# [amsat-bb] Re: e: Satellite technical question

Robert Bruninga bruninga at usna.edu
Sun Sep 9 09:26:47 PDT 2012

```> Assume a cubesat with a monopole ¼ wave antenna at 400 mhz.
>The satellite is in full sun with a 500km orbit. What is the antenna
> temperature in full sun and in eclipse?

It depends entirely on its color (surface properties).  If it black it will
get to about 55 farenheight in the sun and to about very cold in the dark.
If it is white, it will get to about -60 F in the sun (Notice that is MINUS
60) and very cold in the dark.  If it is clean shiny aluminum, it could get
to +250 F in the sun and very  cold in the dark all assuming they have no
other way to conduct away heat.

Those are steady state hot temps for the surfaces given.  I dont remember
the cold temps, though they will all reach the same very cold temps if they
never see the sun.  Notice that these are steady state.  A metal sphere
with these colors going in and out of eclipse will never reach these
extremes because of their thermal mass that cannot get that hot in 60
minutes and cool down that much in 35 minutes of dark.

Our basically black PCsat (solar panels mounted to the aluminum body with
good conductivity only got to about room temperature in the sun and no
colder than about freezing (32 F) in the dark every 90 minutes.

But it was a shock to us when we designed a flip-out solar panel for a
cubesat that is exposed on both sides to space.  It gets to almost boiling
on the sun side and down to about -70F in the dark... EVERY orbit.

SO, I assumed that a thin tiny whip antenna could not conduct very much
heat to the spacecraft, so its extremes will be high.  But a piece of wire
can easily handle these temps.  But any solder joint that cannot
communicate heat to/from the rest of the spacecraft might have problems.

This is an off-the-cuff answer.  Doing thermal in space is a real ART!

Good luck.

Bob, Wb4aPR

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