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,
Dick Jansson, KD1K
kd1k(a)amsat.org
kd1k(a)arrl.net
