Hi Dick,
Thanks for the
information. As you know, the SAW filters are rated for a minimum operating
temperature of -35C and storage of -40C. We might need to get creative and attach
miniature strip heaters to those to keep them warm. As soon as John gets his
IF test board running and tuned up I want to do a temp run to see how they
behave over temperature. They appear to be very touchy in terms of matching.
The matching appears to be the cause of the passband ripple we’ve been
fighting. With luck we’ll have some information to share at the symposium…
73,
Juan
From:
eagle-bounces@amsat.org [mailto:eagle-bounces@amsat.org] On Behalf Of Dick Jansson-rr
Sent: Saturday, September 15, 2007
1:17 PM
To: AMSAT Eagle
Subject: [eagle] Module
Temperatures & Eclipse
John, Juan, Bob D., & Bob M.:
I have been preparing for my presentation to the Space Symposium on the
subject of internal module heat sinks. As a concurrent subject, not in my
paper, I have been preparing to discuss the temperatures that modules can
achieve during a solar eclipse of the Eagle satellite. In this vein, things do
get interesting and pretty darned chilly. I am showing the outboard, deployed
solar panels getting down to the -117°C to -125°C! I also show body-mounted
solar panels getting down to -81°C and other body sheet metal in the -60°C
range.
This analytic effort has pretty heavily exercised this new, high speed
computer with some runs taking from 40 to 70 minutes, that is a lot of number
crunching!
The spaceframe temperatures for the start of the analysis was set at
+10°C and modules at +20°C.
For the modules I have analyzed both power off and with modest power
dissipation in some modules. Some modules, with the necessary coatings to be
able to handle 3.5W dissipation (e.eg. the URx in full operation), show a
considerably deeper cooling than those with only the lowest emittance of a
low-power module. Unpowered, or those with very low dissipation, show
temperatures near to zero Celsius after three hours of eclipse while those of
the higher emittance, for higher power operation, can get down to -30° to -38°C
in that same time. This clearly illustrates why I have been pushing, wherever
possible, to keep the module emittance low and to keep the module thermally
decoupled from the spacecraft to the greatest extent possible. It also
reinforces my high degree of upset with our German friends who painted not only
the inside of their P3E modules black, but did me a “favor” by
painting the outside black as well, failing to follow my instructions. The P3E
situation will have to be dealt with as another issue.
In eclipse, modules with low emittance and modest power dissipation
show temperatures of +10° to +20°C. But the modules with the necessarily higher
emittances, and dissipating a modest 1.0W of power, are only 10°C warmer than
the unpowered condition, running at -25° to -28°C.
I need to further refine this analytic model and to try different power
dissipation situations. I felt, however, that it was necessary for me to report
the results of these analyses to you at this time. These results are in line
with the AO-10 telemetry for an eclipse condition, that was reported to me many
years ago.
’73,