NASA Uses GPS On the Moon For the First Time (popsci.com)
- Reference: 0176617967
- News link: https://science.slashdot.org/story/25/03/05/0155218/nasa-uses-gps-on-the-moon-for-the-first-time
- Source link: https://www.popsci.com/science/blue-ghost-gps-moon/
> On March 2, Firefly Aerospace's Blue Ghost made history, becoming the first commercial lunar lander to successfully touchdown on the moon's surface. The groundbreaking lander is wasting no time in getting to work. According to NASA, the joint public-private mission has already [1]successfully demonstrated the ability to use Earth-based GPS signals on the lunar surface , marking a major step ahead of future Artemis missions. Accurate and reliable navigation will be vital for future astronauts as they travel across the moon, but traditional GPS tools aren't much good when you're around 225,000 miles from Earth. One solution could be transmitting data from the Global Navigation Satellite System (GNSS) to the lunar surface in order to autonomously measure time, velocity, and position. That's what mission engineers from NASA and the Italian Space Agency hoped to demonstrate through the Lunar GNSS Receiver Experiment (LuGRE), one of the 10 projects packed aboard Blue Ghost. [...]
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> "On Earth we can use GNSS signals to navigate in everything from smartphones to airplanes," Kevin Coggins, deputy associate administrator for NASA's SCaN (Space Communications and Navigation) Program, [2]said in a statement . "Now, LuGRE shows us that we can successfully acquire and track GNSS signals at the Moon." LuGRE relied on two GNSS constellations, GPS and Galileo, which triangulate positioning based on dozens of medium Earth orbit satellites that provide real-time tracking data. It performed its navigational fix at approximately 2 a.m. EST on March 3, while about 225,000 miles from Earth. Blue Ghost's LuGRE system will continue collecting information over the next two weeks almost continuously while the lander's other tools begin their own experiments.
[1] https://www.popsci.com/science/blue-ghost-gps-moon/
[2] https://www.nasa.gov/general/nasa-successfully-acquires-gps-signals-on-moon/
I'm surprised (Score:2)
That there was any question of it working or not. It would work a little weirdly, since the receiving station (blue ghost) would receive its data from outside the GPS sats orbits, but the principal is the same. Geolocation via Time Delay of Arrival with highly accurate clocks, and known satellite positions. Possibly they were worried about signal strength?
All that said, this is pretty cool.
Re: (Score:2)
Possibly the time shift too. The longer the distance from your triangulation points, and the more chances of relativity affecting their signals, the more accurate they need to be.
Re: (Score:2)
Yes. But that's a receiver problem. It may be beyond the capabilities of commercial GPS units. But the algorithms can be tweaked.
Re: (Score:2)
The (radial) difference in gravitational gradient is most severe near the surface of the Earth, so between GNSS orbit and Earth you'd probably get considerably more relativistic error than between GNSS orbit and the Moon. How much more ... beyond my calculations. but the gradient is in that direction.
The problem with using it would most likely be that the proportional difference between Receiver and Satellite01 versus Satellite 02 would be smaller. From the Earth's surface, IIRC GNJSS is at about 4~5 ear
I'm surprised this works at all (Score:4, Informative)
GPS works on triangulation, and gets much more accurate measurements from satellites that are positioned such that the satellites and the receiver on earth form triangles with large angles. Small angles (such as those from satellites almost directly overhead) provide very low precision. If all the satellites you can hear are right above you, the distance between the satellites is small compared to your distance from them, and the vertex at your location is a very small angle.
But when you're on the moon, ALL the satellite you can receive are at almost the same arc from you, so the angles at the receiver are ALL very small. (all the satellites are "directly above you" or at least in the same location in the sky no matter where you go) That should produce very poor precision information. Maybe it's not as big of a deal on the moon where you're not looking for inches-precision, and getting within say a mile is okay? We're so used to getting turn-by-turn accuracy right to someone's door here. On the moon I suppose they might be happy to just know which crater they landed in?
Re: (Score:2)
Down side, all angles are narrow
Up side, you can see more sats at once
Re: I'm surprised this works at all (Score:3)
In the [1]previous article [slashdot.org], several people estimated between 4 and 50m accuracy on this basis. Seems to be in the ballpark of what they are getting. Whether or not that is useful enough I will leave to those who know better.
[1] https://m.slashdot.org/story/439117
Re: (Score:1)
I wonder what happened to this (2022) [1]https://scitechdaily.com/satel... [scitechdaily.com]
[1] https://scitechdaily.com/satellites-around-the-moon-are-another-step-closer/
Re: (Score:2)
***checks GPS***
"Yep, still on the moon."
Re: (Score:2)
> But when you're on the moon, ALL the satellite you can receive are at almost the same arc from you,
If my memory is correct ( if !), then the GNSS constellation is about 120,000 km in diameter, and you're viewing it form about 380,000 km range. So they'll cover a 17~18 wide patch on the sky.
Far from ideal ; but not unusable.
Adding one or two clocks in peri-lunar orbit would help a lot. Putting 4 or more in Earth orbit at ... 600,000 km forn Earth would probably help a lot.
Oh, hang on - they're only looking
Re: (Score:2)
GPS works on trilateration which is similar to but not the same as triangulation. It measures the time that it takes signals to propagate from three or more sources with known positions and then converts those times to distance using the speed of light. The calculated position is then the point of intersection of the spheres. trilateralization does not suffer from the "small angle" issue. It still works if all three satellites are on top of each other at different altitudes -- there will only be one solu
Some very fancy mathematics involved (Score:2)
Since time passes at a different rate on the moon from earth, relativity and all that.
Of course, not much good on the far side of the moon.
ATMOS (Score:2)
This is your final destination.
Hey Siri, Where am I? (Score:2)
You are on the moon.
Re: (Score:2)
Only if Siri knows the Moon's orbit well enough, otherwise the position is just a lat,lon with an altitude of 362 million meters.