Satellites, how many can there be ?

[Lohan2008]

If there are 50 satellites at 20, 000 km for navigation and China wants to put up its own GPS system, will there be enough room ??

2> With all the space junk and derelict satellites, how many can there be ??

3> Is there a future date when signals will start interfering with the other satellites ?

[J.Random]

Surface area of the sphere with 20000 km radius is 5 billions square kilometers.

[Frozen_Heart]

I think that we aren't too far from the maximum amount.

However the amount could be increased if we found a way of removing debris and derelict satellites from orbit. The amount of junk up there is staggering!

After that combining satellites may be necessary. Two companies may have to share a single 10 ton satellite rather than have two 5 ton satellites.

[Sandworm]

If you put them all into the same orbit, all in one ring, then you could put up several billion. As they aren't moving much relative to each other Kessler wont happen. That's basically what the geostationary orbit looks like. The problem is when they are in different orbits that cross paths. That's where collisions happen. Two giant sats inclined at 180* to each other, crashing at 2x orbital velocity, might trigger Kessler with only two objects.

So I'd say you cannot come up with a number without first defining what types of orbits you are most interested in protecting.

[Bill Phil]

There is a limit.... If infinity is a limit. GPS takes only a few satellites, so, if China wanted to, they could easily do it.

The amount of space up there is STAGGERING!

[kerbiloid]

Geostationary orbit radius ~= 42 000 km.

Orbit length = 2 * pi * 42 000 ~= 260 000 km.

Satellite size ~= 10 m.

According to http://aviation.stackexchange.com/questions/2806/how-much-is-the-minimum-safe-distance-between-two-planes-in-flight

For a commercial airliner (as the question asked), separation will usually be at least 3 miles laterally, or 1,000 feet vertically. In the enroute environment -- at higher operating speeds above 10,000 feet and based on the type of Radar and distance from the antennae -- a 5 mile rule is applied laterally. This is true in most but not all situations. There are exceptions: see below.

let safe zone around a satellite be ~= 5 miles ~= 10 km.

So, you would place not more than 260 000 / 10 ~= 26 000 satellites and launcher parts.

Also, maybe several thousands of them are already there.

[Linear]

^And thats just Geostationary(below). The amount of space we have is absolutely crazy - it's hard to get your head around.

[kerbiloid]

^And thats just Geostationary(below). The amount of space we have is absolutely crazy - it's hard to get your head around.

Looks, not that absolutely crazy.

The satellites placed in geostationary orbit keep their mutual positions.

Of cause, the satellites in any same orbit keep their mutual positions, but it's doubtful whether somebody would precisely launch three satellites to the same, say, 514 x 678 km 34 deg incl., orbit.

So, you would treat positions of non-stationary satellites as nearly random.

I.e any satellite occupies a ring with radius R, W x H at least 10 x 10 km also.

Sphere area = 4 * pi * R^2.

So, an orbits "layer" (R..R + 10km) would keep maximum: 4 * pi * R^2 / (2 * pi * R * 10) = 0.2 * R satellites (R, km).

For, say:

h = 400 km there would be maximum 0.2 * (6400 + 400) = 1360 satellites.

h = 2000 km there would be maximum 0.2 * (6400 + 2000) = 1680 satellites.

I.e. ~= 1500 satellites in every "layer".

From, say, 400 to 2000 there would be ~= (2000 - 400) / 10 ~= 160 such "layers".

So, rough maximum of satellites you can have on meaningful heights ~= 160 * 1500 ~= 200 000..300 000 satellites.

In this case the near-Earth space would look like an air route in rush hour.

So, you would decrease this value at least by a magnitude and get an answer "tens of thousands".