Glossary of Space Exploration Terminology

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T
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.
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.
Thruster
Rocket engines used for maneuvering spacecraft in space.
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.
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.
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.
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.

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Rocketry & Space Technology

Glossary courtesy of Robert Braeunig's
Rocketry & Space Technology website.