Please do post the results. excellent Robert WB5MZO
> From: [email protected] > To: [email protected] > Date: Wed, 18 Nov 2009 09:34:18 -0500 > Subject: [amsat-bb] Satellite Thermal Lesson > > Lesson learned on Satellite Thermal. > > For years, we have been trying to demonstrate to students the > extreme differences in Temperature of a satellite based simply > on its color. In space, far from earth, here is what you should > get for three identical satellites: > > Black will be about +55 deg F > White will be about -60 deg F > Aluminum will be about +225 deg F > > (from memory anyway)... But we have never been able to see the > extreme temperature of the aluminum in our vacuum chamber. Of > course, we are not using a SUN, but an incandescent lamp which > has 95% of its radiation as heat and only 5% as light, so we > attribtuted our wishy-washy results as due to the lack of real > solar spectrum. > > This year, we finally have a Tvac chamber that has a liguid > nitrogen cold plate so we can actually better simulate the > blackness (and cold) of space.. Again, same result. Aluminum > was about the same as black. This was a frustrating result from > this new chamber. > > Then I noticed the fingerprints on the aluminum. I cleaned the > aluminum with a swab of alcohol to eliminate all the surface > contaminants, and fingerprints and re-did the test... > > BINGO. Now the temperature of the aluminum goes up and off > scale HOT, way way different from the black or White. And now > the WHITE also goes colder.. > > So just the thinneest innvisible layer of surface contamination > completely changed the thermal emissivity of the Aluminum. And > we all know this anyway, since "low-E" coatings of glass and > other materials is now so common. It is only the outer surface > of molecules that set the absorbtivity and emissivity... And > the differnce between Black and Aluminum is 30-to-1 (if the > aluminum is clean)... That's why we wrap baked potatos in > Aluminum foil! (don't use greasy hands)... > > Of course we always clean our actual spacecraft to clean-room > conditions before flight, so this does not impact our on-orbit > results, but it sure does make a difference in the lab when we > are demonstrating absorbtivity and emissivity in the chamber > with samples handled by the students! > > When I get a chance, Ill post the results... > > Bob, WB4APR > > _______________________________________________ > Sent via [email protected]. Opinions expressed are those of the author. > Not an AMSAT-NA member? Join now to support the amateur satellite program! > Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb _________________________________________________________________ Windows 7: I wanted simpler, now it's simpler. I'm a rock star. http://www.microsoft.com/Windows/windows-7/default.aspx?h=myidea?ocid=PID24727::T:WLMTAGL:ON:WL:en-US:WWL_WIN_myidea:112009 _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
