ESA Technical Note on RTU Reconfigurations

The following COBS functions trigger RTU reconfigurations (Hope I got them all):

Note that a CDMU reconfiguration implies a reboot of the COBS and thus (even without any RTU reconfigurations) a TM acquisition interruption.

For each RTU reconfiguration from nominal to redundant the sequence commanded by the COBS can be described as follows:

  1. Switch nominal power off
  2. Switch redundant power off
  3. Wait 5 seconds
  4. Select redundant RCC (Remote Control Core)
  5. Select redundant IUB (Internal User Bus)
  6. Switch redundant power on
  7. Wait 600 msec

Such a sequence is called a PRCG (Peripheral Reconfiguration Command Group) sequence in COBS jargon. Before a PRCG sequence starts the COBS stops all activity on the OBDH bus:

The sending of telemetry packets to the transfer frame generator (and the ground) is not interrupted, but the contents of the packets are completely undefined during the PRCG sequence.

All normal COBS TM and TC processing is resumed when the PRCG sequence is finished.

For any RTU reconfiguration there will be an interruption in the TM acquisitions from the instruments. However, as long as the PLM RTU is not reconfigured the various BCPs (Broadcast pulses) are still distributed, i.e BCP1 (the major frame pulse, approximately every 15 seconds) and BCP4 (the clock signal, typically used for updating of the local OBT). For a PLM reconfiguration these signals also disappear (since the PLM RTU is switched off). This means you might miss a BCP1 if it is sent out during the time the PLM RTU is off (or when the CDMU is rebooting).

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