Status 5 January 2000, 6:15 PM PST
Terra mission activation is having its ups and downs. The manufacturer of
the High Gain Antenna (HGA) has expressed concern about flying through the
South Atlantic Anomaly (SAA) with the gimbal drive power turned on. They
are worried that the associated high radiation doses on a particular
transistor, while it is powered, could eventually lead to burn out of the
device. To provide time to assess this situation, the HGA was turned off
this afternoon (possibly for 1-3 days) and contact with the spacecraft is
temporarily relying only on the omnidirectional antenna. The omni is being
used at its nominal 1 kilobit-per-second (kbps) data rate, with occasional
bursts at 16 kbps. At the lower transmission rate, only instrument health
and safety telemetry data are available. More detailed instrument and
camera telemetry data are being provided during the 16 kbps contacts.
Resolution of the power subsystem anomaly which occurred at the end of
yesterday's propulsion burn has not been finalized. In light of this and
the more limited data capability currently available, the 11-second
engineering burn of the spacecraft thrusters, originally scheduled for
tomorrow, has been postponed for at least a day.
MISR instrument and camera telemetry data are looking good. The optical
bench has reached a temperature of about 20 degrees Centigrade, and the
camera focal planes have stabilized at around 25 degrees Centigrade.
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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