PDS_VERSION_ID       = PDS3
RECORD_TYPE          = STREAM
OBJECT               = TEXT
PUBLICATION_DATE       = 1999-04-20
NOTE                   = "MGS RST Instrument Health Report HEA9110B.TXT"
END_OBJECT           = TEXT
END


Miscellaneous
=============

     Following is a slightly edited report on this morning's Spacecraft Team
telecon with JPL regarding the HGA azimuth anomaly and a subsequent Mission
Planning meeting at JPL.  These notes were received from Jesse Glance.

A. SCT Telecon:

1)  The SCT has reviewed engineering data (from HGA anomaly) played back
yesterday.
2)  LMA's "best" theory is that HGA motion stopped due to mechanical
obstruction or restraint.  Thermal blanket wrap/interference and/or cable
problems are being evaluated as strong possibilities.
3)  The HGA movement interruption was abrupt enough to cause S/C body
perturbations similar in magnitude to the (commanded) start of motion.
4)  Both the HGA's azimuth motion at time of unplanned stop and a
subsequent c-mode-commanded motion were in the negative direction.  No
attempt to move HGA in positive direction has yet been made.
5)  A current "guestimate" of torque required to stop the HGA's movement
was given as ~30 in/lb -- well within blanket or cabling restraining force
capabilities.
5)  Possible problem(s) with Gimbal Drive Electronics (GDE) units (such as
encoder value indication) are not entirely ruled out as being involved.
6)  LMA is designing an HGA test which will run (TBD, before end of Wed).
Features of the test are:
    a.  Attempt to move HGA approx. 0.5 deg in positive direction then
        return to present 41.3 deg (indicated) position.
    b.  Movement will be by commanding approx. 52 "steps" (step mode
        vs. rate mode) to avoid relying on position encoder data (which
        may be faulty).
    c.  0.5 deg was chosen as large enough to detect movement of HGA
        beam, but not large enough to lose engineering (2k) telemetry.
    d.  A small movement also provides protection against degrading HGA
        capability in case the "hard-stop" creeps/moves (further limiting
        HGA useful range of motion).
    e.  REDMAN will be disabled during the test to avoid undesired entry
        into fault protection routines.  The minisequence, therefore,
        will have to include protection against forseen problems.
    f.  Current plan is to perform the test in real-time vs. record &
        playback.
    g.  Sequence will be of load-n-go type.

B.  Mission Planning Meeting:

1)  Based upon discussion, MSOP management has decided to delay OTM-4 and
start of Science Campaign-A by one week.  The slip is to accommodate HGA
anomaly recovery activities.
2)  MOC Team stated that slipping Campaign-A by a month or more would
require MOC coordination -- since Campaign-A objectives require good
atmospheric weather conditions, which after this Mars season, are less
likely to exist again until one earth-year from now.
3)  Certain Radio Science objectives may not be movable by a month or year.
Radio Science Campaign-A objectives may have to be accomplished outside of
formal Campaign-A (assuming the HGA problem can be resolved within weeks).
4)  DSN resources (i.e. 70M continuous tracking) apparently cannot be
extended.  Slipping start of Campaign-A by more than one week will shorten
the duration of Campaign-A (Even a one week slip may do so).
5)  DSN Scheduler was hopeful that it may be possible to accomplish a
portion of Campaign-A with less-than-continuous tracking -- but it's up to
Science Team to confirm.
6)  OTM-4 is necessary for MOC Team to meet Campaign-A objectives.
7)  Since OTM-4 preparation & execution takes a minimum of one week, MOC
Team prefers to accomplish the OTM within the campaign vs. shorten the
campaign (due to waiting for OTM prep. & execution).
8)  Rationale for Campaign-A duration of 4-weeks vs. 3-weeks was given:
The 4th week is needed to fill "gores" in the "30-day map" products.