Would a handheld GPS work on the International Space Station?

Title says it all; would a consumer handheld GPS unit work accurately on-board the ISS?

To put it another way, what is the maximum altitude that GPS actually works at?

I think you would have more problems with the velocity than with the altitude.

Handheld GPS devices are programmed to assume you're on the surface of the planet, so it would probably suggest that you're on the ground directly below where you're moving.

This is a required assumption when you're only locked into 3 satellites, the minimum required to give your location.

One satellite gives you a sphere.
Two satellites gives you a circle.
Three satellites gives you two points on that circle, one of which is on the surface of Earth and one is either out in space or way below the surface, so an assumption is made.

With four satellites your position is pretty much nailed down and usually you can lock on more than four, but if the result is you being in space then it may or may not return that position.

But yes, the GPS will work on the ISS. The satellites are still within range.

GPS systems that work at an altitude above of 18km and a speed above 1000 knots are export controlled items in many countries (in particular, most western industrialized ones; see Wassenaar Arrangement). Therefore, products marketed to consumers don't work above those limits. Details how the limits are implemented vary between products (altitude OR speed, vs. altitude AND speed) but satellites in orbit easily exceed both. Unlimited GPS systems are available, e.g. from NovAtel, but those are expensive and involve additional paperwork. I don't believe anybody builds unlimited GPS receivers in the handheld form factor (not much of a market for that ;-) ).

Reinhard

No. The tracking loops on a consumer unit won’t close on a 7 km/s doppler.