- A telescope which collects light by means of a lens or system of lenses.
Also called refractor.
- The process in which the direction of energy propagation
is changed as the result of a change in density within the propagating medium,
or as the energy passes through the interface representing a density
discontinuity between two media. In the first instance the rays undergo a
smooth bending over a finite distance. In the second case the index
of refraction changes through an interfacial layer that is thin compared
to the wavelength of the radiation; thus, the refraction is abrupt,
essentially discontinuous. See atmospheric
refraction. Compare reflection,
- refraction error
- See astronomical
refraction error, terrestrial
refraction error, curved-path
- refraction index = index of refraction.
- refractive index = index of refraction.
- refractive modulus = modified index of refraction.
- 1. The algebraic difference between an index
of refraction and unity.
- For the atmosphere, refractivity may be more conveniently expressed in
N-units: N = (n - 1) 10E6 The deviation of the refractivity at any altitude
from the usual standard profile is expressed in B-units (for radiofrequencies
up to 20 kilomegacycles):
B = N + 0.12h where h is altitude in feet.
The deviation of the refractivity at any altitude from the gradient at
which the refraction curvature of a tangential ray will match the curvature of
the earth may be expressed in M- units:
M = N + 0.048h where 0.048 is 10E6
divided by the radius of the earth in feet.
- 2. = index
- This usage should be discouraged.
- An instrument for measuring the index
of refraction of a liquid, gas or solid.
- refractor = refracting telescope.
- A material, usually ceramic, that
resists the action of heat, does not fuse at high temperatures, and is very
difficult to break down.
- refractory metal
- A metal with melting point above 4000 degrees F.
- Usually refers to columbium, molybdenum, tantalum, or tungsten.
- Capable of undergoing refraction.
- 1. = positive
- 2. In computer
operations, the process of restoring a storage device,
whose information storing state may deteriorate, to its latest undeteriorated
state. See rewrite.
- regenerative cooling
- The cooling of a part of an engine by the fuel or propellant being
delivered to the combustion chamber; specifically, the cooling of a
chamber or nozzle by
circulating the fuel or oxidizer, or
both, around the part to be cooled.
- regenerative detector
- A demodulator
whose gain or conversion ratio is increased by the addition of positive feedback or
regeneration at the carrier frequency.
- The sensitivity, small-signal selectivity, and distortion are increased
over those found in a detector without regeneration.
- regenerative engine
- A liquid propellant rocket
engine cooled by regenerative
- A device used in a thermodynamic
process for capturing and returning to the process heat that would
otherwise be lost. Also called a heat exchanger (which see).
- A portion of the ionosphere
usually characterized by a particular altitude or range of altitudes, in which
concentration of free
electron tend to form.
- region of escape = exosphere.
- A device capable of retaining information, often that contained in a small
subset (e.g., one word) of the aggregate information in a digital computer. See
- The statistical counterpart or analog of the functional expression, in
ordinary mathematics, on one variable in terms of others. Thus, regression
curve, regression coefficient.
- regression of the nodes
- Precessional motion of a set of nodes. See precession.
- The expression is used principally with respect to the moon, the nodes
of which make a complete westerly revolution in approximately 18.6 years.
- regular reflection = specular reflection.
- regular reflector = specular reflector.
- reheat = reheating (especially in sense 1).
- 1. The addition of heat to a working
fluid in an engine after a partial expansion.
- 2. The retention of heat in a fluid, as after passing through a turbine
stage, owing to the inefficiency of the stage.
- Of angle measurements in navigation, measured from the heading of a
craft, as relative bearing.
- relative angular momentum
- The moment of the relative
momentum about a point. See angular
- relative coordinate system
- Any coordinate
system which is moving with respect to an inertial
- Referred to a relative system, various apparent forces arise in Newton
laws owing to motion of the system. See, e.g., centrifugal
- relative distance
- See relative
- relative humidity (symbol U )
- The (dimensionless) ratio of the actual vapor
pressure of the air to the saturation
vapor pressure. The corresponding ratios of specific
humidity or of mixing
ratio give approximations of sufficient accuracy for many purposes in
meteorology. The relative humidity is usually express in percent. Also called
humidity. See absolute
humidity, dew point.
- The ratio of mixing ratio to saturation mixing ratio is preferred as a
definition of relative humidity by the International Meteorological
- relative momentum
- The product of the mass of a particle and its relative velocity; or, in
the case of a fluid, the product of density and relative velocity. See momentum.
- relative motion = apparent motion, relative movement. See
- relative movement
- Motion of one object or body measured relative to another. Usually called
apparent motion when applied to the change of position of a celestial
body as observed from the earth. Also called relative motion.
- The expression is usually used in connection with problems involving
motion of one craft or vehicle relative to another, the direction of such
motion being called direction of relative movement and the speed of such
motion being called speed of relative movement or relative speed. Distance
relative to a specified reference point, usually one in motion, is called
- relative position
- A point defined with reference to another position,
either fixed or moving.
- The coordinates of such a point are usually bearing, true
or relative, and distance from an identified reference point.
- relative scattering function
- See relative
- relative scatter intensity
- For scattering
under any given set of physical conditions: the ratio of the radiant
intensity scattered in any given direction to the radiant intensity
scattered in the direction of the incident beam.
- The value of this ratio is a function of the angle between the
direction in question and the directions of the incident beam. Thus, it may be
symbolized as f(ρ), the relative scattering function. Compare scattering
function. See scatter
- relative speed = speed of relative movement.
- relative sunspot number
- A measure of sunspot activity, computed from the formula R = k
(10 g + f) where R is the relative sunspot number; f is the
number of individual spots; g is the number of groups of spots; and
k a factor that varies with the observer (his personal equation), the
seeing, and the observatory (location and instrumentation). Also called
sunspot number, sunspot relative number, Wolf number, Wolf-Wolfer number,
- relative vorticity
- See absolute
- In general, pertaining to material, as a particle, moving at speeds which
are an appreciable fraction of the speed of
light thus increasing the mass.
- relativistic mass equation
- The equation
m = m0 [1 - (v2/c2)]-1/2 = m0/(1 - β2)1/2
where β = v/c for the relativistic mass m
of a particle or body of rest mass m 0 when its velocity is v. See relativistic
- relativistic particle
- A particle with a velocity so large that its relativistic mass exceeds its
by an amount which is significant for the computation or other considerations
at hand. See relativistic
- relativistic red shift
- See red
- relativistic velocity
- A velocity sufficiently high that some properties of a particle of this
velocity have values significantly different from those obtaining when the
particle is at rest. See rest mass.
- The property of most interest is the mass. For many purposes, the
velocity is relativistic when it exceeds about one-tenth the velocity of
light. See also Fitzgerald-Lorentz
- A principle that postulates the equivalence of the description of the
universe, in terms of physical laws, by various observers, or for various
frames of reference. See relativistic
mass equation, mass-energy
- relativity theory
- See relativity.
- relaxation time
- 1. In general, the time required for a system, object, or fluid to recover
to a specified condition or value after disturbance.
- 2. Specifically, the time taken by an exponentially decaying quantity to
decrease in amplitude by a factor of 1/ e = 0.3679.
- Of a piece of equipment or a system, the probability
of specified performance for a given period of time when used in the specified
- Abbreviation for roentgen-equivalent-man.
- remaining body
- That part of a rocket or vehicle that
remains after the separation of a fallaway
section or companion
- In a multistage rocket, the remaining body diminishes in size
successively as each section or part is cast away and successively becomes a
- remanence (symbol B)
- The magnetic flux
density which remains in a magnetic circuit after
the removal of an applied magnetomotive force. Also called retentivity.
- This should not be confused with residual flux density. If the magnetic
circuit has an airgap, the remanence will be less than the residual flux
- remote control
of an operation from a distance, especially by means of electricity or
electronics; a controlling switch, lever, or other device used in this kind of
control; as in remote-control armament, remote-control switch , etc.
- remote indicating
- Of an instrument, displaying indications at a point remote from its
sensing element, often by electrical or electronic means.
- remote velocity
- The velocity of an
object taken as a whole relative to the surrounding fluid at a point
undisturbed by the moving object. Distinguished from the local
velocity of any of the object's parts.
- Pertaining to the kidneys.
- 1. The event of two or more objects meeting with zero relative velocity at
a preconceived time and place.
- 2. The point in space at which such an event takes place, or is to take
- A rendezvous would be involved, for example, in servicing or
resupplying a space station.
- Abbreviation for roentgen-equivalent-physical.
- An electrode
whose primary function is to reverse the direction of an electron
stream. Also called reflector.
- 1. To restore a storage device
to a prescribed state.
- 2. To place a binary cell
in the initial or zero state. See clear.
- In celestial
mechanics and trajectory
analysis, the deviation between an observed and a computed value, usually in
the sense observed minus computed.
- residual flux density (symbol Br)
- The magnetic flux
density at which the magnetizing force is zero when the material is in a
symmetrically magnetized condition. See remanence.
- residual air
- The volume of air remaining in the lungs after a maximal expiration.
- residual load
- Of a vehicle, the
sum of the payload, all items directly associated with the payload, and other
relatively fixed weights of the overall vehicle; calculated as the difference
between gross weight and the sum of propellant, tank, structure, and
- residual stress
- In structures, any stress in an
unloaded body. These stresses arise from local yielding of the material due to
machining, welding, quenching, cold work, etc.
- resistance (symbol R )
- 1. In electricity, the factor by which the square of the instantaneous
conduction current must be multiplied to obtain the power lost by heat
dissipation or other permanent radiation of energy away from the electrical
- 2. In mechanics, the opposition by frictional effects to forces tending to
- resistivity (symbol ρ)
- In electricity, a characteristic proportionality factor equal to the
resistance of a centimeter cube of a substance to the passage of an electric
current perpendicular to two parallel faces. Also called specific
resistance. R = ρ( l/A ) where R is the resistance
of a uniform conductor, l is the length, A is its
cross-sectional area, and ρ is its resistivity.
- 1. The ability of a film, a lens, a combination of both, or a vidicon system
to render barely distinguishable a standard pattern of black and white lines.
- When the resolution is said to be 10 lines per millimeter, it means
that the pattern whose line plus space width is 0.1 millimeter is barely
resolved, the finer patterns are not resolved, and the coarser patterns are
more clearly resolved. In satellite television systems the limiting element is
the television scanning pattern.
- 2. In radar, the
minimum angular separation at the antenna at which two targets can be
distinguished (a function of beamwidth);
or the minimum range at which two targets at the same azimuth can be separated
(equal to one-half the pulse length).
- 3. Of a gyro, a measure of
response to small changes in input; the maximum value of the minimum input
change that will cause a detectable change in the output for inputs greater
than the threshold, expressed as a percent of one half the input range.
- resolving power
- 1. = resolution,
senses 1 and 2.
- 2. In a unidirectional antenna, the
reciprocal of its beam width measured in degrees.
- The resolution
of a directional radio system can be different from the resolving power of its
antenna, since the resolution is affected by other factors.
- 1. The phenomenon of amplification of a free wave or
of a system by a forced wave
or oscillation of exactly equal period. The
forced wave may arise from an impressed force upon the system or from a
boundary condition. The growth of the resonant amplitude is characteristically
linear in time.
- 2. Of a system in forced
oscillation, the condition which exists when any change, however small, in
the frequency of
excitation causes a decrease in the response of the system.
- resonance frequency
- A frequency at
exists. Also called resonant frequency.
- In case of possible confusion, the type of resonance must be indicated,
as velocity resonance frequency.
- resonant frequency = resonance frequency.
- In radio and radar applications, a circuit which
will resonate at a
given frequency, or
over a range of frequencies, when properly excited.
- A very important type of resonator is the cavity resonator, a closed
hollow volume having conducting walls. The frequency at which these cavities
will resonate is a function of their volume and shape; thus, they are used for
making accurate frequency comparisons and for generating radio frequencies,
usually in the microwave region.
- The interchange of gases of living organisms and the gases of the medium
in which they live.
- Respiration applies to the interchange by any channel as pulmonary
respiration, cutaneous respiration, etc.
- 1. In general, an instrument that indicates reception of an electric or
- 2. = transponder.
- responder beacon = transponder beacon.
- Of a device or system, the motion (or other output) resulting from an excitation
under specified conditions.
- Modifying phrases must be prefixed to the term response to indicate
what kinds of input and output are being utilized. The response
characteristic, often presented graphically, gives the response as a function
of some independent variable such as frequency or direction. For such purposes
it is customary to assume that other characteristics of the input (for
example, voltage) are held constant.
- A radio receiver which
receives the reply from a transponder
and produces an output suitable for feeding to a display system.
- A responsor is usually combined in a single unit with an interrogator,
which sends out the pulse that triggers a transponder, the combined unit being
called an interrogator-responsor.
- Specifically, the act of firing a stage of a rocket after a
previous powered flight and a coast phase in a parking
- rest mass
- According to relativistic
theory, the mass which a body has when it is at absolute rest. Mass increases
when the body is in motion according to
where m is its mass in motion; m0 is its rest mass; v is the body's speed
of motion; and c is the speed of light.
- Newtonian physics, in contrast with relativistic physics, makes no
distinction between rest mass and mass in general.
- restricted propellant
- A solid
propellant having only a portion of its surface exposed for burning, the
other surfaces being covered by an inhibitor.
- In solid-propellant
rockets, a layer of fuel containing no oxidizer, or
of noncombustible material, adhered to the surface of the propellant so as to
prevent burning in that region.
- The sum of two or more vectors.
- resultant wind
- The vectorial average of all wind directions and speeds at a given place
for a certain period.
- Ret, Reti
- International Astronomical Union abbreviations for Reticulum. See
- retentivity = remanence.
- International Astronomical Union abbreviation for Reticulum. See constellation
- A system of lines, wires, etc., placed in the focal plane of an optical
instrument to serve as a reference. Also called reticule.
- A crosshair is a hair, thread, or wire constituting part of a reticle.
- reticule = reticle.
- Reticulum (abbr Ret, Reti)
- See constellation.
- See trace,
- To ignite a retrorocket.
- retroflector = retroreflector.
- retrograde motion
- 1. Motion in an orbit opposite to
the usual orbital direction of celestial
bodies within a given system. Specifically, of a satellite,
motion in a direction opposite to the direction of rotation of the primary.
- 2. The apparent motion of a planet westward among the stars. Also called
- retrogression = retrograde motion.
- A rocket unit built into or strapped to a spacecraft
that provides retrothrust.
wherein the reflected rays return along paths parallel to those of their
corresponding incident rays. Also called retroflection.
- Any instrument used to cause reflected rays to return
along paths parallel to those of their corresponding incident rays. Also
- One type of retroreflector, the corner reflector, is an efficient radar
- (From retro acting.) A rocket fitted on
or in a spacecraft, satellite, or the like to produce thrust opposed
to forward motion.
used for a braking maneuver; reverse thrust.
- The sequence of events preparatory to, and programmed to follow, the retrofiring
- 1. The persistence of sound in an
enclosed space, as a result of multiple reflections after the sound source has
- 2. The sound that persists in an enclosed space, as a result of repeated
reflection or scattering after the source of the sound has stopped.
- reverberation time
- In acoustics, the time required for the time average of the sound
energy density, initially in a steady state, to decrease, after the source
is stopped, to one-millionth of its initial value. The unit is the second.
- reverse thrust
applied to a moving object in a direction to oppose the object's motion.
- reversing layer
- See photosphere,
- A wall of concrete, earth, sandbags, or the like installed for protection,
as against the blast of exploding fuel during a rocket abort.
- 1. Motion of a celestial
body in its orbit; circular motion about an axis usually external to the
- In some contexts, the terms revolution and rotation are used
interchangeably but, with reference to the motions of a celestial body,
revolution refers to motion in an orbit or about an axis external to the body,
whereas rotation refers to motion about an axis within the body. Thus, the
earth revolves about the sun annually and rotates about its axis daily.
- 2. One complete cycle of the movement of a celestial
body in its orbit, or of a body about an external axis, as a revolution
of the earth about the sun.
- To move in a path about an axis, usually external to the body
accomplishing the motion, as in the planets revolve about the sun.
- In a storage device
whose information storing state may be destroyed by reading, the
process of restoring the device to its state prior to reading.
- Reynolds number (symbol R, NRe)
- (After Osborne Reynolds (1842-1912), English scientist.) A nondimensional
parameter representing the ratio of the momentum
forces to the viscous forces
in fluid flow.
- In aerodynamics, the Reynolds number of fluid flow about a body is
often expressed as the fraction ρ = Vl/μ where ρ
is the density of the fluid, V is its velocity,
l is a characteristic dimension of the body, and
μ is the coefficient of viscosity of the fluid.
See critical Reynolds number, effective Reynolds number. As applied to the
flow of gas through a circular tube the Reynolds number is a dimensionless
quantity equal to the product of the gas density, ρ
, in grams per cubic centimeter; times the flow
velocity v, in centimeters per second; times the tube diameter, d, in
centimeters; divided by the viscosity coefficient μ, in poises:
R = ρ vd/μ
- Reynolds stresses
- In the mathematical treatment of a viscous, incompressible, homogeneous
fluid in turbulent motion, terms which represent the transfer of momentum due
to turbulent fluctuations.
- RF (abbr) = radiofrequency.
- A satellite of
Saturn orbiting at a mean distance of 527,000 kilometers.
- rhombic antenna
- An antenna
composed of long-wire radiators comprising the sides of a rhombus. The antenna
usually is terminated in an impedance. The sides of the rhombus, the angle
between the sides, the elevation, and the termination are proportional to give
the desired directivity.
- rho-theta system
- 1. Any electronic navigation system in which position is defined in terms
of distance, or radius ρ and bearing θ with respect to a transmitting station. Also
called an R-theta system.
- 2. Specifically, a polar
coordinate navigation system providing data with sufficient accuracy to
permit the use of a computer which will provide arbitrary course lines
anywhere within the coverage area of the system.
- ribbon parachute
- A type of parachute having a canopy consisting of an arrangement of
closely spaced tapes. This parachute has high porosity with attendant
stability and slight opening shock.
- rice grains = granules.
- Of a combustible mixture: having a relatively high proportion of fuel to oxidizer; more
precisely, having a value greater than stoichiometric.
- Richardson number (symbol NRi)
- A nondimensional number arising in the study of shearing flows of a
NRi = gβ/(u/z)2
where g is the acceleration of gravity;
β is a representative vertical stability (commonly
θ is potential temperature); and
a characteristic vertical shear.
- In Richardson's original interpretation, the Richardson number is a
characteristic ratio of work done against gravitational stability to energy
transferred from mean to turbulent motion. Theoretical studies have placed the
critical Richardson number variously from 1/4 to 2, with instability for
smaller values and stability for greater.
- right ascension
- Angular distance east of the vernal
equinox; the arc of the celestial
equator, or the angle at the celestial pole, between the hour circle
of a point on the celestial
sphere, measured eastward from the hour circle of the vernal equinox
through 24 hours.
- Angular distance west of the vernal equinox, through 360 degrees, is
sidereal hour angle.
- (from German rille meaning groove ). A deep, narrow,
depression on the lunar surface which cuts across all other types of lunar
- rime icing
- Rime aircraft icing is opaque, brittle, and granular. It is formed by the
rapid freezing of small supercooled water droplets, allowing air to be trapped
in. It is generally less hazardous than glaze
icing, because it usually forms more slowly and is more conformal to the
existing aerodynamic surface. It is the most frequent type, composing about
75% of icing reports.
- ring around
- Self-interrogation of a beacon due to
insufficient isolation between receiver and transmitter, i.e., the beacon
transmitter pulse passes through the receiver and retriggers the transmitter.
- ring counter chain
- A series of bistable
elements triggered in sequence.
- An open chain is reset by an externally applied reset pulse; a closed
chain, by feedback from the last element in the chain.
- See lunar
- riometer = relative ionospheric opacity meter.
- Rirti (abbr)
- Recording infrared tracking instrument.
- rise time
- The time required for the leading edge of a pulse to rise
from one-tenth of its final value to nine-tenths of its final value. Rise time
is proportional to time constant. See decay time.
- See tektite.
- Robitzsch actinograph
- A pyranometer
developed by M. Robitzsch. Its design utilizes three bimetallic strips which
are exposed horizontally at the center of a hemispherical glass bowl. The
outer strips are white reflectors, and the center strip is a blackened
absorber. The bimetals are joined in such a manner that the pen of the
instrument deflects in proportion to the difference in temperature between the
black and white strips.
- A high-altitude sounding system consisting of a small solid-propellant
research rocket carried
aloft by an aircraft. The rocket is fired while the aircraft is in vertical
- 1. A projectile, pyrotechnic device, or flying vehicle
propelled by a rocket
- 2. A rocket
engine; any one of the combustion chambers or tubes of a
- rocket airplane
- An airplane using a rocket or rockets for its chief or only propulsion.
- rocket-assisted take-off
- The full term for RATO.
- rocket booster
- A booster, senses
2 and 3.
- rocket engine
- A reaction
engine that contains within itself, or carries along with itself, all the
substances necessary for its operation or for the consumption or combustion of
its fuel, not
requiring intake of any outside substance and hence capable of operation in
outer space. Also called rocket motor.
- Chemical rocket engines contain or carry along their own fuel and
oxidizer, usually in either liquid or solid form, and range from simple motors
consisting only of a combustion chamber and exhaust nozzle to engines of some
complexity incorporating, in addition, fuel and oxygen lines, pumps, cooling
system, etc., and sometimes having two or more combustion chambers.
Experimental rocket motors have used neutral gas, ionized gas, and plasma as
propellants. See liquid-propellant
rocket engine, solid-propellant
rocket engine, ion rocket,
- rocket fuel
- A fuel,
either liquid or solid, developed for, or used by, a rocket.
- rocket launcher
- A device for launching a rocket. See launcher.
- Rocket launchers are wheel mounted, motorized, or fixed for use on the
ground; or they are mounted on aircraft, as under the wings; or they are
installed below or on the decks of ships.
- rocket motor = rocket
- rocket nozzle
- The exhaust nozzle of a rocket.
- rocket plane
- An airplane powered by rocket
- rocket propellant (abbr RP)
- 1. Any agent used for consumption or combustion in a rocket and from which
the rocket derives its thrust, such as a fuel, oxidizer,
additive, catalyst, or any compound or mixture of these.
- 2. The ejected fluid in a
- rocket propulsion
propulsion by a rocket
- rocket ramjet
- A ramjet
engine having a rocket mounted
within the ramjet duct, the rocket being used to bring the ramjet up to the
necessary operating speed. Sometimes called a ducted rocket.
- The science or study of rockets,
including theory, research, development, experimentation, and application; the
art or science of using rockets.
- rocket ship
- An aircraft, space-air vehicle, or spacecraft using rocket
- rocket sled
- A sled that runs on a rail or rails and is accelerated to high velocities
by a rocket
- This sled is used in determining g-tolerances and for developing crash
survival techniques. Rocket sleds are at Edwards Air Force Base, Holloman Air
Force Base, and the Naval Ordnance Test Station. See snort
- rocketsonde = meteorological rocket.
- rocket thrust
- The thrust of a rocket
engine usually expressed in pounds.
- On a test stand, rocket thrust may be measured by use of strain gages,
thrust-balancing pistons, dynamometers, or spring scales, each calibrated in
pounds to represent the static weight moved by the engine.
- rocket thrust chamber
- That part of a rocket engine comprised of the combustion
chamber and the diverging section of the nozzle.
- rocket vehicle
- A vehicle
propelled by a rocket
engine, used to place a satellite in orbit, place a missile upon target,
carry a passenger over a rail as on a rocket sled, etc.
- A high-altitude sounding
system consisting of a small solid-propellant
research rocket carried
aloft by a large plastic balloon.
- The rocket is fired near the maximum altitude of the balloon flight. It
is a relatively mobile sounding system and has been used extensively on
- A type of photoreceptive cell in the retina of the mammalian eye. Rods are
involved in detection of movement and scotopic
vision (night vision).
- rod threshold
- The dimmest illumination in which the rods of the retina
- A unit of radiation, that quantity of X-rays or gamma rays which will
produce, as a consequence of ionization, 1 electrostatic unit of electricity
in 1 cubic centimeter of dry air measured at 0 degrees C and standard
- (abbr rem) A unit of radiation which when absorbed by a human being,
produces the same effect as the absorption of 1 roentgen of
- (abbr rep) A unit measuring a purely physical effect of radiation by
the number of ion pairs produced per unit volume of target material per time
unit. One rep is equivalent to the absorption of 93 erfs per gram of tissue.
- Roentgen ray = X-ray.
- 1. The act of rolling; rotational or oscillatory movement of an aircraft
or similar body about a longitudinal
axis through the body - called roll for any degree of such
- 2. The amount of this movement, i.e., the angle of roll.
- roll axis
- A longitudinal
axis through an aircraft, rocket, or similar body, about which the body
- A roll axis may be a body, wind, or stability axis, or any other
- rolling axis = roll axis.
- rolling moment
- A moment
that tends to rotate an aircraft, a rocket, etc., about a longitudinal
axis. This moment is considered positive when it tends to depress the
starboard side of the body.
- roll out
- In computer terminology, to read out of a storage device
by simultaneously increasing by one the value of the digit in each column and
repeating this r times (where r is the radix) and, at the
instant the representation changes from ( r - 1) to zero: generating a
particular signal, or
terminating a sequence of signals, or originating a sequence of signals.
- Romotar (abbr) = range-only measurement of trajectory and
- root chord
- In aerodynamics, the chord of a
lifting surface at the intersection of that surface with its supporting body,
e.g., wing root chord.
- root-mean-square error (symbol σ)
- In statistics, the square root of the arithmetic
mean of the squares of the deviations of the various items from the arithmetic
mean of the whole. Also termed standard deviation.
- root-mean-square sound pressure = effective sound
- Code name for window, sense 2.
- To turn about an internal axis. Said especially of celestial
bodies. Hence rotation.
- rotating cylinder gage
- A type of molecular
- rotating disk gage
- A type of molecular
- rotating Reynolds number
- A nondimensional number arising in problems of a rotating viscous fluid. Also
called rotation Reynolds number.
- It may appear either as Ωh2/v in which case it equals one-half the square root
of the Taylor number, or as Ωr2/v where r is a suitable radius, h is a
representative depth, &Omega is the absolute angular speed, and v is the
- 1. Turning of a body about an axis within the body, as the daily
rotation of the earth. See revolution.
- 2. One turn of a body about an internal axis, as a rotation of the
- rotational speed (symbol n)
- Revolutions per unit time.
- rotational wave = shear wave.
- rotation Reynolds number = rotating Reynolds number.
- Roti (abbr)
- Recording optical tracking instrument.
- See gyro.
- rotor angular momentum
- (symbol H) Of a gyro, the product
of spin angular
velocity and rotor
moment of inertia, usually expressed in gram centimeters squared per
second. It is a measure of the ability of a gyrorotor to maintain the spin axis
fixed in space.
- rotor moment of inertia
- The moment of
inertia of a gyro rotor about
- rounding error
- In computations, the error resulting from deleting the less significant digits of a
quantity and applying some rule of correction to the part retained. Also
called round-off error.
- round off
- To delete less significant digits from a
number and possible apply some rule of correction to the part retained.
- round-off error = rounding error.
- A set of instructions
arranged in proper sequence to cause a computer to
perform a desired operation, such as the solution of a mathematical problem.
- RP (abbr) = rocket propellant.
- Used with a number in designations of different propellants, as in RP-1
- A rocket fuel consisting
essentially of kerosene.
- R-theta system = rho-theta system.
- R-T unit
- The receiver-transmitter portion of a radar
- rubber-base propellant
- A solid
propellant mixture in which the oxygen supply is obtained from a
perchlorate and the fuel is provided by a synthetic rubber latex.
- A form of combustion
instability, especially in a liquid-propellant
rocket engine, characterized by a low-pitched, low-frequency rumbling
noise; the noise made in this kind of combustion.
- rupture disk = burst disk.