why there are 24 satellites in the Global Positioning system?

Question

at what angle are they inclined to each other? what is the least number of satellites required to determine the position of an object on the earth?

Answer 1

The "Professor" answer is largely but not entirely correct. There are slightly more than 24 GPS satellites in orbit at any one time; some are used as spares should one fail. They are NOT in geosynchronous orbit. They are in a lower orbit such that at any given moment several are visible (i.e. above the horizon) from any point on the earth. The orbit height is ~20000 km, and the 24 satellites are distributed among six orbital planes angled at 60 degrees to one another.

In order to get an accurate fix on your location, your receiver needs to get signals from at least 3 at any given moment; the more it "sees" at once, the more accurate a fix it can calculate based on the time differences between the transmitted signals from each satellite.

Answer 2

There are more than 24 satellites, Your receiver may only can pick up 24 of them at a time or there are only 24 visible to the GPS at one time. Each satellite is in a Geo-stationary position at a certain altitude above a datum. You will need a minimum of 4 satellites to receive a GPS reading. 3 satellites to triangulate the position and one time keeper. to determine distance to each satellite. Errors in measurement occur due to the transmission time delay between the time keeper satellite and the GPS receiver unit. However the more satellites you are receiving the mare accurate the measurement will be.