Would satellites orbits rise like the moon's?

[Deadpangod3]

Since the moon is basically undergoing the same tidal forces iirc as earth orbiting satellites, don't the satellites orbits rise slowly from earths rotation?

[kahlzun]

the tidal bulge is pulling the moon slowly faster and faster due to the difference between the moons orbital period (28d) and the Earths rotation: the moon pulls the water towards it, and the Earth twists it away, pulling the moon along also.

Any satellite orbiting higher than geosynchronous orbit would experience the same effect.

There aren't many satellites in orbits that high (i think) and the effect would be very small in any case, and would probably be offset by gravity drag from the moon in any case.

[mic_e]

More interesting question: To what degree, and under what circumstances, is a geosynchronous orbit tidally stable?

I.e. if the moon had a precisely geosynchronous orbit, would that be a stable or an unstable condition?

What about smaller satellites, ignoring radiation pressure, perturbations, ...?

Intuition tells me that double-locked systems like Duna-Ike or Pluto-Charon should be extremely stable, but on the other hand we know that sub-geosynchronous satellites are falling, while super-geosynchronous satellites are rising, which would imply that the geosynchronous orbital period is unstable.

I can only assume that a certain mass ratio is required to 'snap' a geosynchronous orbit to 'stable'.

Edited May 9, 2014 by mic_e

[Ralathon]

Above geostationary they'd move away since the earth spins faster and drags the satellite along.

Below geostationary they'd fall down since the earth spins slower and the bulge will drag them back.

Anyway, since the satellites have only very little gravity and there are a myriad of other factors adjusting orbits you really don't need to worry about tidal drag that much. By the time you'd notice anything the drag caused by the upper atmosphere, the uneven field of earth or the moon's gravity will have already thoroughly scrambled your orbits.

[undercoveryankee]

More interesting question: To what degree, and under what circumstances, is a geosynchronous orbit tidally stable?

I.e. if the moon had a precisely geosynchronous orbit, would that be a stable or an unstable condition?

What about smaller satellites, ignoring radiation pressure, perturbations, ...?

Intuition tells me that double-locked systems like Duna-Ike or Pluto-Charon should be extremely stable, but on the other hand we know that sub-geosynchronous satellites are falling, while super-geosynchronous satellites are rising, which would imply that the geosynchronous orbital period is unstable.

I can only assume that a certain mass ratio is required to 'snap' a geosynchronous orbit to 'stable'.

Imagine we have an ideal doubly-locked system. Then something comes along and perturbs it to increase the orbital distance slightly, so they are farther out than synchronous. Tidal forces will push the distance further out, as discussed, while at the same time slowing down the bodies' rotation.

The final equilibrium will be synchronous again, but with the slower rotation rate the synchronous orbit will be farther out.

[softweir]

The short answer is "it depends".

There are very many forces acting on artificial satellites: Tidal forces, the moon's gravity, the sun's gravity, solar radiation pressure, atmospheric drag, and even irregular impulses caused by continents and even mountains as satellites pass nearly overhead. These do not add up in any way that is easily predictable.

However, as a general rule Rathlon's answer holds good: satellites above geostationary/geosynchronous orbit tend to move away from Earth, those below tend to move towards it. Those in very low Earth orbit are so very affected by atmospheric drag that tidal drag is almost irrelevant and they fall fast!

[Moon Goddess]

Isn't the graveyard orbit above Geostationary, thus all non functional comm satellites are being slowly flung away?

[cantab]

The Moon's orbit is boosted because of the tidal bulge it raises on the Earth. The tidal bulge raised by a satellite will be absolutely negligible. Even if it wasn't, surely the fact that near-Earth space is full of satellites will lead to no overall effect.

[lajoswinkler]

The effect is pathetic in comparison with the sunlight pushing against parts of the satellite with different albedo. I doubt it's even measurable.

[Moar Boosters]

Isn't the graveyard orbit above Geostationary, thus all non functional comm satellites are being slowly flung away?

I think it's a fairly low percentage which are successfully pushed into graveyard orbit. Most of the time the first thing to break is the gyros, so they become uncontrollable and it's impossible for them to complete their final maneuver.