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,