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GPS cannot be used on the moon Yes it can: https://tempo.gsfc.nasa.gov/news/using_GPS_signals_at_the_moon https://tempo.gsfc.nasa.gov/news/using_GPS_signals_at

by avar 3y ago

GPS cannot be used on the moon Yes it can: https://tempo.gsfc.nasa.gov/news/using_GPS_signals_at_the_moon https://tempo.gsfc.nasa.gov/news/using_GPS_signals_at_the_mo... There's a paper about it here, they're planning a Moon-based experiment: https://ntrs.nasa.gov/api/citations/20230012191/downloads/NC3m-GNSS-Receiver-ION2023_paper-final.pdf https://ntrs.nasa.gov/api/citations/20230012191/downloads/NC... Figure 10 in the paper shows that after a few hours of signal acquisition positioning errors should be down to the single or low double digit meters. In case it's unclear, this isn't a "lunar GPS system", but listening to the scatter of the Earth-based GPS signals we've got now, on the Moon. I don't know about the rest of your comments or claims, but in general GNSS signals are used for lots of unexpected and novel things. E.g. people are detecting North Korean missile launches with GPS (the rocket plume casts a measurable "shadow" as the signals travel through it).

jessriedel 3y ago
> Yes it can: No it cant (but maybe in the future). You’re linking to active research about a future device. In any case it doesn’t matter, for the reasons I already said.
- avar 3y ago
  You asked for a "real planned experiment" and then asserted that "GPS cannot be used on the moon". This is a real, planned experiment to use GPS on the Moon. NASA has already conducted experiments to use GPS in Earth orbits halfway to the Moon[1]. I'd think the physics of further signal propagation and the ability to receive them would be well understood. 1. https://www.nasa.gov/missions/mms/record-breaking-satellite-advances-nasas-exploration-of-high-altitude-gps/ https://www.nasa.gov/missions/mms/record-breaking-satellite-...
  - jessriedel 2y ago
    I’m not saying your comment wasn’t relevant context, just that (a) your assertion that GPS can be used on the Moon is not currently true and (b) the future possibility doesn’t answer my original question for reasons mentioned.
    - avar 2y ago
      NASA hasn't been to the surface of the Moon in any meaningful way since the 70s. So, you're correct, but how is that relevant? Obviously all discussions about "NASA plans to do X on the Moon" and "if NASA's doing X on the Moon, we've worked out that they can use Y to accomplish X" are hypothetical at this point. So, in that context, what's the relevance of your claim that "GPS cannot be used on the Moon". I agree that if you're going to insist on empirical evidence that no, we don't actually know if it works on the Moon. But if that's your goalposts then I'd think you'd worry more about the hypothetical astronaut reading that GPS position or GPS time having long since asphyxiated. After all we've got no empirical evidence that the space suits planned for use on the Moon actually work there, etc. It's all inferred at this point, we'll see about the experiment. But if I had to bet that signal propagation works the way we expect (GPS), v.s. say some joint failing when filled with lunar regolith (spacesuit), then my money's on the GPS experiment.

by avar 3y ago

jessriedel 3y ago

> Yes it can: No it cant (but maybe in the future). You’re linking to active research about a future device. In any case it doesn’t matter, for the reasons I already said.

avar 3y ago
You asked for a "real planned experiment" and then asserted that "GPS cannot be used on the moon". This is a real, planned experiment to use GPS on the Moon. NASA has already conducted experiments to use GPS in Earth orbits halfway to the Moon[1]. I'd think the physics of further signal propagation and the ability to receive them would be well understood. 1. https://www.nasa.gov/missions/mms/record-breaking-satellite-advances-nasas-exploration-of-high-altitude-gps/ https://www.nasa.gov/missions/mms/record-breaking-satellite-...
- jessriedel 2y ago
  I’m not saying your comment wasn’t relevant context, just that (a) your assertion that GPS can be used on the Moon is not currently true and (b) the future possibility doesn’t answer my original question for reasons mentioned.
  - avar 2y ago
    NASA hasn't been to the surface of the Moon in any meaningful way since the 70s. So, you're correct, but how is that relevant? Obviously all discussions about "NASA plans to do X on the Moon" and "if NASA's doing X on the Moon, we've worked out that they can use Y to accomplish X" are hypothetical at this point. So, in that context, what's the relevance of your claim that "GPS cannot be used on the Moon". I agree that if you're going to insist on empirical evidence that no, we don't actually know if it works on the Moon. But if that's your goalposts then I'd think you'd worry more about the hypothetical astronaut reading that GPS position or GPS time having long since asphyxiated. After all we've got no empirical evidence that the space suits planned for use on the Moon actually work there, etc. It's all inferred at this point, we'll see about the experiment. But if I had to bet that signal propagation works the way we expect (GPS), v.s. say some joint failing when filled with lunar regolith (spacesuit), then my money's on the GPS experiment.