H

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.
Greek symbols may not appear correctly in some browsers. For example a gamma may appear as γ.

Hagen-Poiseuille flow = Poiseuille flow.

half life

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 t_(1/2) = (ln 2) / λ where λ is the decay constant.

half-period zone = Fresnel zone.

half-power points

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

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 that plane in which the radiation intensity is one-half the maximum value of the lobe.

half-width

See line width.

Hall constant

In an electrical conductor, the constant of proportionality R in the relation E_h = RJ X H where E_h is 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

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 mobility

A measure of the flow of charged particles perpendicular to both a magnetic and an electric field.

hangfire

A faulty condition in the ignition system of a rocket engine.

hard landing

An impact landing of a spacecraft on the surface of a planet or natural satellite destroying all equipment except possibly a very rugged package.

hardness

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.

hard radiation

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

A very high vacuum, usually considered to be a pressure less than about 10E7 torr.

hardware

Physical equipment as contrasted to ideas or design that may exist only on paper.

hard wire telemetry = wire link telemetry.

harmonic

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

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

A machine which resolves a periodic curve into its harmonic constituents.

A machine performing the opposite function is called a harmonic synthesizer.

harmonic distortion

Nonlinear distortion characterized by the appearance in the output of multiples of the fundamental when the input wave is sinusoidal.

harmonic function

Any solution of the Laplace equation.

harmonic motion

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.

harmonics of the earth's gravitational fields

A series representing the gravitational potentials of the earth in which the terms form a harmonic progression.

harmonic synthesizer

A machine which combines elementary harmonic constituents into a single periodic function.

A machine performing the opposite function is called a harmonic analyzer.

hartley

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 ₂ (10).
(log ₂ (10) = 3.323), or one decimal digit.

Hartley bands

See absorption band.

hazemeter = transmissometer.

H-display

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.

heading

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

See plan position indicator.

head pressure = inlet pressure.

head-to-foot acceleration

See physiological acceleration.

heat

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 balance

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 = thermal barrier.

heat conductivity = thermal conductivity.

heat dump = heat sink.

heat engine

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

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 function = enthalpy.

heat index

The difference between the absolute visual magnitude of a star and the absolute radiometric magnitude (M_v - M_r).

heat of ablation

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 (q_c + q_r - σεT_w⁴)/m where q_c is convective heat transfer in the absence of ablation; q_r is radiative heat transfer from hot gases to ablation material; σεT_w⁴ is rate of heat rejection by radiation from external surface of ablation material; and m 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 &<; σεT_w⁴, for moderate values of stream enthalpy h_s, heat of ablation is given by H_v + μ (h_s - h_w) where H_s is heat required to cause a unit weight of mass to be injected into boundary layer; μ 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

See latent heat.

heat of sublimation

See latent heat.

heat of vaporization

See latent heat.

heat pulse

Specifically, the sudden rise and subsequent fall in the temperature of a vehicle on reentry.

heat shield

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 sink

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

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 coefficient

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.

heat treatment

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.

heavenly body = celestial body.

Heaviside layer = E-layer.

heavy cosmic-ray primaries

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 = deuterium.

heavy ion = large ion.

heavy water

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 20 degrees 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 (abbr h)

A prefix meaning multiplied by 100.

hectometric wave

See frequency bands.

height (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 = antenna effect.

height gain

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.

helical antenna

An antenna used where circular polarization is required. The driven element consists of a helix supported above a ground plane.

helical scanning

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

heliocentric

Relative to the sun as a center, as a heliocentric orbit.

heliocentric parallax

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

Referring to positions on the sun measured in latitude from the sun's equator and in longitude from a reference meridian.

Helmholtz free energy = Helmholtz function.

Helmholtz function (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 theorem

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).

hemispherical

Referring to thermal radiation properties, in all possible directions from a flat surface.

hemispherical emittance (symbol ε_h, E_h)

The ratio of the emissive power of a specimen to that of a black body at the same temperature, considering radiation emitted in all possible directions.

hemmungspunkt = stopping point.

henry (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.

Her, Herc

International Astronomical Union abbreviations for Hercules. See constellation.

Hercules (abbr Her, Herc)

See constellation.

hertz (abbr Hz)

The unit of frequency, cycles per second.

Hertzian waves

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

Herzberg bands

See absorption band.

heterodyne

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.

heterosphere

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 = sexidecimal notation.

hibernating spacecraft

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

Variant of hydyne.

high frequency (abbr HF)

See frequency bands.

high-intensity gamma

A level a gamma radiation flux on the order of 10E4 roentgens or higher.

high-pass filter

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

high-precision shoran (abbr hiran)

See shoran.

high-speed motion-picture photography

The picture-taking frequency range from 32 to 500 pictures per second.

high vacuum

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
very high vacuum	10-6 to 10-9 torr
ultrahigh vacuum	10-9 torr and below

H-indicator = H-display.

hiran (abbr) = high precision shoran

See shoran.

hiss

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

hohlraum

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 black-body radiation at the temperature of the interior of the container.

Hohmann orbit

A minimum energy transfer orbit.

hold

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 = holddown test.

holddown test

The testing of some system or subsystem in a rocket while the rocket is firing but restrained in a test stand.

holding beam

An electron beam which regenerates the electrostatic charges stored in an electrostatic-storage tube.

hole

A mobile vacancy in the electronic valence structure of a semiconductor which acts like an electron with a positive charge.

home

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 = homing beacon.

homing

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

A beacon providing homing guidance. Also called homer.

homing guidance

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.

homogeneous atmosphere

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 barotrophy.

homologous turbulence

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

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.

homosphere

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

A lightweight strengthening material of a structure resembling a honeycomb mesh. See sandwich construction.

hop

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

See absorption band.

Hor, Horo

International Astronomical Union abbreviations for Horologium. See constellation.

horizon

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

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

horizontal parallax

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 scanning

In radar scanning, rotating the antenna in azimuth around the horizon or in a sector. Also called searchlighting.

horizontal stratification

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

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 = horn.

horn radiator = horn.

Horo

International Astronomical Union abbreviation for Horologium. See constellation.

Horologium (abbr Hor, Horo)

See constellation.

hot cathode

A cathode that functions primarily by the process of thermionic emission. Also called thermionic cathode.

hot-cathode ionization gage

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 = hot-cathode ionization gage.

hot test

A propulsion system test conducted by actually firing the propellants. Compare cold-flow test.

hot-wire transducer

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.

hour angle

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

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.

H-scan = H-display.

H-scope = H-display.

Huggins bands

See absorption band.

hum

Electrical disturbance at the power-supply frequency or harmonics thereof.

human engineering

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

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

humidity

1. The amount of water vapor in the air.

2. Specifically, relative humidity. See absolute humidity, dew point.

hunt

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

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.

Huygens principle

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.

Huygens wavelets

The assemblage of secondary waves asserted by Huygens to be set up at each instant at all points on the advancing surface of a wave, or phase front.

Many phenomena of wave optics can be neatly explained on this assumption ( Huygens principle) of the continual creation of new wavelets and the subsequent destructive or constructive interference between the wavelets to set up the next-imagined state of the advancing wave front.

Hya, Hyda

International Astronomical Union abbreviations for Hydra. See constellation.

Hydi

International Astronomical Union abbreviations for Hydrus. See constellation

Hydra (abbr Hya, Hyda)

See constellation.

hydrodynamics

The study of fluid motion. See aerodynamics.

Fluid here refers ambiguously to liquids and gases.

hydromagnetics = magnetohydrodynamics.

hydrometeor

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

hydrometer

An instrument used for measuring the specific gravity of a liquid.

hydrophone

A microphone suitable for use in water or other liquid.

hydrosphere

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

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 = -pgdZ where P is the atmospheric pressure; p 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

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.

Hydrus (abbr Hyi, Hydi)

See constellation.

hydyne

A hydrazine-base liquid rocket fuel. Also called hidyne.

Hyi, Hydi

International Astronomical Union abbreviations for Hydrus. See constellation.

hyperbaric

Pertaining to breathing atmosphere pressure above sea level normal.

hyperbarism

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

hyperbola

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

hyperbolic

Of or pertaining to a hyperbola.

hyperbolic Dovap (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

The error in an interferometer system arising from the assumption that the directions of the wave fronts incident at two antennas of a baseline are parallel, whereby the equiphase path is a cone.

Mathematically, the equiphase path is a hyperbola.

hyperbolic fix

A fix established by means of hyperbolic lines of position.

hyperbolic guidance

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

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

Radio navigation in which a hyperbolic line of position is established by signals received from two stations at a constant time difference.

hyperbolic system

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

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

Hyperdop (abbr) = hyperbolic Dovap.

hypergolic propellants

Rocket propellants that ignite spontaneously when mixed with each other.

Hyperion

A satellite of Saturn orbiting at a mean distance of 1,481,000 kilometers.

hyperon

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

A condition in which the total oxygen content of the body is increased above that normally existing at sea level.

hypersonic

1. Pertaining to hypersonic flow.

2. Pertaining to speeds of Mach 5 or greater.

hypersonic flow

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

An unpowered vehicle, specifically a reentry vehicle, designed to fly at hypersonic flow.

hypersonics

That branch of aerodynamics that deals with hypersonic flow.

hypervelocity

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

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

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

Pertaining to low atmospheric pressure, particularly the low atmospheric pressure of high altitudes.

hypobarism

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

hypocapnia

Deficiency of carbon dioxide in the blood and body tissues, which may result in dizziness, confusion, and muscular cramps.

hypothetical parallax = dynamic parallax.

hypoventilation

A respiratory-minute volume, or pulmonary ventilation, that is less than normal. Also called underbreathing.

hypoxaemia

The condition of reduction of the normal oxygen tension in the blood. Also called anoxaemia.

hypoxia

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.

hysteresis

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.