[AR] Re: Lunar GPS navigation.
- From: David McMillan <skyefire@xxxxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Fri, 2 Aug 2019 09:05:48 -0500
On 7/31/2019 3:09 PM, Henry Spencer wrote:
On Wed, 31 Jul 2019, David McMillan wrote:
...given how unstable Lunar orbits tend to be...
As Bill has already pointed out, it's not quite that bad. Especially
since we now have complete lunar gravity maps, giving rather better
orbit prediction than we used to have.
Well, from what (little) I understand of current GPS systems,
they're /really/ vulnerable to even tiny changes in their
position/velocity -- or, rather, the accuracy of the guidance at the
receiver's end scales with something like the square or cube (or worse)
of the positional error of each satellite. So I wasn't expressing
concern over the "LGPS" birds falling out of orbit, but rather how much
worse the accuracy effects would be, compared to GPS/Galileo/GLONASS/etc.
My (purely intuitive) off-the-cuff take was that an LGPS would have
a greater need for high-accuracy "ground references" and regular
ephemeris updates than a terrestrial GPS, all other factors being
equal. OTOH, the underlying technologies /have/ improved since the
'80s, so there might be opportunities to compensate using less "drifty"
onboard clocks, higher accuracy sat-to-sat ranging, and a "swarm of
cubesats" type approach with lots of averaging and rejection on the
receivers (as I think Uwe was alluding to upthread).
Other related posts:
