Status 21 January 2000
Checkout of Terra's capability for downlinking science data is progressing. Next week promises
to be very busy, with MISR, MODIS, and the ASTER visible and shortwave-infrared instruments
planning to transition to science mode. This past week, motion tests and calibration mode
checkouts of the CERES instrument's scanners were all performed successfully. The more
gradual start-up procedure that was used for the cooling system required by the ASTER
thermal-infrared instrument, along with additional actions taken by the spacecraft thermal
engineers, have led to longer operation of the loop than seen previously, though it is
running slightly warmer than expected. MOPITT is currently in a planned "safe" mode.
The instrument and spacecraft activation schedule continues to be affected by the uncertainty
regarding the cause of the spacecraft roll during the propulsion burn on January 11. The
available data have been insufficient to definitively establish whether the problem is
exclusively in the performance of a particular set of thrusters (with the expectation that
the redundant set will perform differently) as opposed to a problem with how the thrusters
are being controlled by the spacecraft software (and therefore a more generic issue). Several
scenarios for getting Terra to the final orbit are being discussed. The option to use a
different set of thrusters could see the series of ascent burns re-starting on January 31,
with final orbit achieved in mid-to-late February. A change to the thruster control software
would stretch this timeline out. The good news is that achieving the proper orbit is not in
question; what we don't know yet is how soon it will happen.
Loading of the MISR flight software, originally scheduled for a few days ago but postponed
after the orbit ascent anomaly occurred, is now planned for next Wednesday, January 26. This
software will allow MISR's computer to send out science data from the nine cameras. In the
meanwhile, the cameras and optical bench heaters remain on and the instrument will benefit
from an extra week of bake-out heating. Despite bitterly cold weather in Maryland, and a
couple of cool, damp days here in California, our instrument operations and science data
teams are also feeling the heat associated with preparing for this exciting milestone.
Initial "science" data from MISR will be taken with the instrument cover closed. Although
this is sort of like having the lens cap in place on your camera, it will provide an important
set of information about how the instrument and cameras are performing. The electronic
detectors used in MISR's cameras put out a background signal, called the "dark current", which
is present even when no light is falling on the lenses. One component of the dark current
increases as the detectors get warmer, and to reduce it the cameras contain devices called
"thermo-electric coolers" which will cool the detectors to -5 degrees Centigrade. About one
day's worth of data will be acquired with these coolers turned off, after which we will issue
the command to turn them on. This is the configuration the cameras will be in at the time we
open the cover. The initial data will also give our science software system a dress rehearsal
in anticipation of that big event.
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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