[eagle] Re: Module Temperatures & Eclipse
John B. Stephensen
kd6ozh at comcast.net
Sat Sep 15 15:54:16 PDT 2007
I'm planning on cutting power dissipation in the U-band receiver to 3 W maximum in the next version. The SAW filters should then remain above -35 C under any conditions.
----- Original Message -----
From: Dick Jansson-rr
To: AMSAT Eagle
Sent: Saturday, September 15, 2007 20:16 UTC
Subject: [eagle] Module Temperatures & Eclipse
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.
Dick Jansson, KD1K
kd1k at amsat.org
kd1k at arrl.net
Via the Eagle mailing list courtesy of AMSAT-NA
Eagle at amsat.org
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