4 Terms and Definitions

   For the purposes of this specification, the following terms and definitions apply.

   (from IEEE Std 1000 [1972]) “Measurement with the aid of intermediate means that permit the measurement to be interpreted at a distance from the primary detector.? All measurements on board the spacecraft are transmitted to the ground system in a telemetry stream. Telemetry as used here refers to these measurements whether on-board the spacecraft or transmitted to the ground system. Most telemetry measurements will require engineering unit conversion and measurements will have associated validation ranges or lists of acceptable values.

   Messages that instruct an action on a remote system. Spacecraft commanding usually implies coding and packaging of the command information, validation and verification, as well as authorization to perform. Telemetry and Commanding data are necessarily related to one another, with some command information originating from telemetry and commands relating to particular telemetry measurements. Therefore, the ability to relate individual telemetry with one another and to commands is a very important part of this specification. Packaging of both telemetry and commands can be performed in a number of ways. The most common way to package data for transmission is to use the CCSDS Telemetry and Commanding Packaging format.