> The CCS has five fault-protection algorithms (FPAs) stored in memory, as
summarized in Table 3-9. The two algorithms most directly related to the
telecommunications system are named RF Loss and Command Loss [19].
> 3.7.3.1 RF Loss. RF Loss provides a means for the spacecraft to automatically
recover from an S- or X-band exciter or power amplifier degradation or failure
affecting the unit’s RF output. The CCS monitors the output RF power at four
points in the RFS: the S-band exciter and S-band power amplifier and the X-
band exciter and X-TWTA. If the output RF power from one or more powered-
on units drops below a threshold level, the algorithm will attempt to correct the
problem by switching to the redundant unit.
> 3.7.3.2 Command Loss. Command Loss provides a means for the spacecraft
to automatically respond to an onboard failure resulting in the inability to
receive or recognize ground commands. If a period of time set in the flight
software goes by without the spacecraft recognizing a valid uplinked command,
the Command Loss timer expires. The algorithm responds to the presumed
spacecraft failure28 and attempts to correct that failure by systematically
switching to redundant hardware elements until a valid command is received.
Command Loss will be executed four consecutive times if command reception
is not successful. After four unsuccessful executions, the CCS will disable
Command Loss and activate a set of sequences of commands named the backup
mission load (BML) and described below.
> 3.7.3.3 Backup Mission Load. In the event of permanent loss of command
reception capability, a BML command sequence stored onboard each spacecraft
is programmed to continue controlling the spacecraft and achieving
fundamental VIM objectives. The BML will begin execution two weeks after
the first execution of Command Loss and continue until the spacecraft stops
operating. It will transmit cruise science and engineering telemetry, store
science observations on the tape recorder, and downlink playbacks regularly.
https://voyager.gsfc.nasa.gov/Library/DeepCommo_Chapter3--14...
Page 74-75
> 3.7.3 Spacecraft Fault Protection
> The CCS has five fault-protection algorithms (FPAs) stored in memory, as summarized in Table 3-9. The two algorithms most directly related to the telecommunications system are named RF Loss and Command Loss [19].
> 3.7.3.1 RF Loss. RF Loss provides a means for the spacecraft to automatically recover from an S- or X-band exciter or power amplifier degradation or failure affecting the unit’s RF output. The CCS monitors the output RF power at four points in the RFS: the S-band exciter and S-band power amplifier and the X- band exciter and X-TWTA. If the output RF power from one or more powered- on units drops below a threshold level, the algorithm will attempt to correct the problem by switching to the redundant unit.
> 3.7.3.2 Command Loss. Command Loss provides a means for the spacecraft to automatically respond to an onboard failure resulting in the inability to receive or recognize ground commands. If a period of time set in the flight software goes by without the spacecraft recognizing a valid uplinked command, the Command Loss timer expires. The algorithm responds to the presumed spacecraft failure28 and attempts to correct that failure by systematically switching to redundant hardware elements until a valid command is received. Command Loss will be executed four consecutive times if command reception is not successful. After four unsuccessful executions, the CCS will disable Command Loss and activate a set of sequences of commands named the backup mission load (BML) and described below.
> 3.7.3.3 Backup Mission Load. In the event of permanent loss of command reception capability, a BML command sequence stored onboard each spacecraft is programmed to continue controlling the spacecraft and achieving fundamental VIM objectives. The BML will begin execution two weeks after the first execution of Command Loss and continue until the spacecraft stops operating. It will transmit cruise science and engineering telemetry, store science observations on the tape recorder, and downlink playbacks regularly.