Bruce Wielicki and Phil Hess
October 14, 1998
- The MAM Assembly temperature rose to a peak of about 17.1C. The start of the DAA +15 volt converter's
sensitivity to temperature occurred at about 16.4C. The voltage followed the MAM Assembly temperature
above this minimum level with the same sensitivity seen in August data. The current Tmin value is about
0.8C lower than seen at the end of August, and indicates some further degradation of the DAA +15V
converter, but only about 14% of the degradation rate seen through most of August. This again indicates
that the degradation of the converter has slowed greatly from that experienced in August (roughly a drop
of 0.13C per day in Tmin from Aug 3 to Aug 29).
- Tommorrow the instrument will be operated in a higher temperature orientation (greater sunlight incident
on the DAA electronics box) and we expect roughly 2C higher temperatures to be reached. Voltages are expected
to still be well below our new limit of 18V. Given today's data and an expected 2C rise in MAM assembly
temperatures, we might see maximum voltages of around 16.6V. The instrument is now set to go to safe mode
if the voltage exceeds 18V, even during periods when the spacecraft is not in direct communication with
the operations center.
- Over the next 6 days the instrument will be operated in a variety of modes designed to isolate the impacts
of individual instrument functions (elevation scan motor, azimuth scan motor, SWICS calibration lamp, etc),
culminating with the full RAPS scanning mode on day 6 of the test. The tests will include 2 calibration
sequences to verify the calibration stability over the last 6 weeks.
- This next 6 days should also help to determine if further degradation in Tmin during instrument operation
occurs in Tmin at the rate of 0.13C/day (August) or closer to the 0.02C/day since then.
- The latest quick-look data for the last three orbits have revealed that the DAA+15-volt converter is now
starting to show expected variations. Some observations: (provided by Phil Hess)
- The voltage is essentually following the MAM TOT Assy temperature cycle as has occurred prior to the
September 1 shutdown.
- The start of the voltage variations (i.e., "lose" regulation) for each of the three orbital temperature
peaks occurred as the MAM TOT Assy temperature increased through ~16.5 degrees C. The end of the voltage
variation cycle (i.e., "regain" regulation) occur as the temperature drops below ~16.4 degrees C.
- Some approximate peak data values for these three orbits (time is GMT):
- There is a noticable positive "jump" of ~0.1 volts at sunrise (coincident with a "sharp" ECA Radiator
Temperature peak). This seems to be in the opposite direction that we've seen prior to September
shutdown. (There the "jump" was in the negative direction, not the positive direction.) We'll be
looking into this in further detailed, so I wouldn't want to draw any conclusions about this just yet.
- Based on the MAM data, it would suggest that the diurnal peak has passed. We will know when the next
quick-look data arrive.
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