27 February 2000
It has been a busy weekend! Yesterday morning we performed the MISR mechanisms test, which
deploys and stows the two calibration panels, and also runs the goniometer (a mechanized device
which enables one set of calibration photodiodes to view the calibration panels at different
view angles). From what we were able to discern from the "real-time" engineering telemetry,
the currents on the various motors looked normal. However, a set of microswitches which are
supposed to indicate that each of the calibration panels had reached the full deploy position
did not provide this indication. We suspected that the panel motion worked fine and that the
problem was with the microswitches themselves, as they are notoriously unreliable devices.
The good news is that the microswitches which indicate the "stow" position are working, and
this is the more important set. Since instrument health and safety are prime considerations,
however, we called off that portion of yesterday afternoon's calibration sequences that would
have once again deployed the panels until we had a chance to analyze the "high-rate" motor
current data.
Those data arrived late yesterday afternoon, and they provided much more detailed insight
into how the motors performed. Analysis of the motor currents by our mechanisms engineer
showed that the panels had indeed deployed and stowed normally. Consequently, we declared
the mechanisms test a success and proceeded with the set of calibration sequences that were
scheduled for this afternoon. From the indications present in the real-time telemetry, all
instrument actions programmed into the sequences took place as planned. By tomorrow (Monday)
we should receive the high-rate motor, engineering, and camera data and will be able to perform
a much more in-depth analysis.
A major on-going activity has been coordination of MISR overflights of a snow and ice study
area in Wisconsin with simultaneous field measurements and flights of AirMISR, MISR's little
sibling which flies on a high-altitude aircraft. Unfortunately, the study area has been warming
and the snow is melting. AirMISR did underfly MISR this morning and the simultaneous data will
be quite interesting, but the outlook for continuing this particular campaign is not encouraging.
In the coming weeks, the operation will move to a specially instrumented site maintained by
the Department of Energy in Oklahoma for the study of clouds.
Calling off yesterday's calibration sequences required inhibiting all pre-programmed commands
to MISR for two orbits. As a result, the cameras remained continuously off during these few
hours. Afterwards, our operations team noted that the optical bench had warmed up by about 2
degrees Centigrade. Subsequent detective work suggested that a consequence of the cooldown
which occurred as a result of keeping the cameras off was activation of one set of instrument
survival heaters. We conducted a special test this afternoon which confirmed this hypothesis.
We will devise a strategy to return the instrument to the earlier configuration, but in the
meanwhile the instrument and cameras are operating fine at the slightly warmer temperatures.
This experience has provided us a valuable piece of operational information.
Many thanks to all who have been working long hours to support each of these activities!
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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