Glossary - T

Telecommand
instruction intended to modify the mode or configuration of a satellite sent over a dedicated radio link between the satellite control centre and the satellite
(spacecraft technology)

Telemetry
continuous stream of data transmitted by the satellite to the satellite control centre providing information on the status of the satellite and the values of key operational parameters
(spacecraft technology)

Terminator
the line between the sunlit and dark regions on the surface of a planet or moon
(astronomy)

Terrestrial planet
one of the four inner rocky planets (Mercury, Venus, Earth and Mars)
(astronomy, planetary science)

Thermosphere
the layer in the Earth’s upper atmosphere between the mesosphere and the exosphere
(atmospheric physics)

Thruster
a chemical or electrical propulsive device used for station keeping, attitude control and for long duration, low thrust acceleration
(launcher technology, spacecraft technology)

Time Division Multiple Access (TDMA)
a technique in which several earth stations share a repeater by transmitting on the same frequency but at different times
(communications)

Tine
see finger
(technology)

Trajectory
the path followed by a spacecraft or launch vehicle
(launcher technology, spacecraft technology)

Transceiver
a transmitter and receiver in a single unit
(communications)

Transducer
an electronics device which converts energy from one form to another, generally to an electrical signal
(launcher technology, spacecraft technology)

Transponder
signal path through a communications satellite payload which receives, amplifies and retransmits a channel; another name for transponder is repeater
(satellite communications)

Travelling wave tube
a type of vacuum tube used for the wideband amplification of microwave signals; as the microwaves travel down a helical coil in the tube, they absorb power from a beam of electrons directed along the axis of the helix resulting in amplification of the microwave signal; travelling wave tubes have now been replaced by more reliable solid state amplifiers in many applications
(earth station technology, spacecraft technology)

Troposphere
the lowest layer of the Earth’s atmosphere
(atmospheric physics)

True anomaly
the angular distance (measured in degrees) of a point in an orbit past the point of periapsis
(orbital geometry)