[eagle] Re: Module Temperatures

Robert McGwier rwmcgwier at gmail.com
Tue Aug 28 13:16:46 PDT 2007

Good my toilet paper calculations assuming spherical black bodies and 
SWAGS at reflectivities, emissitivities, etc. produced numbers that are 
like this.

This is good work.

Thank you,

Dick Jansson-rr wrote:
> 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 <mailto:kd1k at amsat.org>
> kd1k at arrl.net <mailto:kd1k at arrl.net>
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