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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.
If only we had a plan for recurring orbital missions... A "space pickup" that would launch on a regular basis to make pit stops for things like extra helium.
To think how many multi-decade projects like this will "rot on the vine".
"What party balloons?", he replies in a squeaky voice.
Have gnu, will travel.
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.
SpaceX should go after it and salvage it robotically for use as a solar thermal concentrator. 3.5M mirrors that are already in space don't exactly grow on trees. A simple high-efficiency Ion engine (Dawn-class)and a robonaut should be able to handle the job. They can then lease the asset to Planetary Resources or whoever wants to do industrial experiments. Doesn't have to be quick. Cheap and slow is the way to go here.
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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They knew at some point helium will be gone and the telescope will become useless. It ran for four years more or less. Not as bad as the summary made it sound like.
They are in deep space, so they have an infinite sink at nearly zero deg kelvin. It should be possible to design a closed circuit cooling system that just uses energy from solar panels to pump the refrigerant. But in space applications the weight of such a system of compressors, radiators and pumps might prove to be prohibitive.
Still feel sad such a fine piece of machinery is rotting away. Well, may be a better design next time.
No, they have near perfect insulation. The only heat they can get rid of has to happen by radiating it away.
Go step outside.
Notice how warm it is in the sun?
There's no way you can radiate much heat if you're in direct sunlight -- that's why the space shuttle flew upside down in orbit. It kept the heat shield towards the sun, so it had a chance to radiate heat away from the other side.
"So, put a big sun shade and block the sun", you might say... well that's easier said than done, the solar wind would apply a lot of pressure to it, and (for that matter) the solar wind itself is well above the operating temperature of the telescope.
But by all means, I'm sure you're smarter than the experts to designed it.
Andy Griffith says "finders keepers".
the preceding comment is my own and in no way reflects the opinion of the Joint Chiefs of Staff
Thanks, I did not realize things are different in space. So how would one design an active cooling system to dissipate heat in space?
I am not a rocket scientist; but my understanding is that the space-equivalent of a 'heatsink' is a fin, with a surface that approximates a black body as closely as engineering constraints allow, aligned so that as much surface area as possible(the flat faces) receives as little incoming light as possible, with as little as possible exposed to the sun(so, in practice, the alignment is pretty much the opposite of a solar panel, where you want as much surface area getting sunlight as you can and as little being wasted by facing into deep space as you can). Depending on the orbit, and whether your thermal load is constant or can accept variations, this may or may not require the fins to move.
If you need active cooling(as you probably would here, since ultrasensitive IR hardware generates some heat on its own and works less well for every additional kelvin) you use a heat pump of some sort, just as on earth; but your 'sink' is thermal radiation from the fins, rather than conduction from the fins into the atmosphere or coolant water.
The real problem(in addition to the fact that solid-state heat pumps are miserably inefficient, and ones with moving parts have mechanical levels of reliability in an area where you can't just schedule a tech visit), is that thermal radiation alone is miserable compared to conduction/convection into air, which is weak compared to conduction into forced air.
If you have a large enough payload budget, it isn't necessarily insurmountable, all it takes is more surface area radiating heat; but the engineering challenges of having a cryogenic heat pump capable of keeping the instruments at liquid helium temperatures and enough fin surface area to dump the waste heat from both the instruments and the heat pump's own inefficiencies are significant.
Liquid helium isn't cheap, and relying on a consumable cuts mission lifespan; but "just let the helium boil off where you need things to be colder" simplifies the engineering considerably.
I do know how it works and all, but still, I find it kind of ironic that the Herschel Space Telescope is bricked for lack of the second most abundant element in the universe.
Proverbs 21:19
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.