Limits of GPS

[agentgonzo]

Does anyone know what the theoretical/practical limits of GPS are? From a little digging on the web, they constellations orbit at 22,000km altitude and presumably do not have omnidirectional transmitters, so the maximum altitude is probably somewhere below 22,000km. I know that they use GPS on the shuttle (and probably ISS) whilst in orbit and that ITAR regulations cap 'consumer' GPS units at a max altitude of 60,000 feet and 1,000 knots.

Anyone know what the actual limit of 'unrestricted' GPS is in terms of altitude and speed?

 

[Urwumpe]

In terms of altitude, it does work even above the 20000 km of the GPS, record is 61,000 km, but you get severe limitations in terms of accuracy at higher altitudes and speeds.

http://cat.inist.fr/?aModele=afficheN&cpsidt=2003088

 

[garyw]

Shuttle only uses GPS during the final phases of landing so it's going to be used well below 200,000 feet.

I know sounding rockets use GPS to allow payload recovery but do they use GPS to track the location, speed & altitude of the mission?

Edit to add: I know that some of the consumer GPS units have trouble with high speed. There was a classic example of a UK high speed Police unit who was averaging 140MPH and had to slow down to let the sat nav catch up. Of course, this is more a limitation of the unit than the GPS system.

 

[Urwumpe]

You can use GPS on satellites, that is not the problem - making it accurate is it. You have generally bad GPS constellations in your local sky (satellites too close together, or not enough satellites properly visible).

The ATV for example uses GPS as input for the state vector, one Shuttle could do that, but generally doesn't.

 

[Wishbone]

http://en.wikipedia.org/wiki/TacSat-2 uses a GPS occultation receiver.

 

[tori]

We've been using GPS in a number of stratospheric missions (the upcoming flight is called "czANSO") in well over 120,000 ft. Accuracy and stability was just as good as on the ground.