- Good Sphere
- Jun 16, 2018
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https://www.youtube.com/watch?v=QeiQEG450gc
Really cool video from yesterday that relays everything about the mission that is easy to understand. One thing I learned is one side of the telescope will be hot enough to boil water. The opposite side is cold enough to freeze air!
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Dec 29, 2021 21:06
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May 17, 2024 06:38
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- Good Sphere
- Jun 16, 2018
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Why does it orbit "vertically" while orbiting with Earth "horizontally"?
I'm very stupid, hope that made sense
Don't worry, I am in the same boat. I don't know why so far I've just accepted it.
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Feb 15, 2022 06:30
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- Good Sphere
- Jun 16, 2018
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This is how they're described in pretty much every scifi novel, especially the ones where the FTL drive only works in those spots. It's not the worst handwave description for them, but it's not true. Reality is both more complicated and much more mundane.
Lagrange points aren't flat areas of gravity. If the "rubber sheet" was flat that would mean no gravity at all, and stuff would just fly away. If I could use a device on you that flattened gravity, you'd be flung off the earth. That's not what happens to stuff at Lagrange points.
Two basic principles of orbital mechanics:
1. The lower / tighter your orbit, the faster you move. The ISS is in low earth orbit, 420km above us. It's moving 7.66 kilometers per second and goes around the Earth once every 90 minutes. The Moon is about 380,000 km up. It moves at just over 1km/second and takes 28 days to do an orbit. Higher orbit = slower.
2. The bigger (more massive) the thing you're orbiting, the faster your orbit velocity. The Earth is orbiting the Sun at almost 30km/s, despite the fact that we're a long way from the Sun. That's because the Sun is stonkin' huge. The Parker Solar Probe is the fastest object built by man -- it dives so close to the Sun that it enters the outer layers of the solar corona. It goes over 190km/second at its fastest.
So, the JWST is in orbit around the Sun, just like Earth. But it's 1.5 million km further out. This means that by principle #1, it should be going slower than the Earth, and taking longer to orbit. If that were the case it would start "falling behind", getting further and further away. That would be annoying, it would need bigger radios to communicate. And eventually it would be 180° out of sync, on the opposite side of the Sun to us. You can't radio through the Sun, so we'd be out of contact for a while. Then we'd start "catching up" and getting closer.
But now you want to think about fact #2. The Lagrange point L2 is on the line from the Sun through the Earth. Along that line you are adding the Earth's gravity to the Sun's. In effect, it's as if the Sun is a little bit heavier. The specific L2 point along that line is where that Earth+Sun equals an orbit velocity that's the same as Earth.
tl;dr the Earth has JWST on a string and is pulling it along saying "keep up, don't fall behind!"
I can imagine the string thing a bit, with Sun's plus a tiny bit more gravity, which is the the Earth. Does the James Webb go up and down in a circle because of constant corrections, or does it mostly naturally do that? I can kinda see it being able to orbit vertically like that because it's the Sun's gravity pulling it in one direction, and then the Earth's gravity pulling it in another direction.
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Feb 15, 2022 22:41
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Dec 29, 2021 21:06
