(Used with permission from The Dream Is Alive - Space Flight and Operations Earth Orbit © 1991)


Ablative material Designed to provide thermal protection to a spacecraft, especially on reentry, through a loss of mass in a fluid stream.

Abort To cut short or break off an action, operation, or procedure with a vehicle, especially when a piece of equipment fails.

Acceleration The rate of change of velocity.

Aerobrake A mushroom-shaped structure on a spacecraft used as an airbrake to slow it in the upper layers of a planet's atmosphere, used to conserve propellants.

Aerodynamic vehicle A device, such as an airplane, capable of flight only within a sensible atmosphere and relying on aerodynamic forces to maintain flight.

Airlock A hermetically sealed chamber used for passage between modules having different pressures.

Anti-satellite (ASAT) A system or device (satellite) whose purpose is to negate the mission of an enemy's operational satellite. Methods employed could be the physical destruction of a satellite (exploding ballistic satellite), or interference with the satellite's communications or power systems (laser beams or particle beam).

Aphelion Point which is farthest from the Sun on an elliptical orbit around the Sun.

Apogee The point which is farthest from the Earth on an elliptical orbit around the Earth.

Apogee motor A propulsive device for boosting a payload from an initial parking orbit to a higher apogee (LEO to GEO).

Argument of perigee The angular arc traversed from the ascending node to perigee as seen by observer at near focus; measured in orbital plane in satellite's direction of travel.

Ascending node The point along the equator which a satellite passes when traveling from the southern hemisphere to the northern hemisphere.

Astronautics The art, skill, or activity of operating space vehicles, or in a broader sense, the science of space flight.

Attenuation Reduction in intensity.

Attitude The position or orientation of a vehicle.

Automation The use of electronic or mechanical machines to perform routine functions with minimal human intervention.

Avionics Contraction of aviation and electronics; the application of electronics to systems and equipment used in aircraft and spacecraft.

Azimuth Horizontal direction or bearing.


Backup An item kept available to replace an item that fails to perform satisfactorily.

Baffle An obstruction in a combustion chamber used to prevent combustion instability by maintaining uniform mixtures and equalizing pressures; in a fuel tank, used to prevent sloshing by damping propellant oscillation.

Ballistic trajectory The path followed by a body being acted upon only by gravitational forces and by the resistance of the medium through which it passes.

Bent-pipe communication Use of relay stations to achieve non-line-of-sight transmission links.

Beta Trade name for a very fine fiberglass fabric.

Biosphere The total environment of Earth that supports self-sustaining and self-regulating human, plant, and animal life, or an artificial closed ecology system in which biological systems provide mutual support and recycling of air, water, and food.

Bit A binary digit; a unit of a byte of computer data stored in binary notation.

Black box Colloquially, any electronic device such as an amplifier or radio, that can be mounted or removed as a single package.

Blackout A fadeout of radio and telemetry transmission between ground stations and vehicles traveling at high speeds in the atmosphere caused by signal attenuation in passing through ionized boundary-layer (plasma sheath) and shockwave regions generated by the vehicle.

Bootstrap Referring to a self-generating or self-sustaining process.

Buffer A storage device used to compensate for a difference in rate of flow of information or time of occurrence of events when transmitting information or data.

Burn Rocket engine firing.

Burnout An act or instance of fuel or oxidizer depletion or ideally, the simultaneous depletion of both.

Bus A main circuit or conductor path for the transfer of electrical power or, in the case of computers, information.


Cathode-ray tube (CRT) A vacuum tube (television screen) consisting of an electron gun that directs a beam that impinges on a phosphorescent coating in the back of viewing screen.

Cislunar Referring to the space between the Earth and the Moon.

Coldsoak The exposure of equipment to low temperature for a long period of time to ensure that the temperature of the equipment is lowered to that of the surrounding atmosphere.

Command, control, and communications (C3) The electronic network which oversees, manages, and directs the globally distributed support and combat forces.

Composite material Structural material made of metal alloys or plastics with built-in strengthening agents which may be in the form of filaments, foils, or flakes of a strong material.

Countdown The time period in which a sequence of events is carried out to launch a rocket; the sequence of events.

Cryogenic Requiring or involving the use of very low temperature.


Decoder A device for translating electrical signals into predetermined functions.

Deorbit burn A retrograde rocket engine firing which slows vehicle velocity to less than that required to remain in orbit.

Diurnal Referring to a daily occurrence.

Docking The act of joining two or more orbiting objects.

Doppler effect The change in frequency with which energy reaches a receiver when the receiver and the energy source are in motion relative to each other; also called Doppler shift.

Dynamic pressure The pressure of a fluid resulting from its motion.


Elevon A horizontal aerodynamic control surface combining the functions of an elevator and an aileron.

Electromagnetic pulse (EMP) A by-product of nuclear explosions which is created by gamma ray interaction with atmospheric molecules. The interaction produces strong electromagnetic fields which can render electronic devices useless over a large area.

Electromagnetic spectrum The range of wavelengths of electro-magnetic waves including (in order of decreasing wavelength): radio, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma rays.

Electronic intelligence (Elint) The interception and analyzing of electromagnetic signals of other countries including radars, radio, telephone, and microwave transmissions. Done effectively utilizing satellites.

Electrophoresis A process by which different materials mixed together in a fluid are separated from one another by the application of an electrical field; used in making pharmaceutical in the weightlessness of space.

End effector The device on the end of a robot "arm" used to grasp.

Endoatmospheric Taking place within the atmosphere. For SDI, those weapons used in the boost or terminal phases of a missle's flight.

Ephemeris The set of numbers which specifies the location of a celestial body or satellite in space.

Epoch A particular instant for which certain data are valid.

Epoxy A polymer characterized by low shrinkage, good adhesion, mechanical and electrical and electrical strength, and chemical resistance.

Escape velocity The radial speed which a particle or larger body must attain in order to escape from the gravitational field of a planet or star.

Exoatmospheric Taking place outside of the atmosphere; generally above 75 miles in altitude above the Earth. For SDI, those weapons systems that are used in the post-boost or midcourse phase.

Expansion ratio The ratio between the gas pressure in a rocket combustion chamber to the gas pressure at the nozzle outlet.


Fairing Structural member designed to reduce drag or air resistance.

Footprint An area within which a spacecraft is intended to land.

Frangible Ready or easily broken.

Fuel cell A device that converts chemical energy directly into electrical energy by reacting chemicals supplied continuously.


g Symbol representing the acceleration due to gravity.

Geostationary Earth Orbit (GEO) A circular orbit approximately 22,300 statute miles above the Earth's surface in the plane of the equator. An object in this orbit rotates at the same rate as the planet and appears to be stationary with regard to any point of Earth's surface. It is a specific type of geosynchronous orbit.

Geosynchronous orbit An orbit in which a satellite revolves about the Earth at the same rate at which the Earth rotates on its axis. It is 22,300 statute miles, 19,300 nautical miles, or 35,880 kilometers above the surface of the Earth. From the Earth, the satellite appears to be stationary over a point on the Earth.

giga A prefix meaning multiplied by 1 billion.

Gimbal A device with two mutually perpendicular and intersecting axes of rotation, thus giving free angular movement in two directions, on which an engine or other object may be mounted. Also, to move a reaction engine about on a gimbal to obtain pitching and yawing correction movements.

Grapple A fixture attached to a satellite or payload so the end effector of the Orbiter's remote manipulator arm can grasp it and maneuver it.

Gyro A device which utilizes the angular momentum of a spinning rotor to sense the angular motion of its base about one or two axes at right angles to the spin axis.


Hardcopy A written record or electrocopy of a cathode-ray tube display.

Heat exhanger A device for transferring heat from one fluid to another without inter-mixing the fluids.

Hohmann transfer Transfer orbit which requiring the minimum amount of energy or delta V.

Hold During a countdown: to halt the sequence of events until an impediment has been removed so that the countdown can be resumed.

Housekeeping Those routine tasks required to maintain spacecraft in habitable and operational condition during flight.

Hypergolic A rocket propellant that ignites spontaneously on contact; referring to the ignition of a hypergolic fuel and oxidizer.


Inclination The angle between the plane of an orbit and a reference plane, usually the Equator, measured at the point where the spacecraft crosses from the southern hemisphere to the northern hemisphere. The angle of inclination is also equal to the maximum latitude (north and south) that the groundtrack will reach.

Inertial guidance Guidance by means of acceleration measured and integrated within the craft.

Infrared Electromagnetic waves with wavelengths just below visible light (1 to 1,000 micrometers).

Infrastructure The basic facilities, installations, and support equipment needed for an organization or system to operate.

Interkosmos Soviet space organization which includes Bulgaria, Cuba, Czechoslovakia, German Democratic Republic, Hungary, Mongolia, Poland, Romania, and Vietnam.


Kapton Trade name for a high-temperature polymide film.

Kevlar Trade name for an epoxy glass fabric.

Ku-band A frequency band extending approximately from 15.35 to 17.25 gigahertz.


L-band A frequency band extending from approximately 0.39 to 1.55 gigahertz.

Libration points Unique locations in space where the gravitational attraction of two or more celestial bodies add to zero; a neutral point in the gravitational field. Also known as Lagrangian points.

Light-emitting diode (LED) Semiconductor device that radiates in the visible regions which is used for alphanumeric displays.

Limb The edge of the disk of the Sun or Earth.

Limber hole A drain hole near the bottom of a frame or other structural member.

Line of apsides Major axis of an elliptical orbit.

Lithium hydroxide Chemical compound used to remove carbon dioxide from a closed atmosphere.


Mass The amount of matter in a body; a measure of a body's resistance to acceleration.

Mach number The ratio of the speed of a body with respect to the surrounding fluid to the speed of sound in the medium. In a standard atmosphere at sea level, the speed of sound is approximately 760 mph and increases with temperature.

Metric data (downlink) Telemetered systems condition information.

Meteor Bright streak of light caused by a meteoroid falling and burning up in the Earth's atmosphere.

Meteorite A meteoroid which has survived the fall through the atmosphere and lands on the Earth's surface.

Meteoroid A piece of rock, metal, or frozen gas in space.

Micro a prefix meaning divided by 1 million.

Microgravity An extremely low level of gravity. Shuttle crews experience about one-millionth the level of gravity on the Earth's surface.

Microwave Of, or pertaining to, radiation in that region of the radio spectrum between approximately 1,000 and 300,000 megahertz.

Mockup A full-sized replica, which may incorporate actual functioning equipment.

Multiplexing Simultaneous transmission of more that one signal through a single transmission path (conductor).

Mutual Assured Destruction (MAD) A strategic deterrent philosophy which assumes that if neither superpower possesses a credible ballistic missile defensive system neither side will launch a nuclear strike because large portions of both countries will inevitably be destroyed. MAD was cornerstone of US approval of the ABM treaty, which severely limited ballistic missile defenses.

Mylar Trade name for a polyester film with high strength and extremely good transparency and electrical properties.


Nano A prefix meaning divided by 1 billion.

Nautical mile One minute of a great circle of the Earth (latitude), equivalent to 6080 feet or 1.9 km.

Nomex Trade name for a high-temperature resistant nylon.


Occultation The disappearance of a body behind another body of larger apparent size.

Ordnance Pyrotecnic or explosive devices.


Particle beam weapons Devices which generate, accelerate, and direct high-velocity particles in a narrow beam, usually to destroy a target by means of the tremendous kinetic energy of the particles (electrons, protons, or neutrons).

Perihelion The point which is closest to the Sun on an elliptical orbit around Earth.

Perigee The point which is closest to the Earth on an elliptical orbit around the Earth.

Period The time required for a spacecraft to complete one orbit as viewed from space.

Pitch An angular displacement about an axis parallel to the lateral (widthwise) axis of a vehicle. For the Orbiter, a pitch change would result in the nose moving up or down.

Pogo Term used to describe longitudinal dynamic oscillations generated by the interaction of vehicle structural dynamics with propellant and the engine combustion process.


Radar Radio Detecting and Ranging; a device which transmits a microwave pulse, and calculates the distance, direction, and speed of an object from the returned pulse reflected by the object.

Real time Time in which reporting on events or recording of events is simultaneous with the events.

Reconnaissance Gathering of intelligence data including images, telemetry, etc. from an area of interest over a short period of time.

Redline Critical limit of a parameter.

Remote sensing Using satellite platforms to examine the electromagnetic waves emitted and reflected from the surface of the Earth or other objects.

Rendezvous The bringing together of two or more objects at a specified time and place.

Resolution The size of the smallest object that can be distinguished from its surroundings.

Rib A fore-and-aft structural member of an airfoil used for maintaining the correct covering contour and also for stress bearing.

Robotics The use of automated machines to replace human effort, although they may not perform functions in a humanlike manner.

Rocket engine A reaction engine that contains both fuel and oxidizer and that therefore can be operated in the absence of air.

Roll Rotational or oscillatory movement about the longitudinal (lengthwise) axis of a vehicle; for the Orbiter a wing up (other wing down) or wing down maneuver.

Rollout That portion of landing an aerodynamic vehicle following touchdown.


Satellite An object in orbit around a larger object; a man-made object in orbit around the Earth. Also, moons are satellites of planets; planets are satellites of the Sun.

S-band A frequency band extending approximately from 1.55 to 5.2 gigahertz.

SCRAMJET A supersonic combustion ramjet engine which can operate in the hypersonic region of flight.

Scrub To cancel a scheduled rocket firing.

Shirt-sleeve environment Cabin atmosphere similar to the Earth's surface, not requiring a pressure suit.

Signature Referring to remote sensing, the characteristic intensities of various wavelengths of electromagnetic radiation coming from an object which uniquely identifies that object.

Solid-state device A device that uses the electric, magnetic, and photic properties of solid materials.

Space The part of the universe lying outside of the limits of the Earth's atmosphere. More generally, the volume in which all spatial bodies move.

Spacecraft Devices, manned or unmanned, which are designed to be placed into an orbit about the Earth or into a trajectory to another celestial body.

Spar A main spanwise member of an airfoil, or control surface

Specific impulse A performance parameter of a rocket propellant, expressed in seconds, equal to the thrust divided by the weight flow rate. It is the ratio of the pounds of thrust produced by the engine, minus the drag from the engine, per pounds of fuel flowing through the engine each second.

State vector Ground-generated spacecraft position, velocity, and timing information uplinked to the spacecraft computer for use as a navigational reference by the crew.

Station keeping The sequence of maneuvers that maintains a vehicle in a predetermined orbit.

Stringer A slender, lightweight, lengthwise fill-in structural member in a rocket body serving to reinforce and give shape to the skin.

Sublimation The vaporization of a solid without the intermediate formation of a liquid.

Sun-synchronous A special retrograde (satellites appear to move from east to west) orbits which retain their relative positions with respect to the Sun. Satellite crosses the equator at precisely the same local time on each pass.

System-generated electromagnetic pulse (SGEMP) A phenomenon in which EMP is generated directly within a system after encountering gamma- and X-radiation from a nuclear detonation. Nuclear hardening defers to design features incorporated to minimize SGEMP.


Telemetry The science of measuring a quantity or quantities, transmitting the results to a distant station, and then interpreting, indicating, or recording the quantities measured; also, the data so treated.

Terminator On a planet, the line which divides daylight from darkness.

Terraform Modify the environment of a planet to make it more Earth-like and habitable by humans.

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

Trajectory Path followed by a vehicle.

Transducer General term for any device that converts a physical magnitude of one form of energy into another form (e.g. electrical to acoustic as in a speaker).

Translation Movement in a straight line without rotation.

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

Trim Adjustment of an aerodynamic vehicle's controls to achieve stability in a desired condition of flight.

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


Ullage The amount that a container, such as a fuel tank, lacks of being full.

Ultrahigh frequency (UHF) A frequency between 0.3 and 3 gigahertz

Umbilical A servicing electrical or fluid line between the ground or tower and an uprighted rocket vehicle before launch.

Universal time Time defined by the rotational motion of the Earth and determined from the apparent daily motions that reflect this rotation; also called Greenwich mean time.


Vehicle A structure, machine, or device such as an aircraft or rocket, designed to carry a payload through air or space.

Velcro Trade name for hook and pile fastener, generally of nylon, used to replace zippers and to secure miscellaneous items.


Weight The force with which an earthbound body is attracted toward the center of the Earth.


Yaw Rotational or oscillatory movement about the vertical (height-wise) axis of a vehicle; on the Orbiter it would cause a nose movement left or right.


Zero g Weightlessness.


© 2015-2019 by Ernest W. Maurer, Ph.D.