[eagle] Module Temperatures

Dick Jansson-rr rjansson at cfl.rr.com
Tue Aug 28 12:32:53 PDT 2007


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,

Dick Jansson, KD1K

kd1k at amsat.org 

kd1k at arrl.net 

 

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