Dec. 29, 1999
Status 29 December 1999, 3:30 P.M. P.S.T. All continues to go well with MISR and Terra. Yesterday afternoon the Terra spacecraft controls computer (SCC) was re-initialized, and transfer of control from the safehold processor to the SCC occurred, bringing the spacecraft back to normal operations. The Terra Project Office reports that all spacecraft subsystems continue to operate extremely well. A flight software fix for the "solstice bug", which caused the SCC to halt on December 21, has been developed and tested and will be loaded after the New Year. Telemetry monitoring ("TMON", pronounced "tee-mon") software has been developed to deal with the occasional high gain antenna gimbal stoppages which have occured over the South Atlantic Anomaly (SAA). This TMON has been uplinked and activated, and will automatically restore HGA tracking if another event occurs over the SAA. So far, the resets have only occurred during the nighttime or south-to-north passes through the SAA, a region of higher-than-normal charged particle radiation that extends from Brazil and Argentina to the southern tip of Africa. Earlier this afternoon three TMON's for MISR were activated. These provide "watchdog" functions to automatically safeguard the instrument in the event of unexpected temperature, electrical, or computer telemetry readings. All readings continue to be fine and the instrument remains in safe mode. Because of reduced staffing over the New Year's "standdown" period, turn-on of the cameras and focal plane heaters to begin the intensive outgas period has been deferred until January 5. (The flight software to enable readout of the camera science data will not be uploaded until later in January, so no images will be available until then). The heat provided during the outgas period "cleans" the instrument by accelerating the evaporation of gases and water present in some of the materials out of which the cameras and electronic components are constructed. Four major firings of the spacecraft thrusters are scheduled to trim the orbit to its final 705-kilometer altitude and circularity. Small test burns of the hydrazine propellant will occur on or before January 11. Then, two 500-second duration burns will take place, one on January 11 and the other on January 18. These will be followed by two 250-second duration burns, one on January 21 and the other on January 24. The dates of the burns are chosen to put Terra into the same orbit as Landsat 7. The MISR cover will remain closed during this period to avoid contamination. The MISR timeline over the next month looks like this: *January 5: Turn on cameras and focal plane heaters. *January 19: Load flight software and begin acquisition of camera science data. (The cover will still be closed, so this will provide readings of the "dark" levels.) *January 25: Open the instrument cover. First Earth images! *January 27: Mechanisms testing. *January 28 or 29: First radiometric calibration. *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 can be accessed at
http://terra.nasa.gov. Best wishes for a very happy New Year!
David Diner