Working with liquid nitrogen all day, I am constantly bothered by their boiling away, forcing me to go get more from the storage dewar. Likewise should be the case with any cryogen, e.g. LH2 and LOX that are the most common rocket propellants.

From what I've read, nearly all robotic probes use propellants that don't require any refrigeration: hydrazine, MMH, N2O2, and so on, as they can sit happily in a steel ball for years. Driven by another question that brings up the proposition to "bring hydrogen to Mars" to produce rocket fuel, my query is how practical is that? Hydrogen is not liquid at any (reasonable) pressure unless cooled below ~33 K, a difficult feat to maintain that requires lots of insulation and/or evaporative cooling.

What is the longest that any mission (manned or unmanned) has stored cryogens? (used for fuel; WISE doesn't count). Apollo at a couple weeks? I can't find what Soyuz/Progress use, or the ISS's engine, the Shuttle's OMS seems to use MMH/N2O2.

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    $\begingroup$ The problem is not one of having enough insulation/appropriate pressure, since the costs there have, apparently, been quickly decreasing and are quite acceptable. In the long term, dealing with the built-in micro-temperature leaks - struts, in/out feeds, etc - which can lead to accumulated temperature changes over time (see web.njit.edu/~muratov/iacreport11.pdf for a recent discussion). I haven't found an exact, current, time record (are you restricting to missions for a reason?). I'd estimate what's possible to be in the range of a few months, though. $\endgroup$ – blueberryfields Nov 21 '13 at 1:49
  • $\begingroup$ Just a passing comment on this, the temperature in space when shadowed from the sun is about 3K. 15K if you're facing the Earth. It seems like as long as you can keep this cryogen thermally separate from the spacecraft when in sunlight and then use radiators during shadow you could keep it cold enough indefinitely. $\endgroup$ – ThePlanMan Apr 16 '14 at 10:38
  • $\begingroup$ @FraserOfSmeg: How can you maintain the tank at 15K? You need to protect it from all radiations: planet albedo, planet IR, IR from spacecraft, and all conduction heat transfer (this one may be easier to achieve). If the cryogenic liquid starts to boil off, then a little bit must be released to evacuate pressure from the tank. This seems not possible for long mission. I may be wrong, just a question. $\endgroup$ – mins Jan 23 '15 at 11:24
  • $\begingroup$ Well the Earth shine is is about 15K. So assuming you don't get any other radiation input from elsewhere 15K should be you're standing temperature (assuming you're constantly in Earth shadow). $\endgroup$ – ThePlanMan Jan 23 '15 at 15:27
  • $\begingroup$ Earth 15K? I thought it was more like 300. $\endgroup$ – HopDavid Jun 24 '15 at 16:23

The best I can find on this is a presentation from 2011 about the (discontinued) Altair Lunar Lander's needs, written in conjuction with the Department of Energy, in which the state of the art about cryogenics was discussed. This specifically focuses on Hydrogen, the most challenging cryogenic used in space flight. During the "Power Reactant Storage Hydrogen Tank" test, fuel was stored for 21 days in a state where it could be used, with a boil off of about 2% per day. It also mentions the Titan-Centaur 5, which stored fuel for about 9 hours, with a drop off of 21%/day for extended coasting.

I can't find a quote anywhere, but I believe the desire of NASA with the Altair program was to extend this storage to about 6 months.

Apollo's fuel beyond the Saturn 5 launch was not cryogenic, in fact it was Aerozine 50 as fuel and nitrogen tetroxide, neither of which is cryogenic. The Apollo Service module, as well as the Space Shuttle, used hydrogen and oxygen as a fuel cell to make electricity. The Space shuttle had a small liquid hydrogen tank it kept on orbit, for using as a fuel cell fuel and for water generation. From Wikipedia, "The hydrogen and oxygen for the fuel cells was kept in pairs of cryogenic storage tanks in the mid-fuselage underneath the payload bay liner, and a variable number of such tanks could be installed (up to five) depending on the requirements of the mission."

  • $\begingroup$ Was the liquid oxygen just used for breathing (and electricity generation with the hydrogen)? $\endgroup$ – Nick T Jun 24 '15 at 20:09
  • $\begingroup$ It was just used for breathing and for electricity generation. $\endgroup$ – PearsonArtPhoto Jun 25 '15 at 2:17
  • $\begingroup$ Are the %/day figures given as a percentage of the initial volume, or e.g. did the Altair lose 2% of the full volume the first day, then 2% of the remaining 98% (1.96% of the total) the second day, and so on? $\endgroup$ – KRyan Jun 30 '15 at 17:43

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