[AR] Re: Lunar GPS navigation.
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Tue, 30 Jul 2019 18:32:56 -0400 (EDT)
On Tue, 30 Jul 2019, Anthony Cesaroni wrote:
Is anyone on the list familiar with a lunar GPS scheme that combines the
Navistar and Galileo constellations?
The lunar navsat concepts that I'm vaguely aware of -- not something I
follow closely -- all use new lunar-orbit satellites. The existing
Navstar/GPS and Galileo constellations are all in one small area of the
lunar sky, giving poor navigation precision (Geometric Dilution of
Precision is the buzzphrase) at the best of times... and they're totally
invisible from half of the Moon.
There's no reason why a GPS-type system wouldn't work in lunar orbit,
given about the same number of satellites as the Navstar constellation for
Earth (it doesn't work without four satellites simultaneously visible, and
preferably more). If you want to use a smaller number of satellites, you
can reinvent Geostar, which requires that the ground terminals transmit as
well as receive (GPS is receive-only because of its military origins), and
can do low-bandwidth messaging too. If you can settle for occasional
position updates rather than fresh positions every second, you *might* be
able to reinvent Transit, which will give you a fairly precise position
from a single pass of a single satellite, although it might not work quite
as well on a world rotating as slowly as the Moon.
Henry
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