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)

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
(spacecraft technology)

Thruster
a chemical device used for attitude control
(launcher 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)

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

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directed along the axis of the helix resulting in amplification of the microwave signal; travelling wave tubes have now been replaced by more reliable solid state amplifiers in many applications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)