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The James Webb telescope is parked in a halo orbit around SEL2, beyond the Earth's umbra, to avoid solar eclipse by Earth or Moon. Is there anything else which could shade JWST?

Woody
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Josh Berryman
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    There is a large amount of easily available information that describes the exact opposite of JWST in "permanent shadow". In effect JWST has a pseudo-orbit (halo orbit) "about" L2 which keeps JWST in constant uniform sunlight. This is to keep the solar heat load very constant and well managed. – BradV Dec 21 '23 at 18:40
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    What does this mean " Is anything else up there?" Also the title does not seem to match the rest of your question. I suggest you take the time to edit your question and title to clearly explain exactly what you are asking. – Organic Marble Dec 21 '23 at 19:13
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    Is . anything . else . at . L2? – Josh Berryman Dec 21 '23 at 19:16
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    Hi @JoshBerryman, Welcome to Space SE! Despite the wording of the title List of objects at Lagrange points so far objects are never really (to my knowledge) ever put at the Lagrange points themselves. Instead they are put in orbits that are associated with Lagrange points but orbit around them in some way. That article indicates there are several objects in halo orbits associated with the Sun-Earth L1 & L2 points. And as the answer points out it's got nothing to do with shadows – uhoh Dec 21 '23 at 23:17
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    Related: Are any Earth orbits in continual shadow of the Earth? and Exoplanet orbitable in permanent umbra? – uhoh Dec 21 '23 at 23:19
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    The JWST is in a halo orbit near L2. Its distance from L2 ranges from ~500000 km to ~850000 km. Please see https://space.stackexchange.com/a/57832/38535 & https://astronomy.stackexchange.com/a/49616/16685 for details & diagrams. – PM 2Ring Dec 22 '23 at 14:01

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Answer: nothing shades JWST

In https://ntrs.nasa.gov/api/citations/20150017756/downloads/20150017756.pdf it is stated:

Shadows, or eclipses of the spacecraft by either the Earth or the Moon, are not permitted at all during the mission… these constraints conspire to limit the maneuverability of the spacecraft and couple the orbital dynamics to the rhythms of the Earth, Moon, and Sun.

The mission design criteria specifically forbids eclipses, even partial eclipses by the moon transiting the sun. The science instruments require a high degree of thermal stability. A relatively brief eclipse period would require an extended period for the instrument temperature to re-stabilize. Even attitude changes for eclipse avoidance maneuvers could potentially threaten temperature stability. https://ntrs.nasa.gov/api/citations/20190028885/downloads/20190028885.pdf

Because of the JWST's large diameter halo orbit (compared with the moon’s orbit), it is anticipated there will be no eclipse events during the planned mission duration.

See also Why are eclipses of the James Webb by the Earth or Moon not permitted during the mission?

Woody
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    It also needs to stay in sunlight to provide power for the solar arrays. For JWST to remain in Earth's shadow it would require an RTG for power. – Steve Pemberton Dec 22 '23 at 16:01
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The James Webb telescope is parked at L2 of the Earth-Sun pair to minimise solar interference.

The JWST is not at the the Sun-Earth L2 point. It is instead in a large halo orbit (pseudo-orbit is a better term) about the Sun-Earth L2 point that always keeps the JWST in sunlight.

This constant sunlight is needed so as to ensure that the telescope always has power. To completely eliminate solar interference, half of the telescope is shielded by itself. The JWST has a tennis court sized, five layer thick sunshield. Very little heat is transmitted from the hot side to the cold side of the JWST. The side that constantly faces the Sun is about 85° Celsius while the side that constant faces away from the Sun is about -235° Celsius -- a difference of 320° Celsius.

David Hammen
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  • As a side remark, staying perpetually in Earth shadow would not only require an RTG for power but would also require a lot more propellant to maintain that highly suboptimal position. – David Hammen Dec 27 '23 at 15:33