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,