Last evening I tried to convey the concept
that the critical-command modules needed to be of low-power design to insure
their operability during the occasional rather lengthy eclipse cooling of the
spacecraft. My message apparently did not sink in. John reports that his design
of such a U band receiver would be dissipating some 3.5W due to its bullet-proof
nature against 3rd-order IM products needed for protection on the U
band.
If we go forward with such a module of that
nature, it will need to have thermal control tapes on it to provide a mean
emittance of about e=0.45. In a 3 hour eclipse we can expect to see spaceframe
temperatures down to -100°C (173K) or lower. With such an environment John's
module would be expected to see temperatures down to at least -44°C, which is a
bit frosty for electronics that are expected to provide the critical services of
commanding the spacecraft. Such operating temperatures are not felt to be
advisable for that service.
If John's module were of the 1W category,
temperatures of the receiver could be expected to be in the range of -15°C to
-20°C which would be more operable for the service.
The above numbers are, of course, based
on estimates which will be confirmed after we have the
new spaceframe fully designed and analyzed. The "warmer" temperatures
of the lower power modules are those that have been experienced and measured by
telemetry from AO-10 and AO-13. These projections are thus based on 25
years of experience in these design concepts.
Dick Jansson
---------------------------
---------------------------