Aerospace Science and Technology Dictionary W Page

Aerospace Science
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Technology Dictionary

W

W: Watt, a measure of electrical power equal to potential in volts times current in amps.
W: West.
wadis: A term used in the desert regions of Southwest Asia and Northern Africa for a stream bed or channel, or a steep sided and bouldery ravine, gully or valley, or a dry wash, that is usually dry except during the rainy season and that often forms an oasis.
walk-around bottle: A personal supply of oxygen for the use of crewmembers when temporarily disconnected from the craft's system.
wall clouds: A localized, persistent, often abrupt lowering from a rain-free base. Wall clouds can range from a fraction of a mile up to nearly five miles in diameter, and normally are found on the south or southwest (inflow) side of the thunderstorm. When seen from within several miles, many wall clouds exhibit rapid upward motion and cyclonic rotation.
walled plain: See lunar crater, note.
wander: Short for apparent wander.
waning moon: The moon between full and new when its visible part is decreasing. See phases of the moon.
warhead: Originally the part of a missile carrying the explosive, chemical, or other charge intended to damage the enemy. By extension, the term is sometimes used as synonymous with payload or nose cone .
warheads: Originally the parts of the missile carrying the explosive, chemical, or other charge intended to damage the enemy. By extension, the term is sometimes used as synonymous with payload or nose cone.
warm advection: Transport of warm air into an area by horizontal winds.
warmup time: The time interval required for a gyro to reach specified performance from the instant that it is energized.
waste treatment: The processing of waste materials (liquid and solid) with chemicals, high temperature, chopping, grinding, and filtering equipment, bacterial action, dryers, separators, for conversion to useful products.
water: Dihydrogen oxide (molecular formula H20). The word is used ambiguously to refer to the chemical compound in general and to its liquid phase; when the former is meant, the term water substance is often used.
Water is distinguished from other common terrestrial substances in existing in all three phases at atmospheric temperatures and pressures (see ice, water vapor). The phase changes, are of great significance in many geophysical processes. The same is true of the large specific heat of liquid water and ice relative to both land surface and atmosphere. Water's complex absorption spectrum gives rise to the greenhouse effect.
water currents: Net transport of water along a definable path. Used for currents (oceanography).
water heating: The heating of water by any means including solar technology.
water sampling: The process of obtaining a representative sample of water from any natural or artificial environment.
water spout: In general, a tornado occurring over water. Specifically, it normally refers to a small, relatively weak rotating column of air over water beneath a towering cumulus cloud. Waterspouts are most common over tropical or subtropical waters.
water substance: See water.
water suit: A g-suit in which the fluid used in the interlining is a liquid, thereby automatically approximating the required hydrostatic pressure gradient under acceleration.
water vapor: Water (H2O) in gaseous form. Also called aqueous vapor . See vapor.
The amount of water vapor present in a given gas sample may be expressed in a number of ways. See absolute humidity, mixing ratio, dewpoint, relative humidity, specific humidity, vapor pressure.
water-flow pyrheliometer: An absolute pyrheliometer, developed by C. G. Abbot, in which the radiation-sensing element is a blackened water calorimeter.
It consists of a cylinder blackened on the interior and surrounded by a special chamber through which water flows at a constant rate. The temperatures of the incoming and outgoing water, which are monitored continuously by thermometers, are used to compute the intensity of the radiation. This instrument is used by the Smithsonian Institution as its standard instrument.
water-vapor absorption: The absorption of certain wavelengths of infrared radiation by atmospheric water vapor. See absorption band.
The water-vapor absorption spectrum is composed of bands near 1.4, 1.8, 2.7, and 6.3 microns and a series of bands beginning at 11 microns and growing stronger with increasing wavelength.
waterfall effect: = Lenard effect.
waterways: Navigable streams or canals; also channels for the passage or escape of water.
watt: Unit of power, the rate at which energy is supplied. One watt is the power which supplies 1 joule per second, 1 kilowatt = 1000 watts.
watt: (abbr w, W)
The unit of power in the MKSA system; that power which produces energy at the rate of 1 joule per second.
wattmeters: Instruments for measuring the magnitude of the active power in an electric circuit. They are provided with a scale usually graduated in either watts, kilowatts, or megawatts. If the scale is graduated in kilowatts or megawatts, the instruments are usually designated as kilowattmeters or megawattmeters.
wave: A disturbance which is propagated in a medium in such a manner that at any point in the medium the quantity serving as measure of disturbance is a function of the time, while at any instant the displacement at a point is a function of the position of the point.
Any physical quantity that has the same relationship to some independent variable (usually time) that a propagated disturbance has, at a particular instant, with respect to space, may be called a wave.
wave equation: The partial differential equation of the form

where is usually a function of the position and time coordinates; is the Laplacian operator; t is the time; and C² is a constant. Also called equation of wave motion . See wave, gravity wave.
The general solution to this equation is any function defined over a plane, the phase front, moving perpendicular to itself at the speed c.
wave filter: A transducer for separating waves on the basis of their frequency. It introduces relatively small loss to waves in one or more frequency bands and relatively large loss to waves of other frequencies. Also called filter .
wave front: A continuous surface drawn through the most forward point in wave distrubances that have the same phase.
wave front: = phase front.
wave interference: The phenomenon which results when waves of the same or nearly the same frequency are superposed; characterized by a spatial or temporal distribution of amplitude of some specified characteristic differing from that of the individual superposed waves. Also called interference .
wave motion: The oscillatory motion of the particles of a medium caused by the passage of a wave, produced by forces external to the medium, but propagated through the medium by internal forces. Wave motion per se involves no net translation of the medium.
Various types of oscillation are found in natural wave motions. Among the simplest are the linear oscillation parallel to the direction of propagation of a longitudinal wave, the linear oscillation perpendicular to the direction of propagation of a transverse wave, and the orbital motion produced by the passage of a progressive gravity wave.
wave number: (symbol )
The reciprocal of wavelength; the number of waves per unit distance in the direction of propagation; or, sometimes times this quantity.
In spectroscopy, wave number is usually expressed in reciprocal centimeters, as 100,000 cm^-1 (100,000 per centimeter).
wave of translation: A wave in which the individual particles of the medium are shifted in the direction of wave travel, as ocean waves in shoal waters; in contrast with an oscillatory wave, in which only the form advances, the individual particles moving in closed orbits, as ocean waves in deep water.
wave particle duality: The principle of quantum mechanics which implies that light (and, indeed, all other subatomic particles) sometimes act like a wave, and sometimes act like a particle, depending on the experiment you are performing. For instance, low frequency electromagnetic radiation tends to act more like a wave than a particle; high frequency electromagnetic radiation tends to act more like a particle than a wave.
wave rotors: Rotor devices that use gasdynamic waves to transfer energy rather than the motion of solid surfaces. Typically, they consist of a series of passages arranged on a drum which rotates about an axis. Through rotation, the ends of the passages are periodically exposed to various circumferentially arranged ports which initiate the traveling expansion or compression waves within the passages. The particular circumferential location of the ports determines the thermodynamic cycle of the working fluid.
wave speed: = phase velocity.
wave theory of light: See electromagnetic radiation.
wave train: A limited series of waves caused by a periodic disturbance of short duration, e.g., the radiofrequency waves in a single pulse, or a succession of pulses themselves.
wave velocity: = phase velocity.
waveband: Portions of the electromagnetic spectrum. Examples of different wavebands include the infrared, visual, and radio wavebands.
waveform: The graphical representation of a wave, showing variation of amplitude with time.
waveguide: A system of boundaries capable of guiding wave.
waveguide lasers: Pump sources for deuterium oxide lasers.
wavelength: (symbol ) In general, the mean distance between maximums (or minimums) of a roughly periodic pattern. Specifically, the least distance between particles moving in the same phase of oscillation in a wave disturbance.
The wavelength is measured along the direction of propagation of the wave, usually from the midpoint of a crest (or trough) to the midpoint of the next adjoining crest (or trough). It is related to frequency f and phase speed v by

= v/f
where is wavelength. The reciprocal of wavelength is the wave number.
wavelength division multiplexing: The process in which each modulating wave modulates a separate subcarrier and the subcarriers are spaced in wavelengths. This term is used in optical communication where wavelength usage is preferred over frequency.
weak interactions (field theory): One class of the fundamental interactions among elementary particles responsible for beta decay of nuclei, and for the decay of elementary particles with lifetimes greater than about 10(-10) seconds such as muons, K mesons, and lambda hypersons; it is several orders of magnitude weaker that the strong and electromagnetic interactions and fails to conserve strangeness or parity. Used for beta interactions.
weakly interacting massive particles: Hypothetical elementary particles predicted by supersymmetry theories, that interact only through gravity and weak-type interactions; postulated to account for dark matter in the Universe. (Abbreviated WIMPs)
weapon systems: A combination of one or more weapons with all related equipment, materials, services, personnel, and means of delivery and deployment (if applicable) required for self-sufficiency.
weapons delivery: Total requirements for locating the target, establishing the release conditions, and maintaining to the target (if required); includes the detection, recognition, and acquisition of the target, the weapons release as well as guidance.
wear: Damage to a solid surface, generally involving progressive loss of material, due to relative motion between that surface and a contacting substance or substances.
weathering: The process of disintegration and decomposition as a consequence of exposure to the atmosphere, to chemical action, and to the action of frost water and heat.
web: The wall of a grain or propellant with an internal cavity.
weber: (abbr wb)
The unit of magnetic flux; the magnetic flux which, linking a circuit of one turn, produces in it an electromotive force of 1 volt as it is reduced to zero at a uniform rate in 1 second.
Weber law: = Weber-Fechner law.
Weber-Fechner law: An approximate psychophysical law relating the degree of response or sensation of a sense organ and the intensity of the stimulus. The law asserts that equal increments of sensation are associated with equal increments of the logarithm of the stimulus, or that the just noticeable difference in any sensation results from a change in the stimulus which bears a constant ratio to the value of the stimulus. Also called Weber law .
The Weber-Fechner law is applied to the detection of contrast in the problem of visual range, as well as to many other psychophysical problems.
Weibel instability: An instability of collisionless plasmas characterized by the unstable growth of transverse electromagnetic waves and large magnetic field fluctuation brought about by an anisotropic distribution of electronic velocities.
weight: The force exerted on a body by gravity.
weight: (symbol w )
1. The force with which a body is attracted toward the earth.
2. The product of the mass of a body and the acceleration acting on a body.
In a dynamic situation, the weight can be a multiple of that under resting conditions. Weight also varies on other planets in accordance with their gravity.
weight flow rate: (symbol )
Mass flow rate multiplied by gravity, or

Where m is mass and t is time; usually expressed in pounds per second.
weightlessness: 1. A condition in which no acceleration, whether of gravity or other force, can be detected by an observer within the system in question.
Any object failing freely in a vacuum is weightless, thus an unaccelerated satellite orbiting the earth is weightless although gravity affects its orbit. Weightlessness can be produced within the atmosphere in aircraft flying a parabolic flightpath.
2. A condition in which gravitational and other external forces acting on a body produce no stress, either internal or external, in the body.
welding: Joining two or more pieces of metal by applying heat, pressure, or both, with or without filler material to produce a localized union through fusion or recrystallization across the interface.
The thickness of the filler material is much greater than the capillary dimensions encountered in brazing.
West comet: A comet discovered in 1976..
wet: To come in contact with, and flow across (a surface, body, or area) - said of air or other fluid.
wet emplacement: A launch emplacement that provides a deluge of water for cooling the flame bucket, the rocket engines, and other equipment during the launch of a missile. See flame deflector, dry emplacement.
wet spinning: The production of synthetic and man-made filaments by extruding the chemical solution through spinnerets into a chemical bath where they coagulate.
wet-fuel rocket: = liquid rocket.
wetlands: Lands which have the water table at, near, or above the land surface, or which are saturated for long enough periods to promote hydrophylic vegetation and various kinds of biological activity which are adapted to the wet environment.
wheelchairs: Four wheeled ambulatory devices for persons with minimal or no use of lower extremities which can be either manually or electrically powered. They are often individually fitted.
wheels: Rims fitted with disks for affixment to axles.
whip antennas: Thin flexible monopole antennas.
whispering gallery modes: Electromagnetic (or elastic) waves that differ in frequency by more than an order of magnitude.
whistler: A radiofrequency electromagnetic signal generated by some lightning discharges.
This signal apparently propagates along a geomagnetic line of force and often bounces several times between the Northern and Southern Hemispheres. Its name derives from the sound heard on radio receivers.
whistling meteor: Name applied to a radio meteor when a detection system is used in which the presence of the meteor is indicated by a rapidly changing audiofrequency radio signal.
The maximum reflection of a radio signal from a radio meteor occurs when the ion column is perpendicular to the line from the column to the transmitter-receiver. During the approach of the meteor to this position, the Doppler effect causes a change in the frequency of the reflected signal. When the reflected signal frequency is then combined with the transmitter frequency, the difference between the transmitted and reflected frequencies produces an audiofrequency beat. The audiofrequency beat, when amplified and fed to a loudspeaker, allows the meteors to be heard as a high-pitched whistle which rapidly falls to zero frequency as the meteor trail becomes normal to the line of sight.
white body: A hypothetical body whose surface absorbs no electromagnetic radiation of any wavelength, i.e., one which exhibits zero absorptivity for all wavelengths; an idealization exactly opposite to that of the blackbody. See gray body.
In nature, no true white bodies are known. Most white pigments possessing high reflectivity for visible radiation are fairly good absorbers in the infrared; hence, they are not white bodies in the sense of the radiation theory. However, the term white body is used for physical objects with respect to a particular wavelength interval.
white dwarf stars: A star that has exhausted most or all of its nuclear fuel and has collapsed to a very small size. Typically, a white dwarf has a radius equal to about 0.01 times that of the Sun, but it has a mass roughly equal to the Sun's. This gives a white dwarf a density about 1 million times that of water!
white holes (astronomy): Time-reversed black holes, expanding sources with growing intensity and photon energy.
white light: Visible light that includes all colors and, therefore, all visible wavelengths.
white noise: A sound or electromagnetic wave whose spectrum is continuous and uniform as a function of frequency.
white room: A clean and dust-free room used for assembly and repair of precise mechanisms such as gyros.
Wien displacement constant: See Wien law.
Wien displacement law: = Wien law.
Wien distribution law: A relation, derived on purely thermodynamic reasoning by Wien, between the monochromatic emittance of an ideal blackbody and that body's temperature.

where is the monochromatic emittance (emissive power) of a blackbody at wavelength and absolute temperature T, and is a function which cannot be determined purely on classical thermodynamic grounds. Compare Wien law.
Wien law: One of the radiation laws which states that the wavelength of maximum radiation intensity for a blackbody is inversely proportional to the absolute temperature of the radiating blackbody:

where is the wavelength of maximum intensity; b is a constant; and T is the absolute temperature. The Wien displacement constant b is equal to 0.28978 centimeter-degree. Also called Wien displacement law .
This law, established experimentally by Wien in 1896, describes the manner in which the wavelength of maximum radiation shifts toward shorter values as the temperature of a radiator rises. It is to be distinguished from Wien distribution law which describes the variation with temperature of the intensity of emission at any wavelength. Wien displacement law is used to compute the color temperature of a radiator by insertion of its wavelength of peak intensity into the above equation to compute T.
Wien's displacement law: For a blackbody, the product of the wavelength corresponding to the maximum radiancy and the thermodynamic temperature is a constant. As a result, as the temperature rises, the maximum of the radiant energy shifts toward the shorter wavelength (higher frequency and energy) end of the spectrum.
WIG vehicles: See wing-in-ground effect vehicles.
wiggler magnets: Components used in the production of coherent x rays by the pumping of a gas with synchrotron radiation in combination with low energy photon beams.
Wild 2 comet: Periodic comet, discovered January 1978, relatively new to the inner Solar System due to a shift in its orbit caused by the gravitational influence of Jupiter.
WIMPs: See weakly interacting massive particles.
wind (meteorology): A natural motion of the air, especially a noticeable current of air moving in the atmosphere parallel to the Earth's surface.
wind axis: Any one of a system of mutually perpendicular reference axis established with respect to the undisturbed wind direction about an aircraft or similar body. See axis, sense 2.
wind direction: The direction from which the wind is blowing, measured in points of the compass or in azimuth degree.
wind shear: A sharp change in wind speed and direction over a short distance
wind shear: See barotropic model.
wind tunnel: A tubelike structure or passage, sometimes continuous, together with its adjuncts, in which a high-speed movement of air or other gas is produced, as by a fan, and within which objects such as engines or aircraft, airfoils, rockets (or models of these objects), etc., are placed to investigate the airflow about them and the aerodynamic forces acting upon them.
Tunnels are designated by the means used to produce the gas flow, as hot shot tunnel, arc tunnel, blow down tunnel; by the speed range, as supersonic tunnel, hypersonic tunnel; or by the medium used, as plasma tunnel, light gas tunnel.
wind tunnels: Tubelike structures or passages, sometimes continuous, together with their adjuncts, in which high speed movements of air or other gases are produced, as by fans, and within which objects such as engines or aircraft, airfoils, rockets (or models of these objects), are placed to investigate the airflow about them and the aerodynamic forces acting upon them.
wind turbines: Machines which convert wind energy into electricity.
wind-tunnel balance: A device or apparatus that measures the aerodynamic forces and moments acting upon a body tested in a wind tunnel.
window: 1. Any device introduced into the atmosphere for producing an appreciable radar echo, usually for tracking some airborne device or as a tracer of wind.
2. A World War II code name for a type of radar-jamming device employed to confuse the operators of enemy radars (also referred to by the code names of rope, chaff , and clutter ).
One type of window consists of packages containing thousands of small strips of paperbacked tinfoil which may be dropped from aircraft and balloons, ejected from rockets, and carried within balloons. The packages burst open upon ejection, scattering the tinfoil widely, producing a radar echo which looks like a small shower or a tight formation of aircraft on plan-position-indicator scopes.
3. Any gap in a linear continuum, as atmospheric windows , ranges of wavelengths in the electromagnetic spectrum to which the atmosphere is transparent, or firing windows , intervals of time during which conditions are favorable for launching a spacecraft on a specific mission.
wing nacelle configurations: Aerodynamic configurations involving various arrangements of wings and nacelles (over-the-wing, etc.).
wing rock: A high angle-of-attack, nonlinear, dynamic phenomenon of limited cycle motion predominantly in roll.
wing-in-ground effect vehicles: Vehicles designed to fly about half their mean chord above the surface, taking advantage of the reduced drag and increased lift caused by ground effect. These vehicles, also known as WIGs or WIGEs, normally operate above a water surface.
winglets: In aerospace engineering, small nearly vertical, winglike surfaces mounted rearward above the wing tips to reduce drag coefficients at lifting conditions.
winter solstice: 1. That point on the ecliptic occupied by the sum at maximum southerly declination. Sometimes called December solstice, first point of Capricornus .
2. That instant at which the sun reaches the point of maximum southerly declination, about December 22.
wire: A rod or filament of drawn or rolled metal whose length is great in comparison with the major axis of its cross section.
wire link telemetry: Telemetry in which no radio link is used. Also called hard wire telemetry .
wireless: Sometimes used as the equivalent of radio, particularly in British terminology.
Wolf number: = relative sunspot number.
Wolf-Rayet stars: Very luminous, very hot (as high as 50,000K) stars whose spectra have broad emission lines (mainly He I and He II, which are presumed to originate from material ejected from the stars at very high velocities. Some W-R spectra show emission lines due to carbon CWC stars; others show emission lines due to nitrogen (WN stars). Used for W stars and W-R stars.
Wolf-Wolfer-Wolfest number: = relative sunspot number.
word: In electronic computers, an ordered set of characters which is the normal unit in which information may be stored, transmitted, or operated upon within a computer.
word processing: The use of a computer, often with a CRT under full-screen control, to facilitate the recording, storage, editing, updating, and organization of information in the form of words, especially sentential information.
word rate: In computer operations, the frequency derived from the elapsed period between the beginning of transmission of one word and the beginning of transmission of the next word.
work: (symbol W )
Energy resulting from the motion of a system against a force and existing only during the process of energy conversion.
work function: The energy required for an electron to escape a solid surface. See Helmholtz function.
In ion engines, the work function of the ionizer must be greater than the ionization potential of the neutral atoms in the propellant gas.
work softening: The phenomena of a drop in the yield strength of a metal when it has been strained or cold worked at low temperature and subsequently strained at an elevated temperature to cause the dislocations to become unstable.
working fluid: A fluid (gas or liquid) used as the medium for the transfer of energy from one part of a system to another part.
World Geographic Reference System: A geographic reference system for the world, used in the Air Force for aircraft position reports and target designation, and for the control and direction of air units engaged in air defense, air-sea rescue, and tactical air operations.
The short title for this system is georef.
World Wide Web: A loose linkage of Internet sites which provide data and other services from around the world.
write: In computer terminology, record.
WWW: World-Wide Web.

Aerospace Science & Technology Dictionary

Aerospace Science
&
Technology Dictionary