Jan. 12, 2000
Status 12 January 2000, 10:45 AM PST About 1 minute into yesterday afternoon's firing of the Terra propulsion system, telemetry from the GN&C (guidance, navigation, and control) subsystem detected an excessive rate of change of spacecraft roll and the burn was shut down. The spacecraft went into "safe" mode, which prompted all the instruments to follow suit. MISR's computer automatically commanded the cameras to turn off, and the set point for optical bench temperature control was lowered to 5 degrees Centigrade. The optical bench cooled to 10 degrees C within about 8 hours of the safing event. It is currently at about 6 degrees C. No explanation for the excessive roll rate has been provided as yet, but a team to investigate the anomaly has been formed. At this time, the spacecraft remains in safe mode, and is stable. Unlike the safe condition that occurred as a result of the December "solstice bug", the spacecraft controls computer (SCC) is fully operational (though a different processor is in charge right now); therefore an "IMOK" ("I'm OK") signal from the spacecraft is being received by MISR, and telemetry monitors are activated. In light of this, and in order to maintain the bake-out benefit of keeping the instrument warm, MISR was taken out of safe this morning and the cameras and heaters were once again turned on. All looks fine. A re-try of the ascent burn is now scheduled for no earlier than January 19. Loading of MISR flight software and opening of the cover are consequently delayed by at least a week. 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