Feb. 27, 2000
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