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In this answer to Why is the hot part of Webb's MIRI cryocooler in the 300K area? and comments below discusses the helium refrigerator used for cooling JWST's Mid-Infrared Instrument or MIRI.

A comment there talks about the disadvantages of using a dewar or reservoir of helium that performed passive cooling by a slow boil-off. Advantages are that it doesn't fail like a compressor would nor does it vibrate (though it can slosh). Disadvantage is that it runs out, which might come a lot sooner than a(n extremely well-designed) compressor failure would.

...what the 'dewar flask' cooling is... a flask of liquid helium provides liquid helium to locations needing cooling where the liquid absorbs heat, turns to gas which is then vented to space. Long service life would mean a very large, very heavy amount of helium. It would also mean an absolute hard limit to useable lifetime.

That "hard limit" sounds familiar, though I think the limit was softened by limited operation at shorter wavelengths. In any event, I'd like to ask:

Question: Which (if any) space telescope would have worked longer if it hadn't simply run out of helium?

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2 Answers 2

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Past infrared telescopes (IRAS, Spitzer, others I can't remember) in space have generally used expendable liquid He. They either ceased operation or lost a large part of their capability when the He ran out.

Also there were failures caused by design errors in the difficult-to-test cryogenic systems. WIRE lost its cryogen store (hydrogen, not He) when its aperture cover came off prematurely. The x-ray quantum calorimeter on Suzaku lost its He due to a thermal runaway caused by inadequate venting.

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    $\begingroup$ Yes, Spitzer and specifically the "Spitzer Warm Mission" is what I was trying to remember, thanks! $\endgroup$
    – uhoh
    Commented Sep 4, 2022 at 18:49
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The Herschel infrared telescope is another recent telescope that stopped working once it ran out of Helium for its coolant.

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