7 ms·

More details at https://www.gpsworld.com/lugre-receiver-captures-gnss-signals-in-lunar-orbit/ https://www.gpsworld.com/lugre-receiver-captures-gnss-signal... "

by 7952 2y ago

More details at https://www.gpsworld.com/lugre-receiver-captures-gnss-signals-in-lunar-orbit/ https://www.gpsworld.com/lugre-receiver-captures-gnss-signal... "Despite the challenges of distance and velocity, the receiver achieved position accuracy within 1.5 km and velocity accuracy within 2 m/s. It successfully acquired signals from four GPS satellites (L1 and L5 frequencies) and one Galileo satellite (E1-E5 bands) during a one-hour observation window. Post-landing,"

madaxe_again 2y ago
At that resolution the utility is somewhat questionable - I suppose the next inevitable step is LPS, and having a fleet of selenostationary satellites performing the same function locally.
- thatcherc 2y ago
  A challenge there is that there are very few stable lunar orbits! High orbits are perturbed by Earth's gravity (3-body problem) and low lunar orbits are perturbed by the lumpy distribution of mass in the Moon's interior [0]. Lunar GNSS satellites with a little bit of onboard propulsion could probably correct for some of these perturbations but once they ran out of fuel they would have a limited orbital lifetime. [0] - https://en.wikipedia.org/wiki/Lunar_orbit#Perturbation_effects_and_low_orbits https://en.wikipedia.org/wiki/Lunar_orbit#Perturbation_effec...
  - adgjlsfhk1 2y ago
    could the legrange points work? dealing with the 3 body orbits would be a pain, but they would give you nice separation
    - mkl 2y ago
      You need signals from 3+ different locations to navigate, and the two stable Lagrange points, L4 and L5, are as far from the moon as Earth is: https://en.wikipedia.org/wiki/Lagrange_point https://en.wikipedia.org/wiki/Lagrange_point.
      - mlyle 2y ago
        But-- GPS already produces an okayish fix. Improving it with another signal from somewhere else would make a big difference. > and the two stable Lagrange points, L4 and L5 We have plenty of spacecraft hanging out around L1, etc. It's possible to orbit it without too much issue. Having one broadcast a navigation signal synchronized with GPS would not be too bad. > are as far from the moon as Earth is The issue isn't that they're far away-- it's that they're all in pretty much the same direction. There's very small uncertainties in orbits and measured path length, but if they're all in the same direction you get very poor lateral position. This is the same effect you can get if you can only see a little tiny bit of the sky with GPS. You might have enough satellites to navigate, but since they're all close to the same direction the navigation solution is much worse.
      - adgjlsfhk1 2y ago
        I meant the earth/moon, not earth/sun Lagrange points.
  - ekianjo 2y ago
    Is the 3 body problem mostly meaningful above a certain mass? If you had small satellites could you deal with it?
    - xnorswap 2y ago
      The mass of a satellite is already trivial compared to the mass of the moon.
    - itishappy 2y ago
      The restricted three-body problem deals with the case when the third mass is trivial and the orbits are circular. The new solutions in this case are the Lagrange points. That's helpful, but doesn't make finding dynamic solutions much easier on it's own.
  - 0_____0 2y ago
    Oh wow, good reading in that link. I had no idea the moon was that lumpy. The wiki entry says that despite the mascons there are 4 known stable orbital inclinations?
    - shagie 2y ago
      That is correct. The NASA page link (now 404) has a bit more on the orbits and their history. https://web.archive.org/web/20210307002503/https://science.nasa.gov/science-news/science-at-nasa/2006/06nov_loworbit/ https://web.archive.org/web/20210307002503/https://science.n... And they're very lumpy. > The mascons' gravitational anomaly is so great—half a percent—that it actually would be measurable to astronauts on the lunar surface. "If you were standing at the edge of one of the maria, a plumb bob would hang about a third of a degree off vertical, pointing toward the mascon," Konopliv says. Moreover, an astronaut in full spacesuit and life-support gear whose lunar weight was exactly 50 pounds at the edge of the mascon would weigh 50 pounds and 4 ounces when standing in the mascon's center.
      - mmooss 2y ago
        That is a great link. Do you know if any of it is outdated now?
        shagie 2y ago
        It is still all completely correct. There may be some new findings, but the lunar prospector ( https://en.wikipedia.org/wiki/Lunar_Prospector https://en.wikipedia.org/wiki/Lunar_Prospector ) did all the work and this was written after that.
  - BWStearns 2y ago
    I wonder if lunar space elevators might be the fix here. If I understand correctly, such an elevator would not be as subject to the perturbations since the tension would keep it's orbit stable (is it still an orbit if it's tethered?). Another option might be a LORAN style system put up on towers. With lower gravity and no atmosphere I imagine we could stick transmitters up very high without super complex construction, maybe even just a giant carbon fiber tube with a transmitter at the top.
    - kridsdale1 2y ago
      Let’s put a high power laser on the end to send advertisements in Morse code to anyone looking towards the moon.
      - datadrivenangel 2y ago
        Raster-scan it to deliver persistence of vision ads!
  - staplung 2y ago
    Technically, satellite positioning only needs 1 satellite. GPS requires several but one of its forerunners was Transit[1] which I believe only needed a signal from a single satellite at a time. It worked by measuring the doppler shift of the signal coming from the satellite. Of course that only works if the orbit can eventually cover all (or much of) the surface and for all I know there is no such frozen orbit for the moon. Also, it would still presumably require extensive surface-based tracking and correction. [1] https://en.wikipedia.org/wiki/Transit_(satellite) https://en.wikipedia.org/wiki/Transit_(satellite)
- mhb 2y ago
  Wouldn't the next step be plopping some down on the moon?
  - mannykannot 2y ago
    I was wondering that too, and that led to the question whether, without an atmosphere, all radio communications at any wavelength would be strictly line-of-sight. It turns out, however, that the moon has something of an ionosphere, though I don't know whether it would support over-the-horizon radio (or, for that matter, whether it tends to interfere with the accuracy of GPS, as it does on Earth.) https://phys.org/news/2011-11-mystery-lunar-ionosphere.html https://phys.org/news/2011-11-mystery-lunar-ionosphere.html
- t43562 2y ago
  Lunar Pathfinder. https://www.sstl.co.uk/what-we-do/lunar-mission-services https://www.sstl.co.uk/what-we-do/lunar-mission-services QUOTE: A constellation of interconnected lunar orbiters will enable surface missions operating on the far side of the Moon, without direct to Earth line of sight, to keep constant contact with Earth. It will also provide lunar navigation signals to support critical mission phases such as precision landing of scientific equipment and the operation of rovers. In addition to communication services, the Lunar Pathfinder spacecraft has been selected by ESA and NASA to host a number of experimental payloads: An ESA GNSS receiver capable of detecting weak signals coming from the Earth GNSS infrastructure (GPS and Galileo), demonstrating its potential role into Lunar navigation A NASA retro-reflector to demonstrate laser ranging capabilities An ESA radiation monitor to study orbital radiation conditions Acting both as technology and service demonstrator, Lunar Pathfinder is the opportunity for scientific and commercial mission developers to support the development, test and standardisation of Lunar communication infrastructure, and for emerging off-planet telcos to acquire experience of lunar asset operations and off-planet service delivery. Lunar Pathfinder is due to operate in an Elliptical Lunar Frozen Orbit (ELFO) for an operational lifetime of 8 years. The spacecraft can operate 2 simultaneous channels of communication with lunar assets: 1 in S-band and 1 in UHF. Performance, such as coverage and data-rate, depend both on the relative position of the user asset to Pathfinder at the moment of the connection, as well as the capabilities of the communication module onboard the user asset. Once safely retrieved onboard Lunar Pathfinder, communications are relayed back to Earth ground stations in X-band.
- hammock 2y ago
  1.5km is not bad. Chris Columbus could resolve latitude to about 100-200km, and longitude only by dead reckoning. I do wonder though with computers and cameras and celestial navigation, why that is not used vs GPS on the moon
  - patmorgan23 2y ago
    Are there any existing systems for that? Would you be able to resolve to a similar level of accuracy with computer vision looking at the stars? Ussally enhancing an existing technology that is widely deployed and understood to fit a new situation is better than inventing something wholly new (though not always)
    - hammock 2y ago
      What are GPS sats if not artificial stars used for celestial nav? (In a roundabout way, no pun intended)
      - zokier 2y ago
        GPS navigation is based on measuring the distance between observer and the satellites to triangulate position. Celestial navigation does not care about distance to stars at all, in many ways stars are considered to be infinitely far away.
    - infinet 2y ago
      https://en.wikipedia.org/wiki/Celestial_navigation https://en.wikipedia.org/wiki/Celestial_navigation > Sextants can be read accurately to within 0.1 arcminutes, so the observer's position can be determined within (theoretically) 0.1 nautical miles (185.2 meters, or about 203 yards). Most ocean navigators, measuring from a moving platform under fair conditions, can achieve a practical accuracy of approximately 1.5 nautical miles (2.8 km) Some napkin math, assuming using a Sextant to achieve similar accuracy of 0.1 arcminutes on the Moon, because Moon is about 3.7 times smaller than Earth, that 0.1 arcminutes is around 50 meters on the Moon. One can expect extremely clear sky and certainly not riding waves on the Moon, so the practical accuracy should be close.
- deleted 2y ago
  [deleted]
- mlyle 2y ago
  I'm curious what the assumptions are. Looking forward to reading the paper. a kilometer-or-so is about what you get on Earth without a lot of sophisticated corrections, averaging, and kinematics. So, if they're not doing all that stuff, they could be doing quite well. (on the other hand, one of the bigger correction terms-- the ionospheric delay -- they don't have to deal with-- but they have to deal with all of their measurements being in "one direction"). If e.g. they don't know about the moon's relative motion, that's a big disadvantage. If, on the other hand, they get the kilometer after a -loooot- of averaging, that's quite bad. I don't know how big of a fleet you need to make this worthwhile, though. Just one satellite in a different direction would collapse that big error ellipse to a much shorter arc.
- mmooss 2y ago
  > I suppose the next inevitable step is LPS That has been planned for awhile as part of Artemis.
- wildzzz 2y ago
  Selenostationairy seems to be impossible. It would be too close to earth to fly undisturbed. Orbiting the moon is hard because of the moon's uneven mass concentrations, the gravity is not as uniform as here on earth. An space-based LPS would be pretty hard to build out. Star trackers alongside GNSS would provide a better system for positioning. However, building out a ground system using towers on the moon would work. With the low gravity of the moon and no wind, you could build pretty tall structures with beacons for positioning. You'd need line of sight so it would be costly to build out this system across the entire surface. A 1km tall tower built every 58km would give you similar positioning as GPS (three intersecting circles). But also, the moon is not terribly interesting so the few long trips that would put you far from base wouldn't require instant positioning. A star tracker and an hour of watching GNSS would work just fine. If there ever was a significant population on the moon, they'd have the lunar equivalent of busses (traveling over marked paths) or light rail to get them in-between facilities.
  - srigi 2y ago
    Well, in that case, why not build a hybrid—a low-orbit satellite network synced to a few ground bases that will give the exact position of flying over satellite(s)? Building a network of a very tall tower every 58km around a globe of the Moon seems very uneconomic.
throw0101d 2y ago
> 2 m/s 7.2 kph; 4.5 mph.
- jiehong 2y ago
  > 7.2kph You mean 7.2 km/h. Thanks for the conversion, though!
  - queuebert 2y ago
    7.2 km h^-1 if you want to be fully SI correct
    - card_zero 2y ago
      Why don't the ISO like writing km/h?
      - jakeinspace 2y ago
        Because if there are multiple inverted units, you'd need to add parentheses to put them all in the denominator. Tidily giving each a ^-1 is clearer (especially with superscript exponents).
        gattr 2y ago
        You can use superscript Unicode characters on HN: km·h⁻¹.
        jakeinspace 2y ago
        Ah but you see, I am on my phone and very lazy.
        Evidlo 2y ago
        What's wrong with a/b/c
querbu 2y ago
More details: + 44dBm GPS transmit power -210dB path loss + 15dB rx antenna gain -151dBm received signal strength That's slightly worse (5dB) than signal strength of a handheld device/ phone (~15dB typical handheld loss, urban environment). There is still ~15dB margin. They are cheating a little with the 15dB narrow antenna gain, which requires accurate pointing. Nice result and there is room for improvement. Note: -210dB = 10^-21
- slow_typist 2y ago
  That number doesn’t tell much without knowing the background noise on the L-bands out there. It would also be interesting to know whether they achieved this with commercial Gnss receivers.
  - querbu 2y ago
    Since the high gain antenna is pointed at the entire earth, the noise temperature is similar earth temperature. Semi-custom gnss receiver, they collect mostly correlator outputs, and 2.5 seconds of raw IQ
    - slow_typist 2y ago
      Angular size of the earth should be about 2 degrees. That is about nothing compared to the beam width of a 15 dB antenna. So space noise is definitely a factor here. However they made it work, and could have used an antenna with much more gain (think voyager dish) if necessary. Probably the idea behind the experiment is to track rovers on the surface where the antenna is only roughly pointed at earth - without the complexity and energy budget coming with a rotator.
  - zokier 2y ago
    > It would also be interesting to know whether they achieved this with commercial Gnss receivers They used Qascom QN400 receiver.
    - slow_typist 2y ago

by 7952 2y ago

madaxe_again 2y ago

At that resolution the utility is somewhat questionable - I suppose the next inevitable step is LPS, and having a fleet of selenostationary satellites performing the same function locally.

thatcherc 2y ago
A challenge there is that there are very few stable lunar orbits! High orbits are perturbed by Earth's gravity (3-body problem) and low lunar orbits are perturbed by the lumpy distribution of mass in the Moon's interior [0]. Lunar GNSS satellites with a little bit of onboard propulsion could probably correct for some of these perturbations but once they ran out of fuel they would have a limited orbital lifetime. [0] - https://en.wikipedia.org/wiki/Lunar_orbit#Perturbation_effects_and_low_orbits https://en.wikipedia.org/wiki/Lunar_orbit#Perturbation_effec...
- adgjlsfhk1 2y ago
  could the legrange points work? dealing with the 3 body orbits would be a pain, but they would give you nice separation
  - mkl 2y ago
    You need signals from 3+ different locations to navigate, and the two stable Lagrange points, L4 and L5, are as far from the moon as Earth is: https://en.wikipedia.org/wiki/Lagrange_point https://en.wikipedia.org/wiki/Lagrange_point.
    - mlyle 2y ago
      But-- GPS already produces an okayish fix. Improving it with another signal from somewhere else would make a big difference. > and the two stable Lagrange points, L4 and L5 We have plenty of spacecraft hanging out around L1, etc. It's possible to orbit it without too much issue. Having one broadcast a navigation signal synchronized with GPS would not be too bad. > are as far from the moon as Earth is The issue isn't that they're far away-- it's that they're all in pretty much the same direction. There's very small uncertainties in orbits and measured path length, but if they're all in the same direction you get very poor lateral position. This is the same effect you can get if you can only see a little tiny bit of the sky with GPS. You might have enough satellites to navigate, but since they're all close to the same direction the navigation solution is much worse.
    - adgjlsfhk1 2y ago
      I meant the earth/moon, not earth/sun Lagrange points.
- ekianjo 2y ago
  Is the 3 body problem mostly meaningful above a certain mass? If you had small satellites could you deal with it?
  - xnorswap 2y ago
    The mass of a satellite is already trivial compared to the mass of the moon.
  - itishappy 2y ago
    The restricted three-body problem deals with the case when the third mass is trivial and the orbits are circular. The new solutions in this case are the Lagrange points. That's helpful, but doesn't make finding dynamic solutions much easier on it's own.
- 0_____0 2y ago
  Oh wow, good reading in that link. I had no idea the moon was that lumpy. The wiki entry says that despite the mascons there are 4 known stable orbital inclinations?
  - shagie 2y ago
    That is correct. The NASA page link (now 404) has a bit more on the orbits and their history. https://web.archive.org/web/20210307002503/https://science.nasa.gov/science-news/science-at-nasa/2006/06nov_loworbit/ https://web.archive.org/web/20210307002503/https://science.n... And they're very lumpy. > The mascons' gravitational anomaly is so great—half a percent—that it actually would be measurable to astronauts on the lunar surface. "If you were standing at the edge of one of the maria, a plumb bob would hang about a third of a degree off vertical, pointing toward the mascon," Konopliv says. Moreover, an astronaut in full spacesuit and life-support gear whose lunar weight was exactly 50 pounds at the edge of the mascon would weigh 50 pounds and 4 ounces when standing in the mascon's center.
    - mmooss 2y ago
      That is a great link. Do you know if any of it is outdated now?
      - shagie 2y ago
        It is still all completely correct. There may be some new findings, but the lunar prospector ( https://en.wikipedia.org/wiki/Lunar_Prospector https://en.wikipedia.org/wiki/Lunar_Prospector ) did all the work and this was written after that.
- BWStearns 2y ago
  I wonder if lunar space elevators might be the fix here. If I understand correctly, such an elevator would not be as subject to the perturbations since the tension would keep it's orbit stable (is it still an orbit if it's tethered?). Another option might be a LORAN style system put up on towers. With lower gravity and no atmosphere I imagine we could stick transmitters up very high without super complex construction, maybe even just a giant carbon fiber tube with a transmitter at the top.
  - kridsdale1 2y ago
    Let’s put a high power laser on the end to send advertisements in Morse code to anyone looking towards the moon.
    - datadrivenangel 2y ago
      Raster-scan it to deliver persistence of vision ads!
- staplung 2y ago
  Technically, satellite positioning only needs 1 satellite. GPS requires several but one of its forerunners was Transit[1] which I believe only needed a signal from a single satellite at a time. It worked by measuring the doppler shift of the signal coming from the satellite. Of course that only works if the orbit can eventually cover all (or much of) the surface and for all I know there is no such frozen orbit for the moon. Also, it would still presumably require extensive surface-based tracking and correction. [1] https://en.wikipedia.org/wiki/Transit_(satellite) https://en.wikipedia.org/wiki/Transit_(satellite)
mhb 2y ago
Wouldn't the next step be plopping some down on the moon?
- mannykannot 2y ago
  I was wondering that too, and that led to the question whether, without an atmosphere, all radio communications at any wavelength would be strictly line-of-sight. It turns out, however, that the moon has something of an ionosphere, though I don't know whether it would support over-the-horizon radio (or, for that matter, whether it tends to interfere with the accuracy of GPS, as it does on Earth.) https://phys.org/news/2011-11-mystery-lunar-ionosphere.html https://phys.org/news/2011-11-mystery-lunar-ionosphere.html
t43562 2y ago
Lunar Pathfinder. https://www.sstl.co.uk/what-we-do/lunar-mission-services https://www.sstl.co.uk/what-we-do/lunar-mission-services QUOTE: A constellation of interconnected lunar orbiters will enable surface missions operating on the far side of the Moon, without direct to Earth line of sight, to keep constant contact with Earth. It will also provide lunar navigation signals to support critical mission phases such as precision landing of scientific equipment and the operation of rovers. In addition to communication services, the Lunar Pathfinder spacecraft has been selected by ESA and NASA to host a number of experimental payloads: An ESA GNSS receiver capable of detecting weak signals coming from the Earth GNSS infrastructure (GPS and Galileo), demonstrating its potential role into Lunar navigation A NASA retro-reflector to demonstrate laser ranging capabilities An ESA radiation monitor to study orbital radiation conditions Acting both as technology and service demonstrator, Lunar Pathfinder is the opportunity for scientific and commercial mission developers to support the development, test and standardisation of Lunar communication infrastructure, and for emerging off-planet telcos to acquire experience of lunar asset operations and off-planet service delivery. Lunar Pathfinder is due to operate in an Elliptical Lunar Frozen Orbit (ELFO) for an operational lifetime of 8 years. The spacecraft can operate 2 simultaneous channels of communication with lunar assets: 1 in S-band and 1 in UHF. Performance, such as coverage and data-rate, depend both on the relative position of the user asset to Pathfinder at the moment of the connection, as well as the capabilities of the communication module onboard the user asset. Once safely retrieved onboard Lunar Pathfinder, communications are relayed back to Earth ground stations in X-band.
hammock 2y ago
1.5km is not bad. Chris Columbus could resolve latitude to about 100-200km, and longitude only by dead reckoning. I do wonder though with computers and cameras and celestial navigation, why that is not used vs GPS on the moon
- patmorgan23 2y ago
  Are there any existing systems for that? Would you be able to resolve to a similar level of accuracy with computer vision looking at the stars? Ussally enhancing an existing technology that is widely deployed and understood to fit a new situation is better than inventing something wholly new (though not always)
  - hammock 2y ago
    What are GPS sats if not artificial stars used for celestial nav? (In a roundabout way, no pun intended)
    - zokier 2y ago
      GPS navigation is based on measuring the distance between observer and the satellites to triangulate position. Celestial navigation does not care about distance to stars at all, in many ways stars are considered to be infinitely far away.
  - infinet 2y ago
    https://en.wikipedia.org/wiki/Celestial_navigation https://en.wikipedia.org/wiki/Celestial_navigation > Sextants can be read accurately to within 0.1 arcminutes, so the observer's position can be determined within (theoretically) 0.1 nautical miles (185.2 meters, or about 203 yards). Most ocean navigators, measuring from a moving platform under fair conditions, can achieve a practical accuracy of approximately 1.5 nautical miles (2.8 km) Some napkin math, assuming using a Sextant to achieve similar accuracy of 0.1 arcminutes on the Moon, because Moon is about 3.7 times smaller than Earth, that 0.1 arcminutes is around 50 meters on the Moon. One can expect extremely clear sky and certainly not riding waves on the Moon, so the practical accuracy should be close.
deleted 2y ago
[deleted]
mlyle 2y ago
I'm curious what the assumptions are. Looking forward to reading the paper. a kilometer-or-so is about what you get on Earth without a lot of sophisticated corrections, averaging, and kinematics. So, if they're not doing all that stuff, they could be doing quite well. (on the other hand, one of the bigger correction terms-- the ionospheric delay -- they don't have to deal with-- but they have to deal with all of their measurements being in "one direction"). If e.g. they don't know about the moon's relative motion, that's a big disadvantage. If, on the other hand, they get the kilometer after a -loooot- of averaging, that's quite bad. I don't know how big of a fleet you need to make this worthwhile, though. Just one satellite in a different direction would collapse that big error ellipse to a much shorter arc.
mmooss 2y ago
> I suppose the next inevitable step is LPS That has been planned for awhile as part of Artemis.
wildzzz 2y ago
Selenostationairy seems to be impossible. It would be too close to earth to fly undisturbed. Orbiting the moon is hard because of the moon's uneven mass concentrations, the gravity is not as uniform as here on earth. An space-based LPS would be pretty hard to build out. Star trackers alongside GNSS would provide a better system for positioning. However, building out a ground system using towers on the moon would work. With the low gravity of the moon and no wind, you could build pretty tall structures with beacons for positioning. You'd need line of sight so it would be costly to build out this system across the entire surface. A 1km tall tower built every 58km would give you similar positioning as GPS (three intersecting circles). But also, the moon is not terribly interesting so the few long trips that would put you far from base wouldn't require instant positioning. A star tracker and an hour of watching GNSS would work just fine. If there ever was a significant population on the moon, they'd have the lunar equivalent of busses (traveling over marked paths) or light rail to get them in-between facilities.
- srigi 2y ago
  Well, in that case, why not build a hybrid—a low-orbit satellite network synced to a few ground bases that will give the exact position of flying over satellite(s)? Building a network of a very tall tower every 58km around a globe of the Moon seems very uneconomic.

throw0101d 2y ago

> 2 m/s 7.2 kph; 4.5 mph.

jiehong 2y ago
> 7.2kph You mean 7.2 km/h. Thanks for the conversion, though!
- queuebert 2y ago
  7.2 km h^-1 if you want to be fully SI correct
  - card_zero 2y ago
    Why don't the ISO like writing km/h?
    - jakeinspace 2y ago
      Because if there are multiple inverted units, you'd need to add parentheses to put them all in the denominator. Tidily giving each a ^-1 is clearer (especially with superscript exponents).
      - gattr 2y ago
        You can use superscript Unicode characters on HN: km·h⁻¹.
        jakeinspace 2y ago
        Ah but you see, I am on my phone and very lazy.
      - Evidlo 2y ago
        What's wrong with a/b/c

querbu 2y ago

More details: + 44dBm GPS transmit power -210dB path loss + 15dB rx antenna gain -151dBm received signal strength That's slightly worse (5dB) than signal strength of a handheld device/ phone (~15dB typical handheld loss, urban environment). There is still ~15dB margin. They are cheating a little with the 15dB narrow antenna gain, which requires accurate pointing. Nice result and there is room for improvement. Note: -210dB = 10^-21

slow_typist 2y ago
That number doesn’t tell much without knowing the background noise on the L-bands out there. It would also be interesting to know whether they achieved this with commercial Gnss receivers.
- querbu 2y ago
  Since the high gain antenna is pointed at the entire earth, the noise temperature is similar earth temperature. Semi-custom gnss receiver, they collect mostly correlator outputs, and 2.5 seconds of raw IQ
  - slow_typist 2y ago
    Angular size of the earth should be about 2 degrees. That is about nothing compared to the beam width of a 15 dB antenna. So space noise is definitely a factor here. However they made it work, and could have used an antenna with much more gain (think voyager dish) if necessary. Probably the idea behind the experiment is to track rovers on the surface where the antenna is only roughly pointed at earth - without the complexity and energy budget coming with a rotator.
- zokier 2y ago
  > It would also be interesting to know whether they achieved this with commercial Gnss receivers They used Qascom QN400 receiver.
  - slow_typist 2y ago