3 ms·
Actually, if I read various web sources correctly (IANA rocket scientist, sadly), the Earth-Sun-L2 point is always in the sun. The earth is not big enough to p
by jholman 14y ago
Actually, if I read various web sources correctly (IANA rocket scientist, sadly), the Earth-Sun-L2 point is always in the sun. The earth is not big enough to provide shade from that far away, especially since the Hershel's orbit is 700Mm across. Like how a (cruising-altitude) 747 cannot shade (sea-level) me from the sun, no matter where I stand.
So it's always in the sun, which means it has continuous heating, and thus reaches thermal stability, and doesn't expand/contract/whatever as it passes in and out of shade.
- mturmon 14y agoYes, I was being facile for the sake of a one-liner. Sorry about that. It will be in a certain kind of orbit around the L2 point, not right on top of the L2 point. This means it is not in Earth's shadow, as you note. It's in its own shadow. But if it were in a conventional orbit centered around Earth, it would have thermal issues, observational issues, etc., because pointing to keep the telescope away from the sun would be a big problem. My friend across the hall uses data from Planck, which is at L2, and I used to use data from SoHO (before its camera was shut down), which is at L1. We used to joke around about how each other's instrument was in a too cold/too hot place. Here's a nice illustration of Planck's orbit. (Planck was the sister satellite to Herschel.) http://planck.cf.ac.uk/mission/orbit http://planck.cf.ac.uk/mission/orbit