Re: pinhole Cooling satelites in space?

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From: Wayne Brock (ekcorb@yahoo.com)
Date: Thu Feb 03 2005 - 20:55:15 PST 

Message-ID: <20050204045515.63544.qmail@web30509.mail.mud.yahoo.com>
Date: Thu, 3 Feb 2005 20:55:15 -0800 (PST)
From: Wayne Brock <ekcorb@yahoo.com>
Subject: Re: pinhole Cooling satelites in space?

Some satellites use what they call "heat pipes" to
move heat around the satellite. They were basically
tubes that carry liquid (or a gas, I can't remember
what goes through the pipes) through the panels.
Having large temperature differences on different
parts of a spacecraft is troublesome because of how
materials expand and contract. A reflective foil with
several layers is sewn together and covers the outer
surfaces. The outer layer often contains a thin layer
of gold (Gold is quite good at reflecting). They also
use thin layers of insulating material between the
foil layers so the outer layer does not conduct heat
inward as it is warmed by the sun. I used to work on
those things but I haven't thought about that stuff
for a while.

wayne

--- Paul Doherty <pauld@exploratorium.edu> wrote:

> 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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>
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