If a spacecraft is in low earth orbit, I’m used to thinking that eventually the object will slow and fall back to Earth if it isn’t accelerated every now and then.
If a spacecraft is placed in an orbit at a Lagrangian point, such as the James Webb Space Telescope will be, does its orbit decay? If so, what happens to it? Does it become increasingly eccentric, or maybe “fall” into the L2 (or whatever) point?
Any answers written at the seventh grade level would be wonderful.
Low earth orbits decay because there is still (extremely thin) atmosphere at those altitudes that aerobrake the satellite very slowly. Lagrange points, geo-synchronous orbits, and other such higher orbits are far enough out that they don’t suffer this issue to any appreciable degree.
Can the solar wind cause a non-negligible amount of drag on a satellite? Just like terrestrial wind, the drag force when approaching the sun would be greater than the drag force when fleeing the sun, so theoretically it should gradually piss away the satellite’s kinetic energy. But is the magnitude of the drag high enough to matter?
Solar wind would indeed, over a very long time cause some sort of radial motion out from the sun. How long and how much would have a lot of variables based upon cross section, shape, albedo etc.
The L5 and other points are still affected by external gravitational forces, (The sun and Jupiter being the main components here). Eventually, over a very long period, the right alignment of forces could conceivably pull L5 objects out of those points of equilibrium.
Actually, no. The solar wind exerts an inverse square outward force, just like gravity, so the net effect is that objects in orbit behave as though G were a tiny bit smaller (just how tiny a bit depending on the object’s sectional density). It’ll only result in a non-Keplerian orbit if the object’s sectional density changes (especially changes with the same period as its orbit), or if it gets significant drag from the interplanetary medium (which is also not a perfect vacuum).
Any Lagrange point is far enough away from the Earth that drag is insignificant for any plausible satellite over any timescale relevant to humans. But you also have to consider the stability of the Lagrange point itself. L4 and L5 (the two which form the equilateral triangles, leading and trailing the secondary body) are inherently stable, meaning that even if an object is perturbed from one of those points, it’ll tend to stay in its vicinity. But L1, L2, and L3 are all saddle points, stable in two dimensions but unstable in the third: Something placed in one of those points without stationkeeping rockets (or with them, after they run out of fuel) will eventually wander off to some other orbit.