On 1/31/13 1:09 PM, Chris Albertson wrote:
I know for sure my handheld Garmin works at 27000 feet, at
530mph... ...I was actually surprised it worked up there.
It made me wonder what the actual limits are.
What are the limits of your hand held unit or what are the limits of
GPS in general. I think GPS works as long as you are under the orbit
of the satellites. The company I used to work for placed GPS on some
low orbit spacecraft, so say roughly 200 miles up and 18,000 mph but
I'd guess most hand held units would not work in those conditions
GPS will even (maybe) work at the Moon: with a gain antenna pointed back
at earth.. you're looking at the satellites on the opposite side of the
earth radiating around the limb. I don't know that anyone has actually
tried it but it's certainly been analyzed to death.
The potential problem with a handheld GPS in space (depending on where
you are) would be whether you can keep track of the constellation and
acquire new s/v's fast enough with lots o'Doppler.
You already have to deal with the Doppler from the S/Vs buzzing around
at 3-4 km/sec. Whether your receiver can handle the extra 7 km/sec
Doppler in LEO is a good question. 7 km/sec is about 20 ppm, and I
suspect that the receiver can already deal with that much change in the
oscillator frequency. It might be doppler rate that it would have a
hard time with (because the designer cranked down on the loop bandwidth
for noise reasons)
What are those folks flying GPS on CubeSats using?
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