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| Authored by: bprice on Thursday, April 25 2013 @ 07:45 AM EDT |
Do the GPS receivers work in orbit? I thought commercial units had
height/speed restrictions.
The mathematics of GPS do not include
the distance to the primary body (earth, in this case): the math depends
strictly on the time differences among receipt from the various transmitters by
the receiver. The solution of the hyperboloids' intersections, however, may
include some assumptions, like the distance to the geoid (mathematical
description of the earth's surface)...
In other words:
There's no
inherent reason that a GPS receiver wouldn't work in orbit — or even in a
non-orbital path, so long as enough orbiting transmitters could be
received.
It's entirely possible that the algorithms used in any particular
receiver would fail above some altitude.
It's also possible that the
particular receiver might not have enough channels to get enough simultaneity of
the transmitters, so it misplaces the hyperboloids, because of the speed of the
receiver through space.
or might have a slow processor, such that the
hyperboloids' intersections aren't computed in a timely manner. The receiver
can never say "this is where I am right now"; the best it can do is "this is
where I was n microseconds ago", for some implementation-dependent value
of n.
The transmitters may use directional antennas (I would think
they would, unless they are designed for space use rather than just terrestrial
use – the various agencies [USAF, Galileo, Glonast] would know, but I
don't.). If so, there could be signal-strength issues whenever there are not
enough satellites in low-enough view. (This could be a problem for receiver
locations above the satellites' orbits.)
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--Bill. NAL: question the
answers, especially mine. [ Reply to This | Parent | # ]
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