How long do satelites stay up?

[lyssword]

I've heard that some satellites eventually fall down to earth. Do all satellites fall down to earth after some time or does it depend on how close it is to earth? Would any satellite be able to orbit earth for a million years provided nothing knocks them off course? Sorry for my lack of knowledge in physics 🙂

 

[Braznor]

Well, the moon has been orbiting earth a few billion years now.

 

[mobobuff]

Low Earth Orbit satellites will fall due to atmospheric drag, but higher satellites in higher orbit (like the Clarke Orbit), are usually pretty safe. There are things like solar pressure that effect the path of these satellites, but due to a method called station-keeping, onboard propellants are used to correct deviances. When a satellite runs out of fuel, instead of letting it go astray in the Clarke Orbit, they are usually raised to an orbiting graveyard of decommissioned satellites.

Geostationary orbits

 

[Markbnj]

For all practical purposes most of them stay up until they run out of fuel for making orbit adjustments.

 

[Modelworks]

Echostar has a sat right now at 129 degrees that is failing fast. Its life span went from several years to several months because of problems on the sat and they used up a large portion of the fuel to keep it where they needed it.

I imagine that one will be left to burn up.


Could you place a man made satellite in a orbit for millions of years, sure.
You wouldn't do it with one that you would use though because you need it to be stationary for it to be of any use.

 

[robisbell]

depends on the altitude and orbit they are placed in, plus how much fuel they have to adjust themselves over times, and solar winds, gavitation pull, micrometeoroid impacts, etc...

 

[eLiu]

Originally posted by: Markbnj
For all practical purposes most of them stay up until they run out of fuel for making orbit adjustments.

Not anymore. For a while now, satellites launched by any nation are equipped with 'abort me' systems which come in 2 forms: 1) carry enough fuel to send yourself back into the atmosphere & drop into the ocean OR 2) carry enough fuel to boost yourself into a very high orbit--often into the van allen (sp) belt (b/c nobody wants to put satellites there due to boatloads of radiation).

Anyway, the idea is to avoid a buildup of space junk that we can't control. So we choose to kill satellites or put them in orbital purgatory.

 

[Markbnj]

Originally posted by: eLiu

Originally posted by: Markbnj
For all practical purposes most of them stay up until they run out of fuel for making orbit adjustments.

Not anymore. For a while now, satellites launched by any nation are equipped with 'abort me' systems which come in 2 forms: 1) carry enough fuel to send yourself back into the atmosphere & drop into the ocean OR 2) carry enough fuel to boost yourself into a very high orbit--often into the van allen (sp) belt (b/c nobody wants to put satellites there due to boatloads of radiation).

Anyway, the idea is to avoid a buildup of space junk that we can't control. So we choose to kill satellites or put them in orbital purgatory.

I didn't mean to suggest what their ultimate fate was, so perhaps I should have said "remain operational" rather than "stay up." In any event, fuel is the limiter.

 

[jagec]

Yeah, most stuff that goes into space has a "Delta-V" budget, which is basically how much fuel you have and how powerful/efficient your motor is. It ends up being a convenient way of expressing a craft's ability to make course corrections/changes.

One fun way of learning more about orbital mechanics is the space simulator Orbiter. I recommend it highly, but the learning curve is steep.
http://orbit.medphys.ucl.ac.uk/