Re: pinhole Cooling satelites in space?

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From: Paul Doherty (pauld@exploratorium.edu)
Date: Thu Feb 03 2005 - 08:38:05 PST 

Message-Id: <l0311073ebe2802560808@[192.168.112.4]>
Date: Thu, 3 Feb 2005 08:38:05 -0800
From: Paul Doherty <pauld@exploratorium.edu>
Subject: Re: pinhole Cooling satelites in space?

Hi Mike

A satellite with no internal heat sources and an albedo equal to the earth
would reach an equilibrium temperature similar to the earth at the earth's
distance from the sun. (about 0 °C) (The surface of the earth is warmer due
to the greenhouse effect.)

Apollo 13 had a problem which removed internal heat sources, the
temperature dropped in the spacecraft and the astronauts got cold.

The problem comes in when there are heat sources on the spacecraft. They
must get rid of the generated heat or the temperature of the spacecraft
will increase.

Spacecraft use black radiators not in sunlight to radiate excess heat.
The insides of the space shuttle hatch doors open in space because they are
covered with radiators. If the doors don't open the shuttle has to return
to earth or it will overheat.

The spacecraft going to Mercury has a metal foil shield on the sun side to
reflect sunlight.

Paul D

>Hello,
>
>I have a question about space satellite design. I understand that despite the
>super low temperatures in space, satelites actually have a problem with
>overheating because without air, they can't lose heat by conduction or
>convection. They are stuck with radiative heat loss as the only mechanism to
>cool off. Furthermore, with the intense radiation above the atomosphere, they
>are subject to a lot of radiative warming and their electronics generate heat
>too.
>
>I'd like to pose an engineering problem to my students but figure I ought to
>understand the answer first. What kind of design features do satelites use to
>thermoregulate properly? They are often covered in some sort of foil. Is
>part
>of the idea here to reduce warming by radiative absorbtion? I wonder, are the
>backs of the solar arrays black? This would increase cooling by radiative
>emission on a part of the satelite that isn't exposed to the sun but I wonder
>if they are actually designed this way.
>
>Cheers,
>Mike Geluardi
>
>
>
>
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