[Server-sky] [Beowulf] Server Sky - Internet and computation in orbit

[Eugen Leitl]

----- Forwarded message from Lawrence Stewart <stewart at serissa.com> -----

Date: Sat, 22 Jun 2013 19:58:11 -0400
From: Lawrence Stewart <stewart at serissa.com>
To: "beowulf at beowulf.org List" <beowulf at beowulf.org>
Cc: Lawrence Stewart <stewart at serissa.com>
Subject: Re: [Beowulf] Server Sky - Internet and computation in orbit
X-Mailer: Apple Mail (2.1508)

I've been imagining that these thinsats are a sandwich:  Solar cells on the sun side, computation in the middle, and a radiator on the back.

It might be best to have two sheets, with a vacuum gap between the solar cells and the computation, to prevent conduction.  Presumably the solar cells would have thin film filters to reflect (not absorb!) the radiation except at wavelenghts with good PV efficiency.

Insolation at Earth orbit is about 1 KW/m**2, and PV efficiency about 20%.  Suppose that
with the filters, you can reject 60% while absorbing 20%.  So for 1 m**2 you get about 200 watts electric and 200w heat, total 400w to dispose of via radiation.

According to (that excellent source!) Wikipedia, at 307K with good emissivity,  you can
radiate about 1000 w from the 2 m**2 area.

Consequently, it appears to me that you can have a thinsat that is solar powered and radiatively
cooled, with an equilibrium temperature below room temperature.

Of course my figures could be way wrong, but it seems plausible.  To do better you just need a bigger radiator on the back.

I suppose the radio is a phased array of antenna elements or even integrated lasers with mems mirror steering.

-Larry

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Eugen* Leitl <a href="http://leitl.org">leitl</a> http://leitl.org
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