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,