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
Return to top
Return to 2000 Index.
Return to News section.
|
