At 05:46 AM 11/18/2009, Bruce wrote: >On 11/18/2009 8:34 AM, Robert Bruninga wrote: > > 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 >snip... > >This was sent by Bob on April 26, 1996. I found it interesting and kept it. > >KEEPING ELECTRONICS COOL IN THE SUN. > >WHile building a GPS unit for mounting on my dashboard and noting the >comming summer months, I looked up the difference in absorption and >emissivity for Aluminum, Black paint, and white paint. Satellite builders >are well aware of these facts, but many of us landlubbers are not. > >ALUMINUM will get 30 TIMES hotter than WHITE paint! (in a vacuum) > >The following table is for a vacuum and accounts for RADIATIVE effects. It >does not account for convective or conductive cooling (air).. > > Absorbtion Emissivity Ratio Temp C > >ALUMINUM .4 .03 11:1 400 >STEEL .6 .4 3:2 150 >BLACK PAINT .9 .9 1:1 110 >WHITE PAINT .25 .85 1:3 72 > >Most people are aware that Black gets hotter than white, but the fact that >bright, reflective, shinny Aluminum gets 10 times hotter than BLACK is a >surprise to most people... > >So, if it sits in the sun, paint it white! If you dont believe this, put >an aluminum baking sheet in the sun. I baked my first roof mount GPS >stand alone tracker thinking that the upside down baking pan would reflect >the sun... WRONG! Painted it white and it is now as cool as a cucumber. > >The difference in Aluminum is the POOR EMISSIVITY at infrared. It can't >radiate the heat away... > > > > > >_______________________________________________ >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
Second thought on this: I painted my eme dish flat-gray for visual environmental reasons, but the color aids melting ice/snow from the surface. It was previously white. 73, Ed - KL7UW, WD2XSH/45 ====================================== BP40IQ 500 KHz - 10-GHz www.kl7uw.com 500-KHz/CW, 144-MHz EME, 1296-MHz EME DUBUS Magazine USA Rep [email protected] ====================================== _______________________________________________ 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
