Bruce A. Wielicki
August 28, 1998
We have experienced our first hardware glitch on the otherwise fantastic performance of the CERES instruments.
A brief summary of what we know so far is given below courtesy of Jack Cooper and Greg Stover:
- The CERES Proto-Flight Model (PFM) instrument aboard the Tropical Rainfall Measuring Mission (TRMM) exceeded
a yellow high limit for the Data Acquisition Assembly (DAA) +15 volt measurement on August 18, 1998.
Upon review of instrument data it was noted the +15 volt level began increasing on July 31. The data shows
that the +15 volt reading increases cyclically during each orbit with a peak at satellite sunset. The data
also shows an enveloping peak that occurs several hours into each operational day. The trend for the
enveloping peak has been gradually upward since July 31st with an amplitude peak reaching approximately
16.5 volts. At first the data only indicated that the biaxial and along-track scan modes were susceptible
to this cyclic behavior, but recently the increases appear in the cross-track mode as well.
- LaRC, TRW, and the TRMM Flight Operations Team continue to monitor and examine the instrument data for an
explanation and resolution to the anomaly. In the interim, a decision has been made to operate the instrument
in the cross-track mode only. In this mode the voltage peaks have shown to be lower in amplitude and this mode
provides for continued science data collection.
- We will keep you posted as we strive to further understand this anomaly. For now, however, we will leave
the CERES instrument in its normal crosstrack scan mode until the anomaly is better characterized and
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