Mass, Power and Telemetry

The Cluster FGM has been designed with minimised resources while ensuring full redundancy and reliability. The Electronics box is only 0.6mm thick in places and power has been reduced through the use of very low-power, radiation-hardened devices combined with intelligent fault tolerant electronic design. The robust nature of the instrument is illustrated by the fact that the FGM on all four spacecraft have continuously operated on all main hardware since switch-on in 2000 and remain in good shape for the the forseeable future.

Telemetry Formats & Commanding

The table above details the FGM operation modes routinely used in flight. The data stream from each sensor is controlled by selecting one of the sensors to be primary (high data rate), the other secondary (lower data rate) - by default the OB sensor is set to the high data rate. The selection of a particular mode is controlled by the mission timeline which is derived from the Cluster Master Science Plan. Command sequences for mode switches are finalised some weeks before their execution time so that they can be integrated into the overall command lists prepared by the operations centre. On occasion The FGM team also runs dedicated command sequences for the purpose of instrument calibration during solar wind passages.