Terra and MISR are A-OK in Y2K!

Status, 4 January 2000 Terra and MISR are A-OK in Y2K! The transition from 1999 to 2000 turned up no problems associated with Y2K, though a small end-of-year glitch occurred at the White Sands ground station (which controls the TDRSS communications satellite contacts), when the day-of-year counter incremented from 365 to 366. This was quickly fixed. Today, the first "calibration" burn of the spacecraft propulsion system took place. The thruster firing went perfectly. After the short burn, an anomaly in the telemetry readings for the propulsion power subsytem occurred. Lockheed Martin reports that they understand the problem and that it will not adversely impact the upcoming burns. Other minor issues regarding spacecraft performance are being watched. Last Friday, telemetry indicated that the temperature of a cell in one of the battery packs began to fluctuate, then took an abrupt 1 degree Centigrade drop. Power and thermal subsystem engineers are investigating, but there is no effect on system performance since the batteries are designed to operate over a wide temperature range. "South Atlantic Anomaly" may become household words--besides causing occasional resets of the high gain antenna drive (though none have been seen in the last six days), the SAA has caused some occasional spurious readings from the spacecraft star trackers and Earth horizon sensors. The data are being analyzed, but no compromise in the performance of the sensors is anticipated. The star trackers are used to locate certain guide stars; this celestial navigation keeps the spacecraft accurately pointed and in the proper orientation. The Earth horizon sensors, which locate the Earth's limb against cold space, provide an alternate method of accomplishing the same function, though with less accuracy. Terra is currently flying using the Earth horizon sensors, since this is a simpler mode of operation. The star trackers will be used for more accurate navigation, however, once science data starts to flow. MISR continues to operate fine, and as of today is still in safe mode. Some sporadic current "spikes" associated with operation of the optical bench heaters have shown up in spacecraft telemetry; however, these were observed during ground testing and are not cause for concern. An issue being investigated is that the spacecraft's translation of the engineering data numbers to current values does not properly report values which exceed 1.008 Amps. This is above the normal operating current for MISR, but because of the presence of the occasional spikes, options for how to deal with the 1.008-Amp limit are being looked into. A major milestone in the MISR activation sequence, turn-on of the nine cameras and focal plane heaters, is scheduled to take place during a 28-minute-long TDRSS contact with Terra, beginning at 6:38 AM PST tomorrow (Wednesday), January 5. 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