This list of aerospace terms and abbreviations was compiled by Dave, I just agreed to host it on my webpage, and tidy up some of the html code for him.
AACS |
Attitude Articulation Control Subsystem. |
AAF |
Association Astronautique Francaise. |
AAS |
American Astronautical Society. |
ABL |
Allegheny Ballistics Laboratory. |
Ablation
| The erosion of a solid body by a high-temperature gas stream moving with high velocity, e.g. a reentry vehicle's heat shield which melts or chars under the effects of air friction. |
ABMA |
Army Ballistic Missile Agency (USA). |
Abort |
To cancel or cut short a mission. |
Absolute zero |
The temperature at which all heat action ceases, -273.16oC (-459.69oF). |
Acceleration |
A change in velocity, including changes of direction and decreases as well as increases in speed. |
Accelerometer |
A device that senses changes in speed along its axis. |
ACS |
Attitude Control System. |
Active heating |
The use of resistive electric heaters or radioisotope heaters to keep spacecraft components above their minimum allowable temperatures. |
Active sun |
The Sun during times of frequent solar activity such as sunspots, flares, and associated phenomena. |
Actuator |
A device which transforms an electric signal into a measured motion using hydraulic, pneumatic or pyrotechnic (explosive) action. |
Aerobraking |
The process of decelerating by converting velocity into heat through friction with a planetary atmosphere. |
Aerodynamic heating |
The heating of a body due to the passage of air or other gases over the body; caused by friction and compression processes. |
Aeronautics |
The science of building and
operating vehicles for flight. |
Aerozine 50 |
A storable liquid fuel 50%
hydrazine, 50% UDMH. |
AIAA |
American Institute of Aeronautics
and Astronautics (USA). |
AIDAA |
Associazione Italiana di
Aeronautica e Astronautica. |
Aileron |
A hinged surface on the wing of
an aircraft or spacecraft used to adjust the craft's angle of flight. |
Aimpoint |
The point in the planet's plane
that spacecraft aim for to either fly by or enter orbit. |
Airglow |
The visible light that appears at
night in the upper atmosphere. |
Air lock |
A compartment separating areas a
different environment, especially different air pressures, that is used for entry to and
departure from a spacecraft. |
Albedo |
Reflectivity; the ratio of
reflected light to incident light. The fraction of the sunlight which is reflected off a
planet. |
Algae |
A group of simple organisms,
mostly aquatic, which contain chlorophyll and thus provide a means of photosynthesis. They
could be used to absorb carbon dioxide and provide nourishment in a spaceship. |
ALSEP |
Apollo Lunar Surface Experiment
Package. |
Altimeter |
A device that measures altitude
above the surface of a planet or moon. Spacecraft altimeters work by timing the round trip
of radio signals bounced off the surface. |
Ambient |
Environmental conditions, such as
pressure or temperature. |
Analog computer |
A computing machine that works on
the principle of measuring, as distinct from counting, in which the measurements obtained
(as voltages, resistances, etc.) are translated into desired data. |
Angle of attack |
The angle between the velocity
vector and the longitudinal axis of a missile or rocket. |
Angstrom |
A unit for the measurement of
wavelength. Equals one hundred millionth of a centimeter (0.003937 millionth of an inch). |
Annular |
Pertaining to, or having the form
of a ring. |
Anomaly |
The angular distance between the
position of a planet and its last perihelion, or between that of a satellite and its last
perigee. |
Anti-matter |
A hypothetical form of matter of
which the atoms are composed of anti-particles, as protons, electrons, etc. assumed to
carry charges opposite to those associated with ordinary matter. Particles having such
properties have been produced in particle accelerators. |
Antipodal |
Pertaining to, or located on, the
opposite side of the Earth. |
AOCS |
Attitude & Orbit Control
System. |
Aperture |
The diameter of an opening; the
diameter of the primary lens or mirror of a telescope. |
Apex |
The point towards which a body is
moving. |
Aphelion |
That point in a solar orbit which
is farthest from the Sun. |
Apoapsis |
That point in an orbit which is
farthest from the primary. |
Apogee |
That point in a terrestrial orbit
which is farthest from the Earth. |
Apolune |
That point in a lunar orbit which
is farthest from the Moon. |
Argument |
Angular distance. |
Argument of periapsis |
In an orbit, the angular distance
between the point of periapsis and the ascending node. |
Arianespace |
A private limited company
established for the purpose of producing, financing and marketing the ESA Ariane launch
vehicle. Comprises European companies concerned in the rocket's development, CNES and
several banks. US agent is Grumman Aerospace. |
ARS |
American Rocket Society (USA). |
Artificial gravity |
Use of centrifugal force to
simulate weight reaction in a condition of free-fall. May be achieved by spinning the
vehicle to make the centrifugal force of the outer periphery or bodies within the vehicle
to replace the weight reaction experienced at Earth's surface. |
ASAT |
Anti-satellite. |
Ascending node |
The point at which an orbiting
object or spacecraft, traveling from south to north, crosses the plane of the equator. |
Ascent module |
That part of a spacecraft that
ascends from the surface of a planet or moon to rendezvous and dock with an orbiting
spacecraft. |
Asteroid |
A small, usually irregularly
shaped body orbiting the sun, most often at least partially between the orbits of Mars and
Jupiter. |
Asteroid belt |
A 1/2 AU wide region between the
orbits of Mars and Jupiter where most asteroids are found. |
Astronaut |
A person who flies in space,
whether as a crew member or passenger. |
Astronautics |
The science and technology of
space flight. |
Astronomical unit |
The mean distance of Earth from
the Sun, i.e. 92,955,807 miles (149,597,870 km). |
Astrophysics |
Study of the physical and
chemical nature of celestial bodies and their environs. |
ATDA |
Agena Target Docking Adapter. |
Atmospheric balloon |
An instrumented package suspended
from a buoyant gas bag; deployed in a planet's atmosphere to study wind circulation
patterns. |
Atmospheric pressure |
The weight of air on surfaces
within Earth's atmosphere, about 14.7 psi (101 kPa) at sea level. Such pressure is also
supplied artificially in spacecraft and spacesuits. |
Atmospheric probe |
A small instrumented craft which
separates from the main spacecraft prior to closest approach to a planet to study the
gaseous atmosphere of the body as it drops through it. |
Attenuation |
The decrease of a propagating
physical quantity, such as a radio signal, with increasing distance from the source, or
from some obstruction. |
Attitude |
Orientation of a space vehicle as
determined by the relationship between its axes and some reference plane, e.g. the
horizon. |
Attitude & articulation
control subsystem |
The onboard computer that manages
the tasks involved in spacecraft stabilization via its interface equipment. For attitude
reference, star trackers, star scanners, solar trackers, sun sensors, and planetary limb
trackers are used. |
Attitude control |
The system that turns and
maintains a spacecraft in the required direction as indicated by its sensors. |
AU |
Astronomical Unit. |
Aurora |
Arcs, rays or swaying curtains of
green, yellow or white lights seen in latitudes of about 70o, such as Aurora
Borealis or Northern Lights, and Aurora Australis or Southern Lights; caused by
streams of electrified particles, emitted by the Sun, trapped in the Earth's magnetic
field. |
Autopilot |
A system or device that controls
a vehicle's flight at a preset course and altitude. |
Azimuth |
The angular position of an object
measured in the observer's horizontal plane, usually from north through east. Bearing or
direction in the horizontal plane. As one of the coordinates expressing celestial
location, it is sometimes used in tracking spacecraft. |
Backscattering |
Reflecting light back in the direction of the source. |
Back-up |
An item kept available to replace an item which fails to perform satisfactorily. |
Ballistics |
The science that deals with the
motion, behavior, appearance or modification of missiles acted upon by propellants,
rifling, wind, gravity, temperature or other modifying conditions of force. |
Ballute |
An aerodynamic braking device
which is both balloon and parachute. |
Bar |
A unit of pressure equal to one
million dynes per square centimeter, or 0.99 atmospheres. |
Barycenter |
The common center of mass about
which two or more bodies revolve. |
Basin |
A large, >200 km, circular
depression from the explosive impact of an asteroid or similar sized body on a planet
surface, usually rimmed by mountains. |
Battery |
A device with two or more
connected cells that produce a direct current by converting chemical energy into
electrical energy. |
Big Bang theory |
The theory that the universe was
once clustered and at the 'beginning' it exploded out, as shown by the fact that objects
are still moving out from the center. |
Binary star |
Two stars revolving around a
common center of gravity. |
Bi-propellant |
A rocket propellant consisting of
two unmixed or uncombined chemicals (fuel and oxidizer) fed separately into the combustion
chamber. |
BIS |
British Interplanetary Society. |
Bit |
A basic unit of computer
information; abbreviation of binary digit. |
Black hole |
An object whose gravity is so
strong that the escape velocity exceeds the speed of light. |
Blackout (physiological) |
A temporary loss of vision and/or
consciousness when a person is subjected to high accelerations. |
Blackout (radio) |
A temporary loss of radio
communications which occurs between a spacecraft reentering the atmosphere and ground
stations due to an ionized sheath of plasma which develops around the vehicle. |
Black powder |
A mixture of saltpeter (potassium
nitrate), sulfur, and charcoal, used in explosives and as an early propellant for rockets.
|
Boilerplate |
A metal replica of the flight
model (e.g. of a spacecraft) but usually heavier and cruder for test purposes. |
BOL |
Beginning Of Life. |
Boost |
The extra power given to a rocket
or space vehicle during liftoff, climb or flight, as with a booster rocket. |
Booster |
The first stage of a missile or
rocket. |
Bow shock wave |
The compressed wave that forms in
front of a spacecraft or satellite as it moves rapidly through Earth's atmosphere; more
generally, any such wave that forms between an object and a fluid medium. |
Burn |
Combustion action in rockets.
Propulsion in space is achieved through a sequence of burns. |
Bus |
A major part of the structural
subsystem of a spacecraft which provides a place to attach components internally and
externally, and to house delicate modules requiring a measure of thermal and mechanical
stability. The bus also establishes the basic geometry of the spacecraft. |
Calibration |
Setting an measuring instrument before measuring for accurate results. |
Carrier |
The main frequency of a radio
signal generated by a transmitter prior to application of modulation. |
CAS |
Chinese Academy of Sciences. |
CAST |
Chinese Academy of Space
Technology. |
CAT |
Capsule Ariane Technologique. |
Catalytic decomposition
engine |
A mono-propellant engine in which
a liquid fuel decomposes into hot gas in the presence of a catalyst. The fuel is most
commonly hydrazine. |
C-band |
A range of microwave radio
frequencies in the neighborhood of 4 to 8 GHz, used for spacecraft communications on
Mercury and Gemini flights (~5 Ghz). |
CCD |
Charged Coupled Device. |
CDS |
Command & Data Subsystem. |
Celestial sphere |
The apparent sphere of sky that
surrounds the Earth; used as a convention for specifying the location of a celestial
object. |
Centrifugal force |
A force which is directed away
from the center of rotation. |
Centripetal force |
A force which is directed towards
the center of rotation. |
CEO |
Close Earth Orbit. |
CETI |
Communication with
Extra-Terrestrial Intelligence. |
Chaff |
Metallic foil ejected by a
reentry module to enhance its radar image. |
Charged coupled device |
An imaging device consisting of a
large-scale integrated circuit which has a two-dimensional array of hundreds of thousands
of charge-isolated wells, each representing a pixel. |
Cholorella |
A genus of unicellular green
algae, proposed for converting carbon dioxide into oxygen for use in spacecraft. |
Chromosphere |
A reddish layer in the Sun's
atmosphere, the transition between the photosphere and the corona. |
Cislunar |
Relating to the space between the
Earth and the orbit of the Moon. |
CM |
Command Module. |
CNES |
Centre National d'Etudes
Spatiales (France). |
CO |
Circular Orbit. |
Coherence |
The property of being coherent,
e.g. waves having similar direction, amplitude and phase that are capable of exhibiting
interference. |
Coma |
The cloud of diffuse material
surrounding the nucleus of a comet. |
Combustion |
A chemical reaction between two
or more substances that releases heat, light, and gases. |
Combustion chamber |
The chamber in a rocket where the
fuel and oxidizer are ignited and burned. By common usage the expansion nozzle is included
as part of the combustion chamber, particularly for liquid-propelled rocket engines. |
Comet |
A body of small mass but large
volume, compared to a planet, often developing a long luminous and partly transparent tail
when close to the Sun. |
Command & data subsystem |
The onboard computer responsible
for overall management of a spacecraft's activity. |
Command module |
The compartment of a spacecraft
which contains the crew and main controls, and is used as the reentry vehicle. |
Composites |
Structural materials of metal
alloys or plastics with built-in strengthening agents, e.g. carbon fibers. |
Constellation |
A group of stars that make a
shape, often named after mythological characters, people, animals, and things. |
Control rocket |
A vernier or other rocket used to
control the attitude of, or slightly change the speed of, a spacecraft. |
Coolant |
A medium, usually a fluid, which
transfers heat from a object. |
Core |
The innermost layer of a planet
or star. |
Coreolis effect |
Dizziness or nausea experienced
when an astronaut in a spinning spacecraft moves his head in the opposite direction. |
Corona |
The Sun's outer layer. The
corona's changing appearance reflects changing solar activity. |
Coronal mass ejection |
A huge cloud of hot plasma,
expelled sometimes from the Sun. It may accelerate ions and electrons, and may travel
through interplanetary space as far as the Earth's orbit and beyond it, often preceded by
a shock front. When the shock reaches Earth, a magnetic storm may result. |
Cosmic ray |
An extremely energetic
(relativistic) charged particle. |
Cosmic year |
The time it takes the Sun to
revolve around the center of the galaxy, approximately 225 million years. |
Cosmonaut |
The Russian term for an
astronaut. A space traveler. |
COSPAR |
The Committee on Space Research
(established October 1958). |
Countdown |
A count in inverse numerical
order, in hours, minutes and finally seconds, of time remaining before the launch of a
rocket. |
Crater |
A round impression left in a
planet or satellite from a meteoroid. |
Crust |
The outer layer of Earth and
other terrestrial planets. |
Cryogenic |
A rocket fuel or oxidizer which
is liquid only at very low temperatures, e.g. liquid hydrogen which has a boiling point of
-217.2oC (-423oF). |
CSA |
Chinese Society of Astronautics. |
CSAA |
Chinese Society of Aeronautics
and Astronautics. |
CSM |
Command/Service Module. |
C-stoff |
A rocket fuel used by Germany in
World War II 30% hydrazine hydrate, 57% methanol, 13% water with traces of potassium
cuprocyanate. Used in conjunction with T-stoff oxidizer 80% hydrogen peroxide with 1 to
2% oxiquinoline as a stabilizer. |
Current |
The amount of electric charge
flowing past a specified circuit point per unit time. |
Cut-off |
The action of stopping a process
abruptly, such as shutting off the flow of propellant to a rocket engine. |
Dark matter |
A form of matter which has not been directly observed but whose existence has been deduced by it's gravitational effects. |
Data reduction |
Conversion of observed values into useful, ordered and simplified information. |
DC |
Direct Current. |
Decay |
The action of air drag upon an
artificial satellite causing it to spiral back into the atmosphere, eventually to
disintegrate or burn up. |
Deceleration |
Negative acceleration, slowing. |
Declination |
One of the coordinates, measured
in degrees, used to designate the location of an object on the celestial sphere.
Declination is a north-south value similar to latitude on Earth. |
Decompression |
The relief of pressure. Explosive
decompression would occur if the cabin of a spacecraft was punctured in space. |
Delta V |
Difference or change in velocity.
|
Demodulation |
To extract information from a
modulated carrier wave. |
Density |
Amount of matter per unit volume.
|
Density Wave |
A kind of wave induced in a flat
plane of a resisting medium (such as the rings of Saturn) by gravitational forces, often
assuming the form of a tightly wound spiral. |
Descending node |
The point at which an orbiting
object or spacecraft, moving from north to south, crosses the plane of the equator. |
Descent engine |
The rocket used to power a
spacecraft as it makes a controlled landing on the surface of a planet or moon. |
Descent module |
That part of a spacecraft that
descends from orbit to the surface of a planet or moon. |
DGLR |
Deutsche Gesellschaft fur
Luft-und Raumfahrt (German Company for Air and Space Travel). |
Digital computer |
An electronic device for solving
numerically a variety of problems. |
Dipole |
A compact source of magnetic
force, with two magnetic poles. A bar magnet, coil or current loop, if their size is
small, create a dipole field. The Earth's field, as a first approximation, also resembles
that of a dipole. |
Direct current |
Electrical current flowing in one
direction and substantially constant in value. |
Direct sensing |
Instruments that interact with
phenomena in their immediate vicinity, and register characteristics of them. |
Dish |
A reflector for radio waves,
usually a paraboloid. |
Docking |
The technique of connecting two
or more spacecraft in space. |
DoD |
Department of Defense (USA). |
DOF |
Degrees Of Freedom. |
Doppler effect |
A phenomenon in which waves
appear to compress as their source approaches the observer or stretch out as the source
recedes from the observer. |
Dose |
A quantity of radiation delivered
at a position. In the context of space energetic particle radiation effects, it usually
refers to the energy absorbed locally per unit mass as a result of radiation exposure. |
Dose equivalent |
A dose normally applied to
biological effects and including scaling factors to account for the more severe effects of
certain kinds of radiation. |
Downlink |
The radio signal transmitted from
a spacecraft to Earth. |
Drag |
The resistance offered by a gas
or liquid to a body moving through it. |
Drogue |
A small parachute used to slow
and stabilize a spacecraft returning to the atmosphere, usually preceding deployment of a
main landing parachute. |
DSN |
Deep Space Network. |
Dust |
Particulates which have a direct
relation to a specific solar system body and which are usually found close to the surface
of this body (e.g. Lunar, Martian or Cometary dust). |
Dust detector |
A device for measuring the
velocity, mass, charge, flight direction and number of dust particles striking the
instrument. |
Dynamo process |
The generation of an electric
currents by the flow of an electrically conducting fluid through a magnetic field. For
instance, the magnetic field originating inside the Earth is believed to come from a
dynamo process involving the flow of molten iron in the Earth's hot core. The energy
required by the current is obtained from the motion of the flow. |
Dyne |
A unit of force equal to the
force required to accelerate a 1 g mass 1 cm per square second. |
Earth |
Third planet from the Sun, a terrestrial planet. |
Earth radius |
The average radius of the Earth,
a convenient unit of distance in describing phenomena and orbits in the Earth's
neighborhood in space. 1 RE = 6371.2 km approximately. |
Earth-sensor |
A light-sensitive diode which
seeks the direction of Earth and then informs the attitude control system of a spacecraft.
|
Eccentric |
Noncircular; elliptical (applied
to an orbit). |
Eccentricity |
The amount of separation between
the two foci of an ellipse and, hence, the degree to which an elliptical orbit deviates
from a circular shape. |
Eclipse |
The obscuring of one celestial
body by the passage of another in front of it. |
Ecliptic |
The great circle on the celestial
sphere which traces the path of the Sun during the year. |
ECM |
Electromagnetic Countermeasures. |
EDT |
Eastern Daylight Time. |
Ejection seat |
A seat fitted with an explosive
charge and designed to eject the occupant clear of an aircraft during an in-flight
emergency. |
ELDO |
European Launcher Development
Organization. |
Electric propulsion |
A form of rocket propulsion which
depends on some form of electric acceleration of propellant to achieve low thrust over
long periods of time. E.g. an ion or magnetohydrodynamic engine. |
Electromagnetic |
Relating to the interplay between
electric and magnetic fields. |
Electromagnetic waves |
A wave propagated through space
by simultaneous periodic variation in the electric and magnetic field intensity at right
angles to each other and to the direction of propagation. The electromagnetic spectrum
includes radio waves, microwaves, infrared, visible and ultraviolet radiation, X-rays,
gamma rays and cosmic rays. |
Elevation |
The angular measure of the height
of an object above the horizon; with azimuth, one of the coordinates defining celestial
location and sometimes used in tracking spacecraft. |
ELV |
Expendable Launch Vehicle. |
EMU |
Extravehicular Mobility Unit. |
Energetic particle |
Particles that can penetrate
outer surfaces of spacecraft. For electrons, this is typically above 100 keV, while for
protons and other ions this is above 1 Mev. Neutrons, gamma-rays and X-rays are also
considered energetic particles in this context. |
Engine |
In spacecraft, a rocket or
thruster that burns liquid propellants and can be throttled to adjust thrust. |
EOL |
End Of Life. |
Ephemeris |
Table of predicted positions of
bodies in the solar system. |
Ephemeris time |
A measurement of time defined by
orbital motions. Equates to Mean Solar Time corrected for irregularities in Earth's
motions. |
Epoch |
An instant in time that is
arbitrarily selected as a point of reference, e.g. for a set of orbital elements. |
Equator |
An imaginary circle around a body
which is everywhere equidistant from the poles, defining the boundary between the northern
and southern hemispheres. |
Equatorial orbit |
An orbit in the plane of the
equator. |
ESA |
European Space Agency. |
Escape tower |
A rocket-powered framework
designed to separate spacecraft modules from their booster rockets in case of accident.
Escape towers are mounted atop the spacecraft and jettisoned after launch. |
Escape velocity |
The precise velocity necessary to
escape from a given point in a gravitational field. A body in a parabolic orbit has escape
velocity at any point in that orbit. The velocity necessary to escape from the Earth's
surface is 6.95 miles/sec. (11.2 km/sec.). |
ESMC |
Eastern Space and Missile Center.
|
EST |
Eastern Standard Time. |
Eurospace |
Non-profit-making industrial
association with headquarters in Paris (founded September 1961). |
EVA |
Extravehicular Activity. |
Exhaust velocity |
The velocity of the exhaust
leaving the nozzle of a rocket. |
Exosphere |
The part of the Earth atmosphere
above the thermosphere which extends into space. H and He atoms can attain escape
velocities at the outer rim of the exosphere. |
Extravehicular activity |
Action performed by an astronaut
or cosmonaut outside a vehicle in space; a spacewalk. |
Fairing |
A structure whose main function is to streamline and smooth the surface of an aircraft or space vehicle. |
Fault |
A crack or break in the crust of
a planet along which slippage or movement can take place. |
Fault protection |
Algorithms, which reside in a
spacecraft's subsystems, that insure the ability of the spacecraft to both prevent a
mishap and to reestablish contact with Earth if a mishap occurs and contact is
interrupted. |
Ferret |
Satellite using electromagnetic
surveillance techniques. |
Fission |
The release of energy through
splitting atoms. |
Fluorescence |
The phenomenon of emitting light
upon absorbing radiation of an invisible wavelength. |
Flux |
The amount of radiation crossing
a surface per unit of time, often expressed in "integral form" as particles per
unit area per unit time. |
Flyby |
Space flight past a heavenly body
without orbiting. |
Flyby spacecraft |
A spacecraft which follows a
continuous trajectory past a target object, never to be captured into an orbit. It must
carry instruments that are capable of observing passing targets by compensating for the
target's apparent motion. |
FOBS |
Fractional Orbit Bombardment
System. A Soviet method of delivering a warhead from partial satellite orbit and thus
approaching from any direction. |
Force |
A vector quantity that tends to
produce an acceleration of a body in the direction of its application. |
Forward scattering |
Reflecting light approximately
away from the source. |
FOV |
Field Of View. |
Free-fall |
The motion of any unpowered body
moving in a gravitational field. |
Free-return trajectory |
Path of a spacecraft that
provides for a return to Earth. |
Frequency |
The number of oscillations per
second of an electromagnetic (or other) wave. |
Fuel |
A substance that when combined
with an oxidizer burns to produce thrust in rockets. |
Fuel cell |
A cell in which chemical reaction
is used directly to produce electricity. |
Fussion |
The release of nuclear energy
through the uniting of atoms. |
FY |
Fiscal Year. |
g |
The symbol for the acceleration of a freely moving body due to gravity at the surface of the Earth (9.81 m/s2). Alternatively, 1 g. |
Galaxy |
A very large system of stars, gas
and dust isolated from its neighbors by an immensity of space; an "island
universe". |
GALCIT |
Guggenheim Aeronautical
Laboratory of the California Institute of Technology. |
Gamma rays |
Very short, highly-penetrative
electromagnetic radiation with a shorter wavelength than X-rays; produced in general by
emission from atomic nuclei. |
Gas generator |
A chamber in which propellant is
burned to produce high pressure gas that is then used to drive a turbine, e.g. turbopump. |
Gas giant |
A large planet composed mostly of
gas, e.g. the Jovian planets. |
GATV |
Gemini-Agena Target Vehicle. |
Gauss |
CGS unit of magnetic induction
(after the German mathematician Karl F. Gauss). |
GE |
General Electric Company of the
USA. |
GEO |
Geostationary Orbit. Also
abbreviated GO. |
Geo- |
Prefix referring to the Earth. |
Geocentric |
Earth centered. |
Geodesy |
The science of the Earth's shape.
|
Geomagnetic storm |
A worldwide disturbance of the
Earth's magnetic field, distinct from regular diurnal variations. |
Geospace |
Also called the solar-terrestrial
environment, geospace is the domain of Sun-Earth interactions. It consists of the
particles, fields, and radiation environment from the Sun to Earth's space plasma
environment and upper atmosphere. Geospace is considered to be the fourth physical
geosphere (after solid earth, oceans, and atmosphere). |
Geostationary orbit |
A circular orbit in which a
satellite moves from west to east at such velocity as to remain fixed above a particular
point on the equator. Also called geosynchronous. |
Geostationary transfer orbit |
An elliptical orbit used to
transfer a space vehicle from low earth orbit to geostationary orbit. |
Geosynchronous orbit |
See geostationary orbit. |
g-Force |
A force caused by acceleration
expressed in g's. |
GH2 |
Gaseous Hydrogen. |
GHz |
Gigahertz, equal to one billion
hertz. |
Gimbal |
A mechanical frame for a
gyroscope or power unit, usually with two perpendicular axes of rotation. |
GMT |
Greenwich Mean Time. |
GN&C |
Guidance, Navigation and Control.
|
GO |
Geostationary Orbit. Also
abbreviated GEO. |
GOX |
Gaseous Oxygen. |
Grain |
The rubberlike mass of chemical
propellant that provides propulsion in solid fuel rockets. The shape of the grain
determines the rate and pattern of burn and thus controls thrust. |
Gravitational waves |
Einsteinian distortions of the
space-time medium predicted by general relativity theory (not yet detected as of November
1995). |
Gravity |
The force responsible for the
mutual attraction of separate masses. |
Gravity assist trajectory |
A trajectory in which angular
momentum is transferred from an orbiting planet to a spacecraft approaching from behind.
The result is an increase in the spacecraft's velocity. |
Gravity field survey |
The mapping of a planet's mass
distribution by studying variations in the in the planet's gravity field strength made
evident by minute Doppler shifts in an orbiting spacecraft's radio signal. |
Gravity waves |
Certain atmospheric waves within
a planet's atmosphere. |
Great circle |
An imaginary circle on the
surface of a sphere whose center is at the center of the sphere. |
Greenwich mean time |
See universal time. |
GSFC |
NASA Goddard Space Flight Center (Greenbelt, Maryland). |
GSO |
Geosynchronous Orbit. |
GTO |
Geostationary Transfer Orbit. |
Guillotine |
A device equipped with explosive
blades used to cut cables, water lines, wires, etc. during separation of spacecraft
modules. |
Gyration |
The circular motion of ions and
electrons around magnetic field lines. |
Gyroscope |
A spinning, wheel-like device
that resists any force that tries to tilt its axis. Gyroscopes are used for stabilizing
the attitude of rockets and spacecraft in motion. |
H2O2 |
Hydrogen Peroxide. |
Hatch |
Door or doorway, usually hermetically sealed. |
Heat shield |
A device which protects people or
equipment from heat, such as a shield in front of a reentry capsule. |
Helio- |
Prefix referring to the Sun. |
Heliocentric |
Centered on the Sun. |
Heliopause |
The boundary theorized to be
roughly circular or teardrop-shaped, marking the edge of the Sun's influence, perhaps 100
AU from the Sun. |
Heliosphere |
The space within the boundary of
the heliopause, containing the Sun and solar system. |
Hertz |
A unit of frequency equal to one
cycle per second, named after Heinrich Hertz. |
Heterosphere |
The Earth atmosphere above 105 km
altitude where species-wise concentration profiles establish due to diffusive equilibrium,
with N2 dominance below 200 km, O dominance from 200 to 600 km, and He dominance as of 600
km altitude. |
HGA |
High-Gain Antenna. |
High-energy particle detector |
A device for measuring the energy
spectra of trapped energetic electrons, and the energy and composition of atomic nuclei. |
High-gain antenna |
A dish-shaped spacecraft antenna
principally used for high rate communication with Earth This type of antenna is highly
directionally and must be pointed to within a fraction of a degree of Earth. |
Hohmann transfer orbit |
An interplanetary trajectory in
which a spacecraft is launched into an elliptical solar orbit whose perihelion (inner
planet) or aphelion (outer planet) reaches the orbit of the target planet on the opposite
side of the Sun. Uses least propellant. |
Homosphere |
The Earth atmosphere below 105 km
altitude where complete vertical mixing yields a near-homogeneous composition of about
78.1% N2, 20.9% O2, 0.9% Ar, and 0.1% CO2 and trace constituents. The homopause (or
turbopause) marks the ceiling of the homosphere. The homosphere can be broadly divided
into three distinct regimes the troposphere (0 to 12 km), the stratosphere (12 to 50 km)
and the mesosphere (50 to 90 km) |
Horizon |
The line marking the apparent
junction of Earth and sky. |
Horizon scanner |
A scanner which automatically
seeks the horizon for purposes of a spacecraft's orientation and control, e.g. one that
detects the sharp discontinuity in infrared intensity at the outer edge of the Earth's
tropopause. |
Hour angle |
The angular distance of a
celestial object measured westward along the celestial equator from the zenith crossing. |
HTP |
High Test Peroxide. |
HTPB |
Hydroxy-terminated polybutadiene.
A polymeric fuel binder. |
Hydrazine |
A rocket fuel which burns
spontaneously with nitric acid or nitrogen tetroxide. Can also be used as a
mono-propellant: when passed through an iridium-bearing catalyst, it decomposes at high
temperature into constituent gases of ammonia, nitrogen and hydrogen. Used in small
thrusters for orbit modification and attitude control of spacecraft. Also see MMU and
UDMH. |
Hydrosphere |
The water on or around the
surface of a planet. |
Hydyne |
A rocket fuel comprised of 60%
UDMH and 40% diethylene-triamine. |
Hyperbolic |
A trajectory path to a planet
shaped like a hyperbola. |
Hypergolic |
A term applied to an oxidizer and
a fuel which ignite spontaneously with each other. |
IAA |
Indian Astronautical Association.
|
IAA |
International Academy of
Astronautics (established August 1960). |
IAF |
International Astronautical
Federation (formally inaugurated 1951). |
IC |
Integrated Circuit. |
ICBM |
Inter-Continental Ballistic
Missile (range >5,500 km). |
IGY |
International Geophysical Year
(1957-58). |
Impulse |
The product of the average force
acting on a body and the interval of time during which it acts, being a vector quantity
equal to the change of momentum of the body during the same time interval. |
IMU |
Inertial Measurement Unit. |
Inclination |
The angular distance between a
satellite's orbital plane and the equator of its primary. |
Inertial guidance |
An on-board system for launch
vehicles and spacecraft where gyroscopes, accelerometers and other devices satisfy
guidance requirements. |
Inertial measurement unit |
An on-board instrument system
that measures the attitude of a spacecraft. It includes accelerometers and gyroscopes. |
Inferior conjunction |
Alignment of Earth, Sun, and an
inferior planet on the same side of the Sun. |
Inferior planets |
Planets whose orbits are closer
to the Sun than Earth's, i.e. Mercury and Venus. Also called inner planets. |
Infrared |
Electromagnetic radiation of
wavelengths between 7500 A, the limit of the visible light spectrum at the red end, and
centimetric radio waves. |
Infrared radiometer |
A telescope based instrument that
measures the intensity of infrared energy radiated by the targets. |
Injection angle |
The angle at which a spacecraft's
return trajectory intersects the Earth's atmosphere. |
Injector |
Typically, a perforated plate
through which liquid fuel and oxidizer are injected into the combustion chamber at a
controlled rate. |
Intelsat |
Organization of 105 countries
(July 1980) owning or operating systems of satellites used by 144 countries and
territories around the world for international communications, and by 16 countries for
domestic communications. |
Interferometer |
Any of several optical, acoustic,
or radio frequency instruments that use interference phenomena between a reference wave
and an experimental wave or between two parts of an experimental wave to determine
wavelengths and wave velocities, measure very small distances and thicknesses, and measure
indices of refraction. |
Interplanetary magnetic field |
The weak magnetic field filling
interplanetary space, with field lines usually connected to the Sun. The IMF is kept out
of the Earth's magnetosphere, but the interaction of the two plays a major role in the
flow of energy from the solar wind to the Earth's environment. |
Interplanetary probe |
Unmanned instrumented spacecraft
capable of reaching the planets. |
Interplanetary shock |
The abrupt boundary formed at the
front of a plasma cloud (e.g. from a coronal mass ejection) moving much faster than the
rest of the solar wind, as it pushes its way through interplanetary space. |
Interstellar ark |
Hypothetical space colony capable
of transporting human intelligence to the stars. |
Interstallar probe |
Unmanned instrumented spaceship
with artificial intelligence capable of reaching the nearer stars. |
Inverse-square law |
The mathematical description of
how the strength of some forces, including gravity, changes in inverse proportion to the
square of the distance from the source. |
Ion |
An atom that has lost or acquired
one or more electrons. |
Ion engine |
A rocket engine, the thrust of
which is obtained by the electrostatic acceleration of ionized particles. |
Ionization |
Formation of electrically charged
particles. Can be produced by high-energy radiation such as light or UV rays, or by
collision of particles in thermal agitation. |
Ionosphere |
An atmospheric layer dominated by
charged, or ionized, atoms that extends from about 38 to 400 miles above the Earth's
surface. |
IR |
Infrared. |
IRBM |
Intermediate Range Ballistic
Missile (range 500-5,500 km). |
IRFNA |
Inhibited Red Fuming Nitric Acid;
85% HNO3 + < 5% H2O + 6-15% NOX |
ISAS |
Institute of Space and
Aeronautical Science; University of Tokyo (Japan). |
Isotropic |
A property of a distribution of
particles where the flux is constant over all directions. |
Isp |
Specific Impulse. Also
abbreviated SI. |
ISRO |
Indian Space Research
Organization. |
IWFNA |
Inhibited White Fuming Nitric
Acid; 97.5% HNO3 + 2% H2O + < 0.5% NOX |
L-band |
A range of microwave radio
frequencies in the neighborhood of 1 to 2 GHz. |
Lander spacecraft |
A spacecraft designed to reach
the surface of a planet or moon and survive long enough to telemeter data back to Earth. |
Langrangian point |
In a system dominated by two
attracting bodies (such as Sun and Earth), a point at which a third, much smaller body
(such as a satellite) keeps the same position relative to the other two. Theoretically,
the Sun-Earth system has 5 Lagrangian points, but only two are important: L1, on the
sunward side of Earth, about 4 times the distance of the Moon, and L2 at approximately the
same distance on the midnight side. The only two lagrangian stable points, L4 and L5, lie
in the orbit of the primary body, leading and trailing it by a 60-degree arc. Jupiter's
trojan asteroids can be found orbiting around the Jupiter-Sun L4 and L5 points. |
Lanyard |
Small rope or cord. |
Laser |
Light Amplification by the
Stimulated Emission of Radiation. A device for producing a coherent monochromatic
high-intensity beam of light. |
Latitude |
Circles in parallel planes to
that of the equator defining north-south measurements, also called parallels. |
Launch complex |
The complex of site, facilities
and equipment used to launch a missile or space rocket. |
Launch pad |
The load-bearing base from which
a rocket or spacecraft positioned on its launcher is fired. |
Launch window |
An interval of time during which
a space vehicle can be launched to accomplish a given mission, e.g. a flight to Venus or
Mars. |
LC |
Launch Center. |
Leading side |
For a satellite that keeps the
same face toward the planet, the hemisphere that faces forward, into the direction of
motion. |
Leap year |
Every fourth year, in which a
366th day is added since the Earth's revolution takes 365 days 5 hr 49 min. |
LEO |
Low Earth Orbit. |
LGA |
Low-Gain Antenna. |
LH2 |
Liquid Hydrogen. |
Liftoff |
The start of a rocket's flight
from its launch pad. Colloquially, "blast-off". |
Light |
Electromagnetic radiation that is
visible to the eye, in the neighbourhood of 1 nanometer wavelength. |
Light speed |
299,792,458 meters per second +/-
1.2 m/sec (186,282.39 miles/sec). U.S. National Bureau of Standards, 1971. |
Light time |
The amount of time it takes light
or radio signals to travel a certain distance at light speed. |
Light year |
The distance light travels in one
year, approximately 9.46 trillion km (5.88 trillion miles). |
LiOH |
Lithium Hydroxide. |
Liquid hydrogen |
A cryogenic rocket fuel which
becomes liquid at -423oF. |
Liquid oxygen |
A cryogenic oxidizer which
becomes liquid at -279oF. |
Lithosphere |
The crust of a planet. |
LM |
Lunar Module. |
LO2 |
Liquid Oxygen. Also abbreviated
LOX. |
Local time |
Time adjusted for location around
the Earth or other planets in time zones. |
LOI |
Lunar Orbit Insertion. |
Longitude |
Great circles that pass through
both the north and south poles, also called meridians. |
Longitude of ascending node |
In an orbit, the celestial
longitude of the ascending node. |
Longitudinal axis |
The fore-and-aft line through the
center of a space vehicle. |
Low-energy charged particle
detector |
A device designed to characterize
the composition, energies, and angular distributions of charged particles in
interplanetary space and within planetary systems. |
Low-gain antenna |
An omni-directional spacecraft
antenna that provides relatively low data rates at close range, several AU for example. |
LOX |
Liquid Oxygen. Also abbreviated
LO2. |
LRBM |
Long Range Ballistic Missile. |
LRV |
Lunar Roving Vehicle. |
LT |
Launch Time. |
Lunar |
Of or pertaining to the Moon. |
Lunar module |
The craft used by Apollo missions
for Moon landings. The lunar module consisted of a decent stage, used to land on the Moon
and as a platform for liftoff, and an ascent stage, used as crew quarters and for
returning to the orbiting command module. |
Lunar roving vehicle |
A battery powered wheeled vehicle
used by Apollo astronauts to explore the lunar surface. |
LV |
Launch Vehicle. |
Mach |
The ratio of the speed of a
vehicle (or of a liquid or gas) to the local speed of sound. |
Magnetic field |
A region of space near a
magnetized body where magnetic forces can be detected. |
Magnetic field line |
Lines everywhere pointing in the
direction of the magnetic force, used as a device to help visualize magnetic fields. In a
plasma, magnetic field lines also guide the motion of ions and electrons, and direct the
flow of some electric currents. |
Magnetic pole |
Two meanings: (1) the points on
Earth towards which the compass needle points. (2) A concentrated source of magnetic
force, e.g. a bar magnet has two magnetic poles near its end. |
Magnetic storm |
A disturbance of the Earth's
magnetic field initiated by a solar flare or sunspot. |
MagnetoHydroDynamics |
The study of plasma motion and
dynamics in the presence of a magnetic field. |
Magnetometer |
A device for measuring the
strength and direction of the interplanetary and solar magnetic fields. |
Magnetopause |
The boundary of the
magnetosphere, lying inside the bow shock. The location in space where Earth's magnetic
field balances the pressure of the solar wind. It is located about 63,000 km from Earth in
the direction of the Sun. |
Magnetosphere |
That region of space surrounding
the Earth which is dominated by the magnetic field. |
Magnetron |
A vacuum tube in which the flow
of electrons is subject to the control of an external magnetic field. |
Major axis |
The maximum diameter of an
ellipse. |
Manned maneuvering unit |
A portable jet-pack device used
by astronauts to propel themselves through space independent of a spacecraft. |
Mantle |
Middle layer of the Earth;
between the crust and the core. |
Maria |
Dark areas on the Moon, actually
lava plains, once believed to be seas. |
Mars |
Fourth planet from the Sun, a
terrestrial planet. |
Mass |
The quantity of matter in a body.
It can be determined by measuring the force of gravity (weight) acting on it and dividing
this by the gravitational acceleration at that point. Thus, the mass of a given body
remains the same everywhere, while its weight changes with the gravitational attraction. |
Mass ratio |
Ratio of the total mass of a
rocket vehicle to the mass remaining when all the propellant is consumed. |
Max Q |
Maximum dynamic pressure; the
point during launch when the vehicle is subjected to its greatest aerodynamic stress. |
Mean |
Synonym for average. |
Mean solar time |
Time based on an average of the
variations caused by Earth's non-circular orbit. |
Medium-gain antenna |
A spacecraft antenna that
provides greater data rates than a low-gain antenna, with wider angles of coverage than a
high gain antenna, about 20-30 degrees. |
Memory |
The faculty of an electronic
device to record and store data and/or instructions for future action on a command. |
Mercury |
First planet from the Sun, a
terrestrial planet. |
Meridian |
Great circle that passes through
both the north and south poles, also called line of longitude. |
Mesosphere |
A division of the Earth's
atmosphere extending from altitudes ranging 18-30 miles to 48-55 miles. |
Meteor |
The luminous phenomenon seen when
a meteoroid enters the atmosphere, commonly known as a shooting star. |
Meteorite |
A part of a meteoroid that
survives through the Earth's atmosphere. |
Meteoroid |
A solid body, moving in space,
that is smaller than an asteroid and at least as large as a speck of dust. Nearly all
meteoroids originate from asteroids or comets. |
MeV |
One million electron volts. |
MHz |
Megahertz, equal to one million
hertz. |
Microgravity |
An environment of very weak
gravitational forces, such as those within an orbiting spacecraft. Microgravity conditions
in space stations may allow experiments or manufacturing processes that are not possible
on Earth. |
Micrometeoroid |
Meteoroid less than 1/250th of an
inch in diameter. |
Micrometeoroid protection |
Shielding used to protect
spacecraft components from micrometeroid impacts. Interplanetary spacecraft typically use
tough blankets of Kevlar or other strong fabrics to absorb the energy from high-velocity
particles. |
Microwaves |
Radio waves having wavelengths of
less than 20 centimeters. |
Milky Way |
The galaxy which includes the Sun
and Earth. |
Minor planet |
An asteroid. |
Missile |
An object or a weapon that is
fired, thrown, dropped, or otherwise projected at a target; a projectile. |
Mixture ratio |
Ratio of the masses of the fuel
to the oxidizer at any given time. |
MMH |
Monomethyl Hydrazine. A liquid
hypergolic fuel. |
MMU |
Manned Maneuvering Unit. |
Mock-up |
A full-size replica or dummy of a
vehicle, e.g. a spacecraft, often made of some substitute material such as wood to assess
design features. |
Modulation |
The variation of a property of an
electromagnetic wave or signal, such as its amplitude, frequency, or phase. |
Module |
A self-contained unit of a
spacecraft or space station which serves as a building block for the total structure. |
Momentum |
The product of the mass of a body
and its velocity. |
Mono-propellant |
A rocket propellant consisting of
a single substance, especially a liquid containing both fuel and oxidizer, either combined
or mixed together. |
Moon |
A small natural body which orbits
a larger one. A natural satellite. |
Motor |
In spacecraft, a rocket that
burns solid propellants. |
MRBM |
Medium Range Ballistic Missile. |
MSFC |
NASA Marshall Space Flight Center (Huntsville, Alabama). |
MT |
Megatonne, equal to 1 million
tonnes. |
MT |
Moscow Time. |
Multiplexer |
A mechanical or electrical device
for sharing a circuit by two or more coincident signals. |
Multistage rocket |
A rocket having two or more
stages which operate in succession each being discarded as its job is done. |
N2O4 |
Nitrogen Tetroxide. Also
abbreviated NTO. |
Nadir |
The direction from a spacecraft
directly down toward the center of a planet. Opposite the zenith. |
NASA |
National Aeronautics and Space
Administration (USA). |
NASDA |
National Space Development Agency (Japan). |
Nautical mile |
The distance spanned by one
minute of arc in latitude, defined internationally as 1,852 meters (6,076.1033 feet). |
Neptune |
Eighth planet from the Sun, a gas
giant or Jovian planet. |
Neutron |
Atomic particles having
approximately the same mass as a hydrogen atom; very penetrating. |
Newton |
That force which gives a mass of
1 kilogram an acceleration of 1 meter per second per second; equal to 100,000 dynes. |
NiCd |
Nickel Cadmium. |
Nitric acid |
A liquid oxidizer that reacts
spontaneously with hydrazine. Also see IRFNA and IWFNA. |
Nitrogen tetroxide |
A liquid oxidizer that reacts
spontaneously with hydrazine. |
Noctilucent clouds |
Weakly-luminous clouds, seen at
night at heights of about 50 miles (80 km) above the Earth. |
Non-coherent |
Communications mode wherein a
spacecraft generates its downlink frequency independent of any uplink frequency. |
NORAD |
North American Air Defense
Command (USA). |
Nose shroud |
A cover on the nose of a rocket
or spacecraft which jettisons before insertion into orbit. |
Nozzle |
The projecting aperture at the
end of a combustion chamber serving as an outlet for the exhaust gases. |
NRC |
National Research Council (USA). |
NTO |
Nitrogen Tetroxide. Also
abbreviated N2O4. |
Nucleus |
The central body of a comet. |
Occultation |
The passage of a celestial body
across a line between an observer and another celestial object; and the progressive
blocking of light, radio waves, or other radiation from a celestial source during such a
passage. |
OKB |
Experimental Construction Bureau.
|
Omnidirectional |
Capable of transmitting or
receiving signals in all directions, as an antenna. |
OMS |
Orbital Maneuvering System. |
One-way |
Communications mode consisting
only of downlink received from a spacecraft. |
One-way light time |
The elapsed time it takes for
light, or a radio signal, to reach a spacecraft or other body from Earth, or vice versa. |
Oort cloud |
A large swarm of comets theorized
to orbit the sun in the neighborhood of 50,000 AU. |
Orbit |
The path of a body acted upon by
the force of gravity. Under the influence of a single attracting body, all orbital paths
trace out simple conic sections. Although all ballistic or free-fall trajectories follow
an orbital path, the word orbit is more usually associated with the continuous path of a
body which does not impact with its primary. |
Orbit insertion |
The placing of a spacecraft into
orbit around a planet or moon. |
Orbit trim maneuver |
The firing of control rockets to
refine a spacecraft's speed and trajectory. |
Orbital elements |
Six quantities used to
mathematically describe an orbit; i.e. semi-major axis, eccentricity, inclination,
argument of periapsis, time of periapsis passage and longitude of ascending node. |
Orbital mechanics |
The study of the motions of
artificial satellites and space vehicles moving under the influence of forces such as
gravity, drag, and thrust. Also called flight mechanics. |
Orbital module |
That part of a spacecraft which
allows additional volume for crew relaxation and/or experiments. Discarded prior to
reentry. |
Orbital period |
The time taken by an orbiting
body to complete one orbit. |
Orbital velocity |
The velocity necessary to
overcome the gravitational attraction of the Earth and so keep a satellite in orbit, about
17,450 mph (28,080 km/hr) close to the Earth. |
Orbiter spacecraft |
A spacecraft designed to travel
to a distant planet or moon and enter orbit. It must carry a substantial propulsive
capability to decelerate it at the right moment to achieve orbit insertion. |
O-stage |
Rocket boosters which operate
during part of the burning time of the first stage of a launch vehicle to provide
additional thrust. |
OTM |
Orbit Trim Maneuver. |
OTRAG |
Orbital Transport- und Raketen-
Atktiengesellsschaft. |
OWLT |
One-Way Light Time. |
Oxidizer |
An agent that releases oxygen for
combination with another substance, creating combustion and gas for propulsion.
Alternatively oxidants. |
P & W |
Pratt and Whitney (USA). |
Parachute |
An apparatus used to retard free fall, consisting of a light, usually hemispherical canopy attached by cords and stored folded until deployed in descent. |
Parallel |
Circle in parallel planes to that
of the equator defining north-south measurements, also called line of latitude. |
Parking orbit |
Orbit in which a space vehicle
awaits the next phase of its planned mission. |
Parsec |
Measure of distance, 1 parsec =
approximately 3.26 light years. |
Pascal |
A unit of pressure equal to one
newton per square meter. |
Passive cooling |
The use of painting, shading,
reflectors and other techniques to cool a spacecraft. |
Payload |
Revenue-producing or useful cargo
carried by a spacecraft; also, anything carried in a rocket or spacecraft that is not part
of the structure, propellant, or guidance systems. |
PBAN |
Polybutadiene acrylic acid
acrylonitrile. A polymetric fuel binder. |
PDT |
Pacific Daylight Time. |
Pegasus |
A rocket-vehicle concept for
transportation of commercial high-priority freight or 172 passengers. |
Periapsis |
That point in an orbit which is
nearest to the primary. |
Perigee |
That point in a terrestrial orbit
which is nearest to the Earth. |
Perihelion |
That point in a solar orbit which
is nearest to the Sun. |
Perilune |
That point in a lunar orbit which
is nearest to the Moon. |
Period of revolution |
Time of one complete cycle in
orbital motion - referred to as a year when applied to Earth. |
Period of rotation |
Time of one complete cycle -
referred to as a day when applied to Earth. |
Perturbation |
Modifications to simple conic
section orbits caused by such disturbances as air drag, non-uniformity of the Earth, and
gravitational fields of more distant bodies such as the Moon. |
Phase |
Two meanings (1) The particular
appearance of a body's state of illumination, such as the full phase of the moon. (2) As
applied to electromagnetic waves, phase is the relative measurement of the alignment of
two waveforms of similar frequency. |
Phase angle |
The angle in which waves come to
a body. |
Photometer |
An optical instrument that
measures the intensity of light from a source. |
Photometry |
The measurement of light intensities. |
Photon |
A quantum of radiant energy. |
Photon propulsion |
The propulsion of a vehicle by
the emission of photons, which possess momentum. |
Photosphere |
The visible surface of the Sun. |
Photovoltaic cells |
Crystalline wafers called solar
cells which convert sunlight directly into electricity without moving parts. |
Pitch |
The rotation of a vehicle about
its lateral (Y) axis, i.e. movement in elevation. |
Planet |
A nonluminous celestial body
larger than an asteroid or a comet, illuminated by light from a star, such as the sun,
around which it revolves. The only known planets are those of the Sun but others have been
detected on physical (non-observational) grounds around some of the nearer stars. |
Planetoid |
An asteroid. |
Plasma |
A gaslike association of ionized
particles that responds collectively to electric and magnetic fields. |
Plasma detector |
A device for measuring the
density, composition, temperature, velocity and three-dimensional distribution of plasmas
that exist in interplanetary regions and within planetary magnetospheres. |
Plasma engine |
A rocket engine in which thrust
is obtained from the acceleration of a plasma with crossed electrical and magnetic fields.
|
Plasma wave |
An oscillation or wave in a
plasma that falls in the audio range of frequency. |
Plasma wave detector |
A device for measuring the
electrostatic and electromagnetic components of local plasma waves in three dimensions. |
Plasmasphere |
The region of the atmosphere
consisting of cold dense plasma originating in the ionosphere and trapped by the Earth's
magnetic field. |
PLSS |
Portable Life Support System. |
Plug nozzle |
A doughnut-shaped combustion
chamber which discharges engine gases against the surface of a short central cone (the
plug). Adapted in the form of an LH2 cooled heat shield, it can be used as a combination
rocket/ aerodynamic braking device. |
Pluto |
Ninth planet from the Sun,
considered by many a minor planet. |
Plutonium-238 |
A form of the radioactive element
plutonium, characterized by high energy emissions. |
PO |
Polar Orbit. |
Polar orbit |
An orbit which passes over the
poles. |
Polarimeter |
An optical instrument that
measures the direction and extent of the polarization of light reflected from its targets.
|
Polymer |
A compound used as a binder for
solid rocket propellant systems; more generally, a compound consisting of repeating
structural units. |
Potential energy |
The energy of a body due to its
position in a field. |
Pound |
The U.S. customary unit of force
defined as the weight of the standard pound at sea level and at the latitude of 45o.
|
ppm |
Parts per million. |
Precession |
A change in the direction of the
axis of spin of a rotating body. |
Pressure suit |
A suit, with helmet attached,
which is inflated to provide body pressure and air, worn by the crew of certain spacecraft
and aircraft which fly at great altitudes. |
Pressurized |
Containing air or other gas at a
pressure higher than the pressure outside the chamber. |
Primary |
The body around which a satellite
orbits. |
Primitive |
Used in a chemical sense,
indicating an unmodified material representative of the original composition of the solar
nebula. |
Probe |
An unmanned instrumented vehicle
sent into space to gather information. |
Prograde |
Orbital motion in the same
direction as the primary's rotation. |
Propellant |
A chemical or chemical mixture
burned to create the thrust for a rocket or spacecraft. |
Propulsion |
The process of driving or
propelling. |
PST |
Pacific Standard Time. |
PTC |
Passive Thermal Control. |
Pulsar |
Discovered in 1967. Pulsars emit
radio signals the pulsations of which are extremely precise. The evidence suggests that
pulsars are fast-spinning neutron stars. |
Pyrotechnics |
The use of electrically initiated
explosive devices to operate valves, ignite solid rocket motors, and explode bolts to
separate from or jettison hardware, or to deploy appendages. |
Radar |
System or technique for detecting the position, motion, and nature of a remote object by means of radio waves reflected from its surface. |
Radian |
Unit of angular measurement equal to the angle at the center of a circle subtended by an arc equal in length to the radius. Equals about 57.296 degrees. |
Radiation |
Energy in the form of electromagnetic waves or particles. |
Radiation belt |
The region of high-energy
particles trapped in the Earth's magnetic field, also known as the Van Allen belts. |
Radio |
The least energetic form of
electromagnetic radiation, having the lowest frequency and the longest wavelength. |
Radio astronomy |
The science of astronomy using
radio waves instead of light waves. |
Radio guidance |
A system which is dependent on
outside signals for information. |
Radioisotopes |
Atomic particles which decay by
natural radioactivity. |
Radioisotope thermoelectric
generator |
A device that converts the heat
produced by the radioactive decay of plutonium-238 into electricity by an array of
thermocouples made of silicon-germanium junctions. The Pu-238 is contained within a crash
resistant housing. |
Radiometry |
The detection and measurement of
radiant electromagnetic energy, usually in the infrared. |
Rankine |
A temperature scale, having a
degree equal to the Fahrenheit degree but having a zero point at absolute zero. The
freezing point of water is at 459.69oR. |
RCS |
Reaction Control System. |
RD |
Reaktivnyi Dvigatel. Russian for
reaction motor. |
RE |
Unit of distance equal to the
radius of the Earth, 6371.2 km. |
Reaction control system |
System of thrusters used to
control spacecraft attitude. |
Reaction wheels |
Electrically-powered wheels
mounted in three orthogonal axes aboard a spacecraft. To rotate the vehicle in one
direction, you spin up the proper wheel in the opposite direction. To rotate the vehicle
back, you slow down the wheel. |
Readout |
The action of a radio transmitter
sending data either at the same time as data are acquired or by playback from an
electronic memory. |
Receiver |
An electronic device that
receives incoming radio signals and converts them to perceptible forms. |
Red dwarf |
A small star, on the order of 100
times the mass of Jupiter. |
Redundancy |
The duplication of certain
critical components in a space vehicle. |
Reentry |
The descent into Earth's
atmosphere from space. |
Reentry interface |
An altitude 400,000 feet; the
point at which reentering spacecraft are considered to enter the Earth's atmosphere. |
Refraction |
The deflection or bending of
electromagnetic waves when they pass from one kind of transparent medium into another. |
Regenerative cooling |
Circulation of a propellant
through a jacket around the combustion chamber in order to cool the chamber wall, the
propellant subsequently being injected into the combustion chamber. |
Relay |
An electrical switch employing an
armature to open and close circuits. |
Rem |
Roentgen Equivalent Man. A
measure of nuclear radiation causing biological damage. |
Remote sensing |
Instruments that record
characteristics of objects at a distance, sometimes forming an image by gathering,
focusing, and recording reflected light from the Sun, or reflected radio waves emitted by
the spacecraft. |
Rendezvous |
A place of meeting at a given
time, for example, a spaceship with a space station. |
Resolution |
Ability to distinguish visual
detail, usually expressed in terms of the size (in kilometers) of the smallest features
that can be distinguished. |
Resonance |
A relationship in which the
orbital period of one body is related to that of another by a simple integer fraction,
such as 1/2, 2/3, 3/5. |
Retrograde |
Orbital motion in the direction
opposite to the primary's rotation. |
Retrorocket |
A rocket fired to reduce the
speed of a spacecraft. |
Revolution |
Orbital motion about a primary. |
RF |
Radio Frequency. |
Right ascension |
With declination, one of the
coordinates used to designate the location of an object on the celestial sphere. Right
ascension is measured in hours, minutes, and seconds and is similar to longitude on Earth.
|
Ring current |
A very spread-out electric
current circling around the Earth, carried by trapped ions and electrons. |
RJ-1 |
A hydrocarbon rocket fuel (a
refined kerosene). |
RLV |
Reusable Launch Vehicle. |
Rocket |
A missile or vehicle propelled by
the combustion of a fuel and a contained oxygen supply. The forward thrust of a rocket
results when exhaust products are ejected from the tail. |
Rocketdyne |
A division of Rockwell
International concerned with the design and development of rocket engines (USA). |
Roll |
The rotational movement of a
vehicle about a longitudinal (X) axis. |
Rotation |
Rotary motion about an axis. |
Round-trip light time |
The elapsed time is takes for
light, or a radio signal, to travel from Earth, be received and immediately transmitted or
reflected, and return to the starting point. |
RP-1 |
A hydrocarbon rocket fuel (a
refined kerosene). |
RTG |
Radioisotope Thermoelectric
Generator. |
RTLT |
Round-Trip Light Time. |
RV |
Reentry Vehicle. |
SAR |
Synthetic Aperture Radar. |
Satellite |
Any body, natural or artificial,
in orbit around a planet. The term is used most often to describe moons and spacecraft. |
Saturn |
Sixth planet from the Sun, a gas
giant or Jovian planet. |
S-band |
A range of microwave radio
frequencies in the neighborhood of 2 to 4 GHz, used for communicating with piloted space
missions (~2 Ghz). |
SCADA |
Supervisory Control And Data
Acquisition. |
Scan platform |
An articulated, powered appendage
to the spacecraft bus which points in commanded directions, allowing optical observations
to be taken independently of the spacecraft's attitude. |
Seismometer |
A device for measuring movements
of the ground. |
Semi-major axis |
Half the major axis of an
ellipse. The mean distance of a planet or satellite from its primary. |
Sensor |
An electronic device for
measuring or indicating a direction or movement. |
SEP |
Societe Europeene de Propulsion
(France). |
Sequencer |
A mechanical or electrical device
which may be set to initiate a series of events and to make events follow a sequence. |
Service module |
That part of a spacecraft which
usually carries a maneuvering engine, thrusters, electrical supply, oxygen and other
consumables external to the descent module. Discarded prior to reentry. |
SETI |
Search for Extra-Terrestrial
Intelligence. |
Sextant |
An instrument that measures
angular distances from fixed celestial objects. |
Shepherd moon |
Moon which gravitationally
confines ring particles. |
Sidereal time |
Time relative to the stars other
than the Sun. |
Simulator |
A device that mimics the
operational conditions of equipment or vehicles. |
SIS |
Satellite Interceptor System. |
SL |
Sea Level. |
SLBM |
Submarine Launched Ballistic
Missile. |
Slug |
The U.S. customary unit of mass
defined as the mass which receives an acceleration of 1 foot per second per second when a
force of 1 pound is applied to it. |
SM |
Service Module. |
Solar |
Of or pertaining to the Sun. |
Solar array |
See solar panel. |
Solar cell |
A cell that converts sunlight
into electrical energy. The light falling on certain substances (e.g. a silicon cell)
causes an electric current to flow. |
Solar constant |
The electromagnetic radiation
from the Sun that falls on a unit area of surface normal to the line from the Sun, per
unit time, outside the atmosphere, at one astronomical unit. |
Solar flare |
A sudden brightening in some part
of the Sun, followed by the emission of jets of gas and a flood of ultra-violet radiation.
The gale of protons which accompanies a flare can be very dangerous to astronauts. |
Solar nebula |
The large cloud of gas and dust
from which the Sun and planets condensed 4.6 billion years ago. |
Solar panel |
An array of light-sensitive cells
attached to a spacecraft and used to generate electrical power for the vehicle in space.
Also called solar array. |
Solar sensors |
Light-sensitive diodes which
indicate the direction of the Sun. |
Solar wind |
A current of charged particles
that streams outward from the Sun. |
Solid propellant |
A rocket propellant in solid
form; usually consisting of a mixture of fuel and oxidizer. |
Solid rocket booster |
A rocket, powered by solid
propellants, used to launch spacecraft into orbit. |
Sounding rocket |
A research rocket used to obtain
data from the upper atmosphere. |
Space |
The universe beyond Earth's
atmosphere. The boundary at which the atmosphere ends and space begins is not sharp but
starts at approximately 100 miles above Earth's surface. |
Space colony |
Hypothetical extra-terrestrial
habitat, for hundreds, thousands or even millions of people, perhaps established on a moon
or planet or as an artificial construction in free space. |
Space debris |
Man-made objects or parts thereof
in space which do not serve any useful purpose. |
Spacecraft |
A piloted or unpiloted vehicle
designed for travel in space. |
Spacecraft clock |
A counter maintained by the
command & data subsystem. It meters the passing of time during the life of the
spacecraft, and regulates nearly all activity within the spacecraft systems. |
Space platform |
A large artificial satellite
conceived as a habitable base in space with scientific, exploratory or military
applications. A space station. |
Space station |
An orbiting spacecraft designed
to support human activity for an extended time. |
Space weather |
The popular name for
energy-releasing phenomena in the magnetosphere, associated with magnetic storms,
substorms and shocks. |
SPADATS |
Space Detection and Tracking
System (USA). |
SPASUR |
Space Surveillance System (USA). |
Specific impulse |
Parameter for rating the
performance of a rocket engine. Indicates how many pounds or kilograms of thrust are
obtained by consumption of a pound or kilogram of propellant in one second. |
Spectrometer |
An optical instrument that splits
the light received from an object into its component wavelengths by means of a diffraction
grating; then measuring the amplitudes of the individual wavelengths. |
Spectroscopy |
The study of the production,
measurement and interpretation of electromagnetic spectra. |
Spectrum |
A particular distribution of
wavelengths and frequencies. |
Spin stabilization |
Spacecraft stabilization
accomplished by rotating the spacecraft mass, thus using gyroscopic action as the
stabilizing mechanism. |
SRB |
Solid Rocket Booster. |
SRB propellant |
Composite propellant used in the
Space Shuttle Solid Rocket Boosters. Consists mainly of ammonium perchlorate as the
oxidizer, powdered aluminum as the metallic fuel, and PBAN, polybutadiene-acrylic
acid-acrylonitrile terpolymer, as the polymeric fuel binder. A small amount of iron oxide
is added to increase the burning rate. The final product is a rubbery material not unlike
a typewriter eraser. |
SRC |
Science Research Council (UK). |
SSO |
Sun-Synchronous Orbit. |
SSPO |
Sun-Synchronous Polar Orbit. |
Stage |
An independently powered section
of a rocket or spacecraft, often combined with others to form multistage vehicles. |
Star |
A self-luminous celestial body
consisting of a mass of gas held together by its own gravity in which the energy generated
by nuclear reactions in the interior is balanced by the outflow of energy to the surface,
and the inward-directed gravitational forces are balanced by the outward-directed gas and
radiation pressures. |
Static firing |
The firing of a rocket on a
special test stand to measure thrust, etc. |
Stratosphere |
A division of the Earth's
atmosphere extending from altitudes ranging 5-10 miles to 18-30 miles. |
Subatomic particles |
Fundamental components of matter
such as electrons or protons. |
Subcarrier |
Modulation applied to a carrier
which is itself modulated with information-carrying variations. |
Sublimator |
An exposed metal plate, located
on the outside of a spacesuit, that functions as a cooling coil to control suit
temperatures. |
Sub-orbital |
Not attaining orbit, i.e. a
ballistic space shot. |
Sub-satellite |
A secondary object released from
a parent satellite in orbit, e.g. an electronic "ferret" released by a
reconnaissance satellite. |
Sunspot cycle |
The recurring, eleven-year rise
and fall in the number of sunspots. |
Sunspots |
Dark regions on the Sun which are
the centers of large vortices and possess powerful magnetic fields. Maximum sunspot
activity occurs in cycles with a period of about 11 years. |
Sun sychronous orbit |
A walking orbit whose orbital
plan precesses with the same period as the planet's solar orbital period. In such an
orbit, a satellite crosses periapsis at about the same local time every orbit. |
Superior conjunction |
Alignment between Earth and a
planet on the far side of the Sun. |
Superior planets |
Planets whose orbits are farther
from the Sun than Earth's, i.e. Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. Also
called outer planets. |
Supernova |
A large dying star, the final
collapse of which is a cataclysmic explosion, hurling its substance into space. |
Surface penetrator |
A probe designed to penetrate the
surface of a body, surviving an impact of hundreds of g's, measuring and telemetering the
properties of the penetrated surface. |
Surface rover |
A semi-autonomous roving vehicle
deployed on the surface of a planet or other body, taking images and soil analyses for
telemetering back to Earth. |
Sustainer engine |
An engine that maintains
propulsion of a launch vehicle once it has discarded its boosters. |
Synthetic aperture radar |
A radar imaging instrument which
provides a penetrating illumination of radio waves, and is capable of imaging surfaces
covered by clouds and haze. SAR images are constructed of a matrix where lines of constant
distance or range intersect with lines of constant Doppler shift. |
Tape recorder |
A mechanical device for recording
digital information on magnetic tape and for playing back the recorded material. |
TCM |
Trajectory Corrective Maneuver. |
TEI |
Trans-Earth Injection. |
Telecommunication |
Any process of communication over
considerable distance. |
Telemetry |
The system for radioing
information, including instrument readings and recordings, from a space vehicle to the
ground. |
Terrestrial |
Of or pertaining to the Earth. |
Terrestrial planet |
Any of the four planets closest
to the Sun: Mercury, Venus, Earth, Mars |
Thermal energy |
Energy in the form of heat. |
Thermal tile |
Silica fiber insulation used to
protect 70% of the exterior of the Space Shuttle orbiter against reentry temperatures of
up to 1430oC. Surface heat dissipates so rapidly that an uncoated tile can be
held by its edges with the bare hand while its interior glows red hot. |
Thermosphere |
The Earth atmosphere between 120
and 250 to 400 km (depending on the solar and geomagnetic activity levels), where
temperature has an exponential increase up to a limiting value Texo at the thermopause.
The temperature Texo is called the exospheric temperature. |
Three-axis stabilization |
Stabilization accomplished by
nudging a spacecraft back and forth within a deadband of allowed attitude error, using
small thrusters or reaction wheels. |
Three-way |
Coherent communications mode
wherein a DSS receives a downlink whose frequency is based upon the frequency of an uplink
provided by another DSS. |
Throat |
That part of a rocket engine
between the combustion chamber and nozzle. |
Throttle |
To decrease the supply of
propellant to an engine, reducing thrust. Liquid propellant rocket engines can be
throttled; solid rocket motors cannot. |
Thrust |
The force that propels a rocket
or spacecraft measured in pounds, kilograms or Newtons. Thrust is generated by a
high-speed jet of gases discharging through a nozzle. |
Thrust chamber |
The area in a propulsion rocket
in which force accumulates before ejection, e.g. the reaction chamber. |
Thruster |
Rocket engines used for
maneuvering spacecraft in space. |
Thrust vector control |
Control of the thrust vector
direction to steer a rocket or spacecraft during powered flight. Thrust vector control is
most often achieved by hydraulically gimbaled engines. |
Time of periapsis passage |
The time in which a planet or
satellite moves through its point of periapsis. |
TLI |
Trans-Lunar Injection. |
TNT |
Trinitrotoluene, a high
explosive. |
Tonne |
Metric ton, a unit of mass equal
to 1,000 kilograms (2,205 pounds). |
Torus |
Solid geometrical figure with the
shape of a doughnut or innertube. |
Tracking |
The science of monitoring
satellite locations by means of radio antennas at ground stations or by using other
satellite systems in space. |
Tracking station |
A station set up to track an
object through the atmosphere or space, usually by means of radar or radio. |
Trailing side |
For a satellite that keeps the
same face toward the planet, the hemisphere that faces backwards, away from the direction
of motion. |
Trajectory |
The flight path of a projectile,
missile, rocket or satellite. |
Transducer |
Device for changing one kind of
energy into another, typically from heat, position, or pressure into a varying electrical
voltage or vice-versa, such as a microphone or speaker. |
Trans-Earth injection |
The firing of a spacecraft's
engines to increase speed and break out of a orbit around the Moon, or another planet, and
begin it on a trajectory to Earth. |
Trans-Lunar injection |
The firing of a spacecraft's
engines to increase speed and break out of a parking orbit around Earth and begin it on a
trajectory to the Moon. |
Trans-Neptunian object |
A small body orbiting the Sun
beyond Neptune in a region known as the Kuiper belt. |
Transmitter |
An electronic device that
generates and amplifies a carrier wave, modulates it with a meaningful signal, and
radiates the resulting signal from an antenna. |
Transponder |
A device that transmits a
response signal automatically when activated by an incoming signal. |
Trojan relay system |
A method of ensuring
uninterrupted radio contact with the surface of any planet in the Solar System at any time
first proposed by James Strong in 1967. Two radio satellites, keeping station along the
Earth orbit, 60o ahead and 60o behind the Earth, transmit/receive
signals from a similar pair of relay satellites at the Trojan equilaterals of another
planet. Radio communications via these satellite links, from surface to surface, then
becomes possible day and night, despite planetary rotation or orbital displacement. It
could be used, for example, in steering a remotely-controlled vehicle on the surface of
Mars. |
Tropopause |
The level separating the
troposphere and the stratosphere, occurring at an altitude of 5-10 miles. |
Troposphere |
A division of the Earth's
atmosphere extending from ground level to altitudes ranging 5-10 miles. |
True anomaly |
The angular distance of a point
in an orbit past the point of periapsis, measured in degrees. |
TT&C |
Tracking, Telemetry and Command. |
Turbopump |
A pump driven by a gas turbine,
generally used to pump propellant into a combustion chamber. |
TVC |
Thrust Vector Control. |
Two-way |
Communications mode consisting of
downlink received from a spacecraft while uplink is being received at the spacecraft. |
UDMH |
Unsymmetrical Dimethyl Hydrazine. A liquid hypergolic fuel. |
UHF |
Ultrahigh Frequency. |
Ullage |
The amount by which a container, such as a tank, falls short of being full. |
Ultrahigh frequency |
Short radio waves used for communicating with spacecraft. |
Ultraviolet |
A band of electromagnetic radiation with a higher frequency and shorter wavelength than visible blue light. Ultraviolet astronomy is generally performed in space, since Earth's atmosphere absorbs most ultraviolet radiation. |
|
Umbilical |
A cable conveying power to a rocket or spacecraft before liftoff. Also a tethering or supply line for an astronaut outside a spacecraft. |
Universal time |
The mean solar time of the meridian of Greenwich, England. Formerly called Greenwich mean time. |
Universal time coordinated |
The world-wide scientific standard of timekeeping; based upon carefully maintained atomic clocks and accurate to within microseconds. The addition or subtraction of leap seconds, as necessary, keeps it in step with Earth's rotation. Its reference point is Greenwich, England; when it is midnight there, it is midnight UTC. |
Universe |
All matter and energy, including Earth, the galaxies and all therein, and the contents of intergalactic space, regarded as a whole. |
Uplink |
The radio signal transmitted to a spacecraft from Earth. |
Uranus |
Seventh planet from the Sun, a gas giant or Jovian planet. |
UT |
Universal Time. |
UTC |
United Technologies Corporation; Chemical Systems Division (USA). |
UTC |
Universal Time Coordinated. |
UV |
Ultraviolet. |