Background:

The instrument is protected against an over current condition by several watchpoints and actionpoints. Watchpoint #28 (decimal) watches the instrument current mnemonic (IIAEMTR) and if the current goes about 25 counts (raw) or 108 mA (engineering converted) for 50 consecutive samples (50 seconds), AP#21 will initiate RTS #37, disabling any active science observing sequences, resetting the focus mechanisms, filter wheels, quadrant selectors and shutter mechanism. It will also enable AP#22. If the condition persists for 10 more samples (10 seconds), AP#22 will initiate RTS #38, disabling the FSP autonomous re-acquisition sequence, transition back to Inertial Sunpoint and reset the wedge motors. Finally, if the conditions persists for 10 more seconds, AP#23 will initiate RTS #39, disabling the mechanisms +15V power supply.

I&T testing has identified several science sequences which will trip the 108 mA threshold, however, with the 50 second delay, none should cause the actionpoint to fail.

Key Telemetry:

When an instrument overcurrent condition exists, event #1021 will be generated. Within that event message, the actionpoint that failed, the RTS that subsequently fired and the number of samples that caused the actionpoint to fail will be given (all values in hex).

1021 - Instrument: Motor OverCurrent #1 Sensed (ActionID, RTSID, fails)

Instrument: Motor OverCurrent #1 Sensed

Value #1: The Actionpoint number that failed its limit.

Value #2: The RTS number that was requested.

Value #3: The number of consecutive failures that triggered this Actionpoint

Value #4: Unused.

Similarly, if the condition persists, the following may be expected:

1022 - Instrument: Motor OverCurrent #2 Sensed (ActionID, RTSID, fails)

1023 - Instrument: Motor OverCurrent #3 Sensed (ActionID, RTSID, fails)

Recovery Procedure:

Notify the TRACE EOF. The cause of the failure should be determined before any recovery is initiated. Most failures that have occurred throughout I&T have been the result of science sequences which move mechanisms in a cadence that is in sync with the 5 second telemetry rate providing failure conditions. This should be kept in mind when investigating failures.

The OE should be present for any recovery procedure.

Depending on the severity, actionpoints will need to be reset and should be reset in the reverse order (i.e. AP #23 is disabled first, then AP#22 is disabled, then AP#21 is reactivated, resetting the safing sequence).

If RTS #37 fires, the problem has been resolved by resetting one of the mechanisms (except the wedges) or by suspending the current sequence. Actioinpoint 21 will have to be reactivated and 22 will need to be restored to disabled. Since the sequence has been paused, it will need to be resumed (/ICSEQRESM).

If RTS #38 fires, the problem has not been found with the previous mechanisms, therefore the wedges are reset, fine sunpoint and GT reacquisition are disabled. Actionpoint #21 will have to be reactivated and #22, #23 set to disabled. The FOT will be required command the S/C back to Fine Sunpoint.

If RTS #39 fires, the previous resets have not worked. It is possible that there is a failure in the power supply or in an individual mechanism. The mechanism +15V supply has been turned off. A cautious approach to recovery would be to turn the +15V on and reset each mechanism individually at the direction of EOF personnel. Refer to TI_ME_ON procedure for commands and step through this procedure a command at a time.

References:

TRACE C&DH FSW User’s Guide

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

For mechanism documentation on-line, see:

http://www.lmsal.com/TRACE/cal/index.html

focus_doc.txt

fw_doc.txt

gt_doc.txt

qs_doc.txt

shutter_doc.txt