03-17-2016, 07:04 PM
Tink - looked at your question again and realized I missed something out.
For space-based observatories such as the Hubble, they are in orbit so can generally be left alone when it comes to navigation. Once you get something into space it generally follows what it thinks is a "straight line". In orbit, that "straight line" is basically being in free-fall towards the center of the earth but is countered by its speed around the planet. It falls to earth but at the same time its speed balances that and it remains in a stable orbit (it's like spinning a ball on a piece of string - look up "centripetal acceleration" if you get the chance).
Because most space-based telescopes are in low earth orbit, they do still encounter a few molecules of our atmosphere which causes drag, slows them down which means their orbit becomes lower. There are some gravitational effects that are incredibly hard to calculate that change the orbit over time as well. (Did you know that the movement of Kilauea's lava or magma affects the orbits of satellites in low earth orbit? It does). Every so often that has to be corrected so the observatory, or any controlled satellite, will be commanded to fire its thrusters to put it back into a slightly higher orbit.
The Hubble doesn't do that because the gases would remain near the telescope and potentially affect observations. Instead, it uses a particularly ingenious technique. It turns on electromagnets which interact with the earth's magnetic field. They repulse each other which moves the Hubble away from the planet. It's a slow process, but it doesn't need to be quick.
Apologies for taking this away from Puna and Hawaii, but Tink reminded me of an undergraduate report I had to write many years ago, and this stuff has just stuck in my head. Just a very elegant use of physics.
I now return you to your normal programming.
For space-based observatories such as the Hubble, they are in orbit so can generally be left alone when it comes to navigation. Once you get something into space it generally follows what it thinks is a "straight line". In orbit, that "straight line" is basically being in free-fall towards the center of the earth but is countered by its speed around the planet. It falls to earth but at the same time its speed balances that and it remains in a stable orbit (it's like spinning a ball on a piece of string - look up "centripetal acceleration" if you get the chance).
Because most space-based telescopes are in low earth orbit, they do still encounter a few molecules of our atmosphere which causes drag, slows them down which means their orbit becomes lower. There are some gravitational effects that are incredibly hard to calculate that change the orbit over time as well. (Did you know that the movement of Kilauea's lava or magma affects the orbits of satellites in low earth orbit? It does). Every so often that has to be corrected so the observatory, or any controlled satellite, will be commanded to fire its thrusters to put it back into a slightly higher orbit.
The Hubble doesn't do that because the gases would remain near the telescope and potentially affect observations. Instead, it uses a particularly ingenious technique. It turns on electromagnets which interact with the earth's magnetic field. They repulse each other which moves the Hubble away from the planet. It's a slow process, but it doesn't need to be quick.
Apologies for taking this away from Puna and Hawaii, but Tink reminded me of an undergraduate report I had to write many years ago, and this stuff has just stuck in my head. Just a very elegant use of physics.
I now return you to your normal programming.