The On-Board Data Handling (OBDH) subsystem, which performs the primary spacecraft control functions, is based on an ESA standard approach and remains unchanged from the original Cluster mission. It consists of:

• A Central Data Management Unit (CDMU)
• A Remote Terminal Unit (RTU)
• One Solid-State Recorders (SSR)

The CDMU and RTU are internally redundant; the SSR provides memory for about 5 Gbit of data at beginning of life. The OBDH decodes and distributes commands, received by the telecommunication subsystem at a command bit rate of 2 kbit/s, and acquires and encodes telemetry from payload and subsystem units. This telemetry is delivered either to the telecommunications subsystem for real-time transmission to ground, and/or to the SSR for later transmission. Dedicated high-data-rate interfaces are provided to the Wide-Band Data (WBD) experiment and the SSR. Stored data will be played back at a much higher rate than real-time data, in order to reduce the duration of the downlink during the limited ground-station visibility periods. WBD telemetry will only be transmitted in real-time.

Telemetry-stream bit rates are fixed at about:

• 2 kbit/s for housekeeping telemetry
• 22 kbit/s for nominal science telemetry
• 131 kbit/s for burst science-data/recorder playback
• 262 kbit/s for WBD transmission/recorder playback

The OBDH also provides timing and synchronisation signals to payload and subsystem units, as well as AOCMS data to the payload. It will perform a surveillance function using on-board software to provide the autonomy required because of the extended non-visibility periods.

	Design in Detail
	Telecoms