Re: Liquid Hydrogen Refrigeration

From: Henry Spencer (henry_at_spsystems.net)
Date: 03/20/05 

Date: Sun, 20 Mar 2005 17:11:54 GMT

In article <EsB9HmCRdFPCFw4L@merlyn.demon.co.uk>,
Dr John Stockton <spam@merlyn.demon.co.uk> wrote:
>But for long range space travel, for most of the journey there's over 12
>steradians of ambient at about 3 K, and not much else apart from maybe a
>Sun at 6000 K occupying under 0.0001 sr.

The situation isn't quite that good, in a couple of ways.

For one thing, the sky is substantially above 3K (more precisely, 2.7K).
That's the cosmic background temperature, yes, but there are foreground
objects as well, some of them moderately bright. I don't remember what
the final total is, but if memory serves, it's noticeably above 3K.

More significantly, depending on what the mission is, a significant part
of the flight time may be spent waiting for things to happen in the
immediate vicinity of a rather warm planet.

Heat leaks from the non-tank portion of the vehicle may also be
significant, although there are various ways of limiting them. 

-- 
"Think outside the box -- the box isn't our friend."    |   Henry Spencer
                                -- George Herbert       | henry@spsystems.net