5 ms·

Is there any reason to park in at a Lagrange point instead of just a high orbit? There aren't that many Lagrange points, so we should probably avoid cluttering

Is there any reason to park in at a Lagrange point instead of just a high orbit? There aren't that many Lagrange points, so we should probably avoid cluttering them with objects that don't need to be there.

m4rtink 6y ago
At least for the Moon, the lunar orbit is generally unstable: https://en.m.wikipedia.org/wiki/Lunar_orbit https://en.m.wikipedia.org/wiki/Lunar_orbit
- gizmo686 6y ago
  You don't need a stable orbit, just one that will keep it in our neighborhood and away from the atmosphere and congested orbits. Put it in a high orbit, and point a telescope at it every now and then to update our record of it's orbit. By the time we are ready to visit it, even if its orbit changed, its new orbit would not be any more inconvenient then where we left it.
  - namibj 6y ago
    The moon's lumpy gravity field actually causes the eccentricity of most orbits to raise quite fast, eventually bringing the periapsis below the surface (or the apoapsis on an escape trajectory, but I recall the former being more of an issue): https://www.youtube.com/watch?v=EadClM4Y45A https://www.youtube.com/watch?v=EadClM4Y45A
rossmohax 6y ago
from what I've read Lagrange point isn't exactly a point, but a region where it's cheap (in terms of fuel) to stay. They are quite large.
- sandworm101 6y ago
  You can orbit the lagrange point, vertically as seen from earth. In such orbits it functions as if it were a point source of gravity.
ChuckMcM 6y ago
Station keeping. The L4 and L5 points are nominally self stable, if you put something there it won't wander off. (this isn't true of the L1 point which is more dynamic). To do station keeping you need reaction mass and working thrusters. That level of infrastructure requires some maintenance, whereas you could put an empty/abandoned ISS in the L4 or L5 point and it would just sit there for no additional cost.
- gizmo686 6y ago
  Right, but why do you need to do station keeping at all. Tracking objects is cheap, and a normal graveyard orbit isn't going to be perturbed so much that it would be notably harder to reach again in any reasonable timeframe.
  - ChuckMcM 6y ago
    Few chances to have a collision with existing space junk in either L4 or L5.
    - aetherson 6y ago
      That's shooting an ant with a rocket launcher. You could avoid space junk in much lower orbits than the Lagrange points. I encourage everyone to get a sense for the sheer scale of this. Do it on your floor or walls. Try a scale of 1cm = 5000km or 1cm = 10,000km. Cut out little Earths and moons and map out geosynch, the lagrange points, etc.
  - interestica 6y ago
    Orbits decay. Things change. Political priorities change. I mean, they didn't want skylab to come down when/where it did.
    - Faark 6y ago
      Skylab was in LEO. There is hardly any decay once you get higher up, you're quickly approach "many lifetimes". That's why the new huge LEO constellations won't be a big space garbage problem.
elihu 6y ago
At some point, if you go too high you end up in the Van Allen belts, which if I understand correctly are a really harsh place for spacecraft to be. Generally those orbits are used for parking bulky rubbish that's too much trouble to de-orbit. Geosynchronous orbits are above the worst parts of the radiation belts, so maybe that's a good place for the ISS. Or even higher; it doesn't need to be geosynchronous. The main advantage of a low orbit is that it's easier to get to from Earth, but if you're just parking it long-term as a museum piece that doesn't matter as much. I wouldn't expect Lagrange points to have much of a problem with clutter unless we decide to start parking enormous quantities of stuff there. Objects can spread out and orbit the points; as long as they're all going in about the same direction they should be able to avoid running into each other.

m4rtink 6y ago

At least for the Moon, the lunar orbit is generally unstable: https://en.m.wikipedia.org/wiki/Lunar_orbit https://en.m.wikipedia.org/wiki/Lunar_orbit

gizmo686 6y ago
You don't need a stable orbit, just one that will keep it in our neighborhood and away from the atmosphere and congested orbits. Put it in a high orbit, and point a telescope at it every now and then to update our record of it's orbit. By the time we are ready to visit it, even if its orbit changed, its new orbit would not be any more inconvenient then where we left it.
- namibj 6y ago
  The moon's lumpy gravity field actually causes the eccentricity of most orbits to raise quite fast, eventually bringing the periapsis below the surface (or the apoapsis on an escape trajectory, but I recall the former being more of an issue): https://www.youtube.com/watch?v=EadClM4Y45A https://www.youtube.com/watch?v=EadClM4Y45A

rossmohax 6y ago

from what I've read Lagrange point isn't exactly a point, but a region where it's cheap (in terms of fuel) to stay. They are quite large.

sandworm101 6y ago
You can orbit the lagrange point, vertically as seen from earth. In such orbits it functions as if it were a point source of gravity.

ChuckMcM 6y ago

Station keeping. The L4 and L5 points are nominally self stable, if you put something there it won't wander off. (this isn't true of the L1 point which is more dynamic). To do station keeping you need reaction mass and working thrusters. That level of infrastructure requires some maintenance, whereas you could put an empty/abandoned ISS in the L4 or L5 point and it would just sit there for no additional cost.

gizmo686 6y ago
Right, but why do you need to do station keeping at all. Tracking objects is cheap, and a normal graveyard orbit isn't going to be perturbed so much that it would be notably harder to reach again in any reasonable timeframe.
- ChuckMcM 6y ago
  Few chances to have a collision with existing space junk in either L4 or L5.
  - aetherson 6y ago
    That's shooting an ant with a rocket launcher. You could avoid space junk in much lower orbits than the Lagrange points. I encourage everyone to get a sense for the sheer scale of this. Do it on your floor or walls. Try a scale of 1cm = 5000km or 1cm = 10,000km. Cut out little Earths and moons and map out geosynch, the lagrange points, etc.
- interestica 6y ago
  Orbits decay. Things change. Political priorities change. I mean, they didn't want skylab to come down when/where it did.
  - Faark 6y ago
    Skylab was in LEO. There is hardly any decay once you get higher up, you're quickly approach "many lifetimes". That's why the new huge LEO constellations won't be a big space garbage problem.

elihu 6y ago

At some point, if you go too high you end up in the Van Allen belts, which if I understand correctly are a really harsh place for spacecraft to be. Generally those orbits are used for parking bulky rubbish that's too much trouble to de-orbit. Geosynchronous orbits are above the worst parts of the radiation belts, so maybe that's a good place for the ISS. Or even higher; it doesn't need to be geosynchronous. The main advantage of a low orbit is that it's easier to get to from Earth, but if you're just parking it long-term as a museum piece that doesn't matter as much. I wouldn't expect Lagrange points to have much of a problem with clutter unless we decide to start parking enormous quantities of stuff there. Objects can spread out and orbit the points; as long as they're all going in about the same direction they should be able to avoid running into each other.