The SAW filters work down to -35 C and the ICs to -40 C so its not too far
off. It's easy to use a lower power RF amplifier and mixer which will lower
the input intercept. Right now, the receiver is designed to tolerate direct hits
from PAVE PAWS at any two frequencies outside the IF passband. As
the input intecept is lowered, the percentage of pulses that cause
interference increases, but the receiver won't go completely deaf as was
reported on earlier satelites.
73,
John
KD6OZH
----- Original Message -----
Sent: Wednesday, October 11, 2006 17:51
UTC
Subject: [eagle] Module
Temperatures
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
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