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Helium Depleted, Herschel Space Telescope Mission Ends
AmiMoJo writes "The billion-euro Herschel observatory has run out of the liquid helium needed to keep its instruments and detectors at their ultra-low functioning temperature. This equipment has now warmed, meaning the telescope cannot see the sky. Its 3.5m mirror and three state-of-the-art instruments made it the most powerful observatory of its kind ever put in space, but astronomers always knew the helium store onboard would be a time-limiting factor."
Reader etash points to a collection of some infrared imagery that Herschel collected.
It'd have to be more than orbital. Herschel is out at Earth-Sun L2. That's not exactly a short trek.
A pickup truck that can get to L2 and back. Whatever you're thinking of, it isn't the shuttle.
They are in deep space, so they have an infinite sink at nearly zero deg kelvin.
What exactly could it 'sink' that heat into? While we consider space to be 'cold' the reality is that it is less 'cold' and more 'generally won't make things warm.'
The vacuum is both a benefit and a problem. When you want to keep things a certain temperature, the vacuum is great as you don't have to sorry about convection/conduction altering the temperature. But when you want to cool things off, that vacuum is a problem because you can't use convection/conduction to remove that heat from your system. You can certainly move the heat from one part of your system to another part of your system, but it takes a long time to take that heat OUT of your system.
You would have to move the heat to a massive radiator and wait a long time for it to cool due to radiation. Whatever you are using to move that heat will have to work the entire time, (and may have to be cooled as well!). Even then, the temperatures involved mean that such a process would take a very long time to get as low as they needed to conduct the experiments.
Don't think of space as cold, think of space as very effective insulation.
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Why not have the cooling system in a closed loop and use solar power to chill the helium back down - keeping the satellite dormant until it could operate again? It seems like a waste of $billions to not think of such a system. Even if it could only operate 10% of the time, it could provide decades of additional science.
If you read one of the linked articles it explains that they did think of this but at the time it was too risky so went for a simpler solution with a known maximum operational life. A new telescope is being designed that will incorporate mechanical cooling and be able to operate for longer.
"You were made as well as we could make you."
"But not to last."
"The light that burns twice as bright burns for half as long - and you have burned so very, very brightly"
You may think me a tired, old, cynic. I'd have to disagree about the tired bit.
It's not exactly an efficient sink, is it? Your only option for heat transfer "outside" is infrared radiation, since vacuum does not exactly support conduction/convection.
If you really want liquid-He temps, then you can't really radiate heat to lose it. At 1 atm it is almost as cold as the cosmic microwave background, and probably colder than the inner solar system. If they're running below 1atm then it is probably colder than the microwave background itself. This means that your radiator will only serve to warm up the spacecraft, not cool it off.
For an IT analogy - how large a heat sink do you need to cool your PC in an oven? The only way to cool under such conditions is using active technologies, like phase change, or maybe Peltier. Since you're fighting entropy, this will ultimately require some source of energy, which will always be depleted eventually in a closed system.