Background:

Three additional overcurrent protections have been established for protection of instrument power busses. The are:

Operational Heater Current > 3.4 Amps (for 2 or more consecutive samples)

Survival Heater Current > 3.0 Amps (for 2 or more consecutive samples)

Decontamination Heater Current > 1.5 Amps (for 2 or more samples)

These limits have been set high enough so that no possible operational condition would trip these limits. If one should fail, most likely the power bus has failed. The expected nominal current draws for each of these busses for normal non-eclipses operations are as follows:

Operational Heater Current 0.5 - 2.0 A

Survival Heater Current (normal ops) 0 A

Survival Heater Current (launch/eclipse ops) 0.5 to 2.1 A

Decontamination Heater Current 0 A

Decontamination Heater Current (bake-out) 0.3 to 0.5 A

Key Telemetry:

PSDECHTRCURR - Decontamination Heater Current

PSINOPHTRCUR - Instrument Operational Heater Current

PSINSRHTRCUR - Instrument Survival Heater Current

All mnemonics can be found on the PSPWRDIS page.

The following AP’s will initiate associated RTS’s for each safing action:

AP#19/RTS#33 - Decontamination Heater Over-Current

AP#18/RTS#35 - Instrument Operational Heater Over-Current

AP#20/RTS#36 - Instrument Survival Heater Over-Current

Recovery Procedure:

1. Notify EOF personnel and S/C OE. Some type of heater reconfiguration will have to be performed to compensate for the failed circuit.

 

2. Reset corresponding Action Point.

 

3. Re-enable thermal control only at the direction of the EOF.

References:

TRACE C&DH FSW User’s Guide

http://tracedata.nascom.nasa.gov/~trace/cdhsw/trace/design/sc/pre_rts.htm