From: email@example.com (Henry Spencer)
Subject: Re: Venting Helium Gas
Date: Thu, 2 Mar 2000 16:20:33 GMT
In article <firstname.lastname@example.org>,
Ephraim Gadsby <Ephraim.Gadsby@The.Drones> wrote:
>I understand that some satellites have liquid helium cooled
>instrumentation, with reservoirs that are well enough insulated so
>that the helium lasts for the course of the mission.
Correct. The mission lifetime is typically limited to a year or two, but
within that, this works reasonably well. It's mostly been done for
infrared astronomy, where detectors work much better if chilled to nearly
>In micro-gravity how do they vent the boil-off, without ejecting
The orthodox way of doing this sort of thing is a "phase-control heat
exchanger". You run the fluid leaving the tank through a pressure drop,
reducing its boiling point. Then you run it through a heat exchanger
connected to the rest of the tank (simply bonding a run of tubing to the
wall of the tank works fairly well). The departing fluid, being at a
lower pressure, boils, and this cools the tank. This kills two birds with
one stone: it ensures gas in the output, while also refrigerating the
I'm not sure this is *exactly* what the liquid-helium guys do, though.
Liquid helium has some strange properties, and I have a dim recollection
that at least some of the helium-cooled systems exploit those to help.
Computer disaster in February? Oh, you | Henry Spencer email@example.com
must mean the release of Windows 2000. | (aka firstname.lastname@example.org)
From: Doug Jones <email@example.com>
Subject: Re: Spacesuit technology - a question...
Date: 06 Aug 1997
Henry Spencer wrote:
> I see some practical problems with helium. For one thing, I expect that
> its much lower density would interfere with air-cooling of electronics
> (which is one major reason for wanting to run at a total pressure not far
> below 14.7psi).
Actually, helium is a far better thermal conductor than air- I had to
release a large amount of helium from a balloon in a launch abort, and
the helium felt cooler than the air at the same temperature. At the
same pressure, He will transport much more heat than air- about 8x,
Helium's thermal conductivity is a problem for saturation divers,
requiring higher temperatures in their habitats for comfort.
Doug Jones firstname.lastname@example.org
If they call it tourist season, why can't we shoot them?