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If an artificial satellite is in orbit around the Earth, it collides with dust and gas and loses a very small amount of kinetic energy to these collisions, and eventually will spiral down towards Earth.

Would it be possible to use solar energy to keep the satellite in orbit forever*?

*as long as the sun is burning, so "forever"="about 5 billion years"

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  • $\begingroup$ How would you use solar energy? $\endgroup$ – HDE 226868 Oct 10 '14 at 23:35
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    $\begingroup$ The simple answer is no. Stuff happens in space. Bad stuff. Vehicles run out of fuel, their solar arrays fail, their computers fail. Even a satellite with solar sails: Those too will fail (along with the computer system to control the spacecraft). Once a satellite is dead it becomes a fun toy with which the Moon and the Sun can have a little fun, at least for a little while. $\endgroup$ – David Hammen Oct 11 '14 at 6:00
  • $\begingroup$ Eventually, even a Star burns out ... $\endgroup$ – Everyone Oct 11 '14 at 12:13
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    $\begingroup$ Wait - even our Moon's orbit is decaying, right? (I think it's ALSO being "pushed out" by tidal forces - is that right?) $\endgroup$ – Fattie Oct 14 '14 at 10:16
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    $\begingroup$ Potentially, an intelligent (think AI vastly beyond what we have today) satellite could keep itself in orbit for that long--assuming its self-correction mechanisms were able to prevent corruption over that time frame, and assuming it was able to continue to self-repair. But once you take the question that direction it becomes too speculative. HDE's answer is the best you can get with our current knowledge. I must emphasize: this is completely beyond anything we know how to do today. If it is possible, we are not remotely close to knowing how. We aren't even sure how to make a 100 year probe. $\endgroup$ – called2voyage May 18 '16 at 14:35
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The answer is a solid 'no'. There is no way a satellite could stay in orbit indefinitely. I'm still not sure what you mean by "solar energy," but that will not work forever. Everything fails, in due course. Any mechanisms onboard will eventually break down, and, over time, the satellite will come crashing to Earth. The only way around this would be to give the satellite an orbital boost and/or repair it, but that is (in my opinion) a cheap loophole. The satellite would not be self-sufficient.

To add in what David Hammen and TildalWave were teaching me: The satellite could be thrown out of orbit by perturbations from another body and sent somewhere completely different, then potentially recapture by another celestial body. Then the forces of orbital decay will go at it again, (and as TildalWave would say) ad nauseum.

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    $\begingroup$ Satellites won't necessarily come crashing to Earth. I suspect a number of the spacecraft in geosynchronous orbit will eventually get ejected from the Earth-Moon system. $\endgroup$ – David Hammen Oct 11 '14 at 17:41
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    $\begingroup$ There are all kinds of things that change satellites' orbits. Perturbations from the Moon, the Sun, and the Earth's non-spherical gravity field. Tidal perturbations. Radiation pressure and its cousin, the Yarkovsky effect. The Kozai mechanism. These can change the shape of the orbit, the orientation of the orbit, and even the size of the orbit. As I said in another comment, once a satellite loses the ability to control its state it becomes a fun toy to play with. That is, until it crashes into the Earth, the Moon, or is ejected. $\endgroup$ – David Hammen Oct 11 '14 at 19:17
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    $\begingroup$ And if it's ejected it'll be in a heliocentric orbit similar to that of the Earth-Moon system and can be later recaptured, ejected again, ad nauseam. Some funny orbits can come out of such dynamics, e.g. horseshoe orbits between L3 to L5 Lagrange points, tadpole orbits between any of these points and the Earth-Moon, around Lagrange points,.. or any other even more bizarre, chaotic, non-resonant orbits. And given an extraordinarily lucky set of circumstances, in orbital mechanics version of the infinite monkey theorem, it might even be ejected out of the Solar system and overtake Voyager 1. :) $\endgroup$ – TildalWave Oct 13 '14 at 0:19
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    $\begingroup$ @HDE226868 Yes, one helluva final slingshot after many more before it in an aphelion rising ping pong, possibly involving more than just two massive celestials, one of which likely the Sun itself and the satellite on a close shave trajectory past it. Infinitesimally small chances of that ever happening, thus the reference to the infinite monkey theorem, but not exactly impossible. But the satellite's instruments wouldn't survive it. Voyagers couldn't afford such luxury during their Grand Tour mission. $\endgroup$ – TildalWave Oct 13 '14 at 0:43
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    $\begingroup$ @HDE226868 For one example, here's a GIF animation of the J002E3 object that was initially mistaken for an asteroid, until they did spectral analysis and realized it is covered with a white titanium oxide paint that stages of Saturn V used. It's a S-IVB third stage of Apollo 12. But notice how it was recaptured by Earth-Moon in 2002 as it went past Sun-Earth Lagrange point 1, and then ejected back into heliocentric regime by a lunar swingby in mid 2003. Funny things can happen in orbital / celestial mechanics. ;) $\endgroup$ – TildalWave May 26 '15 at 16:13
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The answer to the actual question posted, "Can an artificial satellite stay in orbit forever?" (where "forever" is assumed to be a couple of billion of years) is maybe.

There are obvious constraints: the satellite could not be in low-Earth orbit (aka, LEO) due to decay from friction and gravitational variations of the Earth, or even in higher orbits up to and possibly beyond geosynchronous orbit, for the same reason.

Also, the satellite would have to be so massive, that micro-meteoroid impacts would not significantly change its orbit. What is the proof of this? Our moon has been in Earth orbit for several billion years, and while it is drifting (very very slowly) away, it's still there. It is in theory possible to construct a massive artificial satellite that would be in a similar orbit (although not too similar, or the Moon might disturb it). I'm thinking of something along the lines of a Death Star here.

And even then, with a massive Death Star, there is always some tiny chance that something else (close-passing comet, or an asteroid impact) disturbs it. But is it possible? I think that it is.

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You seem to think atmospheric drag is the only influence. Above a certain height there are factors stronger than atmospheric drag. As David Hammen says "Perturbations from the Moon, the Sun, and the Earth's non-spherical gravity field. Tidal perturbations. Radiation pressure and its cousin, the Yarkovsky effect. The Kozai mechanism."

Also as Hammen says, these can result in a number of outcomes: collision with the earth or moon, or ejection from the earth moon system. An indefinite earth orbit is unlikely.

Station keeping with solar power may be possible if the satellite has an electrodynamic tether. But a tether that could last indefinitely seems unlikely. Most man made devices break down over time.

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From the question:

Would it be possible to use solar energy to keep the satellite in orbit forever*?

Followed by the comment:

How would you use solar energy?

Forever (or even 5 billion years) is a long time. As the other posters have pointed out, it's unlikely that any artificial satellite could survive that long in space.

However, possibly of use is a propellantless means by which you can keep the satellite in orbit for an indefinite* amount of time using solar-power. This can be done by running an electric current through a conductive tether to create an electromagnetic field that pushes against the Earth's electromagnetic field to reboost the satellite.

*The problem here is material science: The tether will be be relatively long and exposed, and susceptible to damage by micrometeorite (so will the rest of the satellite, for that matter). One way to engineer around it is to use a multiply-redundant network of cables, a design trademarked as a "Hoytether". Unfortunately, this still only extends the expected lifetime to less than 200 years, which is a far cry from forever.

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    $\begingroup$ TUI doesn't seem to be publicizing their Hoytether anymore, although they do still have E-D tether propulsion systems. $\endgroup$ – Nathan Tuggy May 17 '16 at 22:37
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100 years, possibly yes. 200, with high tech plasma generator (currently in research stage) possibly. 5 billions years.. most likely not. Solar energy gives you energy, yes, but then you cannot just point a battery on your rear and get a push. You need to 'throw' something so in order to get thrust. Rocket engine releases gas at very high speed, which gives you thrust. Microthrusters also pushes gas typically, though you can have ion thrusters nowadays. Ion thrusters still have to carry their own gas to ionize and throw out. So you need some material to throw or consummate (think of it as fuel to burn), and so after a while, you will run out of matter to throw, even if your battery is full. Voyager use gravity assist. Staying in orbit around the Earth does not give you that.

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So, artificial satellite will not stay in orbit without some programming, to correct the trajectory, and use solar fuel.

Amzing design of natural satellites, perhaps if we study it's design we can learn something more on satellites and the Designer.

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    $\begingroup$ Natural satellites don't stay in orbit either. We can't launch satellites that weigh millions of tonnes (which is the lesson to be 'learned' from the 'designer' of natural satellites) so we have to make do with active control, which shortens their life. $\endgroup$ – JCRM Jan 17 at 15:03

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