Do sattelites orbit with the rotation of the earth?

[Russell_B]

Hey there,

The other day i was solving a simple curvilinear motion problem that used a sattelite in orbit around the Earth as an example and it got me thinking.

If a geostationary sattelite is always above the same region of the Earth (and can only occupy an orbit of a certain altitude) it is clearly orbiting in the direction of the Earth's rotation.

But what about non-geostationary sattelites? Can they orbit in any direction? How do we keep track of all these sattelites and make sure they don't collide?

Thanks for your time
Russ

 

[russ_watters]

They can go in any direction, but usually they go with the Earth's rotation because of the lower launch energy (you get a boost due to the speed of the rotation).

How do they keep track? Radar and databases. But the odds of collision really aren't too bad since there is a lot of real-estate up there and only a few tens of thousands of objects worth tracking.

 

[mgb_phys]

But what about non-geostationary sattelites? Can they orbit in any direction?

Yes, other common orbits are low Earth - takes about 90mins, satelites cover all points on earth, used by GPS and sat phones.
Or sun synchronous - satellites orbit pole to pole in a time that it is always along the day-night line, this let's you keep the solar panels in daylight and is useful for taking photographs becaus you can see shadows.

How do we keep track of all these sattelites and make sure they don't collide?

You know the orbit (assuming it doesn't deliberately maneuver) so you can predict it's position a long time in advance. You can move an object out of the way of another but this costs fuel. Mostly you just rely on space being big, satellites being relatively small and a miss being as good as a mile.

 

[Ich]

Mostly you just rely on space being big, satellites being relatively small and a miss being as good as a mile.

Space is big there, but http://en.wikipedia.org/wiki/2009_satellite_collision" .

 

[Russell_B]

Oic. I was under the impression that low Earth orbit was getting cluttered up with sattelites, discarded retrorockets, waste, dropped spanners etc. After all, we have been messing around up there for the last 50 years. Plus you might have trouble tracking the smaller annoying stuff.

 

[Phrak]

Ha! As one in the business of putting this stuff up there, I often ask: How many satellites can be placed in low Earth orbit before a critical density is reached where one initial collision results in a low Earth orbit debris field? And will it look like the rings of Saturn in the evening sun?