Mars Global Surveyor Status 27 September 2000
Wednesday, September 27, 2000 (DOY 264/19:00:00 to DOY 271/19:00:00
UTC)
Launch / Days since Launch = Nov. 7, 1996 / 1421 days
Start of Mapping / Days since Start of Mapping = April 1, 1999 / 545 days
Total Mapping Orbits = 6,959
Total Orbits = 8,562
Recent Events:
Background Sequences — The spacecraft continues to operate nominally
in performing the beta-supplement daily recording and transmission of science
data. The mm072 sequence executed successfully from 00-265 (9/21/00) through
00-267 (9/23/00). The mm073 sequence has performed well since it started
on 00-268 (9/24/00). It terminates on 00-271 (9/27/00). The mm074 sequence,
successfully uplinked on 00-270 (9/26/00), begins executing on 00-272 (9/28/00).
Other – This week MGS completed the second, third, and forth of five
scheduled MOC Focus Calibrations. The results of calibration #2 were inconclusive
due to gaps in the data. The Deep Space Network antenna had difficulty
maintaining the data downlink due to poor weather at the receiver site.
MOC Focus Calibrations #3 and #4 were successful in imaging most of the
targeted stars, providing scientists and engineers with data that will be
used to improve the precision MOC targeting capabilities of MGS.
Spacecraft Health:
All subsystems report nominal health. During the beta-supplement phase
of this mission we have been contending with the issue of how to retrieve
from MGS all of the science and engineering data that is recorded. We knew
that eventually planetary position geometry combined with the need to maneuver
the spacecraft around the HGA gimbal obstruction would result in our inability
to playback all of the data within the available downlink windows. We have
attempted two modifications in the Solid State Recorder (SSR) record/playback
strategy over the past weeks. The modification that works the best is analogous
to pressing the "pause" button on a typical tape recorder. So,
every time we playback SSR Track 7, we command the SSR to "pause"
just before MGS becomes occulted by Mars or it maneuvers around the HGA
gimbal obstruction. We pick up the playback of SSR Track 7 during the next
downlink opportunity. Presently, it takes three separate downlink opportunities
to playback SSR Track 7 completely. With less than 45 minutes of each 2
hour orbit available for playback, it already takes 12 downlink opportunities
over 6 complete orbits to playback SSR Tracks 1 through 6. Therefore, MGS
requires 15 – 16 hours of downlink each day to playback all recorded data.
This situation will gradually improve as planetary geometry becomes more
favorable. The beta-supplement phase of this mission ends in late June
of 2001.
Uplinks:
There have been 13 uplinks to the spacecraft during the last week, including
instrument command loads and sequences cited above. There have been 4,875
command files radiated to the spacecraft since launch.
Upcoming Events:
The mm075 background sequence will be uplinked 00-273 (9/29/00). MOC
Focus Calibration #5 contained in the mz058 mini-sequence, will be performed
on 00-272 (9/28/00). An additional MOC Focus Calibration (#6) is scheduled
for 00-277 (10/3/00) to gain the data lost during MOC Focus Calibration
#2. It’s uplink designation will be mz060. MOLA Polar Scans, contained
in the mz059 mini-sequence, will be performed 00-281 (10/7/00) through 00-285
(10/11/00). Radio Science Occultation Egress Scans are scheduled for 00-287
(10/13/00) and 00-288 (10/14/00).
