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Brilliant! This is both clever and educational. I immediately wondered if it would be possible to do something similar for JWST. Unfortunately LOC DNS records

Brilliant! This is both clever and educational. I immediately wondered if it would be possible to do something similar for JWST. Unfortunately LOC DNS records top out at ~42 million meters (42,000 km altitude) and JWST is 38x further out (~1.5 million km away). So you can’t represent its location with a LOC altitude field. Maybe Hubble?

firesteelrain 1y ago
Not sure how that will work since JWST orbits the second Lagrange point. It would be like asking for the GPS coordinates of the moon. NASA did test receiving weak GPS signals on the moon with LRO in 2023. It wouldn’t be useful for navigation though (not yet unless someone has like a way to do reverse GPS on the moon but not sure how that would work) Reason this works for the ISS is because of the subsatellite point. It can receive GPS signals regardless of altitude above the Earth’s surface. Also TLEs apply to the ISS because it’s earth orbiting. TLEs are designed for satellites in Earth orbit, where they define position and velocity using orbital elements interpreted by models like SGP4.
- TMEHpodcast 1y ago
  Yes, I realize not-having initially understood what LOC DNS actually is. As mentioned, this could of course be applied to Hubble.
  - firesteelrain 1y ago
    Any MEO or LEO satellite Hubble operates in LEO so it’s eligible
- netsharc 1y ago
  > NASA did test receiving weak GPS signals on the moon with LRO in 2023. I doubt very much that the position of the ISS in the article is being sent from the ISS at real time. It's more likely calculated using NORAD / Celestrak orbital elements plus orbital calculations. I remember having a Windows desktop app to show the satellites locations, I'd have to download those text files to keep the information accurate. For the information beyond the snapshot, the app has to calculate distance and trajectory to estimate "If NORAD said it was here at this point in time, and heading that way with that speed, then right now it should be around here.". A bit like "If a train left Chicago 5 hours ago going 60 mph, where is it now?". Nowadays it's all online of course: https://in-the-sky.org/satmap_worldmap.php https://in-the-sky.org/satmap_worldmap.php .
  - firesteelrain 1y ago
    > doubt very much that the position of the ISS in the article is being sent from the ISS at real time. It's more likely calculated using NORAD / Celestrak orbital elements plus orbital calculations. Yes, this is how the referenced site knows the approximate position of the ISS via TLEs. TLEs are updated regularly for space objects
    - echoangle 1y ago
      That doesn't matter for the problem at hand though. You can calculate the current GPS coordinates from any TLE, even if they aren't derived from GPS measurements but from Satellite Laser Ranging or some other method.
      - firesteelrain 1y ago
        You can derive Lat and Lon and Altitude on Earth. Thats the one point of the TLEs. But they aren’t GPS derived coordinates.
        echoangle 1y ago
        Yes, but you don't need GPS derived coordinates for the DNS LOC entry.
        firesteelrain 1y ago
        Correct because the site referenced uses N2YO which is using NASA provided TLEs which some backend that provides an API. GPS and TLEs are not the same.
- echoangle 1y ago
  > It would be like asking for the GPS coordinates of the moon No problem at all, just give the location where the moon is at the Zenith and use the distance as the altitude. > Reason this works for the ISS is because of the subsatellite point. It can receive GPS signals regardless of altitude above the Earth’s surface. No, wether the object can actually receive GPS signals is completely irrelevant to wether its location can be described in the GPS coordinate system. You could describe the location of the Sun in GPS coordinates too, the altitude value would just be very large.
  - firesteelrain 1y ago
    You can use GPS to describe a point on Earth. To use the moon or sun is kind of weird because of their size to use GPS coordinates for this I was referring to finding your position on the moon using Earth referenced GPS signals.
    - echoangle 1y ago
      > You can use GPS to describe a point on Earth. No, you can describe any point in the universe using GPS coordinates. You just lose some resolution the further away from earth you are because it's basically spherical coordinates (like polar coordinates but for 3D). And the system isn't inertial but earth-fixed, of course, so you would have to give the coordinates together with a time. And if you're describing the location of the moon and the sun, you would probably pick their center of gravity.
      - firesteelrain 1y ago
        I believe this isn’t true otherwise NASA would be doing this - Earth isn’t a universal reference - GPS uses WGS84 - GPS is bound to the Earth’s surface and center - It’s Geodetic - There's no universal “equator” or “prime meridian” beyond Earth - Space uses inertial frames or celestial coordinate systems (right ascension and declination, or galactic coordinates)
        1y ago
dotancohen 1y ago
That probably because GSO is right about at that altitude.

firesteelrain 1y ago

Not sure how that will work since JWST orbits the second Lagrange point. It would be like asking for the GPS coordinates of the moon. NASA did test receiving weak GPS signals on the moon with LRO in 2023. It wouldn’t be useful for navigation though (not yet unless someone has like a way to do reverse GPS on the moon but not sure how that would work) Reason this works for the ISS is because of the subsatellite point. It can receive GPS signals regardless of altitude above the Earth’s surface. Also TLEs apply to the ISS because it’s earth orbiting. TLEs are designed for satellites in Earth orbit, where they define position and velocity using orbital elements interpreted by models like SGP4.

TMEHpodcast 1y ago
Yes, I realize not-having initially understood what LOC DNS actually is. As mentioned, this could of course be applied to Hubble.
- firesteelrain 1y ago
  Any MEO or LEO satellite Hubble operates in LEO so it’s eligible
netsharc 1y ago
> NASA did test receiving weak GPS signals on the moon with LRO in 2023. I doubt very much that the position of the ISS in the article is being sent from the ISS at real time. It's more likely calculated using NORAD / Celestrak orbital elements plus orbital calculations. I remember having a Windows desktop app to show the satellites locations, I'd have to download those text files to keep the information accurate. For the information beyond the snapshot, the app has to calculate distance and trajectory to estimate "If NORAD said it was here at this point in time, and heading that way with that speed, then right now it should be around here.". A bit like "If a train left Chicago 5 hours ago going 60 mph, where is it now?". Nowadays it's all online of course: https://in-the-sky.org/satmap_worldmap.php https://in-the-sky.org/satmap_worldmap.php .
- firesteelrain 1y ago
  > doubt very much that the position of the ISS in the article is being sent from the ISS at real time. It's more likely calculated using NORAD / Celestrak orbital elements plus orbital calculations. Yes, this is how the referenced site knows the approximate position of the ISS via TLEs. TLEs are updated regularly for space objects
  - echoangle 1y ago
    That doesn't matter for the problem at hand though. You can calculate the current GPS coordinates from any TLE, even if they aren't derived from GPS measurements but from Satellite Laser Ranging or some other method.
    - firesteelrain 1y ago
      You can derive Lat and Lon and Altitude on Earth. Thats the one point of the TLEs. But they aren’t GPS derived coordinates.
      - echoangle 1y ago
        Yes, but you don't need GPS derived coordinates for the DNS LOC entry.
        firesteelrain 1y ago
        Correct because the site referenced uses N2YO which is using NASA provided TLEs which some backend that provides an API. GPS and TLEs are not the same.
echoangle 1y ago
> It would be like asking for the GPS coordinates of the moon No problem at all, just give the location where the moon is at the Zenith and use the distance as the altitude. > Reason this works for the ISS is because of the subsatellite point. It can receive GPS signals regardless of altitude above the Earth’s surface. No, wether the object can actually receive GPS signals is completely irrelevant to wether its location can be described in the GPS coordinate system. You could describe the location of the Sun in GPS coordinates too, the altitude value would just be very large.
- firesteelrain 1y ago
  You can use GPS to describe a point on Earth. To use the moon or sun is kind of weird because of their size to use GPS coordinates for this I was referring to finding your position on the moon using Earth referenced GPS signals.
  - echoangle 1y ago
    > You can use GPS to describe a point on Earth. No, you can describe any point in the universe using GPS coordinates. You just lose some resolution the further away from earth you are because it's basically spherical coordinates (like polar coordinates but for 3D). And the system isn't inertial but earth-fixed, of course, so you would have to give the coordinates together with a time. And if you're describing the location of the moon and the sun, you would probably pick their center of gravity.
    - firesteelrain 1y ago
      I believe this isn’t true otherwise NASA would be doing this - Earth isn’t a universal reference - GPS uses WGS84 - GPS is bound to the Earth’s surface and center - It’s Geodetic - There's no universal “equator” or “prime meridian” beyond Earth - Space uses inertial frames or celestial coordinate systems (right ascension and declination, or galactic coordinates)
      - 1y ago

dotancohen 1y ago

That probably because GSO is right about at that altitude.