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But why is it at the Lagrange point in the first place? Wouldn’t ultra-high orbit be equally enough?
by vl 3y ago
But why is it at the Lagrange point in the first place? Wouldn’t ultra-high orbit be equally enough?
- areoform 3y agoThe coldhead of one of these sensors (MIRI) functions optimally at temperatures less than 7˚K (i.e. 7˚ above absolute 0). The other sensors run at temperatures under 40˚K. For reference, the melting point of nitrogen is, 63˚K. Any sunlight at all would overwhelm this sensor and severely reduce the operational lifetime (and results!) of the telescope. At L2, the telescope has the sun and the Earth behind a layered sunshield. It's easier to maintain position there and to have both objects always in the sol-ward direction while looking outwards.
- pfdietz 3y agoThere are telescopes on Earth that cool their detectors (not optics, though) well below that temperature. The SPT-3G at the South Pole, for example, has detectors at 3K.
- Tuna-Fish 3y agoBecause it is an infrared telescope, and in earth orbit there are three very bright infrared sources that would mess up the instruments or heat up the telescope too much if they ever shone on the sensitive parts. (Sun, Moon and Earth.) When the telescope is placed in the Sun-Earth L2, all three sources are always very close to each other in the sky, and you can shield against all three with a single directional sunshield.
- cubefox 3y agoI always thought L2 was chosen for Earth to cover up the sun. But apparently Earth covers it only to 84%. https://www.quora.com/Is-the-L2-point-of-Earth-in-a-permanent-shadow-of-the-Earth https://www.quora.com/Is-the-L2-point-of-Earth-in-a-permanen...
- sjburt 3y agoIt’s so the sun and the earth will always be in the same direction and both can be hidden behind the sun shield.
- Tuna-Fish 3y agoBecause the JWST is not at the L2, but in a halo orbit around it, Earth in fact never covers the Sun at all from its point of view. They are just always fairly close to each other.
- cubefox 3y agoInteresting!
- deleted 3y ago[deleted]
- bagels 3y agoIt needs solar power