How many satellites comprise the GPS and expand it?

Answer 1

There are at least 24 GPS satellites in operation at any given time with a number of on-orbit spares in case one fails. Each one is in a 12 hour orbit (meaning it takes 12 hours to orbit the earth). They are in a variety of six different orbits and are not just locked into a geosynchronous orbit (meaning they stay over roughly the same place on earth at all times, like your satellite TV and communications satellites) like some satellites.



All GPS satellites are owned and operated by the US Air Force and are controlled specifically by the 2d Space Operations Squadron at Schriever AFB in Colorado Springs, CO. There is not an easy way to deny the GPS capability to our enemies without also denying our own capability, so it is a free system open to anyone that has the technology to utilize it.



GPS satellites carry not only positional data but also extremely precise timing signals, which help the GPS receivers on the ground to triangulate their position and are even used to validate and secure financial transactions, etc. When the system was first created, artificial timing errors were put into the signal to try to reduce the effectiveness of the system for non-military users, but it was removed in 2000.



The GPS satellites also have NUDET (Nuclear Detonation) sensors on them to detect nuclear detonations almost anywhere on earth.



To use GPS you need to be in clear view of at the very least 3 satellites but you should be in view of 6 satellites at any given time unless some are blocked by objects, mountains, etc. So, GPS usually doesn't work well in-doors or even in a forrest or valley at times.