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R

  
R-T unit
   (NASA SP-7, 1965)
The receiver-transmitter portion of a radar beacon system.
R-theta system
   (NASA SP-7, 1965)
= rho-theta system.
RA
   (Space Flight Glossary - JPL)
Right ascension, the angular distance of a celestial object measured in hours, minutes, and seconds along the celestial equator eastward from the vernal equinox.
rabbit
   (NASA SP-7, 1965)
Video display of a beacon's replies to interrogations from two or more nonsynchronized radars.
racon
   (NASA SP-7, 1965)
(From radar beacon)
A transponder for interrogation by a primary radar.
radar
   (NASA Thesaurus / NASA SP-7, 1965)
(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 guidance.
2. The electronic equipment or apparatus used to generate, transmit, receive, and, usually, to display radio scanning or locating waves; a radar set.
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
   (Global Land Information System Glossary - USGS)
Instrument for measuring altitudes or elevations with respect to a reference level, usually mean sea level. A radar altimeter determines the height of an aircraft above the terrain by measuring the time required for an electromagnetic pulse to travel from aircraft to the ground and back again.
radar altimeter
   (NASA SP-7, 1965)
= radio altimeter.
radar altitude
   (NASA SP-7, 1965)
The altitude of an aircraft or spacecraft as determined by a radio altimeter; thus, the actual distance from the nearest terrain feature.
radar astronomy
   (NASA Thesaurus / NASA SP-7, 1965)
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 astronomy.
radar band
   (NASA SP-7, 1965)
See frequency band.
radar beacon
   (NASA SP-7, 1965)
A beacon transmitting a characteristic signal on radar frequency, permitting a craft to determine the bearing and sometimes the range of the beacon.
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
   (NASA SP-7, 1965)
See beam.
radar cross section
   (NASA SP-7, 1965)
The ratio of power returned in a radar echo to power received by the target reflecting the signal. Compare scattering cross section.
radar duct
   (NASA SP-7, 1965)
See radio duct.
radar echo
   (NASA SP-7, 1965)
See echo.
radar frequency
   (NASA SP-7, 1965)
See frequency band.
radar geology
   (NASA Thesaurus)
The application of imaging radar to geologic problems.
radar homing missiles
   (NASA Thesaurus)
Radar-following missiles designed to attack radar transmitters.
radar horizon
   (NASA SP-7, 1965)
The angle of elevation at which the beam from a radar antenna is intercepted by the earth's horizon. Compare radio horizon.
radar indicator
   (NASA SP-7, 1965)
= radarscope.
radar mile
   (NASA SP-7, 1965)
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 networks
   (NASA Thesaurus)
A series of tracking stations each of which can individually or jointly track a target by utilizing an interchange of radar information. Used for multiradar tracking.
radar range
   (NASA Thesaurus / NASA SP-7, 1965)
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 targets.
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
   (NASA SP-7, 1965)
The relation between the maximum range Rmax at which a point target is detectable and the properties of the radar and the target

R sub max equals open bracket open parens P A squared lambda squared sigma close parens over open parens open parens four pi close parens cubes S min close parens close bracket to the power one quarter

where P is the transmitted power of the radar; lambda is its wavelength; sigma is the scattering cross section of the target; A is the antenna gain; and Smin is the threshold signal.
radar reflectivity
   (NASA SP-7, 1965)
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 and diffraction.
radar reflector
   (NASA SP-7, 1965)
A device capable of or intended for reflecting radar signals. See corner reflector, parabolic reflector.
radar scan
   (NASA SP-7, 1965)
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 scanning.
radar scanning
   (NASA Thesaurus / NASA SP-7, 1965)
The action or process of moving or directing a searching radar beam. See circular scanning, conical scanning, helical scanning.
radar screen
   (NASA SP-7, 1965)
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
   (NASA SP-7, 1965)
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
   (NASA SP-7, 1965)
A condition in which radar frequency signals do not reach a region because of an intervening obstruction.
radar target
   (NASA Thesaurus)
An object which reflects a sufficient amount of a radar signal to produce an echo signal on the radar screen.
radar volume
   (NASA SP-7, 1965)
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
   (NASA SP-7, 1965)
A transmitted or reflected radio wave used in radar; a radio wave in one of the frequency bands used for radar.
Radarsat
   (NASA Thesaurus)
A civilian remote sensing satellite that will be polar orbiting and is jointly being developed by Canada and the United Kingdom with NASA providing the launch. In addition to a synthetic aperture radar, it may carry other instruments such as the Advanced Along Track Scanning Radiometer (AATSR) and the Advanced Radar Altimeter (ARA)/Ocean Wave Spectrometer (OWS). Launch is planned for 1994.
radarscope
   (NASA Thesaurus / NASA SP-7, 1965)
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.
radial
   (NASA SP-7, 1965)
Motion along a radius.
radial motion
   (NASA SP-7, 1965)
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
   (NASA Thesaurus / NASA SP-7, 1965)
In radar, that vector component of the velocity of a moving target that is directed away from or toward the ground station.
radian
   (NASA SP-7, 1965)
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 three hundred sixty degrees over two pi or approximately 57 degrees 17 minutes 44.8 seconds.
radiance
   (NASA Thesaurus / NASA SP-7, 1965)
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 (formerly, brightness).
radiancy
   (NASA Thesaurus / NASA SP-7, 1965)
(symbol R, capital cursive R , W)
The rate of radiant-energy emission for a unit area of a source in all the radial directions of the overspreading hemisphere.
radiant
   (IMO Meteor Glossary)
In astronomy, the point where the backward projection of the meteor trajectory intersects the celestial sphere. More generally, the point in the sky from which meteors from a specific shower seem to come when observed from the surface of the Earth.
radiant
   (NASA SP-7, 1965)
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 of meteors seen during a meteor shower.
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
   (NASA SP-7, 1965)
= radiant energy density.
radiant emittance
   (NASA SP-7, 1965)
See emittance, sense 1.
radiant energy
   (NASA SP-7, 1965)
(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, acoustic energy.
radiant energy density
   (NASA SP-7, 1965)
(symbol u )
The instantaneous amount of radiant energy contained in a unit volume of propagating medium.
radiant energy thermometer
   (NASA SP-7, 1965)
An instrument which determines the blackbody 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 black.
radiant flux
   (NASA SP-7, 1965)
(symbol capital phi)
The rate of flow of radiant energy.
radiant flux density
   (NASA Thesaurus)
The rate of radiant energy emission from a unit area of a source in all the radial directions of the overspreading hemisphere. Used for power density (electromagnetic), radiant intensity, and radiation intensity.
radiant flux density
   (NASA SP-7, 1965)
= 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 (symbol H).
radiant heat
   (NASA SP-7, 1965)
Infrared radiation.
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
   (NASA SP-7, 1965)
Radiant flux per unit solid angle.
radiant temperature
   (NASA SP-7, 1965)
The temperature obtained by use of a total radiation pyrometer when sighted upon a nonblackbody.
This is always less than the true temperature.
radiating element
   (NASA SP-7, 1965)
A basic subdivision of an antenna which in itself is capable of radiating or receiving radiofrequency energy.
radiation
   (NASA Thesaurus)
The process by which energy is emitted or transferred in the form of photons or electromagnetic waves. Used for radiant energy and radiation emission.
radiation
   (NASA SP-7, 1965)
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 energy.
4. = electromagnetic radiation, specifically, high-energy radiation such as gamma rays and X-rays.
5. Corpuscular emissions, such as or -radiation
6. = nuclear radiation.
7. = radioactivity.
radiation belt
   (NASA SP-7, 1965)
An envelope of charged particles trapped in the magnetic field of a spatial body. See Van Allen belt.
radiation chemistry
   (NASA Thesaurus)
The branch of chemistry concerned with the chemical effects, including decomposition, of energetic radiation or particles of matter.
radiation constants
   (NASA SP-7, 1965)
Values used in Planck law and other radiation calculations. The first radiation constant (symbol c1) = 3.7415 erg centimeters squared per second. The second radiation constant (symbol c2) = 1.43879 centimeters degrees K. See physical constants.
radiation cooled
   (NASA SP-7, 1965)
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 low.
radiation counter
   (NASA Thesaurus / NASA SP-7, 1965)
An instrument used for detecting or measuring moving subatomic particles by a counting process.
radiation dosage
   (NASA Thesaurus)
The amount of radiation absorbed by a material, system, or tissue in a given amount of time; usually measured in units as roentgen. Used for radiation exposure.
radiation dose
   (NASA SP-7, 1965)
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, roentgen-equivalent-physical, etc.
radiation laws
   (NASA SP-7, 1965)
1. The four physical laws which, together, fundamentally describe the behavior of blackbody 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 blackbody 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 blackbody to its absolute temperature; (d) the Wien law relates the wavelength of maximum intensity emitted by a blackbody to its absolute temperature.
2. All the more inclusive assemblage of empirical and theoretical laws describing all manifestations of radiative phenomena; e.g., Bouguer law and Lambert law.
radiation lobe
   (NASA SP-7, 1965)
A portion of the radiation pattern bounded by one or two cones of nulls.
radiation medicine
   (NASA SP-7, 1965)
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
   (NASA SP-7, 1965)
A graphical representation of the radiation of an antenna 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
   (NASA Thesaurus / NASA SP-7, 1965)
(symbol Pr)
Pressure exerted upon any material body by electromagnetic radiation incident upon it. See Poynting-Robertson effect.
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 Echo.
radiation pyrometer
   (NASA SP-7, 1965)
See pyrometer, note.
radiation shield
   (NASA SP-7, 1965)
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 shield.
radiation sickness
   (NASA Thesaurus / NASA SP-7, 1965)
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 level.
radiation transport
   (NASA Thesaurus)
The study of radiation from emission to absorption.
radiation trapping
   (NASA Thesaurus)
Confinement of radiation with a magnetic field.
radiative zone
   (SOHO Glossary - GSFC)
An interior layer of the Sun, lying between the core and the convection zone, where energy travels outward by radiation.
radiator
   (NASA Thesaurus / NASA SP-7, 1965)
1. Any source of radiant energy, especially electromagnetic radiation.
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.
radio
   (NASA SP-7, 1965)
1. Communication by electromagnetic waves, without a connecting wire.
2. Pertaining to radiofrequency, as in radio wave.
radio altimeter
   (NASA Thesaurus / NASA SP-7, 1965)
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
   (NASA Thesaurus / NASA SP-7, 1965)
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 spectrum.
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
   (NASA Thesaurus / NASA SP-7, 1965)
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
   (NASA SP-7, 1965)
See beam.
radio blackout
   (NASA SP-7, 1965)
= blackout, sense 1.
radio channel
   (NASA SP-7, 1965)
A frequency band comprised of the emission bandwidth, the interference guard bands, and the frequency tolerance.
radio command
   (NASA SP-7, 1965)
A radio signal to which a rocket, satellite, or the like responds.
radio control
   (NASA Thesaurus / NASA SP-7, 1965)
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
   (NASA Thesaurus / NASA SP-7, 1965)
A radio-receiving set, together with its associated equipment, used to determine the direction from which a radio signal is transmitted.
radio duct
   (NASA SP-7, 1965)
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 propagation, skip effect.
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
   (NASA SP-7, 1965)
Electromagnetic 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 band.
radio fadeout
   (NASA SP-7, 1965)
= fadeout.
radio frequencies
   (NASA Thesaurus)
Frequencies at which coherent electromagnetic radiation of energy is useful for communications purposes.
radio frequency heating
   (Plasma Physics and Fusion Energy Glossary)
Process for heating the plasma by transferring energy to ions or electrons using waves generated by an external oscillator at an appropriate frequency.
radio frequency interference
   (NASA Thesaurus)
Degredation of the reception of a wanted signal caused by radio frequency disturbance.
radio goniometer
   (NASA SP-7, 1965)
= radio direction finder.
radio guidance system
   (NASA SP-7, 1965)
A guidance system that uses radio signals to guide an aircraft or spacecraft in flight; the system includes both the flight-borne equipment and the guidance station equipment on the ground.
radio hole
   (NASA SP-7, 1965)
Strong fading of the radio signal 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
   (NASA Thesaurus / NASA SP-7, 1965)
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

r equals square root of two h

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 horizon.
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
   (NASA Thesaurus / NASA SP-7, 1965)
An interferometer operating at radiofrequencies.
Radio interferometers are used in radio astronomy and in satellite tracking.
radio jets (astronomy)
   (NASA Thesaurus)
Jets of energetic particles occurring in radio galaxies and quasars usually emitted from the nuclear (active) region of the extragalactic radio source.
radio meteor
   (NASA Thesaurus / NASA SP-7, 1965)
A meteor which has been detected by the reflection of a radio signal from the meteor trail of relatively high ion density ( ion column). See whistling meteor. Compare photographic meteor.
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 transmitter-receiver.
radio mirage
   (NASA SP-7, 1965)
See radio duct, note.
radio navigation
   (NASA Thesaurus)
Navigation based upon the reception of radio signals.
radio sources (astronomy)
   (NASA Thesaurus)
Celestial objects that emit radio waves.
radio spectra
   (NASA Thesaurus)
Frequencies of electromagnetic radiation usable for radio communication.
radio telescope
   (NASA Thesaurus / NASA SP-7, 1965)
A device for receiving, amplifying, and measuring the intensity of radio waves originating outside the earth's atmosphere or reflected from a body outside the atmosphere.
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
   (NASA SP-7, 1965)
= radio direction finder.
radio transmission
   (NASA Thesaurus)
The transmission of signals by means of radiated electromagnetic waves other than light or heat waves. Used for radio propagation and radio signal propagation.
radio transmitters
   (NASA Thesaurus)
Devices for producing radio-frequency power, for purposes of radio transmission.
radio waves
   (NASA Thesaurus / NASA SP-7, 1965)
Waves produced by oscillation of an electric charge at a frequency useful for radio communication. Formerly called Hertzian waves. See frequency band, electromagnetic radiation.
radioactive
   (NASA SP-7, 1965)
Exhibiting or pertaining to radioactivity.
radioactive decay
   (NASA Thesaurus)
The spontaneous transformation of a nuclide into one or more nuclides accompanied by the release of radiation.
radioactive gas
   (NASA SP-7, 1965)
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 atoms.
radioactive ionization gage
   (NASA SP-7, 1965)
An ionization gage in which the ions are produced by radiations (usually alpha particles) emitted from a radioactive source.
radioactive wastes
   (Plasma Physics and Fusion Energy Glossary)
Equipment and materials from nuclear operations which are radioactive and for which there is no further anticipated use. Wastes are generally classified as high-level (having radioactivity concentrations of hundreds to thousands of curies per gallon or cubic foot), low-level (in the range of 1 microcurie per gallon or cubic foot), or intermediate (between high and low).
radioactivity
   (NASA Thesaurus / NASA SP-7, 1965)
1. Spontaneous disintegration of atomic nuclei with emission of corpuscular or electromagnetic radiation.
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.
radiobiology
   (NASA Thesaurus / NASA SP-7, 1965)
The study of the effects produced on living organisms by radiation.
radiocardiography
   (NASA Thesaurus)
The technique of recording an intravenously injected radioisotope in the heart chambers.
radiofrequency
   (NASA SP-7, 1965)
(abbr RF)
1. A frequency at which coherent electromagnetic radiation of energy is useful for communication purposes.
Roughly, the radiofrequency of the electromagnetic spectrum lies between 10E4 and 10E12 cycles per second. See frequency band.
2. Specifically, the frequency of a given radio carrier wave.
radiofrequency band
   (NASA SP-7, 1965)
See frequency band.
radioimmunoassay
   (NASA Thesaurus)
A medical diagnostic procedure for the components (hormones and immunoglobulins primarily) as well as pharmaceuticals in the blood. The RIA is based on the antigen antibody reactions.
radiometer
   (NASA SP-7, 1965)
An instrument for detecting and, usually, measuring radiant energy. Compare bolometer. See actinometer, photometer.
radiometer vacuum gage
   (NASA SP-7, 1965)
= Knudsen gage.
radiometric correction
   (NASA Thesaurus)
An effort to correct the intensity range of an image. Used for radiometric rectification.
radiometric magnitude
   (NASA SP-7, 1965)
(symbol mrad). The magnitude of a celestial body measured with reference to the total radiation observable through the atmosphere.
radiometric resolution
   (NASA Thesaurus)
The sensitivity of the sensor to distinguish between gray levels.
radiometry
   (NASA SP-7, 1965)
The science of measurement of radiant energy.
In practice, there is no clear distinction between radiometry and photometry although photometry usually refers to measurement in the visible and near-visible range.
radionuclide
   (NASA SP-7, 1965)
A radioactive nuclide; an atom which emits corpuscular or electromagnetic radiation.
radiophare
   (NASA SP-7, 1965)
= radio beacon.
This term is commonly used in international terminology.
radiosonde
   (NASA Thesaurus / NASA SP-7, 1965)
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 radiofrequency carrier.
radiospectrum
   (NASA SP-7, 1965)
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 band.
radius vector
   (NASA SP-7, 1965)
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 coordinates, spherical coordinates.
radix
   (NASA SP-7, 1965)
= base (of a number system).
radix point
   (NASA SP-7, 1965)
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, decimal point.
radome
   (NASA Thesaurus / NASA SP-7, 1965)
(From radar dome. Pronounced raydome ). A dielectric housing for an antenna.
Raduga satellite
   (NASA Thesaurus)
A Soviet communications satellite in geostationary orbit for radio and TV transmission.
railgun accelerators
   (NASA Thesaurus)
Linear dc motors consisting of a pair of rigid, field-producing rails, and a movable conducting armature.
rain erosion
   (NASA Thesaurus)
The wearing away of the land by rain.
rain-free base
   (Glossary of Weather Terms for Storm Spotters - NOAA)
A dark, horizontal cloud base with no visible precipitation beneath it. It typically marks the location of the thunderstorm updraft. Tornadoes may develop from wall clouds attached to the rain-free base, or from the rain-free base itself - especially when the rain-free base is on the south or southwest side of the main precipitation area.
ram air
   (NASA SP-7, 1965)
Air entering an airscoop or air inlet as a result of the high-speed forward movement of a vehicle.
ram drag
   (NASA SP-7, 1965)
The drag produced by the momentum of air entering an airscoop or an air inlet of an aeronautical vehicle in flight.
Raman spectra
   (NASA Thesaurus)
Spectra of the modified frequencies resulting from inelastic scattering when matter is irradiated by a monochromatic beam of radiant energy. Used for Raman effect and Raman scattering.
ramark
   (NASA SP-7, 1965)
A fixed radar frequency facility which continuously emits a signal so that a bearing indication appears on a radar display. See radar beacon.
ramjet
   (NASA SP-7, 1965)
= ramjet engine.
ramjet engine
   (NASA Thesaurus / NASA SP-7, 1965)
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.
Ramsauer effect
   (Plasma Physics and Fusion Energy Glossary)
Term for a quantum-mechanical effect allowing free electrons within a narrow range of energies to pass through a noble gas with very little elastic scattering.
random
   (NASA SP-7, 1965)
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 access
   (NASA Thesaurus)
The process of obtaining data from, or placing data into, storage when there is no sequential relation governing the access time to successive storage location.
random error
   (NASA Thesaurus / NASA SP-7, 1965)
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 noise
   (NASA Thesaurus / NASA SP-7, 1965)
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 number
   (NASA Thesaurus / NASA SP-7, 1965)
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 sample
   (NASA SP-7, 1965)
A sample taken at random from a population.
random sampling
   (NASA Thesaurus)
The process of selecting units for a sample of size n in such a manner that all cobinations of n units under consideration have an equal or ascertainable chance of being selected as the sample.
random variable
   (NASA Thesaurus / NASA SP-7, 1965)
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 probability theory.
random vibration
   (NASA SP-7, 1965)
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 the Gaussian 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.
range
   (NASA SP-7, 1965)
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 range.
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 Missile Range.
5. = radar range.
range attenuation
   (NASA SP-7, 1965)
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
   (NASA Thesaurus / NASA SP-7, 1965)
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 error.
range gating
   (NASA SP-7, 1965)
The use of circuits in radar to suppress signals from all targets falling outside selected range limits.
range marker
   (NASA SP-7, 1965)
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
   (NASA SP-7, 1965)
(abbr Romotar) A nonambiguous spherical and elliptical, long-baseline, range-only trajectory measuring system utilizing phase comparison techniques with range modulation frequencies.
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
   (NASA SP-7, 1965)
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 velocity.
range ring
   (NASA SP-7, 1965)
A circle on a plan position indicator, particularly one with an adjustable diameter, to indicate distance from the antenna. See distance marker.
range safety officer
   (NASA SP-7, 1965)
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 boundaries.
range strobe
   (NASA SP-7, 1965)
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
   (NASA SP-7, 1965)
See sweep, note.
range wind
   (NASA SP-7, 1965)
The component of a ballistic wind which is parallel to the longitudinal axis of the range.
range-height-indicator scope
   (NASA SP-7, 1965)
Null
rangelands
   (NASA Thesaurus)
Land providing forage for domestic and wild animals, wildlife cover, recreation opportunities, and vegetation for watershed protection.
ranging pulse
   (NASA SP-7, 1965)
In a radar system the pulse used to measure the range of the object being tracked.
ranging system
   (NASA SP-7, 1965)
A radar system which measures range (distance).
Rankine cycle
   (NASA Thesaurus)
An ideal thermodynamic cycle consisting of heat addition at constant pressure, isentropic expansion, heat rejection at constant pressure, and isentropic compression; used as an ideal standard for the performance of heat-engine and heat-pump installations operating with a condensable vapor as the working fluid, such as a steam power plant.
Rankine cycle
   (NASA SP-7, 1965)
An idealized thermodynamic cycle consisting of two constant-pressure processes and two isentropic processes.
Rankine temperature scale
   (NASA SP-7, 1965)
(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
   (NASA SP-7, 1965)
A two-dimensional circular flow in which a circular region about the origin is in solid rotation:
V/R = 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 vortex)
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.
raob
   (NASA SP-7, 1965)
(From radiosonde observation). An observation of the vertical distribution of temperature, pressure, and relative humidity, obtained by means of a radiosonde.
rapid quenching (metallurgy)
   (NASA Thesaurus)
Rapid cooling of molten metals or alloys to achieve maximum uniformity in the crystal structure. Used for rapid solidification.
rare gas
   (NASA SP-7, 1965)
= inert gas.
rare gas-halide lasers
   (NASA Thesaurus)
A class of lasers in which the inert gases are used as the amplifying medium.
rare gases
   (NASA Thesaurus)
Gases such as helium, neon, argon, krypton, xenon, and radon, all of whose shells of planetary electrons contain stable numbers of electrons so that the atoms are almost completely chemically inactive. Used for inert gases and noble gases.
rarefied gas dynamics
   (NASA SP-7, 1965)
The study of the phenomena related to the molecular or noncontinuum nature of gas flow at densities where

lambda over l is greater than 0.01

where lambda is molecular mean free path and l is a characteristic dimension of the flow field.
Flow with lambda over l is greater than 0.01 is called molecular flow.
Flow with lambda over l is less than 0.01 is called continuum flow.
Flow with lambda over l is approximately equal to 0.01 to 1 is called slip flow.
Flow with lambda over l is approximately equal to 0.1 to 10 is called transition flow.
Flow with lambda over l is greater than 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 flow.
rarefraction wave
   (NASA SP-7, 1965)
= expansion wave.
raster
   (Global Land Information System Glossary - USGS)
A raster image is a matrix of row and column data points whose values represent energy being reflected or emitted from the object being viewed.
raster
   (NASA SP-7, 1965)
The pattern followed by the electron beam exploring element scanning the screen of a television transmitter or receiver.
raster line
   (NASA SP-7, 1965)
One line of a raster, or scanning pattern.
raster scanning
   (NASA Thesaurus)
Sweeping a cathode ray screen or an antenna beam characterized by a network of parallel sweeps either from side to side or from top to bottom.
rate gyro
   (NASA SP-7, 1965)
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
   (NASA SP-7, 1965)
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
   (NASA SP-7, 1965)
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
   (NASA SP-7, 1965)
= impingement rate.
ratio deviation
   (NASA SP-7, 1965)
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
   (NASA SP-7, 1965)
= celestial horizon.
See horizon.
RATO
   (NASA SP-7, 1965)
(or Rato, or rato) (From rocket-assisted take-off).
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.
ratrace
   (NASA SP-7, 1965)
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
   (NASA SP-7, 1965)
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.
rawin
   (NASA SP-7, 1965)
A measurement of wind direction and speed at altitude by radar tracking of a balloon-borne target.
rawinsonde
   (NASA SP-7, 1965)
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.
ray
   (NASA SP-7, 1965)
1. An elemental path of radiated energy; or the energy following this path. It is perpendicular to the phase fronts of the radiation. See incident ray, reflected ray, refracted ray.
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.
ray tracing
   (NASA Thesaurus / NASA SP-7, 1965)
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 of refraction.
Rayleigh atmosphere
   (NASA SP-7, 1965)
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 Rayleigh 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 criterion
   (Imagine the Universe Dictionary - NASA GSFC)
A criterion for how finely a set of optics may be able to distinguish. It begins with the assumption that the central ring of one image should fall on the first dark ring of another image; for an objective lens with diameter d and employing light with a wavelength lambda (usually taken to be 560 nm), the resolving power is approximately given by 1.22 x lambda/d.
Rayleigh formula
   (NASA SP-7, 1965)
See aerodynamic force, drag, drag coefficient.
Rayleigh law
   (NASA SP-7, 1965)
See Rayleigh scattering.
Rayleigh limit
   (NASA SP-7, 1965)
See Rayleigh scattering.
Rayleigh number
   (NASA SP-7, 1965)
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

N sub Ra equals g absolute value of (triangle sub z T) alpha d cubed over v k
where g is the acceleration of gravity; triangle sub x T is a characteristic vertical temperature difference in the characteristic depth d ; 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 instability.
Rayleigh scattering
   (NASA Thesaurus / NASA SP-7, 1965)
Any scattering process produced by spherical particles whose radii are smaller than about one-tenth the wavelength of the scattered radiation. Compare Mie scattering.
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

k sub s equals two pi to the power five over three, n open parens m squared minus one over m squared plus two close parens squared d to the power six over lambda to the power four

where n is the number of scatters of diameter d; m is the index of refraction; and lambda is the wavelength of the radiation.
Rayleigh wave
   (NASA Thesaurus / NASA SP-7, 1965)
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.
Rayleigh-Benard convection
   (NASA Thesaurus)
The flow of a fluid contained between horizontal thermally conducting plates and heated from below. The Rayleigh number is proportional to the temperature difference between the plates.
Rayleigh-Taylor instabilities
   (Imagine the Universe Dictionary - NASA GSFC)
Iinstabilities which occur when a heavy (more dense) fluid is pushed against a light fluid . Rayleigh-Taylor instabilities are important in many astronomical objects, because the two fluids trade places by sticking "fingers" into each other. These "fingers" can drag the magnetic field lines along with them, thus both enhancing and aligning the magnetic field.
rayon
   (NASA Thesaurus)
A manufactured fiber composed of regenerated cellulose, as well as fibers composed of regenerated cellulose in which substituents have replaced not more than 15 percent of the hydrogens of the hydroxyl groups.
rays
   (NASA SP-7, 1965)
(abbr R)
See aurora.
RCA Satcom satellites
   (NASA Thesaurus)
Domestic commercial communications satellites launched by NASA for the RCA Corporation.
reacting flow
   (NASA Thesaurus)
Fluid flows in which chemical reactions are occurring or potentially can occur. Used for chemically reacting flow.
reaction balance
   (NASA SP-7, 1965)
A type of thrust meter using a balance to measure the static thrust of a rocket or jet engine.
reaction bonding
   (NASA Thesaurus)
Chemical combining of ingredients to produce silicon nitride ceramics.
reaction engine
   (NASA SP-7, 1965)
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 motor.
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 force
   (From Stargazers to Starships Glossary - GSFC)
The added force implied by the lack of motion (equilibrium) when an applied force exists (e.g. gravity).
reaction motor
   (NASA SP-7, 1965)
= reaction engine.
reaction products
   (NASA Thesaurus)
The substances formed in a chemical reaction -- the desired items as well as the unwanted fumes, sludge, residues, etc.
reaction propulsion
   (NASA SP-7, 1965)
Propulsion by reaction to a jet or jets ejected from one or more reaction engines.
reaction time
   (NASA Thesaurus / NASA SP-7, 1965)
In human engineering, the interval between an input signal (physiological) or a stimulus (psychophysiological) and the response elicited by the signal.
reaction turbine
   (NASA SP-7, 1965)
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 turbine.
reactivity
   (NASA Thesaurus)
The ability to react. For proper use of the term, the reaction in question and the conditions should be stated and the parameter used in measuring reactivity indicated, such as rate, uniformity, or the like.
reactor
   (NASA SP-7, 1965)
= nuclear reactor.
reactor core
   (NASA Thesaurus / NASA SP-7, 1965)
In a nuclear reactor the region containing the fissionable material.
reactor safety
   (NASA Thesaurus)
Theoretical and experimental investigations of the behavior of reactor types and designs under various real or hypothetical accidents.
read
   (NASA SP-7, 1965)
In computer operations, to acquire information, usually from some form of storage. See write.
read in
   (NASA SP-7, 1965)
In computer operations, to introduce information into storage.
read-only memory devices
   (NASA Thesaurus)
Computer devices for storing data in permanent or nonerasable form. Used for ROM devices.
readout
   (NASA SP-7, 1965)
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 readout.
2. The data transmitted by the action described in sense 1.
3. In computer operations, to extract information from storage.
readout indicators
   (NASA SP-7, 1965)
Any type of indicating instrument from which meaningful information and data can be directly obtained and used.
readout station
   (NASA SP-7, 1965)
A recording or receiving radio station at which data are received from a transmitter in a probe, satellite, or other spacecraft.
real time
   (NASA SP-7, 1965)
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 operation
   (NASA Thesaurus)
Time in which reporting on events or recording of events is simultaneous with the events.
real-time data
   (NASA SP-7, 1965)
Data presented in usable form at essentially the same time the event occurs.
The delay in presenting the data must be small enough to allow a corrective action to be taken if required.
Reamer temperature scale
   (NASA SP-7, 1965)
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.
rearward acceleration
   (NASA SP-7, 1965)
See physiological acceleration.
rebreather
   (NASA SP-7, 1965)
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
   (NASA SP-7, 1965)
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 scattered power.
receiver
   (NASA Thesaurus / NASA SP-7, 1965)
1. The initial component or sensing element of a measuring system. For example, the receiver of a thermoelectric thermometer is the measuring thermocouple.
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.
receptor
   (NASA Thesaurus / NASA SP-7, 1965)
A sensory nerve ending or organ in a living organism that is sensitive to physical or chemical stimuli.
recharging
   (NASA Thesaurus)
The restoring of discharged electric storage batteries to a charged condition by passing direct current through them in a direction opposite to that of the discharging current.
reciprocal
   (NASA SP-7, 1965)
1. A direction 180 degrees from a given direction.
2. The quotient of 1 divided by a given number.
reciprocal centimeter
   (NASA SP-7, 1965)
See wave number, note.
reciprocating engine
   (NASA SP-7, 1965)
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 movement.
reciprocity
   (NASA SP-7, 1965)
See principle of reciprocity.
reciprocity theorem
   (NASA Thesaurus)
Any theorem expressing reciprocal relations for the behavior of some physical system in which input and output can be interchanged without altering the response of the system to a given excitation.
recognition
   (NASA Thesaurus / NASA SP-7, 1965)
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.
recombination
   (NASA SP-7, 1965)
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
   (NASA Thesaurus / NASA SP-7, 1965)
A measure of the specific rate at which oppositely charged ions join to form neutral particles (a measure of ion recombination). Compare combination coefficient.
recombination energy
   (NASA SP-7, 1965)
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 molecule.
recombination radiation
   (Plasma Physics and Fusion Energy Glossary)
Radiation produced when a free electron in a plasma is captured by an ion.
recoverable
   (NASA SP-7, 1965)
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.
recovery
   (NASA SP-7, 1965)
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 data.
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
   (NASA SP-7, 1965)
A capsule designed to be recovered after reentry. See reentry vehicle.
recovery gear
   (NASA SP-7, 1965)
The devices and equipment used to mark and locate a nose cone or other part of a rocket vehicle after impact.
recovery package
   (NASA SP-7, 1965)
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
   (NASA SP-7, 1965)
Short for adiabatic recovery temperature.
recrystallization
   (NASA Thesaurus / NASA SP-7, 1965)
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
   (NASA SP-7, 1965)
See curvilinear coordinates.
rectennas
   (NASA Thesaurus)
Devices that convert microwave energy into direct-current power by utilizing a number of small diodes each with its own diode rectifier. Used for rectifier antennas.
rectifier
   (NASA SP-7, 1965)
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.
rectifiers
   (NASA Thesaurus)
Static devices having an asymmetrical conduction characteristic which is used to convert attending current into direct current.
recycle
   (NASA SP-7, 1965)
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.
red dwarf stars
   (NASA Thesaurus)
Red stars of low luminosity, so designated by E. Hertzsprung. Red Dwarf stars are commonly those main sequence stars fainter than an absolute magnitude of plus 1, and are the faintest and coolest of the dwarfs.
red giant stars
   (NASA Thesaurus)
Stars whose evolution has progressed to the point where hydrogen core burning has been completed, the helium core has become denser and hotter than originally, and the envelope has expanded to perhaps 100 times its initial size.
red shift
   (NASA Thesaurus / NASA SP-7, 1965)
In astronomy, the displacement of observed spectral lines toward the longer wavelengths of the red end of the spectrum. Compare space reddening.
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
   (NASA SP-7, 1965)
See Great Red Spot.
red sprites
   (NASA Thesaurus)
See sprites
reddening
   (Galileo Project Glossary - JPL)
The phenomenon of the trailing hemisphere of a planetary body being darker at shorter wavelengths ("redder") than the leading hemisphere.
redout
   (NASA SP-7, 1965)
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, sense 3.
Redox cells
   (NASA Thesaurus)
Cells for converting the energy of reactants to electrical energy; an intermediate reductant in the form of liquid electrolyte reacts at the anode in a conventional manner and is regenerated by reaction with a primary fuel.
reduced frequency
   (NASA SP-7, 1965)
(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.
redundancy
   (NASA Thesaurus)
The existence of more than one means of accomplishing a given task, where all means must fail before there is an overall failure of the system.
redundancy
   (NASA SP-7, 1965)
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
   (NASA SP-7, 1965)
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.
reefs
   (NASA Thesaurus)
Chains of rocks, sand ridges, or coral at or near the surface of water.
reentry
   (NASA Thesaurus / NASA SP-7, 1965)
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
   (NASA SP-7, 1965)
That part of a space vehicle that reenters the atmosphere after flight above the sensible atmosphere.
reentry nose cone
   (NASA SP-7, 1965)
A nose cone designed especially for reentry, consisting of one or more chambers protected by an outer shield. See heat sink.
reentry trajectory
   (NASA Thesaurus / NASA SP-7, 1965)
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
   (NASA Thesaurus / NASA SP-7, 1965)
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 vehicles.
reference ellipsoid
   (NASA SP-7, 1965)
An ellipsoid of revolution used as a datum for geodetic measurements. See geoid.
reference frame
   (NASA SP-7, 1965)
= coordinate system.
reference line
   (NASA SP-7, 1965)
= datum line.
reference plane
   (NASA SP-7, 1965)
= datum plane.
reference point
   (NASA SP-7, 1965)
= datum point.
reference signal
   (NASA SP-7, 1965)
In telemetry, the signal against which data-carrying signals are compared to measure differences in time, phase, frequency, etc.
referent
   (NASA SP-7, 1965)
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
   (NASA Thesaurus / NASA SP-7, 1965)
(symbol rho)
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 rho plus alpha equals one .
reflected code
   (NASA SP-7, 1965)
= cyclic code.
reflected ray
   (NASA SP-7, 1965)
A ray extending outward from a point of reflection.
reflected wave
   (NASA Thesaurus / NASA SP-7, 1965)
1. A shock wave, expansion 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
   (NASA Thesaurus / NASA SP-7, 1965)
A telescope which collects light by means of a concave mirror.
reflection
   (NASA Thesaurus / NASA SP-7, 1965)
The process whereby a surface of discontinuity turns back a portion of the incident radiation into the medium through which the radiation approached. See albedo, reflectivity, radar reflectivity.
For true reflection to occur there must be a real discontinuity of the index 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 blackbody 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
   (NASA SP-7, 1965)
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 with polarization.
reflection law
   (High Energy Astrophysics Dictionary- GSFC)
For a wavefront intersecting a reflecting surface, the angle of incidence is equal to the angle of reflection, in the same plane defined by the ray of incidence and the normal.
reflection nebulae
   (NASA Thesaurus)
Any celestial body having a hazy cloudy appearance whose brightness results from the scattering by dust particles of light from nearby stars.
reflectivity
   (NASA SP-7, 1965)
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 reflection coefficient. See radar reflectivity.
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.
reflectometers
   (NASA Thesaurus)
Instruments for measuring reflectance.
reflector
   (NASA SP-7, 1965)
1. In general, any object that reflects incident energy; usually it is a device designed for specific reflection characteristics. See retroreflector, corner reflector, parabolic reflector, radar reflector.
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.
reflector antennas
   (NASA Thesaurus)
Antennas consisting of one or more reflecting surfaces and a radiating (receiving) feed system.
reforestation
   (NASA Thesaurus)
The reestablishment of a tree crop on forest land.
refracted ray
   (NASA SP-7, 1965)
A ray extending onward from the point of refraction.
refracted wave
   (NASA Thesaurus / NASA SP-7, 1965)
A wave that has had its direction of motion changed by refraction. Used for refracted radiation and refracted rays.
refracting telescope
   (NASA Thesaurus / NASA SP-7, 1965)
A telescope which collects light by means of a lens or system of lenses. Also called refractor.
refraction
   (NASA Thesaurus / NASA SP-7, 1965)
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, diffraction, scattering.
refraction error
   (NASA SP-7, 1965)
See astronomical refraction error, terrestrial refraction error, curved-path error.
refraction index
   (NASA SP-7, 1965)
= index of refraction.
refractive index
   (Galileo Project Glossary - JPL)
The ratio of the velocity of light in a vacuum to the velocity of light within a material.
refractive index
   (NASA SP-7, 1965)
= index of refraction.
refractive modulus
   (NASA SP-7, 1965)
= modified index of refraction.
refractivity
   (NASA SP-7, 1965)
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 of refraction.
This usage should be discouraged.
refractometer
   (NASA Thesaurus / NASA SP-7, 1965)
An instrument for measuring the index of refraction of a liquid, gas or solid.
refractor
   (NASA SP-7, 1965)
= refracting telescope.
refractory
   (NASA SP-7, 1965)
A material, usually ceramic, that resists the action of heat, does not fuse at high temperatures, and is very difficult to break down.
refractory coatings
   (NASA Thesaurus)
Pyrolytic materials used for coating other materials exposed to high temperatures.
refractory metal
   (NASA SP-7, 1965)
A metal with melting point above 4000 degrees F.
Usually refers to columbium, molybdenum, tantalum, or tungsten.
refractory metals
   (NASA Thesaurus)
Usually alloys of high-melting point, hard-to-work metals, but can also refer to certain unalloyed elements.
refrangible
   (NASA SP-7, 1965)
Capable of undergoing refraction.
Refsat
   (NASA Thesaurus)
A proposed satellite that broadcasts navigation aiding signals to low cost user terminals which employ the constellation of 24 NavStar Global Positioning System (GPS) satellites for position determination.
regeneration
   (NASA SP-7, 1965)
1. = positive feedback.
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
   (NASA Thesaurus / NASA SP-7, 1965)
The cooling of a part of an engine by the fuel or propellant being delivered to the combustion chamber; specifically, the cooling of a rocket-engine combustion chamber or nozzle by circulating the fuel or oxidizer, or both, around the part to be cooled.
regenerative detector
   (NASA SP-7, 1965)
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
   (NASA SP-7, 1965)
A liquid propellant rocket engine cooled by regenerative cooling.
regenerator
   (NASA Thesaurus / NASA SP-7, 1965)
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).
region
   (NASA SP-7, 1965)
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
   (NASA SP-7, 1965)
= exosphere.
register
   (NASA SP-7, 1965)
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 storage.
registers (computers)
   (NASA Thesaurus)
Devices capable of retaining information, often that contained in a small subset (e.g., one word) of the aggregate information in a digital computer.
regolith
   (NASA Thesaurus)
The layer rock or blanket or unconsolidated rocky debris of any thickness that overlies bedrock and forms the surface of the land.
regression
   (NASA SP-7, 1965)
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 analysis
   (NASA Thesaurus)
The statistical counterpart or analog of the functional expression, in ordinary mathematics, of one variable in terms of others.
regression of the nodes
   (NASA SP-7, 1965)
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
   (NASA SP-7, 1965)
= specular reflection.
regular reflector
   (NASA SP-7, 1965)
= specular reflector.
regulatory mechanisms (biology)
   (NASA Thesaurus)
Specific processes by which living organisms control the rates of biochemical and physiological reactions involved in processes such as metabolism and cellular differentiation.
reheat
   (NASA SP-7, 1965)
= reheating (especially in sense 1).
reheating
   (NASA SP-7, 1965)
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.
reinforced plastics
   (NASA Thesaurus)
Plastics with some strength properties greatly superior to those of the base resin, resulting from the presence of high-strength fillers imbedded in the composition. Note: The reinforcing fillers are usually fibers, fabrics, or mats made of fibers. The plastic laminates are the most common and strongest.
reinforcing materials
   (NASA Thesaurus)
Fibers, filaments, fabrics, and other substances used for strengthening of matrices in composite materials.
Reissner-Nordstrom solution
   (NASA Thesaurus)
The unique solution of general relativity theory describing a nonrotating, charged black hole.
relational database
   (Global Land Information System Glossary - USGS)
A way of modeling information in a database by relations between the features. Relations are usually represented as a collection of tables where each table contains the occurrences of a particular feature.
relative
   (NASA SP-7, 1965)
Of angle measurements in navigation, measured from the heading of a craft, as relative bearing.
relative angular momentum
   (NASA SP-7, 1965)
The moment of the relative momentum about a point. See angular momentum.
relative coordinate system
   (NASA SP-7, 1965)
Any coordinate system which is moving with respect to an inertial coordinate system.
Referred to a relative system, various apparent forces arise in Newton laws owing to motion of the system. See, e.g., centrifugal force, coriolis force.
relative distance
   (NASA SP-7, 1965)
See relative movement, note.
relative humidity
   (NASA SP-7, 1965)
(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 Organization.
relative momentum
   (NASA SP-7, 1965)
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
   (NASA SP-7, 1965)
= apparent motion, relative movement. See motion.
relative movement
   (NASA SP-7, 1965)
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 distance.
relative position
   (NASA SP-7, 1965)
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 scatter intensity
   (NASA SP-7, 1965)
For scattering of radiation 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 function of theta, the relative scattering function. Compare scattering function. See scatter angle.
relative scattering function
   (NASA SP-7, 1965)
See relative scatter intensity.
relative speed
   (NASA SP-7, 1965)
= speed of relative movement.
relative sunspot number
   (NASA SP-7, 1965)
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, Zurich number.
relative vorticity
   (NASA SP-7, 1965)
See absolute vorticity.
relativistic
   (NASA SP-7, 1965)
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 electron beams
   (NASA Thesaurus)
Beams of electrons traveling at approximately the speed of light. Used for REB.
relativistic mass equation
   (NASA SP-7, 1965)
The equation

m equals m sub zero open bracket one minus open parens v squared over c squared close parens close bracket to the minus one half power equals m sub zero over open parens one minus beta squared close parens to the one half power

where beta equals nu over c for the relativistic mass m of a particle or body of rest mass m0 when its velocity is v. See relativistic velocity.
relativistic particle
   (NASA Thesaurus / NASA SP-7, 1965)
A particle with a velocity so large that its relativistic mass exceeds its rest mass by an amount which is significant for the computation or other considerations at hand. See relativistic velocity.
relativistic red shift
   (NASA SP-7, 1965)
See red shift, note.
relativistic velocity
   (NASA Thesaurus / NASA SP-7, 1965)
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 contraction.
relativity
   (NASA Thesaurus / NASA SP-7, 1965)
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 equivalence.
relativity principle
   (High Energy Astrophysics Dictionary- GSFC)
The principle, employed by Einstein's relativity theories, that the laws of physics are the same, at least qualitatively, in all frames. That is, there is no frame that is better (or qualitatively any different) from any other. This principle, along with the constancy principle, constitute the founding principles of special relativity.
relativity theory
   (NASA SP-7, 1965)
See relativity.
relaxation method (mathematics)
   (NASA Thesaurus)
An iterative numerical method for solving elliptic partial differential equations, e.g., a Poisson equation.
relaxation time
   (NASA Thesaurus / NASA SP-7, 1965)
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.
reliability
   (NASA Thesaurus / NASA SP-7, 1965)
Of a piece of equipment or a system, the probability of specified performance for a given period of time when used in the specified manner.
reliability engineering
   (NASA Thesaurus)
The engineering discipline which formulates an acceptable combination of design features, repair philosophy, and maintenance resources to achieve a specified level of reliability as an operational requirement, at optimum life cycle costs.
relic radiation
   (NASA Thesaurus)
Background radiation resulting from the primordial big bang.
reluctance
   (NASA Thesaurus)
The ratio of the magnetomotive force to the magnetic flux through any cross section of the magnetic circuit.
rem
   (Plasma Physics and Fusion Energy Glossary)
Radiation (or Roentgen) Equivalent for Man. Unit of absorbed radiation dose based on the definition rem = rad * quality. The quality factor depends on the type of radiation involved and is used to scale the radiation dose based on the relative harmfulness of different sorts of radiation, compared toordinary X-rays.
rem
   (NASA SP-7, 1965)
Abbreviation for roentgen-equivalent-man.
remaining body
   (NASA SP-7, 1965)
That part of a rocket or vehicle that remains after the separation of a fallaway section or companion body.
In a multistage rocket, the remaining body diminishes in size successively as each section or part is cast away and successively becomes a different body.
remanence
   (NASA Thesaurus / NASA SP-7, 1965)
(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 density.
remote control
   (NASA Thesaurus / NASA SP-7, 1965)
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
   (NASA SP-7, 1965)
Of an instrument, displaying indications at a point remote from its sensing element, often by electrical or electronic means.
remote links
   (Global Land Information System Glossary - USGS)
Direct connections to a computer-based system located at another data center.
remote manipulator system
   (NASA Thesaurus)
Devices used in space for deploying and retrieving payloads by remote control; also used for space maintenance and/or servicing of satellites and other spacecraft.
remote sensing
   (NASA Thesaurus)
The collection of information about an object or phenomena by a recording device that is not in physical contact with it. The term is usually restricted to mean the methods for, and activity of, recording features and phenomena of the Earth surface from a remote platform or vehicle. Typically the methods used record reflected or radiated electromagnetic energy, such as radiometry, photometry, spectrometry, and photographic and radar techniques.
remote velocity
   (NASA SP-7, 1965)
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.
renal
   (NASA SP-7, 1965)
Pertaining to the kidneys.
rendezvous
   (NASA Thesaurus / NASA SP-7, 1965)
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 place.
A rendezvous would be involved, for example, in servicing or resupplying a space station.
Rene 95
   (NASA Thesaurus)
High-strength nickel-base superalloy.
rep
   (NASA SP-7, 1965)
Abbreviation for roentgen-equivalent-physical.
repeller
   (NASA SP-7, 1965)
An electrode whose primary function is to reverse the direction of an electron stream. Also called reflector.
Reseau grid
   (Global Land Information System Glossary - USGS)
An array of tick marks precisely placed in an image.
reservoirs
   (Glossary of Hydrologic Terms - NOAA)
Man-made facilities for the storage, regulation, and controlled release of water. Types of reservoirs include flood control, water supply, and power generation.
reset
   (NASA SP-7, 1965)
1. To restore a storage device to a prescribed state.
2. To place a binary cell in the initial or zero state. See clear.
residential energy
   (NASA Thesaurus)
Household energy requirements in residences, apartments, etc.
residual
   (NASA SP-7, 1965)
In celestial mechanics and trajectory analysis, the deviation between an observed and a computed value, usually in the sense observed minus computed.
residual air
   (NASA SP-7, 1965)
The volume of air remaining in the lungs after a maximal expiration.
residual anomaly
   (Global Land Information System Glossary - USGS)
Geophysically defined features that represent the difference between total (actual) and regional (modeled) geophysical fields.
residual flux density
   (NASA SP-7, 1965)
(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 load
   (NASA SP-7, 1965)
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 power-plant weights.
residual stress
   (NASA Thesaurus / NASA SP-7, 1965)
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.
resin matrix composites
   (NASA Thesaurus)
Composite materials utilizing a matrix of filaments and/or fibers of glass, metal, or other material bound with a polymer or resin.
resistance
   (NASA Thesaurus / NASA SP-7, 1965)
(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 current.
2. In mechanics, the opposition by frictional effects to forces tending to produce motion.
resistivity
   (NASA SP-7, 1965)
(symbol )
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 equals rho open parens l over A close parens
where R is the resistance of a uniform conductor, l is the length, A is its cross-sectional area, and rho is its resistivity.
resolution
   (NASA Thesaurus / NASA SP-7, 1965)
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 beam width); 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
   (NASA SP-7, 1965)
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.
resonance
   (NASA Thesaurus / NASA SP-7, 1965)
1. The phenomenon of amplification of a free wave or oscillation 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 fluorescence
   (NASA Thesaurus)
The emission of radiation by a gas or vapor as a result of excitation of atoms to a higher energy level by incident photons at the resonance frequency of the gas or vapor. Used for resonance radiation.
resonance frequency
   (NASA SP-7, 1965)
A frequency at which resonance exists. Also called resonant frequency.
In case of possible confusion, the type of resonance must be indicated, as velocity resonance frequency.
resonance lines
   (NASA Thesaurus)
Spectral lines which occur either as absorption or emission lines. Used for dielectronic satellite lines.
resonant frequency
   (NASA Thesaurus / NASA SP-7, 1965)
= resonance frequency.
resonator
   (NASA Thesaurus / NASA SP-7, 1965)
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.
respiration
   (NASA Thesaurus / NASA SP-7, 1965)
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.
responder
   (NASA SP-7, 1965)
1. In general, an instrument that indicates reception of an electric or electromagnetic signal.
2. = transponder.
responder beacon
   (NASA SP-7, 1965)
= transponder beacon.
response
   (NASA Thesaurus / NASA SP-7, 1965)
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.
responsor
   (NASA SP-7, 1965)
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.
rest mass
   (NASA SP-7, 1965)
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

m equals m sub zero over square root of (1 minus open parens v squared over c squared close parens)
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.
restart
   (NASA SP-7, 1965)
Specifically, the act of firing a stage of a rocket after a previous powered flight and a coast phase in a parking orbit.
restricted propellant
   (NASA SP-7, 1965)
A solid propellant having only a portion of its surface exposed for burning, the other surfaces being covered by an inhibitor.
restrictor
   (NASA SP-7, 1965)
In solid propellant rocket engines, 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.
resultant
   (NASA Thesaurus / NASA SP-7, 1965)
The sum of two or more vectors.
resultant wind
   (NASA SP-7, 1965)
The vectorial average of all wind directions and speeds at a given place for a certain period.
Ret, Reti
   (NASA SP-7, 1965)
International Astronomical Union abbreviations for Reticulum. See constellation.
retentivity
   (NASA SP-7, 1965)
= remanence.
Reti
   (NASA SP-7, 1965)
International Astronomical Union abbreviation for Reticulum. See constellation
reticle
   (NASA Thesaurus / NASA SP-7, 1965)
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
   (NASA SP-7, 1965)
= reticle.
reticulite
   (Photoglossary of Volcanic Terms - USGS)
Reticulite is basaltic pumice in which nearly all cell walls of gas bubbles have burst, leaving a honeycomb-like structure. Even though it is less dense than pumice, reticulite does not float in water because of the open network of bubbles. The delicate glass threads between the bubbles are so fragile that reticulite was first called "thread-lace scoria" by the great American mineralogist, James Dana.
Reticulum
   (NASA SP-7, 1965)
(abbr Ret, Reti)
See constellation.
retirement for cause
   (NASA Thesaurus)
Procedure, primarily on aircraft, based on fracture mechanics, which allows safe utilizaton of the full life capacities of each component.
retort processing
   (NASA Thesaurus)
One method for converting shale oil into oil similar to petroleum oils.
retrace
   (NASA SP-7, 1965)
See trace, note.
retrofire
   (NASA SP-7, 1965)
To ignite a retrorocket.
retrofitting
   (NASA Thesaurus)
Modification of equipment to incorporate changes made in later production of similar equipment; the changes may be performed in the factory or in the field.
retroflector
   (NASA SP-7, 1965)
= retroreflector.
retrograde motion
   (From Stargazers to Starships Glossary - GSFC)
Temporary reversal of the apparent motion of a planet along the ecliptic. Caused because (by Kepler's 3rd law) a planet moves faster the closer it is to the Sun, so that (for instance) Jupiter appears to move backward when the faster-moving Earth overtakes it.
retrograde motion
   (NASA SP-7, 1965)
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 orbits
   (NASA Thesaurus)
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.
retrogression
   (NASA SP-7, 1965)
= retrograde motion.
retropack
   (NASA SP-7, 1965)
A rocket unit built into or strapped to a spacecraft that provides retrothrust.
retroreflection
   (NASA Thesaurus / NASA SP-7, 1965)
Reflection wherein the reflected rays return along paths parallel to those of their corresponding incident rays. Also called retroflection.
retroreflector
   (NASA SP-7, 1965)
Any instrument used to cause reflected rays to return along paths parallel to those of their corresponding incident rays. Also called retroflector.
One type of retroreflector, the corner reflector, is an efficient radar target.
retroreflectors
   (NASA Thesaurus)
Class of optical instruments which cause reflected radiation to return along paths parallel to those of their corresponding incident rays.
retrorocket
   (NASA SP-7, 1965)
(From retro acting.) A rocket fitted on or in a spacecraft, satellite, or the like to produce thrust opposed to forward motion.
retrorocket engines
   (NASA Thesaurus)
Rocket engines fitted on or in spacecraft, satellites, or the like to produce thrust opposed to forward motion.
retrosequence
   (NASA SP-7, 1965)
The sequence of events preparatory to, and programmed to follow, the retrofiring for spacecraft reentry.
retrothrust
   (NASA Thesaurus / NASA SP-7, 1965)
Thrust used for a braking maneuver; reverse thrust.
reverberation
   (NASA Thesaurus / NASA SP-7, 1965)
1. The persistence of sound in an enclosed space, as a result of multiple reflections after the sound source has stopped.
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 chambers
   (NASA Thesaurus)
Chambers designed to eliminate outside noise for accurate acoustic measurement.
reverberation time
   (NASA SP-7, 1965)
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 field pinch
   (NASA Thesaurus)
A method of plasma confinement under investigation as part of the mirror and pinch programs.
reverse osmosis
   (NASA Thesaurus)
The application of pressure to stop or reverse the transport of solvent through a semipermeable membrane separating two solutions of different solute concentration. The applied pressure required to prevent the flow of solvent across a perfectly semipermeable membrane is called the osmotic pressure and is a characteristic of the solution.
reverse thrust
   (NASA SP-7, 1965)
Thrust applied to a moving object in a direction to oppose the object's motion.
reversing layer
   (NASA SP-7, 1965)
See photosphere, note.
revetment
   (NASA SP-7, 1965)
A wall of concrete, earth, sandbags, or the like installed for protection, as against the blast of exploding fuel during a rocket abort.
revolution
   (NASA SP-7, 1965)
1. Motion of a celestial body in its orbit; circular motion about an axis usually external to the body.
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.
revolve
   (NASA SP-7, 1965)
To move in a path about an axis, usually external to the body accomplishing the motion, as in the planets revolve about the sun. Hence revolution. See rotate.
revolving
   (NASA Thesaurus)
Moving in a path about an axis, usually external to the body accomplishing the motion. Used for revolution (motion).
rewrite
   (NASA SP-7, 1965)
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
   (NASA Thesaurus / NASA SP-7, 1965)
(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 = Vl/, where rho is the density of the fluid, V is its velocity, l is a characteristic dimension of the body, and mu 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, rho, 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 , in poises:

R = rho vd/ eta lower case

.
Reynolds stress
   (NASA Thesaurus / NASA SP-7, 1965)
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
   (Space Flight Glossary - JPL)
Radio frequency.
RF (abbr)
   (NASA SP-7, 1965)
= radiofrequency.
RFI
   (Space Flight Glossary - JPL)
Radio frequency interference.
Rhea
   (NASA Thesaurus / NASA SP-7, 1965)
A satellite of Saturn orbiting at a mean distance of 527,000 kilometers.
rheocasting
   (NASA Thesaurus)
Use of partially solidified metal alloys (fractions solids) fed directly into a casting machine for forming into machine parts.
rheology
   (NASA Thesaurus)
The study of the deformation and flow of matter.
rho-theta system
   (NASA SP-7, 1965)
1. Any electronic navigation system in which position is defined in terms of distance, or radius rho and bearing 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.
rhombic antenna
   (NASA Thesaurus / NASA SP-7, 1965)
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.
rhomboids
   (NASA Thesaurus)
Parallelograms whose adjacent sides are not equal.
rhyolite
   (Photoglossary of Volcanic Terms - USGS)
Rhyolite is a light-colored rock with silica (SiO2) content greater than 68 weight percent. Sodium and potassium oxides both can reach about 5 weight percent. Common mineral types include quartz, feldspar and biotite and are often found in a glassy matrix. Rhyolite is erupted at temperatures of 700 to 850° Centigrade.
ribbon parachute
   (NASA Thesaurus / NASA SP-7, 1965)
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.
riblets
   (NASA Thesaurus)
Longitudinal striations forming V-shaped grooves on aerodynamic and hydrodynamic surfaces. The riblet devices act to reduce large-scale disturbances near the boundary layer. These grooves are dimensional on the order of the wall vortices and turbulent dimensions.
ribonucleic acids
   (NASA Thesaurus)
A chemical found in the nucleus and cytoplasm of cells. It plays an important role in protein synthesis and other chemical activities of the cell. Used for RNA, messenger RNA, transfer RNA, and ribosomal RNA.
rice grains
   (NASA SP-7, 1965)
= granules.
rich
   (NASA SP-7, 1965)
Of a combustible mixture: having a relatively high proportion of fuel to oxidizer; more precisely, having a value greater than stoichiometric.
Richardson number
   (NASA Thesaurus / NASA SP-7, 1965)
(symbol NRi)
A nondimensional number arising in the study of shearing flows of a stratified fluid:

N sub Ri equals g beta over open parens del u over del z close parens squared

where g is the acceleration of gravity; is a representative vertical stability (commonly del theta over theta del z, where theta is potential temperature); and del u over del z 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.
rift zone
   (Photoglossary of Volcanic Terms - USGS)
A rift zone is an elongate system of crustal fractures associated with an area that has undergone extension (ground has spread apart). On the great shield volcanoes in Hawai`i, a rift zone consists of many different features associated with the rise and eruption of magma from narrow dikes, including eruptive fissures, cinder and spatter cones, spatter ramparts, pit craters, lava flows, ground cracks, and normal faults.
right angle
   (From Stargazers to Starships Glossary - GSFC)
The angle formed when two straight lines intersect and the 4 angles at their crossing are all equal. When measured in degrees it equals 90 deg.
right ascension
   (High Energy Astrophysics Dictionary- GSFC)
A coordinate which, along with declination, may be used to locate any position in the sky. Right ascension is analogous to longitude for locating positions on the Earth.
right ascension
   (Solar System Dynamics Glossary - JPL)
Right ascension (or R.A.) is the angular distance on the celestial sphere measured eastward along the celestial equator from the equinox to the hour circle passing through the celestial object.
right ascension
   (NASA SP-7, 1965)
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.
rigid rotors (plasma physics)
   (NASA Thesaurus)
Ensembles of electrons moving in circular or nearly circular orbits at a constant angular frequency.
rill
   (NASA SP-7, 1965)
(from German rille meaning groove ). A deep, narrow, depression on the lunar surface which cuts across all other types of lunar topographic features.
rime icing
   (NASA SP-7, 1965)
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
   (NASA SP-7, 1965)
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
   (NASA SP-7, 1965)
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.
ring currents
   (Earth's Magnetosphere Glossary - GSFC)
A very spread-out electric current circling around the Earth, carried by trapped ions and electrons.
ringwall
   (NASA SP-7, 1965)
See lunar crater.
riometer
   (NASA SP-7, 1965)
= relative ionospheric opacity meter.
Rirti (abbr)
   (NASA SP-7, 1965)
Recording infrared tracking instrument.
RISC processors
   (NASA Thesaurus)
A type of computer processor designed to optimize total system performance by simple, fast decoding of the instructions most commonly employed in computer operations and characterized by: a simple instruction set with the majority of instructions being single cycle; instructions that are register-to-register with LOAD and STORE commands being the only memory-reference instructions; very few addressing modes; hardwired control; instructions with one or two sizes and with fields at fixed locations; and some degree of pipelining.
rise time
   (NASA SP-7, 1965)
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.
risk
   (NASA Thesaurus)
The combined effect of the liklihood of an unfavorable occurrence and the potential impact of that occurrence.
RIT engines
   (NASA Thesaurus)
Radio frequency ion thrustors which generate thrust by converting electric energy into a reaction force by utilizing an electromagnetic field. Used for radio frequency ion thrustor engines.
rivers
   (NASA Thesaurus)
A general term for natural fresh water surface streams of considerable volume and permanent or seasonal flow, moving in definite channels toward seas, lakes, or other rivers. Rivers are large streams or ones larger than brooks or creeks, such as trunk systems and the larger branches of drainage systems.
rizalite
   (NASA SP-7, 1965)
See tektite.
roadway powered vehicles
   (NASA Thesaurus)
Surface vehicles utilizing a combination of an electrical power source embedded in a roadway and an inductive coupled power pickup.
Robitzsch actinograph
   (NASA SP-7, 1965)
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.
robotics
   (NASA Thesaurus)
A discipline that employs the principles and techniques of mechanical and electrical engineering and artificial intelligence to develop programmable or self-controlled machines that often include sensory systems and a degree of intelligence.
robustness (mathematics)
   (NASA Thesaurus)
Insensitivity of systems to uncontrolled perturbations and independent of changes in environmental parameters as demonstrated mathematically.
Roche limit
   (High Energy Astrophysics Dictionary- GSFC)
The smallest distance from a planet or other body at which purely gravitational forces can hold together a satellite or secondary body of the same mean density as the primary; at less than this distance the tidal forces of the primary would break up the secondary.
Roche Limit
   (Planetary Rings Glossary - ARC)
The Roche Limit was first described by Edouard Roche in 1848. It is the closest distance a body can come to a planet without being pulled apart by the planet's tidal (gravity) force. As a result, large moons cannot survive inside the Roche Limit. On July 7, 1992, Comet Shoemaker-Levy 9 broke apart into 21 pieces due to tidal forces when it passed within Jupiter's Roche Limit; on the subsequent pass, each of the comet's pieces collided with Jupiter. If a planet and a moon have identical densities, then the Roche Limit is 2.446 times the radius of the planet. The Roche Limits for the ringed planets are: Jupiter - 175,000 km (108,000 miles) Saturn - 147,000 km ( 92,000 miles) Uranus - 62,000 km ( 39,000 miles) Neptune - 59,000 km ( 37,000 miles) This limit represents the rough boundary between each planet's ring system and its innermost moons.
Roche lobe
   (Imagine the Universe Dictionary - NASA GSFC)
The volume around a star in a binary system in which, if you were to release a particle, it would fall back onto the surface of that star. A particle released above the Roche lobe of either star will, in general, occupy the `circumbinary' region that surrounds both stars. The point at which the Roche lobes of the two stars touch is called the inner Lagrangian or L1 point. If a star in a close binary system evolves to the point at which it `fills' its Roche lobe, theoretical calculations predict that material from this star will overflow both onto the companion star (via the L1 point) and into the circumbinary environment.
rock intrusions
   (NASA Thesaurus)
Vertical tabular bodies of rock that fill fissures in host rocks. Used for dikes (geology).
rock mechanics
   (NASA Thesaurus)
The theoretical and applied science of the physical behavior of rocks, representing a branch of mechanics concerned with the response of rock to the force fields of its physical environment.
rockair
   (NASA SP-7, 1965)
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 ascent.
rocket
   (NASA SP-7, 1965)
1. A projectile, pyrotechnic device, or flying vehicle propelled by a rocket engine.
2. A rocket engine; any one of the combustion chambers or tubes of a multichambered rocket engine.
rocket airplane
   (NASA SP-7, 1965)
An airplane using a rocket or rockets for its chief or only propulsion.
rocket booster
   (NASA SP-7, 1965)
A booster, senses 2 and 3.
rocket engine
   (NASA Thesaurus / NASA SP-7, 1965)
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 engines, solid propellant rocket engines, ion rocket, plasma rocket.
rocket fuel
   (NASA SP-7, 1965)
A fuel, either liquid or solid, developed for, or used by, a rocket.
rocket launcher
   (NASA Thesaurus / NASA SP-7, 1965)
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 linings
   (NASA Thesaurus)
In solid rockets, the layers of inhibiters applied to the inner surface of the chamber holding the grain.
rocket motor
   (NASA SP-7, 1965)
= rocket engine.
rocket nozzle
   (NASA Thesaurus / NASA SP-7, 1965)
The exhaust nozzle of a rocket.
rocket plane
   (NASA SP-7, 1965)
An airplane powered by rocket engines.
rocket propellant
   (NASA Thesaurus / NASA SP-7, 1965)
(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 nuclear rocket.
rocket propulsion
   (NASA SP-7, 1965)
Reaction propulsion by a rocket engine.
rocket ramjet
   (NASA SP-7, 1965)
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.
rocket ship
   (NASA SP-7, 1965)
An aircraft, space-air vehicle, or spacecraft using rocket propulsion.
rocket sled
   (NASA SP-7, 1965)
A sled that runs on a rail or rails and is accelerated to high velocities by a rocket engine.
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 track.
rocket thrust
   (NASA Thesaurus / NASA SP-7, 1965)
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
   (NASA SP-7, 1965)
That part of a rocket engine comprised of the combustion chamber and the diverging section of the nozzle.
rocket vehicle
   (NASA Thesaurus / NASA SP-7, 1965)
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.
rocket-assisted take-off
   (NASA SP-7, 1965)
The full term for RATO.
rocket-based combined-cycle engines
   (NASA Thesaurus)
Launch vehicle engines that integrate a high specific impulse, low thrust-to-weight, airbreathing engine with a low-impulse, high thrust-to-weight rocket. The engines are often defined by four modes of operation in a single-stage-to-orbit configuration. In the first mode, the engine functions as a rocket-driven ejector. When the rocket engine is switched off, subsonic combustion (mode 2) is present in the ramjet mode. As the vehicle continues to accelerate, supersonic combustion (mode 3) occurs in the ramjet mode. Finally, as the edge of the atmosphere is approached and the engine inlet is closed off, the rocket is reignited and the final accent to orbit is undertaken in an all-rocket mode (mode 4).
rocketry
   (NASA SP-7, 1965)
The science or study of rocket, including theory, research, development, experimentation, and application; the art or science of using rockets.
rocketsonde
   (NASA SP-7, 1965)
= meteorological rocket.
rockoon
   (NASA Thesaurus / NASA SP-7, 1965)
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 shipboard.
rocks
   (Photoglossary of Volcanic Terms - USGS)
Rocks are naturally occurring mixtures of minerals, mineral matter, or organic materials. Three main types occur: sedimentary rocks, formed by weathering and mechanical sorting on the Earth's surface; metamorphic rocks, which are rocks that have been transformed by the effects of high temperature and pressure; and igneous rocks, derived from magma (for example, volcanic rocks ).
rocks
   (NASA Thesaurus)
Naturally formed aggregates of mineral matter occurring in large masses or fragments. Used for stones (rocks).
rod
   (NASA SP-7, 1965)
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
   (NASA SP-7, 1965)
The dimmest illumination in which the rods of the retina can function.
roentgen
   (NASA SP-7, 1965)
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 atmospheric pressure.
roentgen ray
   (NASA SP-7, 1965)
= x ray.
roentgen-equivalent-man
   (NASA SP-7, 1965)
Null
roentgen-equivalent-physical
   (NASA SP-7, 1965)
(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.
Rogowski loop or coil
   (Plasma Physics and Fusion Energy Glossary)
A coiled wire loop which encircles a current-carrying plasma. Changes in total plasma current induce a voltage in the loop; integrating (adding up) the voltage over time gives the plasma current.
roll
   (NASA Thesaurus / NASA SP-7, 1965)
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 rotation.
2. The amount of this movement, i.e., the angle of roll.
roll axis
   (NASA SP-7, 1965)
A longitudinal axis through an aircraft, rocket, or similar body, about which the body rolls.
A roll axis may be a body, wind, or stability axis, or any other lengthwise axis.
roll cloud
   (Glossary of Weather Terms for Storm Spotters - NOAA)
A low, horizontal tube-shaped cloud associated with a thunderstorm gust front (or sometimes with a cold front). Roll clouds are relatively rare; they are completely detached from the thunderstorm base or other cloud features, thus differentiating them from the more familiar shelf cloud.
roll out
   (NASA SP-7, 1965)
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.
rolling axis
   (NASA SP-7, 1965)
= roll axis.
rolling moment
   (NASA Thesaurus / NASA SP-7, 1965)
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.
ROM
   (Space Flight Glossary - JPL)
Read Only Memory.
Romotar (abbr)
   (NASA SP-7, 1965)
= range-only measurement of trajectory and recording.
Ronchi test
   (NASA Thesaurus)
An improvement on the Foucault knife-edge test for curved mirrors, in which the knife edge is replaced with a transmission grating with 15 to 80 lines per centimeter, and the pinhole source is replaced with a slit or a section of the same grating.
room temperature
   (NASA Thesaurus)
A temperature in the range of 20 to 30 C (68 to 85 F).
root chord
   (NASA SP-7, 1965)
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
   (NASA Thesaurus / NASA SP-7, 1965)
(symbol sigma )
In statistics, the square root of the arithmetic mean of the squares of the deviations of the various items from the arimetic mean of the whole. Also termed standard deviation.
root-mean-square sound pressure
   (NASA SP-7, 1965)
= effective sound pressure.
rope
   (NASA SP-7, 1965)
Code name for window, sense 2.
rope cloud rope cloud
   (Glossary of Weather Terms for Storm Spotters - NOAA)
In satellite meteorology, a narrow, rope-like band of clouds sometimes seen on satellite images along a front or other boundary.
ROSAT
   (Imagine the Universe Dictionary - NASA GSFC)
Röntgen Satellite
rotary engines
   (NASA Thesaurus)
A positive displacement engine consisting of a rotor and stator. The control volume which encloses the working fluid during the thermodynamic cycle moves in a generally circular motion rather than a linear motion as in a piston engine.
rotary wing aircraft
   (NASA Thesaurus)
A heavier-than-air aircraft that depends prinicipally for its support in flight on the lift generated by one or more rotors.
rotate
   (NASA SP-7, 1965)
To turn about an internal axis. Said especially of celestial bodies. Hence rotation. Compare revolve.
rotating cylinder gage
   (NASA SP-7, 1965)
A type of molecular drag gage.
rotating disk gage
   (NASA SP-7, 1965)
A type of molecular drag gage.
rotating Reynolds number
   (NASA SP-7, 1965)
A nondimensional number arising in problems of a rotating viscous fluid. Also called rotation Reynolds number.
It may appear either as capital omegah2/v, in which case it equals one-half the square root of the Taylor number, or as capital omegah2/v, where r is a suitable radius, h is a representative depth, capital omega is the absolute angular speed, and v is the kinematic viscosity.
rotation
   (NASA Thesaurus)
The motion of a body about some straight line wherein the particles of the body along the line or its extensions have a zero velocity relative to some reference. The line of stationary particles is called the axis of rotation. Used for rotating, whirl, and whirling.
rotation
   (NASA SP-7, 1965)
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 earth.
rotation Reynolds number
   (NASA SP-7, 1965)
= rotating Reynolds number.
rotational speed
   (NASA SP-7, 1965)
(symbol n)
Revolutions per unit time.
rotational wave
   (NASA SP-7, 1965)
= shear wave.
Roti (abbr)
   (NASA SP-7, 1965)
Recording optical tracking instrument.
Rotifera
   (NASA Thesaurus)
A phylum of multicellular animals in the subkingdom Eumatazoa.
rotor
   (NASA SP-7, 1965)
See gyro.
rotor angular momentum
   (NASA SP-7, 1965)
(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 body interactions
   (NASA Thesaurus)
Aerodynamic interactions between a helicopter rotor and a body.
rotor moment of inertia
   (NASA SP-7, 1965)
The moment of inertia of a gyro rotor about its spin axis.
rotor stator interactions
   (NASA Thesaurus)
Aerodynamic interaction between a rotor and a stator.
round off
   (NASA SP-7, 1965)
To delete less significant digits from a number and possible apply some rule of correction to the part retained.
round-off error
   (NASA SP-7, 1965)
= rounding error.
rounding error
   (NASA SP-7, 1965)
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.
routine
   (NASA SP-7, 1965)
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)
   (NASA SP-7, 1965)
= rocket propellant.
Used with a number in designations of different propellants, as in RP-1 .
RP-1
   (NASA SP-7, 1965)
A rocket fuel consisting essentially of kerosene.
RPIF
   (Space Flight Glossary - JPL)
Regional Planetary Imaging Data Facilities.
RTG
   (Space Flight Glossary - JPL)
Radioisotope Thermo-Electric Generator onboard a spacecraft.
RTLT
   (Space Flight Glossary - JPL)
Round-Trip Light Time, elapsed time roughly equal to 2 x OWLT.
rubber
   (NASA Thesaurus)
A material that is capable of recovering from large deformations quickly and forcibly, and can be, or already is modified to a state in which it is essentially insoluble (but can swell) in boiling solvent such as benzene, methyl ethyl ketone, and ethanol-toluene azeotrope.
rubber-base propellant
   (NASA SP-7, 1965)
A solid propellant mixture in which the oxygen supply is obtained from a perchlorate and the fuel is provided by a synthetic rubber latex.
rumble
   (NASA SP-7, 1965)
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.
runaway electrons
   (Plasma Physics and Fusion Energy Glossary)
Those electrons in a plasma that gain energy from an applied electrical field at a faster rate than they lose it through collisions with other particles. These electrons tend to "run away" in *energy* (not position) from the cooler remainder of the background plasma, because the collision cross-section decreases as the particle's velocity increases, so that the faster the particle goes, the less likely it is to be stopped.
Runge-Kutta method
   (NASA Thesaurus)
A method for the numerical solution of an ordinary differential equation.
runoff
   (Glossary of Hydrologic Terms - NOAA)
That part of precipitation that flows toward the streams on the surface of the ground or within the ground. It is composed of base flow and surface runoff.
runways
   (NASA Thesaurus)
A defined rectangular area on a land airport prepared for the landing and takeoff run of aircraft along its length.
rupture disk
   (NASA SP-7, 1965)
= burst disk.
rutile
   (NASA Thesaurus)
A mineral form of titanium oxide (TiO2) (tetragonal crystallization), but usually produced chemically for use in ceramics and other products.
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