Status 23 December 1999:
MISR continues in safe mode and all telemetry readings are normal. Since
turn-on, the active flight computer has been running on instructions loaded
into its memory from programmable read-only memory (PROM) chips built into
the instrument. The PROM-provided code enables basic instrument functions,
with a major exception being high-rate data generation (e.g., science data).
Generation of science data will not occur until an upload of flight software
takes place in January, at which point the computer will be commanded to
"jump" to the new program instruction set.
The Terra Project reports that the spacecraft solid state star trackers,
science formatting electronics, capillary pumped loop for MOPITT, and solid
state recorder have all been powered-on or configured for nominal operations.
The star trackers are producing excellent results, and the solar array is
producing over 8100 watts of power. CERES has been turned on, while the other
instruments are being maintained thermally stable by survival heaters.
The spacecraft continues in safe mode as well. Telemetry received the other
night showed that the spacecraft controls computer had halted and the independent
safehold processor took control of the spacecraft. Good news: the problem
has been isolated to a bug in a section of code or table entry in the navigation
software and a patch will be developed by the Terra flight software engineers.
The earliest that the navigation software will be reinitialized is Monday,
December 27. In the meanwhile the safehold processor will maintain control
of the spacecraft, which remains in a stable power and thermal configuration.
Calibration of the pressure transducers which regulate firing of the spacecraft
thrusters is taking place through the use of a process called "gauging",
which involves alternately heating and cooling the on-board propellant. This
will take place through Sunday, and is being done in preparation for the
orbit ascent maneuvers which will raise the orbit altitude up to 705 kilometers.
Short test burns will take place prior to the first of four large burns required
to adjust the orbit. The first large burn is scheduled for January 11 and
the remaining burns will take place over the following 10-14 day period.
Although the MISR cover and calibration panels were unlatched yesterday,
we do not plan to open or deploy them until after these maneuvers are completed,
in order to keep our optical surfaces free from contamination.
Given that Terra launch occurred late in the launch window, equator crossing
time is predicted to be about 10:44 AM during the first year of operations.
You can see earlier status reports by checking the "News" link of the MISR
web site at
http://www-misr.jpl.nasa.gov.
Further information on Terra is available at
http://terra.nasa.gov.
David Diner
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