[amsat-bb] Re: Satellite Thermal Lesson
kl7uw at acsalaska.net
Wed Nov 18 08:58:54 PST 2009
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
>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 AMSAT-BB at amsat.org. 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 dubususa at hotmail.com
More information about the AMSAT-BB