Juan & John:
I have finally been able to achieve some analytical results
for projecting the temperatures of Eagle modules after two hour and three hour eclipse
periods of no-solar heating. This has taken some time as I was struggling with
the proper use of the SINDA software and had to call for some help –
which is why we pay money for the license, it comes with help when needed. (I
should also note that with modern versions of this software and a pricey, but
fast and capable, Dell computer, these analytic runs only required 18 seconds
of real run time!)
Nevertheless, I have been able to get some believable
modeling results. The spacecraft model used is what I now call “Small
Eagle”, the formerly proposed, but rejected 600x600x435mm spaceframe
structure. While this is not as large as our currently planned hexagonal
structure, the equipment bays are just about the same size as the larger
spaceframe. I ran the model with one of the E05 20, 125x180mm, modules with
coatings with an effective emittance of about 0.45, rather than 0.04, as would
have to be done for the URx module. There was essentially no power dissipations
in any module, at the most about 20mW in a few modules. This is granted to be
an abnormal situation, but I wanted to see what happens. A later run was made
with only a total spacecraft power dissipation of only 7mW were only lower by
0.1°C to 0.2°C lower temperatures.
Modules started out at temperatures of +20°C and the
spaceframe core structure at +10°C. The propellant tank was empty so it did not
contribute any large thermal mass to delaying the cool-down. After two hours of
eclipse the module temperatures were -5.2°C to -5.4°C (with the high emittance
module being cooler), and after three hours of eclipse the module temperatures
were -15.9°C to -16.2°C. The spaceframe core structure (equipment panels) were
down to -10.2°C and -19.4°C respectively. For these cooling periods, the
spacecraft outer skin temperatures ranged from -35°C down to -55°C. The
deployed solar panels became a bit chilly, down to -113°C.
A subsequent SINDA run was made with some kind of useful
power dissipations in modules – 0.5W to 1.0W – not large but
supposedly enough to keep things from getting out of hand, and with a total
spacecraft dissipation of 16.5W. The two hour eclipse temperatures ran from -3.4°C
(1.0W) to -3.9°C. In three hours of eclipse the module temperatures were at
-13.3°C down to -14.0°C. In other words, these levels of power dissipation did
not significantly warm the modules. The spaceframe core temperatures were at
-8.0°C and -16.3°C respectively., just a few degrees warmer.
What this data tells me is that specifying the “cold”
temperature of a module does not have to be much lower than -20°C, and if it is
operating at all they can be only a little higher. Cold module temperatures
certainly do not need to be in the -60°C range. Beyond these statements, I
shall not presume to be a specification writer.
’73,