Background:

Normally the CCD chip will be kept as cold as possible, on the order of -50° C. At times throughout the mission the CCD will undergo a "bake-out" period in which the temperature of the CCD is warmed so that contaminants are "boiled" off of the CCD chip. This will be performed using the either the Decontamination Heater Bus and/or the CCD Operational Heaters; commands will be either by timeline or with the real-time procedure TI_dhtrs_on. Care should be taken so that the CCD temperature does not exceed 45° C. At this point, the lumigen coating (type of coating used for UV optics) begins to bake off.

Action Points 27 and 28 comprise a chained failure sequence both of which monitor the CCD temperature. AP#27 will initiate RTS#43 if the CCD Header Hi temperature reaches 45° C, removing power to the instrument operational heater zone 7 (CCD) and the decontamination heaters. RTS#43 will also activate AP#28 which continues to monitor CCD temperature. At this point, the temperature should begin to drop, however, if it remains at 45° C for another 40 seconds, RTS#44 will turn off all instrument operational heater power. The instrument survival heaters will provide enough heat until the problem can be isolated and corrected.

Key Telemetry:

Instrument CCD Header Hi Temperature (IOCCDHITEMP) > 45 degrees C

Recovery Procedure:

1. Notify EOF personnel. The most likely reason for this failure would be some type of operator error, i.e. the operational or decontamination heater levels were set too high. Less likely would be some type of heater bus failure.
2. Reset corresponding Action Point #27 to ACTIVE and #28 to DISABLED.
3. Depending on the nature of the problem, heater power may be restored at the direction of the EOF. Restore operational heater power to the remainder of the instrument using TI_th_init and TI_th_all_on, or TI_th_set.

References:

TRACE Flight Software Thermal Control Requirements

Drawing #TRA-001010 - TRACE Instrument Heater Layout

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