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- A satellite of Saturn orbiting at a mean distance of 3,562,000 kilometers.
- ICAO (abbr) = International Civil Aviation Organization.
Usually pronounced as a word.
- ICAO Standard Atmosphere
- See standard
- ice frost
- A thickness of ice that gathers on the outside of a rocket over
surfaces supercooled as by liquid oxygen inside the vehicle.
- This ice frost is quickly shaken loose and falls to the ground once the
rocket begins its ascent.
- ice point
- The temperature at which a mixture of air-saturated pure water and pure
ice may exist in equilibrium at a pressure of one standard atmosphere.
- By decision of the Tenth General Conference on Weights and Measures,
Paris, October 1954 the ice point was established as 273.15 degrees K.
- ICW (abbr) = interrupted continuous wave.
- ISCU (abbr) = International Council of Scientific Unions.
Usually pronounced as a word.
- ideal exhaust velocity
- The exhaust velocity of an ideal
- ideal fluid
- 1. = perfect
- 2. = inviscid
- ideal gas
- A gas which conforms to Boyle law and
has zero heat of free expansion (or also obeys Charles
law). Also called perfect gas.
- ideal gas laws = gas laws.
- ideal nozzle
- The nozzle of an ideal
rocket, or a nozzle designed according to the ideal gas
- ideal rocket
- A theoretical rocket
postulated for parameters that are corrected in practice.
- An ideal rocket assumes a homogeneous and invariant propellant,
observance of the perfect
gas laws, no friction, no heat transfer across the rocket wall, an axially
directed velocity of all exhaust gases, a uniform gas velocity across every
section normal to the nozzle axis, and chemical equilibrium established in the
combustion chamber and maintained in the nozzle.
- ideal transducer
- For connecting a specified source to a specified load, a hypothetical
passive transducer that transfers the maximum possible power from the source
to the load.
- In linear electric circuits and analogous cases, this is equivalent to
a transducer which (1) dissipates no energy and (2) when connected to the
specified source and load presents to each its conjugate.
- ideal velocity
- The velocity acquired by an ideal
rocket in field free space, under the
influence of no external forces except the thrust force.
- In radar, a display in which a target appears
as a complete circle when the radar antenna is
correctly pointed at it and in which the radius of the circle is proportional
to target distance. When not correctly pointing at the target, the circle
reduces to a segment of a circle, the segment length being inversely
proportional to the magnitude of the pointing error and its angular position
being reciprocal to the direction of pointing error. Also called I-scan,
- IGC-1959 (abbr) = International Geophysical Cooperation,
- igneous meteor
- In U.S. weather observing practice, a visible electrical discharge in the
atmosphere. Compare electrometeor.
- Lightning is the most common and important type, but types of corona
discharge are also included.
- A device used to begin combustion, such as a spark plug in the combustion
chamber of a jet engine, or a squib used to ignite the fuel in a rocket.
- ignition delay
- The time lapse occurring between the instance of an igniting action of a
fuel and the onset of a specified burning reaction. Also called ignition
- ignition lag = ignition delay.
- In computer terminology, a code group or character
which indicates that the associated information is to be disregarded.
- Igor (abbr)
- Intercept ground optical recorder. A long-focal-length telescopic camera
used to observe attitude and
other details of a rocket in
- IGY (abbr) = International Geophysical Year.
- I-indicator = I-display.
- The total luminous flux received on a unit area of a given real or
imaginary surface, expressed in such units as the footcandle, lux, or phot.
Illuminance is analogous to irradiance, but is to be distinguished from the
latter in that illuminance refers only to light and contains the luminous
efficiency weighting factor necessitated by the nonlinear wavelength-response
of the human eye. Compare luminous
- The only difference between illuminance and illumination is that the
latter always refers to light incident upon a material surface. A distinction
should be drawn, as well, between illuminance and luminance. The latter is a
measure of the light coming from a surface; thus, for a surface which is not
self-luminance, luminance is entirely dependent upon the illuminance upon that
surface and its reflection properties.
- See illumination,
- illumonometer = photometer.
- ILS (abbr) = instrument landing system
- 1. A single collision of
one mass in motion with a second mass which may be either in motion or at
- 2. Specifically, the action or event of an object, such as a rocket, striking
the surface of a planet or natural satellite, or striking another object; the
time of this event, as in from launch to impact.
- 3. To strike a surface or an object.
- 4. Of a rocket or fallaway section: To collide with a surface or object,
as in the rocket impacted 10 minutes after launch.
- impact acceleration
- The acceleration
generated by very sudden starts or stops of a vehicle.
- The term is usually applied in the context of physiological
- impact area
- The area in which a rocket strikes the surface of the earth or other
- Used specifically in reference to the impact area of a rocket range.
- impact line
- An imaginary line on the outside of a destruct
line and running parallel to it, which marks the outer limits of impact for a
missile destroyed under destruct procedures.
- impact microphone
- An instrument that picks up the vibration of an object impinging upon
another, used especially on space probes to record the impact of small meteoroids.
- impact predictor
- A device which takes information from a trajectory
measuring system and continuously computes the point (in real time) at
which the rocket will strike the earth; based on the assumption that the
rocket power is shut off at that instant and the remaining trajectory is ballistic in
- impact pressure
- 1. That pressure of a
brought to rest which is in excess of the pressure the fluid has when it does
not flow, i.e., total
pressure less static
- Impact pressure is equal to dynamic pressure in incompressible flow,
but in compressible flow impact pressure includes the pressure change owing to
the compressibility effect.
- 2. A measured quantity obtained by placing an open-ended tube, known as an
impact tube or pitot tube,
in a gas stream and noting the pressure in the tube on a suitable manometer.
- Since the pressure is exerted at a stagnation
point, the impact pressure is sometimes referred to as the stagnation
pressure or total pressure.
- impact strength or impact energy
- The amount of energy required to fracture a material.
- The type of specimen and the testing conditions affect the values and
therefore should be specified.
- impact tube
- See impact
pressure, sense 2.
- 1. A device that imparts motion to a fluid; specifically, in a centrifugal
compressor, a rotary disk which, faced on one or both sides with radial
vanes, accelerates the incoming fluid outward into a diffuser. Also
called impeller wheel.
- 2. That part of a centrifugal compressor comprising this disk and its
- impeller blade = impeller vane.
- impeller vane
- Any one of the vanes on the impeller of a
compressor, serving to take in air and accelerate it radially outward.
Also called impeller blade. Compare compressor
- impeller wheel
- The vaned rotary disk in a centrifugal compressor. Usually called the
- impingement rate
- The rate per square centimeter per second at which molecules
strike a plane surface in a gas at rest. Also
called rate of incidence.
- impinging-stream injector
- In a liquid-propellant
rocket engine, a device that injects the fuel and oxidizer into the combustion
chamber in such a manner that the streams of fluid intersect one another.
- The rapid inward collapsing of the walls of a vacuum system or device as
the result of failure of the walls to sustain the ambient pressure.
- 1. The product of a force and the time during which the force is applied;
more specifically, the impulse is
where the force F is time dependent and
equal to zero before time t1 and after time t2.
- 2. symbol It = total
impulse. Compare specific
- impulse noise
generated in discrete energy bursts, not of random nature, which has a
characteristic wave shape of its own.
- impulse turbine
- A type of turbine having
shaped so that the wheel is turned from the impact of the fluid against the
blades, with no pressure drop occurring across the blades.
- inactive leg
- An electrical element within
which does not change its electrical characteristics as a function of the
- Specifically applied to elements which are employed to complete a
Wheatstone bridge in certain transducers.
- Emission of
light due to high temperature of the emitting material. Any other emission of
light is called luminescence.
- inch (abbr in.)
- Exactly 2.540 centimeters.
- Prior to July 1, 1959, the inch was 2.54005 centimeters although the
conversion factor 2.540 has actually been in use in industry in the United
States since 1933.
- 1. Partial coincidence, as a circle and a tangent line.
- 2. The impingement of a ray on a surface. See angle of
- incident ray
- A ray
impinging on a surface.
- 1. = magnetic
- 2. ( symbol i ). The angle between the plane of an orbit and a
- The equator is the
reference plane for geocentric orbits and the ecliptic is
the reference plane for heliocentric orbits.
- included angle
- In aerodynamics, the angle between free stream
velocity and the longitudinal
axis of the vehicle.
- incoming solar radiation
- Full term for insolation.
- incourse guidance = midcourse guidance.
- A change in the value of a variable. A negative increment is also called
- Ind, Indi
- International Astronomical Union abbreviations for Indus. See constellation.
- independent variable
- Any of those variables of a problem, chosen according to convenience,
which may arbitrarily be specified, and which then determine the other or
dependent variables of the problem.
- The independent variables are often called the coordinates,
particularly in problems involving motion in space. Dependent and independent
variables can be interchanges, e.g., height and pressure.
- index of absorption = absorptive index.
- index of refraction (symbol n)
- 1. A measure of the amount of refraction
(a property of a dielectric
substance). It is the ratio of the wavelength or phase velocity of an electromagnetic
wave in a vacuum to that in the substance. Also called refractive
index, absolute index of refraction, absolute refractive index, refractivity.
index of refraction, N-unit, potential
index of refraction.
- It can be a function of wavelength, temperature, and pressure. If the
substance is nonabsorbing and nonmagnetic at any wavelength, then n2 is equal to the dielectric
constant at that wavelength. The complex index of refraction is obtained
when the attenuation of the wave power radian, called the absorptive index k,
is paired with the index of refraction. It is written
n* = n (1 - ik) When the wave passes from one medium n1 to another n2,
the angle of incidence φ and the angle of refraction φ', both measured with respect to the normal to the
interface, are related by
sin φ / sin φ' = n1* / n2* = constant
which becomes, for a nonabsorbing medium, the
ratios of the (noncomplex) indices of refraction. In the particular case that
medium 2 is a vacuum, this ratio is the index of refraction of medium 1. This
is known as Snell law, named after Willebrord Snell who discovered it about
- 2. A measure of the amount of refraction
experienced by a ray as it passes through a refractive interface, i.e., a
surface separating two media of different densities. It is the ratio of the
absolute indices of refraction of the two media (see sense 1 above). Also
called refractive index, relative index of refraction.
- International Astronomical Union abbreviation for Indus. See constellation.
- A device which makes information available but in which there is no
provision for storage of such information, as a radar indicator.
- indirect wave
- Any radio
wave which arrives by an indirect path, having undergone an abrupt change
of direction by refraction
or reflection. See sky wave.
- See tektite.
- induced magnetism
acquired by a piece of magnetic material while it is in a magnetic
field. See permanent
- Indus (abbr Ind, Indi)
- See constellation.
- inelastic collision
- A collision between two particles in which changes occur both in the
internal energy of one or both of the particles and in the sums, before and
after collision, of their kinetic
- inert atmosphere
- A gaseous medium that because of its lack of chemical reaction is used to
enclose tests or equipment..
- inert gas
- Any one of six gases, helium, neon, argon, krypton, xenon, and radon, all
of whose shells of planetary electrons contain stable numbers of electrons so
that the atoms are almost completely chemically inactive. Also called rare
- All these gases are found in the earth's atmosphere but, with the
exception of argon, are found only in very small amounts. Fluorine compounds
of the rare gases have only recently been discovered.
- Resistance to acceleration.
- inertia force = inertial force.
- inertial axes
- Axes that
are not undergoing acceleration
- inertial coordinate system
- A system in which the (vector) momentum of a
particle is conserved in the absence of external forces. Thus, only in an
inertial system can Newton
laws of motion be appropriately applied.
- When relative
coordinate systems are used, moving with respect to the inertial system,
apparent forces arise in Newton laws, such as the coriolis
- inertial force
- A force is
a given coordinate system arising from the inertia of a parcel moving with
respect to another coordinate system. The inertial force is proportional and
directionally opposite to the accelerating force. Also called inertia
- For example, the coriolis
acceleration on a parcel moving with respect to a coordinate system fixed
in space becomes an inertial force, the coriolis
force, in a coordinate system rotating with the earth.
- inertial guidance
- Guidance by
means of the measurement and integration of acceleration from within the
- inertial navigation
reckoning performed automatically by a device which gives a continuous
indication of position by integration of acceleration since leaving a starting
- inertial orbit
- The type of orbit described
by all celestial obides, in conformance with Kepler laws
of celestial motion.
- This applies to all satellites and spacecraft providing they are not
under any type of propulsive power.
- inertial space
- A stationary frame of reference, or set of coordinates,
for calculating trajectories.
- inertial velocity
- Velocity with respect to a fixed system of coordinates.
- inferior conjunction
- The conjunction
of an inferior
planet and the sun when the planet is between the earth and the sun.
- inferior mirage
- A spurious image of an object formed below the true position of that
object by abnormal refraction
conditions along the line of sight; one of the most common of all types of
mirage and the opposite of a superior
- The requirement for the appearance of an inferior mirage is a very
large lapse rate of temperature in the layer of air containing the line of
sight from observer to object. Compare sinking, stooping.
- inferior planets
- The planets with orbits smaller
than that of the earth: Mercury and Venus.
- inferior transit = lower transit.
- 1. A point, line, or region, beyond measurable limits.
- A source of light is regarded as at infinity if it is at such a great
distance that rays from it can be considered parallel. See parallax.
- 2. Any quantity larger than the largest quantity which can be stored in a
register of a specific computer.
- Reversal of direction of curvature.
- A point at which reversal takes place is called point of inflection or
- inflection point
- See inflection.
- in-flight start
- An engine ignition sequence after take-off and during flight. Compare air start, ground
- This term includes starts both within and above the sensible
- Any facts or data which can be used, transferred, or communicated.
- information content
- In a message or a signal from a source, the negative of the logarithm of
the probability that this particular message or symbol will be emitted from
- The choice of logarithmic base determines the unit of information
content. See bit
The probability of a given message or symbol being emitted may depend on one
or more preceding messages or symbols. The quantity has been called
- information gate
- In telemetry, a
device which, when triggered, allows information pulses to pass.
- A live animal other than man used as a substitute for a human in
- infrared (abbr IR)
- 1. = infrared
- 2. Pertaining to infrared
radiation, as an infrared absorber.
- infrared radiation (abbr IR)
radiation lying in the wavelength interval from about 75 microns to an
indefinite upper boundary sometimes arbitrarily set at 1000 microns (0.01
centimeter). Also called long-wave radiation.
- At the lower limit of this interval, the infrared radiation spectrum is
bounded by visible radiation, whereas on its upper limit it is bounded by
microwave radiation of the type important in radar technology. See electromagnetic
spectrum. Whereas visible radiation is generated primarily by intra-atomic
processes, infrared radiation is generated almost wholly by larger scale
intramolecular processes, chiefly molecular rotations and internal vibrations
of many types. Electrically symmetric molecules, such as the nitrogen and
oxygen molecules which comprise most of the earth's atmosphere, are not
capable of absorbing or emitting infrared radiation, but several of the
triatomic gases, such as water vapor, carbon dioxide, and ozone, are infrared
active and play important roles in the propagation of infrared radiation in
the atmosphere. Since a black body at terrestrial temperature radiates with
maximum intensity in the infrared spectrum (near 10 microns), there exist a
complex system of infrared radiation currents within the earth's atmosphere.
- infrasonic frequency
- A frequency below the audiofrequency
- The word infrasonic may be used as a modifier to indicate a device or
system intended to operate at an infrasonic frequency. The term subsonic was
once used in acoustics synonymously with infrasonic; such usage is now
- infrasonic sound
- Sound whose frequency is
below the lower pitch limit, below about 15 cycles per second.
- inherited error
- The error in initial values used in a computation; especially the error
introduced from the previous steps in a step-by-step integration.
- Anything that inhibits; specifically, a substance bonded, taped, or dip
dried onto a solid
propellant to restrict the burning surface and to give direction to the
burning process. See restricted
- inhibitor gate
- In telemetry, a
device which, when triggered, prevents information pulses from
- initial mass
- The mass of
vehicle at launch.
- initial-value problem
- A dynamical problem whose solution determines the state of a system at all
times subsequent to a given time at which the state of the system is specified
by given initial conditions. Also called transient problem. See
boundary value problem.
- The initial-value problem is contrasted with the steady-state problem,
in which the state of the system remains unchanged in time.
- initial velocity
- The velocity of
anything at the beginning of a specific phase of its motion.
- 1. The introduction of fuel, fuel and air, fuel and oxidizer, water, or
other substance into an engine induction system or combustion
- 2. The time following launching when nongravitational forces (thrust,
lift, and drag) become negligible in their effort on the trajectory
of a rocket or spacecraft.
- 3. The process of putting a spacecraft up to escape
- A device that propels fuel or propellant into a combustion chamber under
pressure other than atmospheric. See impinging-stream
- An entrance or orifice for the admission of fluid.
- Frequently used in compounds, such as inlet air, inlet air temperature,
inlet casing, inlet duct, inlet guide van, inlet port, inlet valve, etc.
- inlet pressure
- In connection with performance data on pumps, when not otherwise
specified, the total static
pressure measured in a standard testing chamber by a vacuum gage
located near the inlet port. Also called intake pressure, fine pressure,
- inner liner
- Specifically, a tube mounted coaxially inside the outer cover or shell of
chamber. Also called a flame tube or a combustion-chamber liner.
- inner planets
- The four planets nearest
the sun: Mercury, Venus, Earth, and Mars. See planet, table.
- inner product = scalar product.
- in phase
- The condition of two or more cyclic motions which are at the same part of
their cycles at the same instant. Also called in step.
- Two or more cyclic motions which are not at the same part of their
cycles at the same instant are said to be out of phase or out of step.
- 1. The path through which information
is applied to any device.
- 2. The means for supplying information to a machine. See input
- 3. Information or energy entering
into a system. Compare output.
- 4. The quantity to be measured, or otherwise operated upon, which is
received by an instrument. Also called input signal.
- For a thermometer, temperature is the input.
- input axis
- In a gyro,
an axis normal
to the spin
axis about which a rotation of the base causes a maximum output as a
function of this rotation.
- input equipment
- Specifically, the hardware through which information
is fed into a computer.
- input signal = input.
- The process of putting an artificial
satellite or spacecraftinto
- (Contracted from incoming solar radiation) 1. In general, solar
radiation received at the earth's surface. See terrestrial
solar radiation, global
terrestrial radiation, diffuse
sky radiation, atmospheric
radiation. 2. The rate at which direct
solar radiation is incident upon a unit horizontal surface at any point on
or above the surface of the earth. Compare solar
- 1. The condition of a body if, when displaced from a state of equilibrium,
it continues, or tends to continue, to depart from the original condition.
- 2. Combustion
- instantaneous readout
- Transmission of data by a radio transmitter instantaneous with the
computation of data to be transmitted. See readout
station, real time.
- instantaneous sound pressure
- The total instantaneous pressure at
the point of observation minus the static
pressure. Often called excess pressure.
- in step = in phase.
- 1. Information which tells a computer where
to obtain the operands, what
operations to perform, what to do with the result, and, sometimes, where to
obtain the next instruction.
- 2. = command.
- instruction code
- An artificial language for describing or expressing the instructions which
can be carried out by a digital
- In automatically sequenced computers, the instruction code is used when
describing or expressing sequences of instructions, and each instruction word
usually contains a part specifying the operation to be performed and one or
more addresses which identify a particular location in storage. Sometimes, an
address part of an instruction is not intended to specify a location in
storage but is used for some other purpose. If more than one address is used,
the code is called a multiple-address code. In a typical instruction of a
four-address code, the addresses specify the location of two operands, the
destination of the result, and the location of the next instruction in the
sequence. In a typical three-address code, the fourth address specifying the
location of the next instruction is dispensed with and the instructions are
taken from storage in a preassigned order. In a typical one-address or
single-address code, the address may specify either the location of an operand
to be taken from storage, the destination of a previously prepared result, or
the location of the next instruction. The arithmetic element usually contains
at least two storage locations, one of which is an accumulator. For example,
operations requiring two operands may obtain one operand from the main storage
and the other from a storage location in the arithmetic element which is
specified by the operation part.
- To provide a vehicle or component
- 1. The installation and use of electronic, gyroscopic, and other
instruments for the purpose of detecting, measuring, recording, telemetering,
processing, or analyzing different values or quantities as encountered in the
flight of a rocket or spacecraft.
- 2. The assemblage of such instruments in a rocket, spacecraft, or the
- 3. A special field of engineering concerned with the design, composition,
and arrangement of such instruments.
- instrument landing system
- (abbr ILS) A system which provides, in the aircraft, a display of the
lateral, longitudinal, and vertical references necessary for a landing.
- intake pressure = inlet pressure.
- A whole number; a number that is not a fraction.
- 1. Of or pertaining to an integer.
- 2. Serving to form a whole or part of a whole, as an integral tank.
- integrally stiffened
- Of structures, referring to thin-walled components in which increased
section wall stiffeners and wall are formed as a single structural member
rather than as two separate pieces.
- integral tank
- A fuel or oxidizer tank built within
the normal contours of an aircraft or rocket vehicle and using the skin of the
vehicle as a wall of the tank.
- integrated trajectory system
- (abbr ITS) A multiple trajectory measuring system composed of several
angle-measuring-equipment and distance-measuring-equipment sites whereby
in-flight selection of station combination can be made to provide the best
geometrical solution to space position at any given time of rocket flight.
- integrating accelerometer
- A transducer
designed to measure, and capable of measuring, velocity by means of a time
integration of acceleration.
- 1. In digital
computers, a device for accomplishing a numeric
approximation of the mathematical process of integration.
- 2. A device whose output is proportional to the integral of an input
- 1. In general, the degree or amount, usually expressed by the elemental
time rate or spatial distribution of some condition or physical quantity, such
as electric field, sound, magnetism, etc.
- 2. With respect to electromagnetic
radiation, a measure of the radiant
flux per unit solid angle emanating for some source. Frequently, it is
desirable to specify this as radiant intensity in order to distinguish
it clearly for luminous intensity. Compare emittance.
- Occasionally, intensity, is used as synonymous to flux density. This
usage does not coincide with accepted photometric and radiometric usage, but
is of long standing in meteorology. See sound
- intensity level
- In acoustics,
ten times the logarithm to the base 10 of the ratio of the intensity I of the
sound measured to the reference intensity I0. The
reference intensity I0 must be stated.
- A generally used reference value, especially for air acoustics, is
10-16 watt per square centimeter.
- intensity-modulated indicator
- One of two general classes of radar indicators,
in which echoes from targets are
presented as spots or areas of light whose intensity or brilliance is normally
a function of the power of the echo signal. Compare amplitude-modulated
indicator. See radarscope.
- intensity modulation
- The change of the brilliance (or intensity) of the trace on the
screen of a cathode-ray
tube in accordance with the strength of the applied signal.
- interaction parameter
- In plasma physics, a measure of the relative importance of the magnetic
field and the fluid motion when the magnetic
lines are at least partially frozen into the fluid. It is related to the
ratio of the magnetic energy density and the fluid kinetic energy.
- If the interaction parameter is small, the fluid motion is hardly
affected by the field; if it is large, the motion is largely controlled by the
field; if it is the order of unity, the two strongly interact, with the net
flow a compromise between them.
- intercept = altitude difference.
- interchange coefficient = exchange coefficient.
- To aline two or more sets of fins or projections on a rocket so that each
fin or projection of one set lies in a plane between the planes established by
fins or projections of the other set or sets.
- 1. A common boundary between two parts of a system, whether
material or nonmaterial.
- 2. Specifically, in a rocket vehicle
or other mechanical assembly, a common boundary between two components. See mating.
- 3. Specifically, in fluid dynamics, a surface separating two fluids across
which there is a discontinuity of some fluid property such as density or
velocity or of some derivative of these properties in a direction normal to
- The equations of motion do not apply at the interface but are replaced
by the boundary
- 1. Extraneous signals, noises, etc. that hinder proper reception of the
desired signal in
electronic equipment. See babble, clutter, cosmic
noise, crosstalk, jitter, static.
- 2. The mutual effect of two or more meeting waves or vibrations of any
kind. Sometimes called wave interference.
- interference guard bands
- The two frequency
bands additional to and on either side of the authorized frequency band,
which may be provided to minimize the possibility of interference
between different radio channels.
- interference region
- That region in space in which interference
- In microwave propagation, it refers to the region bounded by the ray
path and the surface of the earth which is above the radio horizon.
Interference lobes and height-gain patterns are formed in this region by the
addition of the direct and the surface-reflected wave. In contrast is the
diffraction zone which lies below the radio horizon.
- An apparatus used to produce and measure interference
from two or more coherent wave
trains from the same source. See radio
- Interferometers are used to measure wavelengths, to measure angular
width of sources, to determine the angular position of sources (as in
satellite tracking), and for many other purposes.
- Pertaining to or measured by an interferometer.
- interior ballistics
- That branch of ballistics
that deals with the propulsion of projectiles,
i.e., the motion and behavior of projectiles in a gun barrel, the temperatures
and pressures developed inside a gun barrel or rocket, etc. Sometimes called
- intermediate frequency (abbr IF)
- The beat frequency used in heterodyne receivers, usually the difference
between the received radiofrequency signal and a locally generated signal.
- intermediate ion
- An atmospheric
ion of size and mobility intermediate between the small ion and
- The mobility of this class of ions lies generally in the interval from
0.01 to 0.1 centimeter per second per volt per centimeter.
- intermediate orbit
- An orbit tangent to an actual orbit and having the same coordinates but
not the same velocity at the point of tangency.
- intermittent pressure breathing
breathing in which different pressures are used at different points in the
respiratory cycle, usually with a high pressure during inspiration and lower
pressure during expiration.
- The modulation
of the components
of a complex wave by each other in a nonlinear system.
- internal ballistics = interior ballistics.
- internal efficiency
- The efficiency
with which a reaction
engine, such as a rocket, converts the available thermal energy of its
combustion gases into kinetic
energy in the exhaust jet, expressed as a ratio.
- internal energy
- A mathematically defined thermodynamic
function of state, interpretable through statistical mechanics as a
measure of the molecular activity of the system. It appears in the first
law of thermodynamics as
du = dq - dw where du is the increment of specific
internal energy, dq the increment of heat, and dw the increment
of work done by the system per unit mass. The differential du is a
perfect differential. Its integral therefore introduces a constant of
integration, the zero-point internal energy , so that care must be
taken when absolute values of the internal energy are employed.
- international candle
- The unit of luminous
intensity formerly used as the international standard. On January 1, 1948,
it was replaced with the candela, which
is equal to 58.9/60 or 0.98 international satellite. Also called English
candle, British candle.
- International Geophysical Cooperation, 1959 (abbr
- An extension of the International
- International Geophysical Year (abbr IGY)
- By international agreement, a period during which greatly increased
observation of worldwide geophysical phenomena is undertaken through the
cooperative effort of participating nations. July 1957 to December 1958 was
the first such year; however, precedent was set by the International Polar
Years of 1882 and 1932.
- International Gravity Formula
- See acceleration
- international nautical mile
- See nautical
- International Polar Year
- The years 1882 and 1932, during which participating nations undertook
increased observation of geophysical phenomena in polar (mostly arctic)
regions. The observations were largely meteorological, but included other such
as auroral and magnetic studies. This program was continued and expanded in
both geographic and scientific scope as the International
- international standard atmosphere = ICAO Standard
Atmosphere; see standard atmosphere.
- International Steam Table calorie
- (abbr calIT) A unit of heat equal to 4.1868 joules. See calorie.
- International System of Units
- (abbr SI) The metric system of units based on the meter, kilogram, second, ampere, kelvin, and candela. Also
called MSKA system. Other SI units are hertz, radian, newton, joule, watt, coulomb, volt, ohm, farad, weber, and tesla.
- International Year of the Quiet Sun
- (abbr IQSY) By international agreement, a period, July 1963 to December
1964, during which intensive observations of the sun and related geophysical
phenomena are being made. Compare International
- Between the lungs and the chest wall.
- In computer terminology, a circuit or
device which translates an instruction from pseudocode
into an instruction
or series of instructions which the computer can
understand and obey.
- interpreter code = pseudocode.
of a radio signal or
combination of signals intended to trigger a transponder
or group of transponders.
- 1. A radar set or other electronic device that transmits an interrogation.
- 2. An interrogator-responsor
or the transmitting component of an interrogator-responsor.
- A radio transmitter and receiver combined to interrogate
and display the resulting replies. Often shortened to interrogator and
sometimes called challenger.
- In Boolean
algebra, the operation in which concepts are described by stating that
they have all the characteristics of the classes involved. Intersection
is expressed as AND.
- intersector = AND gate.
- interval of convergence
- See power
- Any device that may be set so as to accomplish automatically a series of
like actions, such as the taking of photographs, or the closure of electrical
circuits, at constant predetermined intervals.
- In cartography, same as transverse.
- inverse-square law
- A relation between physical quantities of the form: x proportional
to 1/y2 where y is usually a distance; and x
terms are of two kinds, forces and fluxes.
- In meteorology, a departure from the usual decrease or increase with
altitude of the value of an atmospheric property; also, the layer through
which this departure occurs (the inversion layer ), or the lowest
altitude at which the departure is found (the base of the inversion ).
- This term almost always means a temperature inversion.
- inversion temperature
- 1. In the atmosphere, the temperature at the base of an inversion.
- 2. Of a gas, a temperature above which the gas gains heat in expansion.
- 1. A device for changing direct current to alternating current.
- 2. In computers, a device or circuit which inverts the polarity of a
called NOT circuit.
- Not viscous, not clinging or sticky; frictionless, as in inviscid flow.
- inviscid fluid = perfect fluid.
- A satellite of
Jupiter orbiting at a mean distance of 421,800 kilometers. Also called
- 1. A charged atom or
molecularly bound group of atoms; sometimes also a free electron or other
- An ion pair consists of a positive ion and a negative ion (usually an
electron) having charges of the same magnitude and formed from a neutral atom
or molecule by the action of radiation. In spectroscopy, the degree of
ionization of an atom is indicated by a Roman numeral following the symbol for
the element. An un-ionized atom is indicated by the Roman numeral I, a singly
ionized atom, one which has lost one electron, is indicated by II, and so on.
Thus Fe IX indicates the spectrum of an iron atom which has lost eight
- 2. In atmospheric electricity, any of several types of electrically charge
submicroscopic particles normally found in the atmosphere. Atmospheric ions
are of two principle types, small ions
ions, although a class of intermediate ions has occasionally been
- The ionization process which forms small ions depends upon two distinct
agencies, cosmic rays and radioactive emanations. Each of these consists of
very energetic particles which ionize neutral air molecules by knocking out
one or more planetary electrons. The resulting free electron and positively
charged molecule (or atom) very quickly attach themselves to one or, at most,
a small number of neutral air molecules, thereby forming new small ions. In
the presence of Aitken nuclei, some the small ions will in turn attach
themselves to these nuclei, thereby creating new large ions. The two main
classes of ions differ widely in mobility. Only the highly mobile small ions
contribute significantly to the electrical conductivity of the air under most
conditions. The intermediate ions and large ions are important in certain
space charge effects, but are too sluggish to contribute much to conductivity.
The processes of formation of ions are offset by certain processes of
destruction of the ions (see recombination).
- 3. In chemistry, atoms or specific
groupings of atoms which have gained or lost one or more electrons, as the
chloride ion or ammonium ion. Such ions exist in aqueous
solutions and in certain crystal structures.
- ion column
- The trail of ionized gases in the trajectory of a meteoroid
entering the upper atmosphere; a part of the composite phenomenon known as a
type of meteor
train. See meteor. Compare
- ion concentration = ion
- ion counter
- An apparatus which counts the number of unit charges of electricity which
are contained in a sampled volume of the atmosphere. See aspiration
condenser, Ebert ion
counter. Compare ionization
- The design of the ion counter depends upon the mobility of the ions
under investigation. The general procedure is to pass a sample of the
atmosphere through a charged cylindrical condenser. The type of ions collected
will depend upon the capacity of the condenser and the polarizing potential.
The change in the potential drop across the condenser is a measure of the
ionic charge collected.
- ion density
- In atmospheric electricity, the number of ions per unit
volume of a given sample of air; more particularly, the number of ions of a
given type (positive small ion,
negative small ion, positive large ion,
etc.) per unit volume of air. Also called ion concentration.
- Measurement of ion density is used in determining efficiency of
ionizers in ion
- ion engine
- A reaction
engine in which ions, accelerated
in an electrostatic
field, are used as propellant. Also called electrostatic engine. See electric
- ion gage = hot-cathode ionization gage.
- ionic conduction
- Any electrical conduction where the current is sustained by the motion of
opposed to electrons)
within the conductor. All electrical conduction in the atmosphere is of this
- ionic mobility = ion mobility.
- The process by which neutral atoms or groups
of atoms become electrically charged, either positively or negatively, by the
loss or gain of electrons; or
the state of a substance whose atoms or groups of atoms have become thus
- Ionization is a necessary process to produce propellant ions in ion
- ionization by collision
- The removal of an orbital electron from
an atom or molecule by an
impacting particle (often, by the absorption of a photon). The
atom or molecule is then left with an excess positive charge, i.e., it is
- ionization chamber
- An apparatus used to study the production of small ions
in the atmosphere by cosmic ray
and radioactive bombardment of air molecules.
- The chamber is an airtight container usually cylindrical in shape and
25 to 50 liters in volume. An insulated electrode is centrally located in the
chamber. In operation a potential is applied between the electrode and the
chamber wall. The ions produced in the chamber are collected by the electrode
system and measured by an electrometer.
- ionization gage
- A vacuum
gage with a means of ionizing the gas molecules and a means of correlating
the number and type of ions produced with
the pressure of the gas. Various types of ionization gage are distinguished
according to the method of producing the ionization. Some common types are: hot-cathode
ionization gage, cold-cathode
ionization gage, radioactive
- ionization potential
- The energy required to ionize an atom or molecule. The energy is usually
given in terms of electron volts. See work
- A filament, grid, or porous body in an ion engine or other device which
strips an electron from the outer shell of a neutral atom to form a positively
- ionizer efficiency
- The ratio of the number of ions emitted from
to the number of neutral atoms entering the ionizer.
- ionizing efficiency
- See ion
- ionizing event
- Any interaction by which one or more ions are produced.
- ionizing radiation
- Any electromagnetic or particulate radiation
capable of producing ions, directly or indirectly, in its passage through
- ion mobility
- In gaseous electric conduction, the average velocity with which a given
ion drifts through a specified gas under the influence of an electric
field of unit strength. Mobility's are commonly expressed in units of
centimeters per second per volt per centimeter. Also called ionic mobility.
- In a vacuum, a single gaseous ion subjected to any nonzero potential
gradient would accelerate indefinitely; but in the midst of a gas the ion
continually experiences collisions with gas molecules. These encounters tend
to break up its trajectory into a series of short intervals of acceleration
punctuated by deflections. The net result is that the ion's gross motion
resembles drift at a uniform velocity. The mobility depends not only upon the
nature of the ion and gas but also upon the density of the gas, for the latter
controls the mean free path of the ion.
- A unilateral
transducer in which the sound output
results from the interaction between an ionic plasma and the
surrounding sound transmitting medium.
- The atmospheric
shell characterized by a high ion density. Its base is at about 70 or 80
kilometers and it extends to an indefinite height.
- The ionosphere is classically subdivided into layers. Each layer,
except the D-layer, is supposedly characterized by a more or less regular
maximum of electron density. The D-layer exists only in the daytime. It is not
strictly a layer at all, since it does not exhibit a peak of electron or ion
density, starting at about 70 to 80 kilometers and merging with the bottom of
the E-layer. The lowest clearly defined layer is the E-layer, occurring
between 100 and 120 kilometers. The F1-layer and F2-layer occur in the general
region between 150 and 300 kilometers, the F2-layer being always present and
having the higher electron density. The existence of a G-layer has been
suggested, but is questionable. The portions of the ionosphere in which these
layers tend to form are known as ionosphere in which these layers tend to form
are known as ionospheric regions, as in D-region, E-region, F-region,
G-region. Sudden increases in ionization are referred to as sporadic, as in
sporadic E or sporadic D. The above assumption that the ionosphere is
stratified in the vertical into discrete layers is currently under serious
question. Some evidence supports a belief that ion clouds are the basic
elements of the ionosphere. Other investigations appear to reveal the
ionosphere as a generally ionized region characterized by more or less random
fluctuations of electron density.
- ionospheric layer
- See ionosphere.
- ionospheric recorder
- A radio device for determining the distribution of virtual
height with frequency,
and the critical
frequencies of the various layers of the ionosphere.
- A pulse at a certain frequency is transmitted vertically, and the time
for its return is recorded on an oscilloscope; another pulse at a different
frequency is then transmitted and timed. The process is thus repeated until
the entire frequency range of interest, usually from 1 to 20 megacycles, has
- ionospheric region
- See ionosphere.
- ionospheric storm
- Disturbance of the ionosphere,
resulting in anomalous variations in its characteristics and effects on radio
communication. See sudden
- ionospheric wave = sky wave.
- ion pair
- The pair of ions, one
positively and the other negatively charged, formed by the ionization
of an initially neutral gas atom when it collides with a high-energy particle.
- It is customary to measure the ionizing efficiency of cosmic rays and
radioactive materials in terms of the number of ion pairs they produce each
second in 1 cubic centimeter of air. The symbol I is usually employed to
designate the formation of one ion pair per cubic centimeter per second. Thus,
cosmic rays are said to yield about 21 at sea level, and alpha particles from
the radioactive gases contribute about 51 over land areas at the surface.
- ion rocket
- See ion
- IQSY (abbr) = International Year of the Quiet Sun.
- IR (abbr) = infrared or infrared radiation.
- (Infrared amplification by stimulated emission of radiation). A device
which amplifies in the infrared band.
- irradiance = radiant flux density.
- I-scan = I-display.
- I-scope = I-display.
- A line of equal or constant entropy. See Poisson
- In meteorology, it may be considered an isopleth of potential
temperature, i.e., the same as a dry
- Of equal or constant entropy with
respect to either space or time.
- A line of equal or constant pressure, specifically, such a line in a
- Of equal or constant pressure, with
respect to either space or time.
- Because isobar is a common meteorological term, isobaric can be taken
to mean of isobars, therefore leading to some ambiguity. This use should be
- isobaric equivalent temperature
- See equivalent
temperature, sense 1.
- Of equal or constant volume, usually applied to a thermodynamic
process during which the volume of the system remains unchanged. Compare isosteric.
- isoclinic line
- A line through points on the earth's surface having the same magnetic
dip. See aclinic
line. Compare isogonic
- isogonic line
- A line through points on the earth's surface having the same magnetic
variation. See agonic
line. Compare isoclinic
- isogram = isopleth.
- In vibration
studies, a reduction in the capacity of a system to
respond to an excitation,
attained by the use of a resilient support.
- isolator = vibration isolator.
- 1. One of two or more nuclides
having the same mass number
A and atomic
number Z, but existing for measurable times in different quantum states
with different energies and radioactive properties.
- The state of lowest energy is the ground state. Those of higher
energies are metastable states. To indicate the metastable isomer, the letter
m is added to the mass number in the symbol for the nuclide; thus Br80mCommonly, the isomer of higher energy decays to
one with lower energy by the process of isometric
- 2. One of two or more molecules
having the same atomic composition and molecular weight, but differing in
- isometric transition
- A radioactive transition from one nuclear isomer to
another of lower energy.
- The deexcitation of the nuclei in the metastable state may occur by
gamma emission or by internal conversion followed by emission of X-rays and
Auger electrons, or both. It is a type of forbidden transition.
- On a chart or graph, a line of constant value of a given quantity with
respect to either space or time. Also called isogram.
- Of equal or constant density with respect to either space or time;
equivalent to isosteric.
- A supposed equality existing in vertical sections of the earth, whereby
the weight of any column from the surface of the earth to a constant depth is
approximately the same as that of any other column of equal area, the
equilibrium being maintained by plastic flow of material from one part of the
earth to another.
- Of equal of constant specific volume with respect to either time or space;
equivalent to isopycnic.
- isotensoid structure
- A filamentary structure in which the filaments are uniformly stressed
throughout for the design loading condition.
- A line of equal or constant temperature.
- A distinction is made, infrequently, between a line representing equal
temperature in space, choroisotherm, and one representing constant temperature
in time, chronoisotherm.
- isothermal atmosphere
- An atmosphere in hydrostatic equilibrium in which the temperature is
constant with height and in which, therefore, the pressure decreases
exponentially upward. In such an atmosphere the thickness between any two
levels is given by
ZB - ZA = (RdTv /g) ln
(pA/pB) where Rd is the gas
constant for dry air; Tv is the virtual temperature
(K); g is the acceleration of gravity, and pA
and pB are the pressures at the heights
ZA and ZB respectively. In the isothermal atmosphere there
is no finite level at which the pressure vanishes. Also called exponential
atmosphere. See barotropy.
- isothermal equilibrium
- The state of an atmosphere
at rest, uninfluenced by any external agency, in which the conduction of heat
from one part to another has, after a sufficient length of time, produced a
uniform temperature throughout its entire mass. Also called conductive
equilibrium. See diffusive
- isothermal process
- Any thermodynamic
change of state of a system that takes place at constant temperature.
- Pertaining to a quality which has equal value in space at a particular
- 1. On of several nuclides
having the same number of protons in their nuclei, and hence belonging to the
same element, but
differing in the number of neutrons and therefore in mass number A, or in
energy content (isomers). For example, 6C612,
6C713, and 6C814
are carbon isotopes. Small quantitative
differences in chemical properties exist between isotopes.
- 2. A radionuclide
or a preparation of an element with special isotopic composition (allobar) as
an article of commerce, so called because of the principal use of such
materials as radioactive tracers.
- 3. In common usage, a synonym for nuclide (not
- In general, pertaining to a state in which a quantity or spatial
derivatives thereof are independent of direction. Also called isotropous.
- isotropic antenna = unipole.
- isotropic radiation
radiation which has exactly the same intensity in all directions.
- This should not be called perfectly diffuse radiation because of the
likelihood of confusion with the concept of a perfectly
- isotropic radiator
- An energy source that radiates uniformly in all directions. Compare perfectly
- isotropic turbulence
in which the products and squares of the velocity components and their
derivatives are independent of direction, or, more precisely, invariant with
respect to rotation and reflection of the coordinate axes in a coordinate
system moving with the mean motion of the fluid. Then all the normal stresses
are equal and the tangential stresses are zero.
- Atmospheric turbulence is generally nonisotropic, although isotropic
turbulence is that most easily produced in wind tunnel experiments and forms
the basis of much of the theoretical analysis of turbulent flow. A related but
less restricted type of turbulence is known as homologous turbulence, in which
the fluctuations differ only in scale at every point in the flow.
- isotropous = isotropic.