SOT Shift Report

Shift B12
Duration:	 3 Aug 1999 08:19 EDT -  3 Aug 1999 21:19 EDT
		 3 Aug 1999 12:19 GMT -  4 Aug 1999 01:19 GMT

SOT Lead:           Tom Aldcroft
Spacecraft/Aspect:  Mark Freeman
FOT/Science Liason: Mike Juda
HRC:                Martin Zombeck
ACIS:               Yusaf Butt


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A very quiet day for science, since there were no scheduled science
activities or OBSID changes

One ACA fid light was lost (the 9th magnitude one) and we promptly
re-acquired it with CAP 129, option 1.

The key activity was working to plan ACIS and HRC activities for tomorrow
and the next day, and to add an ACA calibration dump for day 217.

There was a meeting involving SAO, Ball, TRW, MSFC to discuss possible
patch options to prevent fid light loss-of-track in the ACA.  After
much spirited discussion, it was decided to pursue four options:
- Patch the PEA to limit the possible velocity of track windows
  for fid lights.  This is considered the best option
- Produce an SCS for each observation which periodically forces
  re-acquisition of the fid.  There is a potential for a conflict
  between OBC and SCS commanding of the ACA, and this is to be
  worked by TRW flight software
- Patch the OBC code to periodically re-acquire fid lights
- Understand the impact of doing nothing

Flight note 195 was issued by Mark and myself describing in more detail
the behavior of the ACA during fid light loss-of-track events.

-Tom