[amsat-bb] Re: Satellite Thermal Lesson

Edward Cole 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.
>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.
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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

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