Skip to comments.Can Astronauts Use GPS to Navigate on the Moon? NASA Scientists Say Yes
Posted on 03/19/2020 10:18:54 PM PDT by BenLurkin
Signals from existing global navigation satellites near the Earth could be used to guide astronauts in lunar orbit, 385,000 km away.
Cheung and Lee plotted the orbits of navigation satellites from the United Statess Global Positioning System and two of its counterparts, Europes Galileo and Russias GLONASS system81 satellites in all. Most of them have directional antennas transmitting toward Earths surface, but their signals also radiate into space. Those signals, say the researchers, are strong enough to be read by spacecraft with fairly compact receivers near the moon. Cheung, Lee and their team calculated that a spacecraft in lunar orbit would be able to see between five and 13 satellites signals at any given timeenough to accurately determine its position in space to within 200 to 300 meters.
To help astronauts, the team suggested using a transmitter located much closer to them as a reference point. Perhaps, the scientists wrote, they could use two satellites in lunar orbita new relay satellite in high lunar orbit to act as a locator beacon, combined with NASAs Lunar Reconnaissance Orbiter, which has been surveying the moon since 2009.
The relay satellite could be very small, take design cues from existing satellite designs, and ride piggyback on a rocket launching other payloads toward the moon ahead of astronauts.
(Excerpt) Read more at spectrum.ieee.org ...
The satellites would all be so close in angular separation as seen from the moon as to make the usual GPS location algorithm rather useless. (Signal processing weenies please clear that up). You have to have some appreciable X-Y-Z to establish a fix.
Curiously, last job I had was working on a system to allow lunar explorers to navigate like with GPS. Øbowel killed the return to the moon mission, and I retired in disgust.
We were working on a local lunar surface based system. I was working the RF propagation and reception segment of the idea.
So, exactly how strong are the signals coming from our cell phones' GPS?
Ah, I see they are talking lunar ORBIT, not surface navigation. My comment may be irrelevant, not unusual for me.
My father Roger Easton invented Timation which was the major predecessor system to GPS. He thought some satellites should be in higher inclinations (GPS has them at 55 degrees) to improve navigation near the poles. Range limitations at Cape Canaveral limit them to 55 degrees. www.gpsdeclassified.com is my website.
I’m an old radio ham. What RF propagation issues are there on the moon? Were they planning on having GPS satellites around the moon? Low orbit? Higher orbit?
No signal. For those using it GPS is a receive only system. You don't transmit anything, just receive signals from multiple satellites and calculate your location based on their location and time to receive the signals.
(In a lilting female British accent): "In one quarter mile, turn left."
"In five hundred yards, turn left again and head back to the off ramp."
"In seven hundreds yards, turn around at the satellite and head back to the off ramp."
"In one mile, turn around and head back to the interstate."
"In two miles, fire maneuvering thrusters and just head back to earth, you inebriated twit."
It sounds like you would be working with something akin to the long defunct Loran ground based nav signals. Very precise in theory but in practice were affected by the Earth's imperfect magnetic field. It was very long ranged but accuracy was such that it was good for getting your boat to the offshore approach to your landfall when on the water or to the right city when using it in an airplane. Not exactly survey level accuracy! Loran C has been shut down for several decades, replaced by GPS. I understand though that US and European governments are developing a new generation of Loran that will very similar accuracy as GPS. The driver for the new generation Loran is to have a backup to GPS in case the GPS is disabled or degraded.
Whether ground based like Loran or satellite based like GPS, a single data point reading does not give an exact position but a circle of position. You're somewhere along that circumference line but that's all you know. If you have two circles of position and lay them on a chart, the circles overlap a two points. Well, that's not much use as the enclosed area is quite large and thus the +/- error is quite large as well. If you have three circles of position now you're cooking because at your actual position the three intersections are grouped closely together. As a navigator, you would assume you're in the center of the area. In practice a Loran C position would be something like +/- 10 miles. Modern consumer grade GPS is something like +/- 20 feet or so when at it's best. The new generation Loran, if implemented, is supposed to similar accuracy to current GPS.
As others have noted, it's an angle thing related to distance that would make earth satellite GPS not practical. The inherent geometry would be as likely to give a position half way to Mars as somewhere around the moon.
“Proceed to the Route.”
Yeah. It ‘might’ work but the position accuracy would be rather large. If you’re trying to drive around that crater... ooops!
Stable orbits around the moon are tricky. That big Earth causes trouble for high altitude orbits.
Hearing “Re-calculating” could be disturbing for them.
It would also seem that new algorithms would be required in the receivers.
Your cell phone does not emit a signal for GPS. It only receives signals from the satellites. It then computes position from the satellites based on time signatures in those signals.
The lunar system we were proposing used multiple transmitting towers. Low gravity allowed very high towers, needed for the short horizon issue.
Towers. Horizon and line of sight issues.
Why Do Lunar Satellites Eventually Crash Into The Moon? | Scott Manley | Published on May 22, 2019
Potsdam Gravity Potato (yes, that's a real thing) keyword, chrono sorted:
If astronuts follow the gps they will drive right into a crater!
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