T

Source edition 1965. Please read the Introduction to find out about this dictionary and our plans for it. Caution, many entries have not been updated since the 1965 edition.
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Tacan (abbr) = tactical air navigation.

tachycardia

Very rapid beating of the heart.

tactical air navigation (abbr Tacan)

A two-dimensional navigation system which provides azimuth and distance to a fixed ground station for navigation in piloted aircraft. Distance is determined by pulse interrogation of the ground station with time comparison to the returned pulse. Azimuth is provided by comparison of a continuous-wave audiosignal from pulse amplitudes to reference pulses.

tail

1. The rear part of a body, as of an aircraft, a rocket, etc.

2. The tail surfaces of an aircraft or rocket.

tail fin

A fin at the rear of a rocket or other body.

tailward acceleration

See physiological acceleration.

take-off

1. The action of a rocket vehicle departing from its launch pad. See lift-off.

2. The action of an aircraft as it becomes airborne.

3. To perform the action of a take-off. Said of a rocket vehicle or aircraft.

tandem launch

The launching of two or more satellites using a single launch vehicle.

tangential acceleration

The acceleration acting at the periphery of a system rotating about an axis.

tangential wavepath

For a direct radio wave, that path of propagation tangential to the surface of the earth. This path is curved slightly by atmospheric refraction.

tangent ogive

An ogive whose circular-arc contours have their centers on a line normal to the axis at the base of the ogive, the arcs thus being tangent to the surface of the cylindrical body behind the ogive. See ogive.

tank

1. A container incorporated into the structure of a liquid propellant rocket from which a liquid propellant or propellants are fed into the firing chamber or chambers.

2. A container for storage of liquid oxygen, liquid fuel, or other liquid propellant until transferred to the rocket's tanks or some other receptacle.

3. In computers, a container of mercury, or other liquid, and associated components used as delay-line storage.

tankage

Of a liquid propellant rocket, the aggregate of the tanks carried by the rocket.

Tare (abbr) = telemetry automatic reduction system.

target

1. Any object, point, etc., toward which something is directed.

2. An object which reflects a sufficient amount of a radiated signal to produce an echo signal on detection equipment. See radar target.

target acquisition

The process of optically, manually, mechanically, or electronically orienting tracking system in direction and range to lock on a target.

target board

A board usually painted in a distinctive pattern, having a known geometrical relationship to a camera, and used for determining the orientation of that camera.

target discrimination

Resolution of a radar.

target glint = scintillation.

target signal

The radar energy returned to a radar by a target. Also called echo signal, video signal. The amount of this energy is termed received power.

Tau, Taur

International Astronomical Union abbreviations for Taurus. See constellation.

Taurus (abbr Tau, Taur)

See constellation.

Taylor number (symbol N_Ta)

A nondimensional number arising in problems of a rotating viscous fluid. It may be written N_Ta = f²h⁴/v² where f is the coriolis parameter (or, for a cylindrical system, twice the rate of rotation of the system); h represents the depth of the fluid; and v is the kinematic viscosity. the square root of the Taylor number is a rotating Reynolds number, and the fourth root is proportional to the ratio of the depth h to the depth of the Ekman layer.

Taylor series

See Taylor theorem.

Taylor theorem

1. If all the derivatives of a function f(x) are continuous in the vicinity of x = a , then f(x) can be expressed in an infinite series (the Taylor series): The case a = 0 is called a Maclaurin series.

2. The theorem of G.I. Taylor in the statistical theory of atmospheric turbulence: where x is the distance traveled by a particle in the time interval T ; u is the fluctuation or eddy velocity of the particle; and R(ξ) is the Lagrangian correlation coefficient between the particle's velocity at time t and t + ξ.

teardrop balloon

A sounding balloon which, when operationally inflated, resembles an inverted teardrop. This shape was determined primarily by aerodynamic considerations of the problem obtaining maximum stable rates of balloon ascension.

technical photography

The recording of photographic images for information relevant to some engineering phenomena of a qualitative nature.

technical sequential photography

Slow or rapid sequence photography serving the study of event occurrence, or duration, by the adjunct of time coordinates recorded on the film simultaneously with the event.

tektite

Small glassy bodies containing no crystals, composed of at least 65 percent silicon dioxide, bearing no relation to the geological formations in which they occur, and believed to be of extraterrestrial origin. Tektites are found in certain large areas called strewn fields. They are named, as are minerals, with the suffix ite , as australite , found in Australia, billitonite, indochinite , and rizalite , found in Southeast Asia, bediasite from Texas, and moldavite from Bohemia and Moravia.

Tel, Tele

International Astronomical Union abbreviations for Telescopium. See constellation.

telefork

A ground support vehicle that serves as a tractor, a forklift, and a crane.

telemeter

1. To measure at a distance. See telemetering, telemetry.

2. The electronic unit which transmits the signal in a telemetering system.

telemetering

1. A measurement accomplished with the aid of intermediate means which allows perception, recording, or interpretation of data at a distance from a primary sensor. The most widely employed interpretation of telemetering restricts its significance to data transmitted by means of electromagnetic propagation.

2. Automatic radio communication intended to indicate or record a measurable variable quantity at a distance.

telemetry

The science of measuring a quantity or quantities, transmitting the results to a distant station, and there interpreting, indicating, and/or recording the quantities measured.

telemetry elsse

An elsse which utilizes the telemetry transmitter as a signal source.

telephotometer

A photometer that measures the received intensity of a distant light source. When specifically used to measure the transmissivity of the intervening atmosphere (or other medium), it is usually termed a transmissometer. See visibility meter.

telephotometry

The body of principles and techniques concerned with measuring atmospheric extinction using various types of telephotometer.

Telescopium (abbr Tel, Tele)

See constellation.

telluric lines

Absorption lines in a solar spectrum produced by constituents of the atmosphere of the earth itself rather than by gases in the outer solar atmosphere such as those responsible for the Fraunhofer lines. The terrestrial nature of the absorption processes responsible for telluric lines is revealed by their intensity variation with solar zenith angle and by their freedom from any Doppler broadening due to their solar rotation. Water vapor produces the strongest of the telluric lines in the visible spectrum.

temperature

1. In general, the intensity of heat as measured on some definite temperature scale by means of any of various types of thermometers.

2. In statistical mechanics, a measure of translational molecular kinetic energy (with three degrees of freedom).

3. In thermodynamics, the integrating factor of the differential equation referred to as the first law of thermodynamics.

tensor

An array of functions which obeys certain laws of transformation. A one-row or one-column tensor array is a vector. The motivation for the use of tensors in some branches of physics is that they are invariants, not depending on the particular coordinate system employed.

tera (abbr T)

A prefix meaning multiplied by 10E12.

teracycle = 1000 gigacycles.

tercentesimal thermometric scale = approximate absolute temperature scale.

terminal

1. A point at which any element in a circuit may be directly connected to one or more other elements.

2. Pertaining to a final condition or the last division of something, as terminal ballistics.

terminal ballistics

That branch of ballistics dealing with the motion and behavior of projectiles at the termination of their flight, or in striking and penetrating a target.

terminal guidance

Guidance from an arbitrary point, at which midcourse guidance ends, to the destination.

terminal velocity

The maximum velocity attainable, especially by a freely falling body, under the given conditions.

terminator

The line separating illuminated and dark portions of a celestial body, as the moon, which is not self luminous.

ternary notation

A system of positional notation using 3 as a base.

terrestrial

Of or pertaining to the earth.

terrestrial coordinates = geographical coordinates.

terrestrial equator = astronomical equator.

terrestrial latitude

Latitude on the earth; angular distance from the equator. See coordinate, Table VI. Terrestrial latitude is named for the datum used to measure angular distance from the equator. Astronomical latitude is the angular distance between the direction of gravity and the plane of the equator. Geodetic or topographical latitude is the angular distance between the plane of the equator and a normal to the spheroid. Geodetic and sometimes astronomical latitude are also called geographic latitude. Geocentric latitude is the angle between a line to the center of the earth and the plane of the equator. Geodetic latitude is used for charts.

terrestrial longitude

Longitude on the earth; the arc of a parallel, or the angle at the pole, between the prime meridian and the meridian of a point on the earth. See coordinate, table VI. Terrestrial longitude is named for the datum used to measure it. Astronomical longitude is the angle between the plane of the reference meridian and the plane of the celestial meridian. Geodetic longitude is the angle between the plane of the reference meridian and the plane through the polar axis and the normal to the spheroid. Geodetic and sometimes astronomical longitude are also called geographic longitude. Geodetic longitude is used for charts.

terrestrial magnetism

The magnetism of the earth. Also called geomagnetism.

terrestrial meridian = astronomical meridian.

terrestrial pole

One of the poles of the earth. See geographical pole, geomagnetic pole, magnetic pole.

terrestrial radiation

The total infrared radiation emitted from the earth's surface; to be carefully distinguished from effective terrestrial radiation, atmospheric radiation (which is sometimes erroneously used as a synonym for terrestrial radiation), and insolation. Also called earth radiation, eradiation.

terrestrial-reference guidance

See guidance, note.

terrestrial refraction

1. Any refraction phenomenon observed in the light originating from a source lying within the earth's atmosphere; as contrasted to astronomical refraction, sense 2. This is applied only to refraction caused by inhomogeneities of the atmosphere itself, not, for example, to that caused by ice crystals suspended in the atmosphere. Terrestrial refraction is responsible for such phenomena of meteorological optics as looming, sinking, stooping, towering, mirages, and terrestrial scintillation.

2. = terrestrial refraction error.

terrestrial refraction error

The angular refraction error, for a ground observer, of an object in the vicinity of the earth. Also called terrestrial refraction.

terrestrial scintillation

Generic term for scintillation phenomena observed in light that reaches the eye from sources lying within the earth's atmosphere; to be differentiated from astronomical scintillation which is observed in light from extraterrestrial sources such as stars. Also called atmospheric boil, atmospheric shimmer, shimmer, optical haze. Terrestrial scintillation is produced by irregular refraction effects due to passage, across the line of sight, of air parcels (schlieren) whose densities differ slightly from that of their surroundings. Density irregularities with dimensions of the order of centimeters, or at most decimeters, are responsible for most such scintillatory effects.

tesla (abbr T)

The unit of magnetic flux density, one weber per square meter.

terrestrial triangle

See navigational triangle.

test

1. A procedure or action taken to determine under real or simulated conditions the capabilities, limitations, characteristics, effectiveness, reliability, or suitability of a material, device, system, or method.

2. A similar procedure or action taken to determine the reactions, limitations, abilities, or skills of a person, other animal, or organism.

test bed

1. A base, mount, or frame within or upon which a piece of equipment, especially an engine, is secured for testing.

2. A flying test bed.

test chamber

A place, section, or room having special characteristics where a person or object is subjected to experiment, as an altitude chamber ; specifically, the test section of a wind tunnel.

test firing

The firing of a rocket engine, either live or static, with the purpose of making controlled observations of the engine or of an engine component.

test flight

A flight to make controlled observations of the operation or performance of an aircraft or rocket, of an aircraft or rocket component, of a system, etc.

test section

The section of a wind tunnel where objects are tested to determine their aerodynamic characteristics. Also called a test chamber.

test stand

A stationary platform or table, together with any testing apparatus attached thereto, for testing or proving engines, instruments, etc. See proving stand. Compare launch stand.

Tethys

A satellite of Saturn orbiting at a mean distance of 295,000 kilometers.

theodolite

An optical instrument which consists of a sighting telescope, mounted so that it is free to rotate around horizontal and vertical axes, and graduated scales so that the angle of rotation may be measured. The telescope is usually fitted with a right-angle prism so that the observer continues to look horizontally into the eyepiece, whatever the variation of the elevation angle.

theoretical rocket = ideal rocket.

thermal

1. Of or pertaining to heat or temperature.

2. A vertical air current caused by differential heating of the terrain.

thermal accommodation coefficient = accommodation coefficient.

thermal barrier

A popular term for speed limitations within an atmosphere imposed by aerodynamic heating. Also called the heat barrier.

thermal conductivity

An intrinsic physical property of a substance, describing its ability to conduct heat as a consequence of molecular motion. The thermal conductivity bears the same relation to the conduction of heat as the dynamic viscosity does to the transfer of momentum. It can be defined by reference to the Newton law of cooling: H = -k ( T / N ) where k is the thermal conductivity; H the rate of heat conduction across a surface per unit area and per unit time; and T / N the temperature gradient normal to the surface. Also called heat conductivity, coefficient of thermal conduction, coefficient of heat conduction.

thermal conductivity vacuum gage

A vacuum gage containing two surfaces at different temperatures between which heat can be transported by the gas molecules so that changes in the temperature (or in the heating power required to maintain constant temperature) of one of the surfaces can be correlated with the gas pressure by calibration against a McLeod gage. Various types of thermal conductivity gages are distinguished according to the method of indicating the temperature change. The common type are: Pirani gage; thermocouple gage; thermistor gage; bimetallic strip gage.

thermal efficiency

1. The efficiency with which a heat engine transforms the potential heat of its fuel into work or output, expressed as the ratio of the useful work done by the engine in a given time interval to the total heat energy contained in the fuel burned during the same time interval, both work and heat being expressed in the same units.

2. = thermodynamic efficiency.

thermal emission

The process by which a body emits electromagnetic radiation as a consequence of its temperature only.

thermal emissive power

The rate of thermal emission of radiant energy per unit area of emitting surface. Also called emissive power.

thermal excitation

In a gas, the translation energy.

thermal fatigue

In metals, fracture resulting from the presence of temperature gradients which vary with time in such a manner as to produce cyclic stresses in a structure.

thermal instability

The conditions of temperature gradient, thermal conductivity, and viscosity which lead to the onset of convection in a fluid. Such gross phenomena as atmospheric winds are an example of this type of instability. In general, if the fluid is conducting, as a plasma, the applications of a magnetic field tends to reduce these thermal instabilities.

thermal jet engine

A jet engine that utilizes heat to expand gases for rearward ejection. This is the usual form of aircraft jet engine.

thermal motions

See Doppler broadening.

thermal noise

The noise at radio frequencies caused by thermal agitation in a dissipative body. Also called Johnson noise.

thermal radiation

The electromagnetic radiation emitted by any substance as the result of the thermal excitation of its molecules. Thermal radiation ranges in wavelength from the longest infrared radiation to the shortest ultraviolet radiation.

thermal shock

The development of a steep temperature gradient and accompanying high stresses within a structure.

thermal stresses

Stresses in metal, resulting from nonuniform temperature distribution.

thermal tide

A variation in atmospheric pressure due to the daily differential heating of the atmosphere by the sun; so-called in analogy to the conventional gravitational tide. See solar atmospheric tide.

thermal transpiration

The passage of gas through a connection between two vessels at different temperatures resulting in a pressure gradient when equilibrium is reached. Under conditions of molecular flow the equilibrium condition is expressed by where p_a and T_a are the pressure and absolute temperature, respectively, in one vessel and p_b and T_b are the pressure and absolute temperature, respectively, in the other.

thermionic

Of or pertaining to the emission of electrons by heat.

thermionic cathode = hot cathode.

thermionic conversion

The process whereby electrons released by thermionic emission are collected and utilized as electric current. The simplest example of this is provided by a vacuum tube, in which the electrons released from a heated anode are collected at the cathode or plate. Used as a method of producing electrical power for spacecraft.

thermionic emission

Direct ejection of electrons as the result of heating and material, which raises electron energy beyond the binding energy that holds the electron in the material.

thermionic tube

An electron tube in which one or more of the electrodes is heated to cause electron or ion emission.

thermistor

An electron device employing the temperature- dependent change of resistivity of a semiconductor.

thermochemical

Pertaining to a chemical change induced by heat.

thermochemistry

A branch of chemistry that treats of the relations of heat and chemical changes.

thermocouple

A device which converts thermal energy directly into electrical energy. In its basic form it consists of two dissimilar metallic electrical conductors connected in closed loop. Each junction forms a thermocouple. See thermopile. If the junctions are at different temperatures, an electrical potentials proportional to the temperature difference will exist in the circuit; the value of the potential generated is different for various combinations of materials. For meteorological purposes couples of copper and constantan are frequently used; these generate approximately 40 microvolts per degree C of couple temperature difference.

thermocouple gage

A thermal conductivity vacuum gage in which pressure change is sensed by a thermocouple in thermal contact with a heated filament which cools as pressure rises. Compare with Pirani gage.

thermodynamic

Pertaining to the flow of heat or to thermodynamics.

thermodynamic efficiency

In thermodynamics, the ratio of the work done by a heat engine to the total heat supplied by the heat source. Also called thermal efficiency, Carnot efficiency.

thermodynamic energy equation

The mathematical statement of the concept of conservation of energy embodied in the first law of thermodynamics. For reversible processes of a perfect gas, it may be written in the form pQ = ρc_v (dT/dt) - (p/ρ) (dρ) (dt) where pQ is the rate of energy addition per unit volume by heating (including the effects of radiation, molecular conduction, condensation water vapor, and the generation of heat by friction); T is the Kelvin temperature; c_v is the specific heat at constant volume; p is pressure; and ρ is density. See energy equation.

thermodynamic equilibrium

A very general result from statistical mechanics which states that if a system is in equilibrium, all processes which can exchange energy must be exactly balanced by the reverse process so that there is no net exchange of energy. For instance, ionization must be balanced by recombination, bremsstrahlung by absorption, etc. If a plasma complies with this statement, the distribution function of particle energies and excited energy levels of the atoms can be obtained from the Maxwell-Boltzmann distribution which is a function only of the temperature.

thermodynamic function of state

Any of the quantities defining the thermodynamic state of substance in thermodynamic equilibrium. Also called thermodynamic variable, state variable, state parameter. For a perfect gas, pressure, temperature, and density are the fundamental thermodynamic variables, any two of which are, by the equation of state, sufficient to specify the state. Quantities defined in terms of these, such as specific volume, potential temperature, etc., may also be used as thermodynamic functions of state. If the composition of the gas varies, this must be specified. Thus, some measure of water vapor is a thermodynamic function of state of the atmosphere.

thermodynamic potential = Gibbs function.

thermodynamic probability

Under specified conditions, the number of equally likely states in which a substance may exist. The thermodynamic probability P is related to the entropy S by S = k ln P where k is Boltzmann constant. See third law of thermodynamics.

thermodynamics

The study of the flow of heat.

thermodynamic temperature scale

The Kelvin temperature scale or the Rankine temperature scale.

thermodynamic variable = thermodynamic function of state.

thermogravimetric analysis

The technique of studying materials by observing weight changes caused by chemical reactions that occur when heat is applied.

thermometer

A device for measuring temperature.

thermonuclear

Pertaining to a nuclear reaction which is triggered by particles of high thermal energy.

thermopile

1. A transducer for converting thermal energy directly into electrical energy, composed of pairs of thermocouples which are connected either in series or in parallel. See Moll thermopile, Eppley pyrheliometer.

2. A battery of thermocouples connected in series to form a single compact unit. The output voltage of N pairs of series-connected thermocouples is N time the voltage developed by a single pair, whereas the current developed by N pairs of parallel-connected thermocouples is N times the current developed by a single pair. Thermopiles are used in thermoelectric radiation instruments when the output of a single pair of thermocouples is not large enough.

thermosphere

See atmospheric shell.

thermoswitch

A temperature-activated switch.

thermotropic model

A model atmosphere used in numerical forecasting in which the parameters to be forecast are the height of one constant-pressure surface (usually 500 millibars) and one temperature (usually the mean temperature between 1000 and 500 millibars). Thus, a surface prognostic chart can also be constructed. The quasi-geostrophic approximation is employed and the thermal wind is assumed constant with height. See equivalent barotropic model.

thindown

The expenditure of heavy primary cosmic ray energy in ionizing the substance, normally air, through which it passes. See bremsstrahlung.

third law of thermodynamics

The statement that every substance has a finite positive entropy, and that the entropy of a crystalline substance is zero at the temperature of absolute zero. See thermodynamic probability. Modern quantum theory has shown that the entropy of crystals at 0 degrees absolute is not necessarily zero. If the crystal has any asymmetry, it may exist in more than one state; and there is, in addition, an entropy residue deriving from nuclear spin.

three-body problem

That problem in classical celestial mechanics which treats the motion of a small body, usually of negligible mass, relative to and under the gravitational influence of two other finite point masses.

threshold

Generally, the minimum value of a signal that can be detected by the system or sensor under consideration.

threshold contrast

The smallest contrast of luminance (or brightness) that is perceptible to the human eye under specified conditions of adaptation luminance and target visual angle. Also called contrast threshold, liminal contrast. Compare threshold illuminance. Psychophysically, the existence of a threshold contrast is merely a special case of the general rule that for every sensory process there is a corresponding lowest detectable intensity of stimulus, i.e., a limen.

threshold illuminance

The lowest value of illuminance which the eye is capable of detecting under specified conditions of background luminance and degree of dark adaptation of the eye. Also called flux-density threshold. Compare threshold contrast. See Allard law. This threshold, which controls the visibility of point light sources, especially at night, cannot be assigned any universal value, but nonflashing lights can generally be seen by a fully dark-adapted eye when the lights yield an illuminance of the order of 0.1 lumen per square kilometer at the eye.

threshold of audibility

For a specified signal, the minimum effective sound pressure level of the signal that is capable of evoking an auditory sensation in a specified fraction of the trials. The characteristics of the signal, the manner in which it is presented to the listener, and the point at which the sound pressure level is measured must be specified. Also called threshold of detectability. Unless otherwise indicated, the ambient noise reaching the ears is assumed to be negligible. The threshold is usually given as a sound pressure level in decibels, relative to 0.0002 microbar. Instead of the method of constant stimuli, which is implied by the phrase a specified fraction of the trials , another psychophysical method (which should be specified) may be employed.

threshold of detectability = threshold of audibility.

threshold of discomfort

In acoustics, for a specified signal, the minimum effective sound pressure level of that signal which, in a specified fraction of the trials, will stimulate the ear to a point at which the sensation of feeling becomes uncomfortable. The term applies similarly for other senses.

threshold of feeling

In acoustics, for a specified signal, the minimum sound pressure level at the entrance to the external auditory canal which, in a specified fraction of the trials, will stimulate the ear to a point at which there is a sensation of feeling that is different from the sensation of hearing. Also called tickle.

threshold of pain

In acoustics, for a specified signal, the minimum effective sound pressure level of that signal which, in a specified fraction of the trials, will stimulate the ear to a point at which the discomfort gives way to definite pain that is distinct from mere non-noxious feeling of discomfort. The term applies similarly for other senses.

threshold sensitivity

Of a transducer, the lowest level of the input signal which produces desired response at the output. The term applies equally to psychophysics.

throat

The narrowest portion of a constricted duct, as in a diffuser, a venturi tube, etc., specifically, a nozzle throat.

throatable

Of a nozzle: designed so as to allow a change in the velocity of the exhaust stream through changing the size and shape of the throat of the nozzle.

throat velocity = critical velocity.

throttling

The varying of the thrust of a rocket engine during powered flight by some technique. Tightening of fuel lines, changing of thrust chamber pressure, pulsed thrust, and variation of nozzle expansion are methods to achieve throttling.

throughput

In vacuum technology, the quantity of gas in pressure-volume units at a specified temperature flowing per unit time across a specified open section of a pump or pipeline. The specified temperature may be the actual temperature of the gas or a standard reference temperature. It is recommended that throughput be referred to standard room temperature. The recommended unit of throughput is the torr liter per second at 20 degrees C. Other units of throughput in common use are micron liters per second at 25 degrees C and micron cubic feet per minute at 68 degrees F. Under conditions of steady-state conservative flow the throughput across the entrance to a pipe is equal to the throughput at the exit. In this case throughput can be defined as the quantity of gas flowing through a pipe in pressure-volume units per unit time at room temperature.

thrust

1. The pushing or pulling force developed by an aircraft engine or a rocket engine.

2. The force exerted in any direction by a fluid jet or by a powered screw, as, the thrust of an antitorque rotor.

3. (symbol F). Specifically, in rocketry, F = mv where m is propellant mass flow and v is exhaust velocity relative to the vehicle. Also called momentum thrust.

thrust augmentation

The increasing of the thrust of an engine or power plant, especially of a jet engine and usually for a short period of time, over the thrust normally developed. The principal methods of thrust augmentation are the introduction of additional air into the induction system, liquid injection, and afterburning. With a piston engine, thrust augmentation usually refers to the direction of exhaust gases so as to give additional thrust.

thrust augmenter

Any device used to increase the thrust of a piston, jet, or rocket engine, such as an afterburner. See augmenter tube.

thrust axis

A line or axis through an aircraft, rocket, etc., along which the thrust acts; an axis through the longitudinal center of a jet or rocket engine along which the thrust of the engine acts; a center of thrust. Also called axis of thrust.

thrust chamber = firing chamber.

thrust coefficient = nozzle thrust coefficient.

thrust horsepower

1. The force-velocity equivalent of the thrust developed by a jet or rocket engine.

2. The thrust of an engine-propeller combination expressed in horsepower. It differs from the shaft horsepower of the engine by the amount the propeller efficiency varies from 100 percent.

thrust loading

The weight-thrust ratio of a jet or rocket-propelled aircraft or other vehicle expressed as gross weight in pounds divided by thrust in pounds. See power loading.

thrust meter

An instrument for measuring static thrust, especially of a jet engine or rocket. See reaction balance.

thrust power

The power usefully expended on thrust, equal to the thrust (or net thrust) times airspeed.

thrust reverser

A device or apparatus for reversing thrust, especially of a jet engine. See reverse thrust.

thrust section

1. A section in a rocket vehicle that houses or incorporates the combustion chamber or chambers and nozzles.

2. In loose usage, a propulsion system.

thrust terminator

A device for ending the thrust in a rocket engine, either through propellant cutoff (in the case of a liquid) or through diverting the flow of gases from the nozzle.

thrust-weight ratio

A quantity used to evaluate engine performance, obtained by dividing the thrust output by the engine weight less fuel. If the pound is used as the unit of measure for thrust and weight, the result is pounds of thrust per pound of engine.

tick

A short audible sound or beat, as that of a clock. A time signal in the form of one or more ticks is called a time tick.

tickle = threshold of feeling.

tidal day = lunar day.

tide

The periodic rising and falling of the earth's oceans and atmosphere. It results from the gravitational forces of the moon and sun acting upon the rotating earth. The disturbance actually propagates as a wave through the atmosphere and along the surface of the waters of the earth. Atmospheric tides are always so designated, whereas the term tide alone commonly implies the oceanic variety.

tilt table

A device used to calibrate linear accelerometers with rated ranges of, or below, +/- 1.0 g. It allows the accelerometer to be positioned at different angles in reference to a surface perpendicular to the direction of the earth's gravity, so that the applied values of acceleration are equal to the cosine of the angle between the reference surface and the direction of the earth's gravity.

timbre

That attribute of auditory sensation by which a listener discriminates between two sounds of similar loudness and pitch, but of different tonal quality. Timbre depends primarily upon the spectrum of the stimulus, but it also depends upon the waveform, the sound pressure, the frequency location of the spectrum, and the temporal characteristics of the stimulus.

time (symbol t or τ)

The hour of the day reckoned by the position of a celestial reference point relative to a reference celestial meridian. Time may be designated solar, lunar , or sidereal as the reference is the sun, moon, or vernal equinox, respectively. Solar time may be further classified as mean or astronomical if the mean sun is the reference, or as apparent if the apparent sun is the reference. Time may also be designated according to the reference meridian, either the local or Greenwich meridian or, additionally, in the case of mean solar time, a designated zone meridian. Standard and daylight saving time are variations of zone time. Time may also be designated according to the timepiece, as chronometer time or watch time , the time indicated by these instruments.

time constant

Generally, the time required for an instrument to indicate a given percentage of the final reading resulting from an input signal; the relaxation time of an instrument. In the case of instruments such as thermometers, whose response to step changes in an applied signal is exponential in character, the time constant is equal to the time required for the instrument to indicate 63.2 percent of the total change, that is, when the transient error is reduced to 1/e of the original signal change. Also called lag coefficient. See lag. Compare rise time, time lag.

time division multiplex

A system for the transmission of information about two or more quantities ( measurands) over a common channel by dividing available time intervals among the measurands to form a composite pulse train. Information may be transmitted by variation of pulse duration, pulse amplitude, pulse position, or by a pulse code. (Abbreviations used are PDM, PAM, PPM, and PCM, respectively.)

time lag

The total time between the application of a signal to a measuring instrument and the full indication of that signal within the uncertainty of the instrument.

time of useful consciousness

The period between loss of oxygen supply (at altitude) and the inability of the individual to function efficiently.

time series

The values of a variable generated successively in time. A continuous barograph trace is an example of a continuous time series , whereas a sequence of hourly pressures is an example of a discrete time series. Graphically, a time series is usually plotted with time as the abscissa and the values of the function as the ordinate.

time signal

1. An accurate signal marking a specified time or time interval. It is used primarily for determining errors of timepieces. Such signals are usually sent from an observatory by radio or telegraph.

2. In photography, a time indication registered on the film to serve as a time reference for interpretation of the date recorded on the film.

time tic

Markings on telemetry records to indicate time intervals.

time tick

A time signal consisting of one or more short audible sounds or beats.

time to unconsciousness

The period between loss of oxygen supply (at altitude) and the onset of unconsciousness.

time zone

See zone time.

timing parallax

The distance on a film between a frame and a time signal which were simultaneously exposed.

timing pulse

In telemetry, a pulse used as a time reference.

Titan

A satellite of Saturn orbiting at a mean distance of 1,222,000 kilometers.

Titania

A satellite of Uranus orbiting at a mean distance of 438,000 kilometers.

tolerance

The allowable variation in measurements within which the dimensions of an item are judged acceptable.

topocentric

Of measurements or coordinates, referred to the position of the observer on the earth as the origin.

topple

Of a gyro, the vertical component of precession or wander, or the algebraic sum of the two.

topple axis

That horizontal axis, perpendicular to the (horizontal) spin axis of a gyroscope, around which topple occurs.

tor = torr.

torching

The degassing of a vacuum system by application of a gas burner flame to the walls during the pumping process.

torque (symbol T)

About an axis, the product of a force and the distance of its line of action from the axis.

torquer

In a gyro, a device which produces torque about an axis of freedom in response to a signal input.

torquing

In a gyro, the application of torque to a gimbal about an axis of freedom for the following purposes: precessing, capturing, slaving, caging, or slewing.

torr

Provisional international standard term to replace the English term millimeter of mercury and its abbreviation mm of Hg (or the French mm de Hg ). The torr is defined as 1/760 of a standard atmosphere or 1,013,250/760 dynes per square centimeter. This is equivalent to defining the torr as 1333.22 microbars and differs by only one part in 7 million form the International Standard millimeter of mercury. The prefixes milli and micro are attached without hyphenation.

total conductivity

In atmospheric electricity, the sum of the electrical conductivities of the positive and negative ions found in a given portion of the atmosphere.

total curvature

The change in direction of a ray between object and observer.

total eclipse

An eclipse in which the entire source of light is obscured.

total emissive power

See emittance.

total emissivity (symbol ε)

See emissivity.

total emittance = total emissive power. See emittance.

total energy equation

In meteorology, an expression relating all forms of energy obtained by combining the thermodynamic energy equation with the mechanical energy equation. This equation expresses the fact that the combined internal, kinetic, and potential energy in a given volume of the atmosphere can vary only as a result of: (a) the transport of these forms of energy across the boundaries of the volume; (b) the work done by pressure forces on the boundary; (c) the addition or removal of heat; and (d) the dissipational effect of friction.

total head = total pressure, sense 3.

total impulse (symbol I_t)

The integral of the thrust F over an interval of time t : I_t = F dtTotal impulse is related to specific impulse I_sp by I_t = I_sp dt, where = propellant flow weight rate.

total potential energy

See internal energy, note.

total pressure

1. = stagnation pressure.

2. = impact pressure.

3. The pressure a moving fluid would have if it were brought to rest without losses.

4. The pressure determined by all the molecular species crossing the imaginary surface.

total-pressure tube

A tube for measuring the stagnation pressure of a fluid; i.e., a pitot tube.

total radiation

Radiation over the entire spectrum of emitted wavelengths.

total refraction

The return of waves out of a medium or layer, due to refraction. Total refraction occurs most readily at low elevation angles. For any suitable layer in the atmosphere, there is a critical beam elevation angle below which total refraction can occur. In the ionosphere this angle is frequency dependent.

total scattering coefficient = scattering coefficient.

total scattering cross section = scattering power; see scattering cross section.

total solar eclipse

See solar eclipse.

toughness

The ability of a metal to absorb energy and deform plastically before fracturing. Toughness is usually measured by the energy absorbed in a notch impact test, but the area under the stress-strain curve in tensile testing is also a measure of toughness.

towering

A refraction phenomenon; a special case of looming in which the downward curvature of the light rays due to atmospheric refraction increased with elevation so that the visual image of a distant object appears to be stretched in the vertical direction. The opposite of towering is stooping.

Townsend discharge

A type of direct-current discharge between two electrodes immersed in a gas and requiring electron emission from the cathode.

Townsend ionization coefficient

The average number of ionizing collisions an electron will make in drifting a unit distance in the direction of the applied electric force. These coefficients were first measured by Townsend and at present they are well tabulated for most gases. A typical value for the coefficient is one pair per centimeter at a pressure of 1 millimeter of mercury and a field strength of 100 volts per centimeter.

TrA, Tr Au

International Astronomical Union abbreviations for Triangulum Australe. See constellation.

trace

The line appearing on the face of a cathode-ray tube when the visible dot repeatedly sweeps across the face of the tube as a result of deflections of the electron beam. See sweep. The path of the dot from the end of one sweep to the start of the next sweep is called a retrace. If more than one trace is shown on the same scope, the traces may be called A-trace, B-trace , etc.

track

1. The path or actual line of movement on an aircraft, rocket, etc., over the surface of the earth. It is the projection of the flightpath on the surface.

2. To observe or plot the path of something moving, such as an aircraft or rocket, by one means or another, as by telescope or by radar - said of persons or of the electronic equipment, as, the observer, or the radar, tracked the satellite.

3. To follow a desired track.

tracking

1. The process of following the movements of an object. This may be done by keeping the reticle of an optical system or a radar beam on the object, by plotting its bearing and distance at frequent intervals, or by a combination of the two.

2. A motion given to the major lobe of an antenna so that a preassigned moving target in space remains in the lobe's field as long as it is within viewing range.

tracking antenna

A directional antenna system which changes in position, or characteristics, automatically or manually to follow the motions of a moving signal source.

tracking filter

An electric device for attenuating unwanted signals while passing desired signals, by means of phase-lock techniques which reduce the effective bandwidth of the circuit and eliminate amplitude variations.

tracking offset error

The angular error, in magnitude and direction, between an object being tracked and the center of reference established for the tracking instrument.

tracking radar

A radar used for following a target.

tracking rate

The rate at which an operator or a system follows a target. Usually expressed in terms of the rate of change of the parameter being measured.

tracking station

A station set up to track an object moving through the atmosphere or space, usually by means of radar or radio. See minitrack.

train

Anything, such as luminous gas of ionized particles, left along the trajectory of a meteor after the head of the meteor has passed.

trajectory

In general, the path traced by any body moving as a result of an externally applied force, considered in three dimensions. Trajectory is sometimes used to mean flight path or orbit , but orbit usually means a closed path and trajectory , a path which is not closed.

trajectory measuring system

A system used to provide information on the spatial position of an object at discrete time intervals throughout a portion of the trajectory or flightpath.

transceiver

A combination transmitter and receiver in a single housing, with some components being used by both units. See transponder.

transducer

A device capable of being actuated by energy from one or more transmission systems or media and of supplying related energy to one or more other transmission systems or media, as a microphone, a thermocouple, etc. The energy in input and output may be of the same or different types (e.g., electric, mechanical, or acoustic).

transducer gain

The ratio of the power that a transducer delivers to a specified load under specified operating conditions to the available power of a specified source. If the input and/or output power consist of more than one component, such as multifrequency signal or noise, then the particular components used and their weighting must be specified. This gain is usually expressed in decibels.

transfer ellipse = transfer orbit.

transfer orbit

In interplanetary travel, an elliptical trajectory tangent to the orbits of both the departure planet and the target planet. Also called transfer ellipse.

transient problem = initial-value problem.

transistor

An active semiconductor device with three or more electrodes.

transit

1. The passage of a celestial body across a celestial meridian, usually called meridian transit.

2. The apparent passage of a celestial body across the face of another celestial body or across any point, area, or line.

3. An instrument used by an astronomer to determine the exact instant of meridian transit of a celestial body.

4. A reversing instrument used by surveyors for accurately measuring horizontal and vertical angles; a theodolite which can be reversed in its supports without being lifted from them.

transition flow = Knudsen flow.

See rarefied gas dynamics, note.

transition maneuver

In lifting flight, a maneuver required to fly smoothly from one equilibrium glidepath to another, performed by changing attitude in some manner.

transition point

In aerodynamics, the point of change from laminar to turbulent flow.

transition temperature

1. An arbitrarily defined temperature within the temperature range in which metal fracture characteristics determined usually by notched tests are changing rapidly such as from primarily fibrous (shear) to primarily crystalline (cleavage) fracture.

2. The arbitrarily defined temperature in a range in which the ductility of a material changes rapidly with temperature.

translation

Movement in a straight line without rotation.

translation energy

In a gas, the energy associated with random straight line motion of the molecules.

translator

A network or system having a number of inputs and outputs and so connected that signals representing information expressed in a certain code, when applied to the inputs, cause output signals to appear which are a representation of the input information in a different code. Sometimes called matrix.

translunar

Outside the moon's orbit about the earth.

translunar space

As seen from the earth at any movement, space lying beyond the orbit of the moon.

transmission

1. The process by which radiant flux is propagated through a medium or body.

2. = transmittance.

transmission coefficient (symbol τ)

1. A measure of the amount of incident radiation which remains in a beam after it passes through a unit thickness of a medium. It is comparable in concept to the extinction coefficient (or attenuation coefficient) and is related to the extinction coefficient σ as follows: τ = e ^-σ where τ is the transmission coefficient. Its relationship to transmissivity r is expressed: r = τ^xwhere x is the total thickness of the medium. Compare absorption coefficient.

2. The fraction of the solar radiation normally incident upon the top of the atmosphere which survives passage through the atmosphere to the earth's surface. As so defined, a better term might be atmospheric transmissivity.

3. The ratio of the sound transmitted through an interface or spectrum between two media, exposed to the sound field, to the sound energy incident on the interface or septum.

transmission loss

The reduction in the magnitude of some characteristics of a signal between two stated points in a transmission system. Also called loss. The characteristic is often some kind of level, such as power level or voltage level; in acoustics, the characteristic that is commonly measured is sound pressure level. Thus, if the levels are expressed in decibels, the transmission level loss is likewise in decibels. It is imperative that the characteristic concerned (such as the sound pressure level) by clearly identified because in all transmission systems more than one characteristic is propagated.

transmission system

A system which propagates or transmits signals.

transmission time

The time interval between dispatch and reception of a signal in a particular transmission system.

transmissivity = transmittance.

transmissometer

An instrument for measuring the extinction coefficient of the atmosphere and for the determination of visual range. Also called telephotometer, transmittance meter, hazemeter. See photoelectric, transmittance meter visibility meter.

transmissiometry

The technique of determining the extinction characteristics of a medium by measuring the transmittance of a light beam of known initial intensity directed into that medium.

transmittance (symbol T)

The ratio of the radiant flux transmitted by a medium or a body to the incident flux. See transmission coefficient. The transmittance T of radiant flux through a medium of thickness x is related to the transmission coefficient τ of the medium by T = τ.

transmittance meter = transmissometer.

transmitted power

The power which is radiated from an antenna. Compare received power.

transmitter

A device used for the generation of signals of any type and form which are to be transmitted. See receiver. In radio and radar, it is that portion of the equipment which includes electronic circuits designed to generate, amplify, and shape the radiofrequency energy which is delivered to the antenna where it is radiated out into space.

transonic

Pertaining to that which occurs or is occurring within the range of speed in which flow patterns change from subsonic to supersonic or vice versa, about Mach 0.8 to 1.2, as in transonic flight, transonic flutter ; that operates within this regime, as in transonic aircraft, transonic wing ; characterized by transonic flow or transonic speed, as in transonic region, transonic zone.

transonic flow

In aerodynamics, flow of a fluid over a body in the range just above and just below the acoustic velocity. Transonic flow presents a special problem in aerodynamics in that neither the equations describing subsonic flow nor the equations describing supersonic flow can be applied in the transonic range.

transonic speed

The speed of a body relative to the surrounding fluid at which the flow is in some places on the body subsonic and in other places supersonic.

transparent plasma

A plasma through which an electromagnetic wave can propagate. In general, a plasma is transparent for frequencies higher than the plasma frequency.

transpiration

The passage of gas or liquid through a porous solid (usually under conditions of molecular flow).

transpiration cooling

A process by which a body having a porous surface is cooled by forced flow of coolant fluid through the surface from the interior. Compare film cooling.

transponder

A combined receiver and transmitter whose function is to transmit signals automatically when triggered by an interrogator. See transceiver.

transponder beacon

A beacon having a transponder. Also called responder beacon.

transport = flux.

transverse

In cartography, pertaining to or measured on a map projection in which a meridian is used as a fictitious equator.

transverse sensitivity = cross sensitivity.

transverse vibration

Vibration in which the direction of motion of the particles is perpendicular to the direction of advance of the vibratory motion, in contrast with longitudinal vibration, in which the direction of motion is the same as that of advance.

transverse wave

A wave in which the direction of displacement at each point of the medium is parallel to the wave front. Contrast longitudinal wave.

trap

A part of a solid-propellant rocket engine used to prevent the loss of unburned propellant through the nozzle.

trapping

The process by which radiation particles are caught and held in a radiation belt.

Tr Au

International Astronomical Union abbreviations for Triangulum Australe. See constellation.

traveling plane wave

A plane wave each of whose frequency components has an exponential variation of amplitude and a linear variation of phase in the direction of propagation.

traveling-wave tube (abbr TWT)

An electron tube in which a stream of electrons interacts continuously or repeatedly with a guided electromagnetic wave moving substantially in synchronism with it, and in such a way that there is a net transfer of energy from the stream to the wave.

Tri, Tria

International Astronomical Union abbreviations for Triangulum. See constellation.

Triangulum (abbr Tri, Tria)

See constellation.

Triangulum Australe

(abbr TrA, Tr Au) See constellation.

Tridop

A continuous-wave trajectory measuring system using the Doppler shift caused by a target moving relative to a ground transmitter and three or more receiving stations.

triple point

The thermodynamic state at which three phases of a substance exist in equilibrium. The triple point of water occurs at a saturation vapor pressure of 6.11 millibar and at a temperature of 273.16 degrees K.

triplexer

A dual- duplexer which permits the use of two receivers simultaneously and independently in a radar system by disconnecting the receivers during the transmitted pulse.

Triton

A satellite of Neptune orbiting at a mean distance of 354,000 kilometers.

trochoid

The path followed by a point in a diameter of a circle as the circle rolls along a straight line.

trochotron

An electron tube in which a magnetic field causes the electrons to travel in trochoidal paths. See beam-switching tube.

Trojan asteroids

Two groups of minor planets that liberate in long-period orbits around the stable Lagrangian points of the Sun and Jupiter. Called Trojan because they are named after heroes of the Trojan War.

tropical

Of or pertaining to the vernal equinox. See sidereal.

tropical month

The average period of the revolution of the moon about the earth with respect to the vernal equinox, a period of 27 days 7 hours 43 minutes 4.7 seconds, or approximately 27 1/3 days.

tropical year

The period of one revolution of the earth around the sun, with respect to the vernal equinox. Because of precession of the equinoxes, the tropical year is not 360 degrees with respect to the stars, but 50 minutes 0.3 seconds less. A tropical year is about 20 minutes shorter than a sidereal year, averaging 365 days 5 hours 48 minutes 45.68 seconds in 1955 and is increasing at the rate of 0.005305 second annually. Also called astronomical, equinoctial, natural, or solar year.

tropic of Cancer

The northern parallel of declination, approximately 23 degrees 27' from the celestial equator, reached by the sun at its maximum declination, or the corresponding parallel on the earth. It is named for the sign of the zodiac in which the sun reached its maximum northerly declination at the time the parallel was so named.

tropic of Capricorn

The southern parallel of declination, approximately 23 degrees 27' from the celestial equator, reached by the sun at its maximum declination, or the corresponding parallel on the earth. It is named for the sign of the zodiac in which the sun reached its maximum southernly declination at the time the parallel was so named.

tropopause

The boundary between the troposphere and stratosphere, usually characterized by an abrupt change of lapse rate. The change is in the direction of increased atmospheric stability from regions below to regions above the tropopause. Its height varies from 15 to 20 kilometers in the tropics to about 10 kilometers in polar regions. In polar regions in winter it is often difficult or impossible to determine just where the tropopause lies, since under some conditions there is no abrupt change in lapse rate at any height.

troposphere

That portion of the atmosphere from the earth's surface to the stratosphere; that is, the lowest 10 to 20 kilometers of the atmosphere. The troposphere is characterized by decreasing temperature with height, appreciable vertical wind motion, appreciable water vapor content, and weather. Dynamically, the troposphere can be divided into the following layers: surface boundary layer, Ekamn layer, and free atmosphere. See atmospheric shell.

tropospheric wave

A radio wave that is propagated by reflection from a place of abrupt change in the dielectric constant or its gradient in the troposphere. In some cases the ground wave may be so altered that new components appear to arise from reflections in regions of rapidly changing dielectric constants; when these components are distinguishable from the other components, they are called tropospheric waves.

trud count

(From time remaining until dive.) A count (in minutes and seconds) that measures the time between a rocket launch and the moment it apogees and begins its dive.

true

1. Related to or measured from true north.

2. Actual, as contrasted with fictitious, as true sun.

3. Related to a fixed point, either on the earth or in space, as true wind; in contrast with relative.

4. Corrected, as true altitude.

true altitude

1. Actual height above sea level; calibrated altitude corrected for air temperature.

2. The actual altitude of a celestial body above the celestial horizon. Usually called observed altitude.

true anomaly

See anomaly.

true meridian

A great circle through the geographical poles, distinguished from magnetic meridian, gridmeridian, etc.

true position

The position of a celestial body (or space vehicle) on the celestial sphere as computed directly from the elements of the orbit of the earth and the body concerned without allowance for light time. Also called geometric position.

true prime vertical

The vertical circle through the true east and west points of the horizon, as distinguished from magnetic, compass, or grid prime vertical through the magnetic, compass, or grid east and west points, respectively.

true sun

The actual sun as it appears in the sky. Usually called apparent sun. See mean sun, dynamical mean sun.

truncation error

In computations, the error resulting from the use of only a finite number of terms of an infinite series or from the approximation of operations in the infinitesimal calculus by operations in the calculus of finite differences.

trunk = bus.

T-time

Any specific time, minus or plus as referenced to zero or launch time, during a countdown sequence that is intended to result in the firing of a rocket propulsion unit that launches a rocket vehicle.

Tucana (abbr Tuc, Tucn)

See constellation.

Tucn

International Astronomical Union abbreviations for Tucana. See constellation.

Tuc, Tucn

International Astronomical Union abbreviations for Tucana. See constellation.

tumble

1. To rotate end over end - said of a rocket, of an ejection capsule, etc.

2. Of a gyro, to precess suddenly and to an extreme extent as a result of exceeding its operating limits of bank or pitch.

tumbling

An attitude situation in which the vehicle continues on its flight, but turns end over end about its center of mass.

tuned damper

A device for reducing vibration of a primary system by the transfer of energy to an auxiliary resonant system which is tuned to the frequency of the vibration. The force extered by the auxiliary system is opposite in phase to the force acting on the primary system.

tunnel

1. A structure, installation, or facility incorporating apparatus to simulate flight conditions in one way or another, specially designed for testing or experimenting with power plants, or with aircraft, rockets, or other aerodynamically designed bodies, engine installations, or models; specifically, a wind tunnel.

2. A longitudinal protuberance on a rocket body used to house wiring, piping, etc., so as to not route the wiring through the propellant tanks.

tunnel axis

Any one of the geometrical axes of a wind tunnel.

turbidity

In meteorology, any condition of the atmosphere which reduces its transparency to radiation, especially to visible radiation. Ordinarily, this is applied to a cloud-free portion of the atmosphere that owes its turbidity to air molecules and suspensoids such as smoke, dust, and haze, and the scintillation effects.

turbidity factor

A measure of the atmospheric transmission of incident solar radiation. If I₀ is the flux density of the solar beam just outside the earth's atmosphere, I the flux density measured at the earth's surface with the sun at a zenith distance which implies an optical air mass m , and I_m,w the intensity which would be observed at the earth's surface for a pure atmosphere containing one centimeter of perceptible water viewed through the given optical air mass, then Linke's turbidity factor θ is given by θ = (ln I₀ - ln I)/(ln I₀ - ln I_m,w)

turbine

1. A machine consisting principally of one or more turbine wheels and a stator.

2. A turbine wheel.

3. A turbine engine. See blowdown turbine, explosion turbine, free turbine, gas turbine, impulse turbine, partial-admission turbine, reaction turbine, single-stage turbine.

turbine blade

Any one of the blades of a turbine wheel.

turbine engine

An engine incorporating a turbine as a principal component; especially, a gas-turbine engine.

turbine wheel

A multivaned wheel or rotor, especially in a gas-turbine engine, rotated by the impulse from or reaction to a fluid passing across the vanes. Often called a turbine.

turbofan

A turbojet engine in which additional propulsive thrust is gained by extending a portion of the compressor or turbine blades outside the inner engine case. The extended blades propel bypass air flows along the engine axis but between the inner and outer engine casing. This air is not combusted but does provide additional thrust caused by the propulsive effect imparted to it by the extended compressor blading.

turbojet

1. = turbojet engine.

2. A craft propelled by a turbojet engine. See jet engine.

turbojet engine

A jet engine incorporating a turbine-driven air compressor to take in and compress the air for the combustion of fuel (or for heating by a nuclear reactor), the gases of combustion (or the heated air) being used both to rotate the turbine and to create a thrust producing jet. Often called a turbojet. See jet engine, sense 2.

turbulence

A state of fluid flow in which the instantaneous velocities exhibit irregular and apparently random fluctuations so that in practice only statistical properties can be recognized and subjected to analysis. Compare laminar flow.

These fluctuations often constitute major deformations of the flow and are capable of transporting momentum, energy, and suspended matter at rates far in excess of the rate of transport by the molecular processes of diffusion and conduction in a nonturbulent or laminar flow.

turbulent boundary layer

The layer in which the Reynolds stresses are much larger than the viscous stresses. When the Reynolds number is sufficiently high, there is a turbulent layer adjacent to the laminar boundary layer.

turbulent flow

Fluid motion in which random motions of parts of the fluid are superimposed upon a simple pattern of flow. All or nearly all fluid flow displays some degree of turbulence. The opposite is laminar flow.

turbulent scatter

See scatter.

turbulent shear stresses

See Reynolds stresses.

turn error

Any error in gyro output due to cross-coupling and acceleration encountered during vehicle turns.

turnover frequency = Nyquist frequency.

turnstile antenna

An antenna composed of two dipole antennas, normal to each other, with their axes intersecting at their midpoints. Usually, the currents are equal and in phase quadrature.

T-wave

In an electrocardiogram, the deflection which represents repolarization on the ventricles. It is normally upright, varying rather widely in amplitude and duration.

twenty-four hour satellite

A synchronous satellite of the earth.

twilight

The periods of incomplete darkness following sunset (evening twilight) or preceding sunrise (morning twilight).

Twilight is designated as civil, nautical, or astronomical, as the darker limit occurs when the center of the sun is at zenith distances of 96 degrees, 102 degrees, and 108 degrees, respectively.

two-body problem

That problem in classical celestial mechanics which treats of the relative motion of two point masses under their mutual gravitational attraction.

two-color pyrometer

A high-temperature thermometer wherein spectral radiation from the object is measured at two different wavelengths.

Temperature may be deduced without knowledge of the emittance if (and only if) the object is a gray body. The method is applicable to gases and to opaque objects.