Aerospace Science and Technology Dictionary H Page

Aerospace Science
&
Technology Dictionary

H

h

Space Flight Glossary - JPL Hour.

H alpha line

SOHO Glossary - GSFC Light emitted at a wavelength of 6563 Å from an atomic transition in hydrogen. This wavelength is in the red portion of the visible spectrum and is emitted by plasma at about 10,000 K, mainly in the solar chromosphere.

H-60 Helicopter

NASA Thesaurus The Black Hawk (Sikorsky) assault helicopter. Used for Black Hawk assault helicopter.

H-display

NASA SP-7, 1965 In radar, a B-display modified to include indication of angle of elevation. The target appears as two closely spaced blips which approximate a short bright line, the slope of which is in proportion to the sine of the angle of elevation. Also called H-scan, H-scope, H-indicator.

H-indicator

NASA SP-7, 1965 = H-display.

H-scan

NASA SP-7, 1965 = H-display.

H-scope

NASA SP-7, 1965 = H-display.

HA

Space Flight Glossary - JPL Hour Angle, the angular distance of a celestial object measured westward along the celestial equator from the zenith crossing. In effect, HA represents the RA for a particular location and time of day.

habitats

NASA Thesaurus The areas or types of environment in which plants or animals normally occur or live.

Hagen-Poiseuille flow

NASA SP-7, 1965 = Poiseuille flow.

hail

NASA Thesaurus Precipitation in the form of spheroidal layered ice pellets that usually fall from cumulonimbus clouds during thunderstorms. The layered structure of hail is produced by successive accretians of clear and frothy ice.

HAL/S (language)

NASA Thesaurus Programming language developed for the flight software of the NASA Space Shuttle program.

Hale-Bopp comet

NASA Thesaurus Long-period comet discovered July 23, 1995; designated C/1995 O1.

half life

NASA Thesaurus / NASA SP-7, 1965 The average time required for one half the atoms in a sample of radioactive element to decay. The half life $t$ _(1/2) is given by

where is the decay constant.

half-period zone

NASA SP-7, 1965 = Fresnel zone.

half-power points

NASA SP-7, 1965 The points on the radiation pattern of an antenna where the transmitted power is one-half that of the maximum of the same lobe. See half-power width.

half-power width

NASA SP-7, 1965 In a plane containing the direction of the maximum of a lobe of the radiation pattern of an antenna, the full angle between the two directions in thatplane in which the radiation intensity is one-half the maximum value of the lobe.

half-width

NASA SP-7, 1965 See line width.

Hall constant

NASA SP-7, 1965 In an electrical conductor, the constant of proportionality R in the relation

E sub h equals R J times H

where E_h is the transverse electric field (Hall field); J is current density; and H is magnetic field.
The sign of the majority carrier can be inferred from the sign of the Hall constant.

Hall effect

NASA Thesaurus / NASA SP-7, 1965 The electrical polarization of a horizontal conducting sheet of limited extent, when that sheet moves laterally through a magnetic field having a component vertical to the sheet.
The Hall effect is important in determining the behavior of the electrical currents generated by winds in the lower ionosphere.

Hall generators

NASA Thesaurus Hall plates, together with leads, and where used, encapsulation and ferrous or nonferrous backing plates.

Hall mobility

NASA SP-7, 1965 A measure of the flow of charged particles perpendicular to both a magnetic and an electric field.

Halley's comet

NASA Thesaurus A member of the solar system with an orbit and a period of about 76 years. It appeared in 1985-1986.

halo CME

SOHO Glossary - GSFC A CME pointed either towards or away from the Earth so that it looks roughly like a halo or ring around the Sun in images from a coronagraph

halocarbons

NASA Thesaurus Compounds consisting of halogen atoms and carbon atoms.

Halogen Occultation Experiment

NASA Thesaurus Shuttle experiment to provide global stratospheric vertical concentration profiles of key chemical species involved in the catalytic destruction of ozone due to chlorine compounds. Used for HALOE.

halon

NASA Thesaurus A bromofluorocarbon compound that was widely used as an agent for fire suppression and explosion protection. After being recognized as an ozone-depleting substance, the U.S. production and import of halons was banned in 1994.

Hamiltonian functions

Plasma Physics and Fusion Energy Glossary Function arising from the Hamiltonian approach to mechanics which characterizes the total energy of a system as a function of generalized coordinates and momenta and can be used to obtain the dynamical equations of motion of the system. (Consult an intermediate or advanced mechanics text for more info.)

hang gliders

NASA Thesaurus Ultralight, unpowered aircraft in which the pilot controls the flight attitude and glide path by shifting his position on a suspended seat (swing seat).

hangfire

NASA SP-7, 1965 A faulty condition in the ignition system of a rocket engine.

harbors

NASA Thesaurus Small bays or sheltered parts of seas, lakes, or other large bodies of water, usually well protected either naturally or artifically against high waves and strong currents. Harbors are furnished deep enough to provide safe anchorage for ships; especially such places in which port facilities are furnished.

hard landing

NASA Thesaurus / NASA SP-7, 1965 An impact landing of a spacecraft on the surface of a planet or natural satellite destroying all equipment except possibly a very rugged package.

hard radiation

NASA SP-7, 1965 Radiation of high penetrating power; that is, radiation of high frequency and short wavelength.
A 10-centimeter thickness of lead is usually used as the criterion upon which the relative penetrating power of various types of radiation is based. Hard radiation will penetrate such a shield; soft radiation will not.

hard vacuum

NASA SP-7, 1965 A very high vacuum, usually considered to be a pressure less than about 10E7 torr.

hard wire telemetry

NASA SP-7, 1965 = wire link telemetry.

hardening (systems)

NASA Thesaurus Techniques for decreasing the susceptibility or vulnerability of weapon systems and components.

hardness

NASA Thesaurus / NASA SP-7, 1965 Resistance of metal to plastic deformation usually by indentation. However, the term may also refer to stiffness or temper, or to resistance to scratching, abrasion, or cutting.
Indentation hardness may be measured by various hardness tests, such as Brinnell, Rockwell, and Vickers.

hardware

NASA Thesaurus / NASA SP-7, 1965 Physical equipment as contrasted to ideas or design that may exist only on paper.

hardware description languages

NASA Thesaurus Formal languages and notations used in the specification, design, simulation, and documentation of computer hardware systems and their component circuits.

harmonic

NASA SP-7, 1965 1. An integral multiple or submultiple of a given frequency; a sinusoidal component of a periodic wave.
2. A signal having a frequency which is a harmonic (sense 1) of the fundamental frequency.

harmonic analysis

NASA Thesaurus / NASA SP-7, 1965 A statistical method for determining the amplitude and period of certain harmonic or wave components in a set of data with the aid of Fourier series.

harmonic analyzer

NASA SP-7, 1965 A machine which resolves a periodic curve into its harmonic constituents.
A machine performing the opposite function is called a harmonic synthesizer.

harmonic distortion

NASA SP-7, 1965 Nonlinear distortion characterized by the appearance in the output of multiples of the fundamental when the input wave is sinusoidal.

harmonic function

NASA Thesaurus / NASA SP-7, 1965 Any solution of the Laplace equation.

harmonic motion

NASA Thesaurus / NASA SP-7, 1965 The projection of circular motion on a diameter of the circle of such motion.
Simple harmonic motion is produced if the circular motion is of constant speed. The combination of two or more simple harmonic motions results in compound harmonic motion.

harmonic synthesizer

NASA SP-7, 1965 A machine which combines elementary harmonic constituents into a single periodic function.
A machine performing the opposite function is called a harmonic analyzer.

harmonics

NASA Thesaurus Eigenfrequency oscillations excited in a vibrating system. Used for overtones.

harmonics of the earth's gravitational fields

NASA SP-7, 1965 A series representing the gravitational potentials of the earth in which the terms form a harmonic progression.

hartley

NASA SP-7, 1965 A unit of information content equal to one of ten possible and equally likely values or states of anything used to store or convey information. One hartley equals log

₂10 bits (log

₂10 = 3.323), or one decimal digit.

Hartley bands

NASA SP-7, 1965 See absorption band.

Hartree approximation

Plasma Physics and Fusion Energy Glossary Hartree-Fock approximation: a refinement of the Hartree method (see entry) in which one uses determinants of single-particle wave functions rather than products, thereby introducing exchange terms into the Hamiltonian.

Hartree-Fock-Slater method

NASA Thesaurus A refined approximation method for the calculation from wave function of electron total energies, kinetic energies, etc., for chemical elements.

Hasselblad 500 EL/M 70 mm cameras

Global Land Information System Glossary - USGS NASA has modified standard off-the-shelf Hasselblad 70 mm cameras to operate in zero gravity aboard the Space Shuttle. A data recording module (DRM) has also been installed on each camera to record the date, time (Greenwich Mean Time), mission number, roll number, and frame number. The cameras utilize a 70 mm film format and operate with one of three lenses (50, 100, or 250 mm) to acquire high quality photographs through four viewing ports on the Shuttle

Hawking radiation

AS&T Dictionary The theory that black holes emit radiation like any other hot body. Virtual particle-antiparticle pairs are constantly being created in supposedly empty space.Occasionally, a pair will be created just outside the event horizon of a black hole.

Hawking radiation

High Energy Astrophysics Dictionary- GSFC The theory that black holes emit radiation like any other hot body. Virtual particle-antiparticle pairs are constantly being created in supposedly empty space. Occasionally, a pair will be created just outside the event horizon of a black hole. There are three possibilities: - both particles are captured by the hole; - both particles escape the hole; - one particle escapes while the other is captured. The first two cases are straightforward; the virtual particle-antiparticle pair recombine and return their energy back to the void via the uncertainty principle. It is the third case that interests us. In this case, one of the particles has escaped (and is speeding away to infinity), while the other has been captured by the hole. The escapee becomes real and can now be detected by distant observers. But the captured particle is still virtual; because of this, it has to restore conservation of energy by assigning itself a negative mass-energy. Since the hole has absorbed it, the hole loses mass and thus appears to shrink. From a distance, it appears as if the hole has emitted a particle and reduced in mass. The rate of power emission is proportional to the inverse square of the hole's mass; thus, the smaller a hole gets, the faster and faster it emits Hawking radiation. This leads to a runaway process; what happens when the hole gets very small is unclear; quantum theory seems to indicate that some kind of "remnant" might be left behind after the hole has emitted away all its mass-energy.

Hawking temperature

High Energy Astrophysics Dictionary- GSFC The temperature of a black hole caused by the emission of Hawking radiation.

hazardous material disposal (in space)

NASA Thesaurus The disposal in space of hazardous material. When radioactive materials are involved, the expected lifetime of orbit exceeds the lifetime of the radioactivity.

haze

NASA Thesaurus Fine particles of dust, salt, or water dispersed through a part of the atmosphere, diminishing transparency of the air, causing colors to assume a characteristic subdued opalescent appearance, and reducing the horizontal visibility to more than one, but less than two kilometers. The obscuration, or lack of transparency, of the atmosphere near the Earth's surface, is often caused by haze or by heat refraction (shimmering).

hazemeter

NASA SP-7, 1965 = transmissometer.

HCL argon lasers

NASA Thesaurus Gas lasers in which the active material is gaseous hydrogen chloride and argon.

HCL lasers

NASA Thesaurus Gas lasers in which the active material is gaseous hydrogen chloride. Used for hydrogen chloride lasers.

HDT-- High Density Tapes

Global Land Information System Glossary - USGS HDTs are high density (high capacity) magnetic tapes.

head pressure

NASA SP-7, 1965 = inlet pressure.

head up tilt

NASA Thesaurus Body posture while lying on a tilt table with the head higher than the rest of the body.

head-to-foot acceleration

NASA SP-7, 1965 See physiological acceleration.

heading

NASA SP-7, 1965 The horizontal direction in which a craft is pointed, expressed as angular distance from a reference direction, usually from 0 degrees at the reference direction clockwise through 360 degrees.
Heading is often designated as true, magnetic, compass, or grid as the reference direction is true, magnetic, compass, or grid north, respectively.

heading-upward plan position indicator

NASA SP-7, 1965 See plan position indicator.

HEAO

Imagine the Universe Dictionary - NASA GSFC The High Energy Astrophysical Observatory satellite series

HEAO 1

NASA Thesaurus The first of three NASA High Energy Astronomy Observatories launched during 1977 for the study of cosmic rays and Earth's magnetic field to study the x ray and gamma ray sky. Used for HEAO A, High Energy Astronomy Observatory A, and High Energy Astronomy Observatory 1.

HEAO 2

NASA Thesaurus The second of three NASA High Energy Astronomy Observatories. It was launched during 1978 for the study of specific x ray objects, quasars, x ray pulsars, and candidate black holes. Used for Einstein Observatory, HEAO B, High Energy Astronomy Observatory B, and High Energy Astronomy Observatory 2.

HEAO 3

NASA Thesaurus The third of four NASA High Energy Astronomy Observatories. It was launched during 1979 for the study of cosmic rays and elemental and isotropic composition as a corollary to a search of narrow gamma ray lines. Used for HEAO C, High Energy Astronomy Observatory C, and High Energy Astronomy Observatory 3.

HEASARC

Imagine the Universe Dictionary - NASA GSFC High Energy Astrophysics Science Archive Research Center

heat

NASA Thesaurus / NASA SP-7, 1965 Energy transferred by a thermal process.
Heat can be measured in terms of the dynamical units of energy, as the erg, joule, etc., or in terms of the amount of energy required to produce a definite thermal change in some substance, as, for example, the energy required per degree to raise the temperature of a unit mass of water at some temperature ( calorie, Btu).

heat affected zone

NASA Thesaurus That portion of the base metal, the structure or properties of which have been altered by the heat of welding or gas-cutting operation. Used for HAZ (metallurgy).

heat balance

NASA Thesaurus / NASA SP-7, 1965 1. The equilibrium which exists on the average between the radiation received by a planet and its atmosphere from the sun and that emitted by the planet and atmosphere.
That the equilibrium does exist in the mean is demonstrated by the observed long-term constancy of the earth's surface temperature. On the average, regions of the earth nearer the equator than about 35 degrees latitude receive more energy from the sun than they are able to radiate, whereas latitudes higher than 35 degrees received less. The excess of heat is carried from low latitudes to higher latitudes by atmospheric and oceanic circulations and is reradiated there.
2. The equilibrium which is known to exist when all sources of heat gain and loss for a given region or body are accounted for. In general this balance includes advective, evaporative (etc.) terms as well as a radiation term.

heat barrier

NASA SP-7, 1965 = thermal barrier.

heat budget

NASA Thesaurus The accounting for the total amount of heat received and lost by a particular system.

heat conductivity

NASA SP-7, 1965 = thermal conductivity.

heat dump

NASA SP-7, 1965 = heat sink.

heat engine

NASA SP-7, 1965 A system which receives energy in the form of heat and which, in the performance of an energy transformation, does work. See thermodynamic efficiency, Carnot engine.
The atmosphere itself is a heat engine.

heat exchanger

NASA Thesaurus / NASA SP-7, 1965 A device for transferring heat from one fluid to another without intermixing the fluids, as (a) a regenerator and (b) an apparatus for cooling or heating the air in a wind tunnel. See radiator, sense 2.

heat flux

NASA Thesaurus The thermal intensity indicated by the amount of energy transmitted per unit area.

heat function

NASA SP-7, 1965 = enthalpy.

heat index

NASA SP-7, 1965 The difference between the absolute visual magnitude of a star and the absolute radiometric magnitude (

M

_v - M_r).

heat of ablation

NASA SP-7, 1965 A measure of the effective heat capacity of an ablating material, numerically the heating rate input divided by the mass loss rate which results from ablation.
In the most general case, heat of ablation is given by

where q_c is convective heat transfer in the absence of ablation; q_r is radiative heat transfer from hot gases to ablation material; T_w⁴ is rate of heat rejection by radiation from external surface of ablation material; and is rate at which gaseous ablation products are injected into the boundary layer. Heat of ablation is sometimes evaluated neglecting the heat rejected by radiation and as a result unrealistically high heats of ablation are obtained. If q_r < T_w⁴ for moderate values of stream enthalpy h_s, heat of ablation is given by

where H_v is heat required to cause a unit weight of mass to be injected into boundary layer; is blocking factor with numerical value from about 0.2 to 0.6 depending on material and type of flow; and h_w is enthalpy at wall temperature.

heat of fusion

NASA Thesaurus The increase in enthalpy accompanying the conversion of one mole, or a unit mass, of a solid to a liquid at its melting point at constant pressure and temperature. Used for latent heat of fusion.

heat of fusion

NASA Thesaurus / NASA SP-7, 1965 See latent heat.

heat of sublimation

NASA SP-7, 1965 See latent heat.

heat of vaporization

NASA Thesaurus / NASA SP-7, 1965 See latent heat.

heat pulse

NASA SP-7, 1965 Specifically, the sudden rise and subsequent fall in the temperature of a vehicle on reentry.

heat resistant alloys

NASA Thesaurus Alloys developed for very high temperature service where relatively high stresses (tensile, thermal, vibratory, and shock) are encountered and where oxidation resistance is frequently required. Used for high temperature alloys and superalloys.

heat shield

NASA SP-7, 1965 1. Any device that protects something from heat.
2. Specifically, the protective structure necessary to protect a reentry body from aerodynamic heating. See heat sink.

heat shielding

NASA Thesaurus The use of devices that protect something from heat. Specifically, the protective structure necessary to protect a reentry body from aerodynamic heating. Used for thermal shielding.

heat sink

NASA SP-7, 1965 1. In thermodynamic theory, a means by which heat is stored, or is dissipated or transferred from the system under consideration.
2. A place toward which the heat moves in a system.
3. A material capable of absorbing heat; a device utilizing such a material and used as a thermal protection device on a spacecraft or reentry vehicle.
4. In nuclear propulsion, any thermodynamic device, such as a radiator or condenser, that is designed to absorb the excess heat energy of the working fluid. Also called heat dump.

heat transfer

NASA Thesaurus / NASA SP-7, 1965 The transfer or exchange of heat by radiation, conduction, or convection within a substance and between the substance and its surroundings.
Radiation represents the transfer of radiant energy from one region to another by electromagnetic waves, with or without an intervening medium. Conduction, or diffusion of heat, implies the elastic impact of fluid molecules, without any net transfer of matter. Convection arises from the mixing of relatively large volumes of fluid because of the fluid motion and may be due either to local temperature inequalities (free convection) or to an applied pressure gradient (forced convection).

heat transfer coefficients

NASA Thesaurus The rate of heat transfer per unit area per unit temperature difference, a quantity having the dimensions of reciprocal length.

heat transmission

NASA Thesaurus Heat transmitted from one substance to another. Used for heat flow.

heat treatment

NASA Thesaurus / NASA SP-7, 1965 Heating and cooling a solid metal or alloy in such a way as to obtain desired conditions or properties.
Heating for the sole purpose of hot-working is excluded from the meaning of this definition.

heat-transfer coefficient

NASA SP-7, 1965 1. The rate of heat transfer per unit area per unit temperature difference, a quantity having the dimensions of reciprocal length.
2. A misnomer for Nusselt number.

heavenly body

NASA SP-7, 1965 = celestial body.

Heaviside layer

NASA SP-7, 1965 = E layer.

heavy cosmic-ray primaries

NASA SP-7, 1965 The positively charge nuclei of elements heavier than hydrogen and helium up to atomic nuclei of iron. See cosmic rays.
These heavy atomic nuclei comprise about 1 percent of the total cosmic-ray particles and less than 4 percent of the total positive charges.

heavy hydrogen

NASA SP-7, 1965 = deuterium.

heavy ion

NASA SP-7, 1965 = large ion.

heavy lift airships

NASA Thesaurus Airships designed to lift heavy materials.

heavy metals

NASA Thesaurus Metals or alloys having a high specific gravity; usually ones with a density greater than 5 grams per cubic centimeter.

heavy water

NASA Thesaurus / NASA SP-7, 1965 Water in which the hydrogen of the water molecule consists entirely of the heavy hydrogen isotope of mass 2 (deuterium).
Written D₂O. Density, 1.1076 at 20º C. It is used as a moderator in certain types of nuclear reactors. The term is sometimes applied to water whose deuterium content is greater than natural water.

hecto

NASA SP-7, 1965 (abbr h)
A prefix meaning multiplied by 100.

hectometric wave

NASA SP-7, 1965 See frequency band.

height

NASA Thesaurus / NASA SP-7, 1965 (symbol h )
1. Vertical distance; the distance above some reference point or plane, as, height above sea level. See altitude.
2. The vertical dimension of anything; the distance which something extends above its foot or root, as blade height.

height effect

NASA SP-7, 1965 = antenna effect.

height gain

NASA SP-7, 1965 A radio-wave interference phenomenon which results in a more or less periodic signal strength variation with height. This specifically refers to interference between direct and surface-reflected waves. See radiation pattern, Fresnel zone.

Helene

NASA Thesaurus A natural satellite of Saturn orbiting at a mean distance of 377,400 kilometers.

helical antenna

NASA Thesaurus / NASA SP-7, 1965 An antenna used where circular polarization is required. The driven element consists of a helix supported above a ground plane.

helical flow

AS&T Dictionary Flow which follows the pattern of a cylindrical spiral, I.e. a corkscrew or screw thread

helical scanning

NASA SP-7, 1965 In radar scanning, varying the azimuth and elevation of the antenna continuously to generate a spiral pattern of the beam. Also called spiral scanning.

helicity

Glossary of Weather Terms for Storm Spotters - NOAA A property of a moving fluid which represents the potential for helical flow (i.e. flow which follows the pattern of a corkscrew) to evolve.

helicity

Plasma Physics and Fusion Energy Glossary A measurement of the topological "tangledness" of magnetic field lines. It is formally defined as the scalar product of the magnetic vector potential with the magnetic field, K = A dot B.

helicopters

NASA Thesaurus Rotorcraft that, for its horizontal motion, depends principally on its engine-driven rotors.

heliocentric

NASA Thesaurus / NASA SP-7, 1965 Relative to the sun as a center, as a heliocentric orbit.

heliocentric distance

Comet Glossary - JPL The comet's distance from the Sun in astronomical units.

heliocentric parallax

NASA SP-7, 1965 The difference in the apparent positions of a celestial body outside the solar system, as observed from the earth and sun. Also called stellar parallax. See parallax.

heliographic

NASA SP-7, 1965 Referring to positions on the sun measured in latitude from the sun's equator and in longitude from a reference meridian.

heliopause

Space Flight Glossary - JPL The boundary theorized to be roughly circular or teardrop-shaped, marking the edge of the sun's influence, perhaps 100 AU from the sun.

helioseismology

SOHO Glossary - GSFC The study of the interior of the Sun by the analysis of its natural modes of oscillation.

heliosphere

NASA Thesaurus The region around the sun whose plasma processes are dominated by solar wind.

heliostats

NASA Thesaurus Instruments consisting of mirrors moved by clockwork for reflecting the sun's rays in a fixed direction.

heliports

NASA Thesaurus An area of land, water, or structure used, or intended to be used, for the landing and takoff of helicopters.

Helmholtz free energy

NASA SP-7, 1965 = Helmholtz function.

Helmholtz function

NASA SP-7, 1965 (symbol a )
A mathematically defined thermodynamic function of state, the decrease in which during a reversible isothermal process is equal to the work done by the system. the Helmholtz function is

$a = u - Ts$

where u is specific internal energy; T is Kelvin temperature; and s is specific entropy. By use of the first law of thermodynamics for reversible processes,

$da = -s dT - dw$

where dw is the work done per unit mass by the system. Also called Helmhotlz free energy, work function. Compare Gibbs function.

Helmholtz resonators

NASA Thesaurus An enclosure having a small opening consisting of a straight tube of such dimensions that the enclosure resonates at a single frequency determined by the geometry of the resonator.

Helmholtz theorem

NASA SP-7, 1965 The statement that if F is a vector field satisfying certain quite general mathematical conditions, then F is the sum of two vectors, one of which is irrotational (has no vorticity), the other solenoidal (has no divergence).

hematite

NASA Thesaurus A common iron mineral; ferric oxide.

hemispherical

NASA SP-7, 1965 Referring to thermal radiation properties, in all possible directions from a flat surface.

hemispherical emittance

NASA SP-7, 1965 (symbol epsilon

_h, E_h). The ratio of the emissive power of a specimen to that of a blackbody at the same temperature, considering radiation emitted in all possible directions.

hemmungspunkt

NASA SP-7, 1965 = stopping point.

hemoperfusion

NASA Thesaurus Type of poison treatment in which the patient's blood is passed over a bed of absorbent material (activated carbon, resin, etc.) to remove the toxin from the bloodstream.

henry

NASA SP-7, 1965 (abbr h)
The unit of electrical inductance; the inductance of a closed circuit in which an electromotive force of 1 volt is produced when the electric current in the circuit varies uniformly at the rate of 1 ampere per second.

hepatitis

NASA Thesaurus An inflammation of the liver, commonly of viral origin, but also associated with other diseases.

Her, Herc

NASA SP-7, 1965 International Astronomical Union abbreviations for Hercules. See constellation.

herbicides

NASA Thesaurus Chemical agents used for the eradication of undesirable plants or for the inhibition of their growth.

Herbig-Haro objects

NASA Thesaurus Celestial objects having many of the characteristics of a T Tauri star (e.g., their spectra show a weak continuum with strong emission lines), believed to be stars in the very early stages of development. All known Herbig-Haro objects have been found within the boundaries of dark clouds. These strong infrared sources are characterized by mass loss.

Hercules

NASA SP-7, 1965 (abbr Her, Herc)
See constellation.

hertz

NASA Thesaurus / NASA SP-7, 1965 (abbr Hz)
The unit of frequency, cycles per second.

Hertzian waves

NASA SP-7, 1965 Electromagnetic waves of any frequency between 10 kilocycles per second and 300,000 megacycles per second. Now generally called radio waves. See frequency bands.

Hertzsprung-Russell diagram

SOHO Glossary - GSFC A diagram which plots temperature (or color) vs. luminosity for a population of stars.

Herzberg bands

NASA Thesaurus / NASA SP-7, 1965 See absorption band.

Hessian matrices

NASA Thesaurus Given a real value function of N variables, an N by N symmetric of all second order partial derivatives.

heterodyne

NASA Thesaurus / NASA SP-7, 1965 To mix two radio signals of different frequencies to produce a third signal which is of lower frequency, i.e., to produce beating.
Radar receivers are of the heterodyne type (as contrasted to the superregenerative type) because the very high radio frequencies used in radar are difficult to amplify. A target signal is heterodyned with a current of lower frequency produced by a klystron oscillator and the resulting intermediate-frequency signal can then be highly amplified for subsequent presentation or analysis.

heterogeneity

NASA Thesaurus Having different properties at different points.

heterojunction devices

NASA Thesaurus Electronic devices utilizing junctions between different semiconducting materials. The characteristics and performance of the devices are dependent on the relative lineup of the energy bands at the junctions.

heterojunctions

NASA Thesaurus Junctions between semiconductors that differ in their doping level conductivities, and also in their atomic or alloy compositions.

heterosphere

NASA Thesaurus / NASA SP-7, 1965 The upper portion of a two-part division of the atmosphere according to the general homogeneity of atmospheric composition; the layer above the homosphere. The heterosphere is characterized by variation in composition and mean molecular weight of constituent gases. See atmospheric shell.
This region starts at 80 and 100 kilometers above the earth, and therefore closely coincides with the ionosphere and the thermosphere.

hexidecimal notation

NASA SP-7, 1965 = sexidecimal notation.

HGA

Space Flight Glossary - JPL High-Gain Antenna onboard a spacecraft.

hibernating spacecraft

NASA SP-7, 1965 A spacecraft maintaining an orbit without using propellant power and without maintaining orientation within the orbit, but with inherent power capability.
A hibernating spacecraft could be in an orbit around the sun for months or years before power is triggered from a station on earth at an opportune time.

hidyne

NASA SP-7, 1965 Variant of hydyne.

high electron mobility transistors

NASA Thesaurus A recently developed field effect transistor based on the technique of modulation doping of GaAs/Al(x)Ga(1-x) as heterojunctions. This technique achieves high mobility in part by introducing carriers into high purity GaAs from donor ions in an adjacent A1GaAs layer, the electrons and ions being separated by the built-in heterojunction potential. Used for HEMT (electronics)

high energy particles

From Stargazers to Starships Glossary - GSFC Charged atomic particles moving rapidly, often at a significant fraction of the speed of light. They can penetrate matter, ionize the material which they traverse and emit energetic photons.

high frequency

NASA SP-7, 1965 (abbr HF)
See frequency band.

high level languages

NASA Thesaurus Computer languages whose instructions or statements each correspond to several machine language instructions.

high pass filters

NASA Thesaurus Wave filters having a single transmission band extending from some critical or cutoff frequency, not zero, up to infinite frequency.

high power lasers

NASA Thesaurus Stimulated emission devices having high energy flux density outputs. Used for high intensity lasers.

high Reynolds number

NASA Thesaurus A Reynolds number above the critical Reynolds number of a sphere.

high sun

Galileo Project Glossary - JPL The condition of the sun being directly overhead (analogous to noon) which eliminates shadows on the surface. When planetary images are obtained in high sun conditions they are examined for albedo information rather than morphologic information (see Terminator). Areas imaged under both high and low sun conditions can be compared to link albedo and morphologic features.

high temperature superconductors

NASA Thesaurus New superconducting materials consisting of mixed metal oxide ceramics that maintain their superconductivity at higher temperature ranges (above 24 K) than the more traditional superconductors.

high vacuum

NASA Thesaurus / NASA SP-7, 1965 The condition in a gas-filled space at pressure less than 10^-3 torr.
The term high vacuum has frequently been defined as a pressure less than some upper limit. High vacuum (and similar vacuum terms) should not be defined as a pressure but rather as the condition or state in a gas-filled space at pressures less than some upper limit or within specified limits. The following classification of degrees of high vacuum has been proposed:

Condition

Pressure Range

high vacuum 10^-3 to 10^-6 torr (microtorr range)

very high vacuum 10^-6 to 10^-9 torr (nanotorr range)

ultrahigh vacuum 10^-9 torr and below

high-intensity gamma

NASA SP-7, 1965 A level a gamma radiation flux on the order of 10E4 roentgens or higher.

high-pass filter

NASA SP-7, 1965 A wave filter having a single transmission band extending from some critical or cutoff frequency, not zero, up to infinite frequency.

high-precision shoran

NASA SP-7, 1965 (abbr hiran)
See shoran.

high-speed motion-picture photography

NASA SP-7, 1965 The picture-taking frequency range from 32 to 500 pictures per second.

highlands

NASA Thesaurus A general term for large areas of elevated or mountainous land standing prominently above adjacent low areas; mountainous regions.

Himalia

NASA Thesaurus A natural satellite of Jupiter, orbiting at a mean distance of 11,480,000 kilometers.

hindcasting

NASA Thesaurus The process of reconstructing the time and space evolution of an atmospheric or oceanic phenomenon that has occurred in the past, through an analysis of historical data, a mathematical-model simulation of the processes involved, or a combination of data analysis and modeling.

Hipparcos satellite

NASA Thesaurus An ESA astrometric satellite to determine trigonometric parallaxes, proper motions, and positions of 100,000 stars, mainly for stars brighter than magnitude 10. The satellite was launched in August 1989.

hiran (abbr)

NASA SP-7, 1965 = high precision shoran
See shoran.

hiss

NASA Thesaurus / NASA SP-7, 1965 Random noise in the audio frequency range, having subjective characteristics analogous to prolonged sibilant sounds.

hiss

NASA Thesaurus Random noise in the audio frequency range, having subjective characteristics analogous to prolonged sibilant sounds.

histochemical analysis

NASA Thesaurus In biochemistry, the analysis of chemical components in tissues.

hodographs

Glossary of Weather Terms for Storm Spotters - NOAA Plots representing the vertical distribution of horizontal winds, using polar coordinates. A hodograph is obtained by plotting the end points of the wind vectors at various altitudes, and connecting these points in order of increasing height. Interpretation of a hodograph can help in forecasting the subsequent evolution of thunderstorms.

hohlraum

NASA SP-7, 1965 In radiation thermodynamics, a cavity whose walls are in radiative equilibrium with the radiant energy within the cavity.
This idealized cavity can be approximated in practice by making a small perforation in the walls of a hollow container of any opaque material. The radiation escaping through such a perforation will be a good approximation to blackbody radiation at the temperature of the interior of the container.

hohlraums

NASA Thesaurus In radiation thermodynamics, cavities whose walls are in radiative equilibrium with the radiant energy with the cavity.

Hohmann orbit

NASA SP-7, 1965 A minimum energy transfer orbit.

hold

NASA SP-7, 1965 1. During a countdown to stop counting and to wait until an impediment has been removed so that the countdown can be resumed, as in T minus 40 and holding. Compare count, recycle.
2. In computer terminology, to retain information in one storage device after copying it into another storage device.

holddown

NASA SP-7, 1965 = holddown test.

holddown test

NASA SP-7, 1965 The testing of some system or subsystem in a rocket while the rocket is firing but restrained in a test stand.

holding beam

NASA SP-7, 1965 An electron beam which regenerates the electrostatic charges stored in an electrostatic-storage tube.

hole

NASA SP-7, 1965 A mobile vacancy in the electronic valence structure of a semiconductor which acts like an electron with a positive charge.

hole burning

NASA Thesaurus A laser process that depletes, spatially or spectrally, the electron/hole pair density in a region of space or frequency of high coherent light, being spatial hole burning and spectral hole burning respectively.

hole geometry (mechanics)

NASA Thesaurus The sizes, locations, and shapes of perforations created in materials.

hollow

NASA Thesaurus Low tract of land surrounded by hills or mountains; small sheltered valley or basin, especially in a rugged area.

holographic optical elements

NASA Thesaurus Holograpms used to control transmitted light beams, rather than to display images, based on the principles of diffraction.

holographic subtraction

NASA Thesaurus A holographic technique by which two dissimilar optical fields can be subtracted to yield only their difference. Used for self subtraction holography.

holography

NASA Thesaurus The interferometry technique used to make three-dimensional pictures of surfaces. One light beam illuminates a surface, and sets up interference patterns with a reference beam.

home

NASA SP-7, 1965 To follow a path of energy waves, especially radio or radar waves, by means of a directional antenna, radar equipment, or other sensing devices, to or toward the point of transmission or reflection of the waves.

homer

NASA SP-7, 1965 = homing beacon.

homing

NASA Thesaurus The following of a path of energy waves to or toward their source or point of reflection.

homing

NASA Thesaurus / NASA SP-7, 1965 The following of a path of energy waves to or toward their source or point of reflection. See home, active homing, passive homing, semiactive homing guidance.

homing beacon

NASA SP-7, 1965 A beacon providing homing guidance. Also called homer.

homing guidance

NASA SP-7, 1965 Guidance in which a craft or missile is directed toward a destination by means of information received from the destination.
It is active homing guidance if the information received is in response to transmissions from the craft, semiactive homing guidance if in response to transmissions from a source other than the craft, and passive homing guidance if natural radiations from the destination are utilized.

homogeneity

NASA Thesaurus Having the same properties at all points.

homogeneous atmosphere

NASA SP-7, 1965 1. A hypothetical atmosphere in which the density is constant with height.
The lapse rate of temperature in such an atmosphere is known as the autoconvective lapse rate and is equal to g/R (or approximately 3.4 degrees C per 100 meters) where g is the acceleration of gravity and R is the gas constant for air. A homogeneous atmosphere has a finite total thickness which is given by RdTv/g, where Rd is the gas constant for dry air and Tv is the virtual temperature (degrees K) at the surface. For a surface temperature of 273 degrees K, the vertical extent of the homogeneous atmosphere on the earth is approximately 8000 meters. At the top of such an atmosphere both the pressure and absolute temperature vanish.
2. With respect to radio propagation, an atmosphere which has a constant index of refraction, or one in which radio waves travel in straight lines at constant speed. Free space is the ideal homogeneous atmosphere in this sense.
3. Same as adiabatic atmosphere. See barotropy.

homojunctions

NASA Thesaurus Junctions between semiconductors that differ in their doping level conductivities but not in their atomic or alloy composition.

homologous turbulence

NASA SP-7, 1965 Turbulence in which the mean value of the squares and products of the velocity components and their derivatives differ only in scale from point to point. See isotropic turbulence.

homopause

NASA SP-7, 1965 The top of the homosphere, or the level of transition between it and the heterosphere. See atmospheric shell.
The homopause probably lies between 80 and 90 kilometers, where molecular oxygen begins to dissociate into atomic oxygen. The homopause is somewhat lower in the daytime than at night.

homopolar generators

NASA Thesaurus Rotating electric machines for converting mechanical power into pure direct current by utilizing poles having the same polarity at the armature.

homosphere

NASA Thesaurus / NASA SP-7, 1965 The lower portion of a two-part division of the atmosphere according to the general homogeneity of atmospheric composition; opposed to the heterosphere. The region in which there is no gross change in atmospheric composition, that is, all the atmosphere from the earth's surface to about 90 kilometers. See atmospheric shell.
The homosphere is about equivalent to the neutrosphere, and includes the troposphere, stratosphere, and mesosphere; it also includes the ozonosphere and at least part of the chemosphere.

honeycomb core

NASA SP-7, 1965 A lightweight strengthening material of a structure resembling a honeycomb mesh. See sandwich construction.

honeycomb mirrors

NASA Thesaurus High strength to weight telescope mirrors constructed of spun-cast borosilicate glass in a honeycomb structure that optically represents a single large mirror.

hop

NASA SP-7, 1965 Travel of a radio wave to the ionosphere and back to earth.
The number of hops a radio signal has experienced is usually designated by the expression one hop, two hop, multihop, etc. The number of hops is called the order of reflection.

Hopfield bands

NASA SP-7, 1965 See absorption band.

Hor, Horo

NASA SP-7, 1965 International Astronomical Union abbreviations for Horologium. See constellation.

horizon

NASA Thesaurus / NASA SP-7, 1965 That great circle of the celestial sphere midway the zenith and nadir, or a line resembling or approximating such a circle.
That line where earth and sky appear to meet, and the projection of this line upon the celestial sphere, is called visible or apparent horizon. A line resembling the visible horizon but above or below it is called a false horizon. That circle of the celestial sphere formed by the intersection of the celestial sphere and a plane perpendicular to the zenith-nadir line is called sensible horizon if the plane is through any point, such as the eye of an observer, geoidal horizon if through any sea-level point, and celestial or rational horizon if through the center of the earth. The geometrical horizon was originally considered identical with the celestial sphere and an infinite number of straight lines tangent to the earth's surface, and radiating from the eye of the observer. If there were no terrestrial refraction, geometrical and visible horizons would coincide. An artificial horizon is a gyroscopic instrument for indicating the attitude of an aircraft with respect to the horizontal. A radio horizon is the line at which direct rays from a transmitting antenna become tangent to the earth's surface. A radar horizon is the radio horizon of a radar antenna.

horizon system of coordinates

NASA SP-7, 1965 A set of celestial coordinates, usually altitude and azimuth, based on the celestial horizon as the primary great circle. See coordinate, table.

horizontal branch stars

NASA Thesaurus Horizontal strips of stars on the Hertzsprung-Russell diagram of globular clusters to the left of the red giant branch.

horizontal integration

Global Land Information System Glossary - USGS The process of mosaicking adjacent parts of a map or image together into a single map or image. This process might require geometric adjustments to the image itself or the features within it so that matching occurs across mosaic seams.

horizontal orientation

NASA Thesaurus The attitude of an object in reference to the plane which is perpendicular to the direction of gravity.

horizontal parallax

NASA SP-7, 1965 The geocentric parallax of a body on the observer's horizon. This is equal to the angular semidiameter of the earth as seen from the body.

horizontal polarization

Global Land Information System Glossary - USGS Transmission of microwaves so that the electric lines of force are horizontal, while the magnetic lines of force are vertical.

horizontal positional accuracy

Global Land Information System Glossary - USGS Horizontal positional accuracy is based upon the use of USGS source quadrangles which are compiled to meet National Map Accuracy Standards (NMAS). NMAS horizontal accuracy requires that at least 90 percent of points tested are within 0.02 inches of the true position. The digital data are estimated to contain a horizontal positional error of less than or equal to 0.003 inches standard error in the two component directions relative to the source quadrangle.

horizontal scanning

NASA SP-7, 1965 In radar scanning, rotating the antenna in azimuth around the horizon or in a sector. Also called searchlighting.

horizontal stratification

NASA SP-7, 1965 Uniform meteorological conditions at a given altitude, over the area under consideration.
The term horizontally stratified atmosphere is generally assumed to mean complete stratification at each altitude. It follows that the vertical profile, which need not be a standard profile, is consistent over the area under consideration. When the condition extends over a large area, the term spherical stratification is used.

horn

NASA SP-7, 1965 An antenna shaped like a horn. Also called horn radiator.
A horn is usually designed as an extension of a waveguide whose sides flare from the original waveguide size to a larger aperture size.

horn antenna

NASA SP-7, 1965 = horn.

horn radiator

NASA SP-7, 1965 = horn.

hornito

Photoglossary of Volcanic Terms - USGS A small rootless spatter cone that forms on the surface of a basaltic lava flow (usually pahoehoe) is called a hornito. A hornito develops when lava is forced up through an opening in the cooled surface of a flow and then accumulates around the opening. Typically, hornitos are steep sided and form conspicuous pinnacles or stacks. They are "rootless" because they are fed by lava from the underlying flow instead of from a deeper magma conduit.

Horo

NASA SP-7, 1965 International Astronomical Union abbreviation for Horologium. See constellation.

Horologium

NASA SP-7, 1965 (abbr Hor, Horo)
See constellation.

hot atoms

NASA Thesaurus Atoms with high internal or kinetic energy as a result of a nuclear process such as beta decay or neutron capture.

hot cathode

NASA Thesaurus / NASA SP-7, 1965 A cathode that functions primarily by the process of thermionic emission. Also called thermionic cathode.

hot corrosion

NASA Thesaurus The corrosion at high temperatures as a result of the reduction of protective oxide coatings and scales and the subsequent accelerated oxidation.

hot isostatic pressing

NASA Thesaurus A thermomechanical process for forming metal-powder compacts or ceramic shapes by use of isostatically applied gas pressure in order to achieve high density in the treated material. Used for HIP (process).

hot pressing

NASA Thesaurus The simultaneous heating and molding of a compact.

hot test

NASA SP-7, 1965 A propulsion system test conducted by actually firing the propellants. Compare cold-flow test.

hot working

NASA Thesaurus Controlled mechanical operations for shaping a product at temperatures above the recrystallization temperature. Used for hot forming.

hot-cathode ionization gage

NASA SP-7, 1965 An ionization gage in which the ions are produced by collisions with electrons emitted from a hot filament (or cathode) and accelerated by an electric field. Also called hot-filament ionization gage, ionization gage , or simply ion gage.
The Bayard-Alpert ionization gage employs a tube with an electrode structure designed to minimize X-ray induced electron emission from the ion collector.

hot-filament ionization gage

NASA SP-7, 1965 = hot-cathode ionization gage.

hot-wire transducer

NASA SP-7, 1965 A unilateral transducer that depends for its operation on the change in resistance of a hot wire produced by the cooling or heating effects of a sound wave.

HOTOL launch vehicle

NASA Thesaurus A British unmanned horizontal takeoff and landing single-stage-to-orbit launch vehicle. Later launches will be manned.

hour angle

Space Flight Glossary - JPL The angular distance of a celestial object measured westward along the celestial equator from the zenith crossing.

hour angle

NASA Thesaurus / NASA SP-7, 1965 Angular distance west of a celestial meridian or hour circle; the arc of the celestial equator, or the angle at the celestial pole, between the upper branch of a celestial meridian or hour circle and the hour circle of a celestial body or the vernal equinox, measured westward through 360 degrees.
Hour angle is usually further designated as local, Greenwich, or sidereal as the origin of measurement is the local or Greenwich celestial meridian or the hour circle of the vernal equinox. See meridian angle.

hour circle

NASA SP-7, 1965 On the celestial sphere, a great circle through the celestial poles. An hour circle through the zenith is called a celestial meridian. Also called circle of declination, circle of right ascension.

HRPT--High Resolution Picture Transmission

Global Land Information System Glossary - USGS HRPT data are full resolution image data transmitted to a ground station as they are collected. The average instantaneous field-of-view of 1.4 milliradians yields a HRPT ground resolution of approximately 1.1 km at the satellite nadir from the nominal orbit altitude of 833 km (517 mi).

HRV--High Resolution Visible Imaging Instrument

Global Land Information System Glossary - USGS The HRV instrument is a multispectral radiometer designed for SPOT spacecraft. The HRV instrument provides for high-resolution imaging in the visible and near-infrared portions of the electromagnetic spectrum. The first three SPOT satellites carry twin HRVs that operate in a number of viewing configurations and in different spectral modes. Some of those viewing configurations and spectral modes include one HRV only operating in a dual spectral mode (i.e., in both panchromatic mode and multispectral mode); two HRVs operating in the twin-viewing configuration (i.e., one HRV in panchromatic mode and one HRV in multispectral mode); and two HRVs operating independently of each other (i.e., not in twin-viewing configuration).

HTPB propellants

NASA Thesaurus Solid rocket propellants containing hydroxyl terminated polybutadiene as bonding material.

Hubble constant

NASA Thesaurus The rate at which the velocity of recession of the galaxies increases with distance.

Hubble constant; H₀

High Energy Astrophysics Dictionary- GSFC The constant which determines the relationship between the distance to a galaxy and its velocity of recession due to the expansion of the Universe. Since the Universe is self-gravitating, it is not truly constant. In cosmology, it is defined as H = (da/dt)/a, where a is the 4-radius of the Universe. When evaluated for the present, it is written H₀ = H_now.
The Hubble constant is not known to great accuracy (only within about a factor of 2), but is believed to lie somewhere between 50 and 100 km/s/Mpc.

Hubble's law

Imagine the Universe Dictionary - NASA GSFC A relationship discovered between distance and radial velocity. The further away a galaxy is from us, the faster it is receding from us. The constant of proportionality is the Hubble constant, H_0. The cause is interpreted as the expansion of spacetime itself.

Huggins bands

NASA SP-7, 1965 See absorption band.

hum

NASA Thesaurus / NASA SP-7, 1965 Electrical disturbance at the power-supply frequency or harmonics thereof.

human engineering

NASA SP-7, 1965 The activity or science of designing, building, or equipping mechanical devices or artificial environments to the anthropometric, physiological, or psychological requirements of the men who will use them.

human factors

NASA SP-7, 1965 The study of psychophysical, psychological, and physiological variables which affect man's performance in an operational system. See human engineering.

human factors engineering

NASA Thesaurus Application of information on physical and psychological characteristics of man to the design of devices and systems for human use. Used for ergonomics and human engineering.

human immunodeficiency virus

NASA Thesaurus A virus which attacks the human immune system and causes acquired immunodeficiency syndrome (AIDS).

human resources

NASA Thesaurus Those elements of support and capability that are provided by persons using their mental and physical capabilities.

humidity

NASA Thesaurus / NASA SP-7, 1965 1. The amount of water vapor in the air.
2. Specifically, relative humidity. See absolute humidity, dew point.

hunt

NASA SP-7, 1965 1. Of an aircraft, rocket, etc.: to weave about its flightpath, as if seeking a new direction of another angle of attack, specifically, to yaw back and forth.
2. Of a control surface: to rotate up and down or back and forth without being deflected by the pilot.
3. Of a control system: to oscillate about a selected value.
4. Of an indicator on a display: to swing back and forth or to oscillate, especially rather slowly.

hunting

NASA SP-7, 1965 Fluctuation about a midpoint due to instability, as oscillations of the needle of an instrument about the zero point, or alternate lead and lag of a synchronous motor with respect to the alternating current.

hurricanes

NASA Thesaurus Tropical cyclones, especially in the West Indies, in which the wind velocity equals or exceeds 64 knots (73 mph).

Huygens principle

NASA Thesaurus / NASA SP-7, 1965 A very general principle applying to all forms of wave motion which states that every point on the instantaneous position of an advancing phase front (wave front) may be regarded as a source of secondary spherical wavelets. The position of the phase front a moment later is then determined as the envelope of all the secondary wavelets (ad infinitum).
This principle, stated by Dutch physicist Christian Huygens (1629-95), is extremely useful in understanding effects due to refraction, reflection, diffraction, and scattering of all types of radiation, including sonic radiation as well as electromagnetic radiation and applying even to ocean-wave propagation.

Hya, Hyda

NASA SP-7, 1965 International Astronomical Union abbreviations for Hydra. See constellation.

hybrid diode:

Plasma Physics and Fusion Energy Glossary An ion diode that uses a field coil in series with the ion diode's accelerating gap to generate sufficient magnetic flux in the diode for electron control. The diode is a combination of the Applied-B diode's ion source and the Ampfion diode's field coil.

hybrid resonance

Plasma Physics and Fusion Energy Glossary A resonance in a magnetized plasma which involves aspects of both bunching of lighter species parallel to the magnetic field, characterized by the plasma frequency; and perpendicular particle motions (heavier species) characterized by the cyclotron frequency.

hybrid structures

NASA Thesaurus An assembly constructed of interconnected rigid and flexible structural shapes; designed to sustain dynamic, static, and other loads.

Hydi

NASA SP-7, 1965 International Astronomical Union abbreviations for Hydrus. See constellation

Hydra

NASA SP-7, 1965 (abbr Hya, Hyda)
See constellation.

hydration

NASA Thesaurus The formation of a compound by the combining of water with some other substance.

hydraulic fluids

NASA Thesaurus Liquids used in hydraulic systems for transmitting power.

hydroclimatology

NASA Thesaurus The study of the physical and often the chemical factors that characterize a particular environment.

hydrocracking

NASA Thesaurus Technique for the catalytic conversion of coal into liquid fuels.

hydrodynamic coefficients

NASA Thesaurus The factors producing motions in floating objects in liquids.

hydrodynamic ram effect

NASA Thesaurus The physical effect (force) transmitted to the walls of a liquid filled container by the action of a projectile penetrating the container and transferring its energy to the liquid as kinetic energy. The fluid, in turn, transfers this kinetic energy to the walls of the container, causing excessive structural damage.

hydrodynamics

NASA Thesaurus / NASA SP-7, 1965 The study of fluid motion. See aerodynamics.
Fluid here refers ambiguously to liquids and gases.

hydroelectricity

NASA Thesaurus Electric power produced by water power using water wheels, turbogenerators, or other conversion equipment.

hydrogen embrittlement

NASA Thesaurus A decrease in fracture strength of metals due to the incorporation of hydrogen in the metal lattice.

hydrogen engines

NASA Thesaurus Internal combustion engines utilizing gaseous hydrogen as the fuel.

hydrogen masers

NASA Thesaurus A stimulated emission device in which hydrogen gas provides an output signal with a high degree of stability and spectral purity.

hydrogen metabolism

NASA Thesaurus The physical and chemical processes by which an organism transforms the complex hydrogen components of foodstuffs into simple hydrogen compounds by disassimilation and catabolism in the production of energy.

hydrogen oxygen engines

NASA Thesaurus Engines using liquid hydrogen as fuel and liquid oxygen as oxidizer. Used for hydrox engines and lox-hydrogen engines.

hydrogen production

NASA Thesaurus Production of hydrogen for fuel purposes by photosynthetic, chemical, electrical, thermal, electrochemical, or other means.

hydrogeology

NASA Thesaurus The science that deals with subsurface waters and with related geologic aspects of surface waters. The term is also used in the more restrictive sense of ground water geology.

hydrography

NASA Thesaurus The science that deals with the physical aspects of all waters on the Earth's surface, especially the compilation of navigational charts.

hydrology

NASA Thesaurus The science that deals with global water (both liquid and solid), its properties, circulation, and distribution, on and under the Earth's surface and in the atmosphere through evapotranspiration or is discharged into oceans. In recent years, the scope of hydrology has been expanded to include environmental and economic aspects.

hydrology models

NASA Thesaurus Mathematical or physical representations by which the circulation, distribution, and properties of the waters of the Earth can be studied.

hydromagnetic wave

Solar Physics Glossary - NASA GSFC A wave in which both the plasma and magnetic field oscillate.

hydromagnetics

NASA SP-7, 1965 = magnetohydrodynamics.

hydrometeor

NASA SP-7, 1965 Any product of condensation or sublimation of atmospheric water vapor, such as rain, snow, fog, or frost. See meteor, sense 2.

hydrometeors

NASA Thesaurus A minute droplet of water or crystal of ice falling through or suspended in the atmosphere.

hydrometer

NASA Thesaurus / NASA SP-7, 1965 An instrument used for measuring the specific gravity of a liquid.

hydrophone

NASA Thesaurus / NASA SP-7, 1965 A microphone suitable for use in water or other liquid.

hydroponics

NASA Thesaurus Growing of plants in a nutrient with the mechanical support of an inert medium such as sand.

hydropyrolysis

NASA Thesaurus A coal-to-liquid process in which bituminous coal, lignite, tars, sand and related materials are rapidly heated to 1000-1100 degrees K in pressurized hydrogen gasification reactors to generate pure methane.

hydrosphere

NASA SP-7, 1965 That part of the earth that consists of the oceans, seas, lakes, and rivers; a similar part of any other spatial body if such a body exists.

hydrostatic equation

NASA SP-7, 1965 In numerical equations, the form assumed by the vertical component of the vector equation of motion when all coriolis, earth- curvature, frictional, and vertical-acceleration terms are considered negligible compared with those involving the vertical pressure force and the force of gravity. Thus,

$dP = -$ gdZ

where P is the atmospheric pressure; is the density; g is the acceleration of gravity; and Z is the geometric light.

For cyclonic-scale motions the error committed in applying the hydrostatic equation to the earth's atmosphere is less than 0.01 percent. Strong vertical accelerations in thunderstorms and mountain waves may be 1 percent of gravity or more in extreme situations.

hydrostatic equilibrium

NASA SP-7, 1965 1. The state of a fluid whose surfaces of constant pressure and constant mass (or density) coincide and are horizontal throughout. Complete balance exists between the force of gravity and the pressure force. See hydrostatic equation.
2. Of a rotating body, a state in which the body maintains, or returns to, the figure generated by this rotation in spite of small disturbances.

hydrostatic pressure

NASA Thesaurus A state of stress in which all the principal stresses are equal (and there is no shear stress).

hydrothermal stress analysis

NASA Thesaurus The evaluation of the combined effects of temperature-humidity cycling.

hydrothermal systems

NASA Thesaurus Energy systems utilizing hot water from geysers, hot springs, solar heating, and other sources.

Hydrus

NASA SP-7, 1965 (abbr Hyi, Hydi)
See constellation.

hydyne

NASA SP-7, 1965 A hydrazine-base liquid rocket fuel. Also called hidyne.

hygral properties

NASA Thesaurus The affinity of something for moisture.

hygrometers

NASA Thesaurus Instruments for measuring the humidity of the atmosphere.

Hyi, Hydi

NASA SP-7, 1965 International Astronomical Union abbreviations for Hydrus. See constellation.

hyperbaric

NASA SP-7, 1965 Pertaining to breathing atmosphere pressure above sea level normal.

hyperbaric chambers

NASA Thesaurus Chambers used to induce a decrease in ambient pressure as would occur in ascending to altitude. This type of chanber is primarily used for training and experimental purposes. It is also called an altitude chamber or a decompression chamber.

hyperbarism

NASA SP-7, 1965 Disturbances in the body resulting from an excess of the ambient pressure over that within the body fluids, tissues, and cavities.

hyperbola

NASA SP-7, 1965 An open curve with two branches, all points of which have a constant difference in distance from two fixed points called focuses.

hyperbolas

NASA Thesaurus Open curves with two branches, all points of which have a constant difference in distance from two fixed points called focuses.

hyperbolic

NASA SP-7, 1965 Of or pertaining to a hyperbola.

hyperbolic Dovap

NASA SP-7, 1965 (abbr Hyperdop)
A system utilizing four or more Dovap stations with a common reference signal which is not coherent with the interrogation signal.
Hyperboloids of position are obtained by differencing phase of one station against another. Space position is computed by intersection of three or more hyperboloids of position.

hyperbolic error

NASA SP-7, 1965 The error in an interferometer system arising from the assumption that the directions of the wave fronts incident at two antennas of a base line are parallel, whereby the equiphase path is a cone.
Mathematically, the equiphase path is a hyperbola.

hyperbolic fix

NASA SP-7, 1965 A fix established by means of hyperbolic lines of position.

hyperbolic guidance

NASA SP-7, 1965 The guidance of a rocket or the like in which radio signals, transmitted simultaneously from two ground stations, arrive at the guided object with a constant time difference, thereby establishing a hyperbolic line of position which the object follows.

hyperbolic line of position

NASA SP-7, 1965 A line of position in the shape of a hyperbola, determined by measuring the difference in distance to two fixed points. Loran lines of position are an example.

hyperbolic navigation

NASA Thesaurus / NASA SP-7, 1965 Radio navigation in which a hyperbolic line of position is established by signals received from two stations at a constant time difference.

hyperbolic system

NASA SP-7, 1965 A system where lines of position are determined from time or phase differences relative to two or more fixed stations which are the focuses of hyperbolas.
In a three-dimensional system, the lines of position become hyperbolic surfaces of position.

hyperbolic velocity

NASA SP-7, 1965 A velocity sufficient to allow escape from the solar system. Comets unless captured by the sun have hyperbolic velocities and their trajectories are hyperbolas.

hypercube multiprocessors

NASA Thesaurus Distributed-memory, message-passing multiprocessors designed to reduce the number of interconnections compared to the number of processors. Other simple geometries such as rings, meshes, or trees of processors can be embedded in hypercubes.

Hyperdop (abbr)

NASA SP-7, 1965 = hyperbolic Dovap.

hypergolic propellants

NASA SP-7, 1965 Rocket propellants that ignite spontaneously when mixed with each other.

Hyperion

NASA Thesaurus / NASA SP-7, 1965 A satellite of Saturn orbiting at a mean distance of 1,481,000 kilometers.

hyperkinesia

NASA Thesaurus Excessive exercise, that is often accompanied by uncontrollable muscular movement.

hyperon

NASA Thesaurus / NASA SP-7, 1965 In the classification of subatomic particles according to mass, the heaviest of such particles. Compare lepton, meson, nucleon.
Some large and highly unstable components of cosmic rays are hyperons.

hyperoxia

NASA Thesaurus / NASA SP-7, 1965 A condition in which the total oxygen content of the body is increased above that normally existing at sea level.

hypersonic

NASA SP-7, 1965 1. Pertaining to hypersonic flow.
2. Pertaining to speeds of Mach 5 or greater.

hypersonic flow

NASA Thesaurus / NASA SP-7, 1965 In aerodynamics, flow of a fluid over a body at speeds much greater than the speed of sound and in which the shock waves start at a finite distance from the surface of the body. Compare supersonic flow.

hypersonic glider

NASA Thesaurus / NASA SP-7, 1965 An unpowered vehicle, specifically a reentry vehicle, designed to fly at hypersonic flow.

hypersonics

NASA Thesaurus / NASA SP-7, 1965 That branch of aerodynamics that deals with hypersonic flow.

hypertext

Global Land Information System Glossary - USGS The use of links between related words, graphics, or documents that allow the user to jump to associated topics or definitions when reading menus or help files.

hypervelocity

NASA Thesaurus / NASA SP-7, 1965 Extremely high velocity.
Applied by physicists to speeds approaching the speed of light, but generally implies speeds of the order of satellite speed and greater.

hyperventilation

NASA Thesaurus / NASA SP-7, 1965 Overbreathing. A respiratory-minute volume, or pulmonary ventilation, that is greater than normal.
Hyperventilation often results in an abnormal loss of carbon dioxide from the lungs and blood, which may lead to dizziness, confusion, and muscular cramps.

hyperventilation syndrome

NASA SP-7, 1965 The syndrome of blurring of vision, (feeling of) tingling of the extremities, faintness, and dizziness, which may progress to unconsciousness, and convulsions, caused by reduction of the normal carbon dioxide tension of the human body, due to increased pulmonary ventilation.

hypobaric

NASA SP-7, 1965 Pertaining to low atmospheric pressure, particularly the low atmospheric pressure of high altitudes.

hypobarism

NASA SP-7, 1965 Disturbances resulting from a decrease of ambient pressure to less than that within the body fluids, tissues, and cavities.

hypocapnia

NASA Thesaurus / NASA SP-7, 1965 Deficiency of carbon dioxide in the blood and body tissues, which may result in dizziness, confusion, and muscular cramps.

hypothetical parallax

NASA SP-7, 1965 = dynamic parallax.

hypoventilation

NASA Thesaurus / NASA SP-7, 1965 A respiratory-minute volume, or pulmonary ventilation, that is less than normal. Also called underbreathing.

hypoxaemia

NASA SP-7, 1965 The condition of reduction of the normal oxygen tension in the blood. Also called anoxaemia.

hypoxemia

NASA Thesaurus The condition of reduction of the normal oxygen tension in the blood.

hypoxia

NASA Thesaurus / NASA SP-7, 1965 Oxygen want or deficiency; any state wherein a physiologically inadequate amount of oxygen is available to, or utilized by, tissue without respect to cause or degree. Compare anoxia.

hypsography

Global Land Information System Glossary - USGS The scientific study of the Earth's topologic configuration above sea level, especially the measurement and mapping of land elevation.

hysteresis

NASA Thesaurus / NASA SP-7, 1965 1. Any of several effects resembling a kind of internal friction, accompanied by the generation of heat within the substance affected.
Magnetic hystersis occurs when a ferromagnetic substance is subjected to a varying magnetic intensity; electric hysteresis occurs when a dielectric is subjected to a varying electric intensity. Elastic hysteresis is the internal friction in an elastic solid subjected to varying stress.
2. The delay of an indicator in registering a change in a parameter being measured.

Hz

Space Flight Glossary - JPL Hertz, cycles per second.

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Condition	Pressure Range
high vacuum	10^-3 to 10^-6 torr (microtorr range)
very high vacuum	10^-6 to 10^-9 torr (nanotorr range)
ultrahigh vacuum	10^-9 torr and below

Aerospace Science & Technology Dictionary

Aerospace Science
&
Technology Dictionary