Status 14 January 2000
As reported the other day, the first full ascent burn to achieve Terra's
final orbit was aborted about 1 minute into the planned 8.5-minute burn.
This happened after the spacecraft had rolled 4 degrees off the normal
pointing attitude, and as the roll angle continued to grow the spacecraft
controls computer (SCC) handed authority over to the safehold processor.
This immediately restored the proper spacecraft orientation but shut down
the burn. All telemetry data were received and the Terra Project Office
reports that spacecraft engineers seem to be converging on a root cause for
the unexpected roll. They expect to have a recommendation in a few days,
and as part of their investigation, some test burns are planned for this
evening. A plan to correct the underlying problem, perform another
engineering burn, and establish a new burn sequence to achieve final orbit
is being developed.
The spacecraft is once again out of safe mode with the SCC in charge. The
High Gain Antenna (HGA) was powered on yesterday but is still in checkout
mode while being used for some data playbacks. Full operations of the HGA
are expected to resume on Monday morning. Late last night the HGA
experienced a reset in the South Atlantic Anomaly, and the telemetry
monitor that was put in place to automatically restore operations of the
motor drive worked as planned.
The problem that occurred with the spacecraft cooling system for the ASTER
thermal-infrared (TIR) instrument is now believed to be due to a vapor
bubble that was created at initial start-up. The normal recovery from such
an occurrence is to restart the cooling system, which has been done and
some spacecraft heaters are being used as a test load while the TIR remains
powered down. So far things look very stable and after the performance has
been monitored for several days the TIR will be powered on.
With MISR cameras and heaters once again turned on after the safing event
that was associated with the ascent burn anomaly, temperatures have
returned to the levels that were seen prior to the event. All continues to
look as expected.
You can see earlier status reports by checking the "News" link of the MISR
web site at http://www-misr.jpl.nasa.gov.
David Diner
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