2 ms·

Thanks for the summary. I suspect you could get this to FAR higher accuracy if you combined it with a recent upload of Starlink et al LEO constellation ephemer

by mapt 2y ago

Thanks for the summary. I suspect you could get this to FAR higher accuracy if you combined it with a recent upload of Starlink et al LEO constellation ephemera, an initial GPS fix at launch, and a planned flight path, because LEO constellations are bright foreground objects (high location-specific parallax differences against background stars) at apparent magnitude of about 5.0. This is simultaneously not reliant on perfect vertical attitude sensing coming off the autopilot IMU, you can do it purely photometrically. The limitation is that this is a dawn/dusk thing, in the middle of the night there isn't a ton of light reflected and in the day you're limited by scattered daylight. EDIT: Medium orbit satellites outside Earth's umbra but within view still provide some sort of visual fix. I wonder what the math is like for the GSO belt at midnight? EDIT2: Or the Moon.

jcims 2y ago
That's a great idea. In the earlier days when they had about 2500 satellites in LEO I built a small visualizer from the fleet TLE data and it was remarkably simple with the skyfield library. If you're in the fringes of a GNSS denial area ADSB might be useful as well. Would need more hardware of course.
- BenjiWiebe 2y ago
  Doesn't ADS-B get the location from GNSS?
  - jcims 2y ago
    Yes it does, but unless we’re talking an entire system failue the GNSS denial does tend to have limits in range. I’ve picked up ADSB traffic from well over 200km with a simple ground antenna, so if you’re in the fringes in could be a useful additional signal for similar reasons to the satellites. Just spitballing though really.
maxglute 2y ago
IMO could synergize well for higher end celestia navigation - there are optics sensors for day time tracking, but daylight sensitivity is limitation, perhaps much less so when fixed to starlink. So maybe feasible $$$ hardware can make daylight celestial starlink navigation workable. Bringing component costs down seems like it would be much more useful for increasing capabilities / proliferating of lower end loitering munitions. You can already pack redundant navigation systems in more expensive platforms that gets them to area of operations. But being able to replace $20,000 inertial navigation system with $200 board + IR camera makes a lot of somewhat cheap smart munitions much smarter, and mitigates a lot of expensive electronics warfare platforms. Starlink ubiquity does seem to open a lot of indirect strategic applications, i.e. research using starlink transmissions as bi/multistatic illumination source to detect stealth flyers.

by mapt 2y ago

jcims 2y ago

That's a great idea. In the earlier days when they had about 2500 satellites in LEO I built a small visualizer from the fleet TLE data and it was remarkably simple with the skyfield library. If you're in the fringes of a GNSS denial area ADSB might be useful as well. Would need more hardware of course.

BenjiWiebe 2y ago
Doesn't ADS-B get the location from GNSS?
- jcims 2y ago
  Yes it does, but unless we’re talking an entire system failue the GNSS denial does tend to have limits in range. I’ve picked up ADSB traffic from well over 200km with a simple ground antenna, so if you’re in the fringes in could be a useful additional signal for similar reasons to the satellites. Just spitballing though really.

maxglute 2y ago

IMO could synergize well for higher end celestia navigation - there are optics sensors for day time tracking, but daylight sensitivity is limitation, perhaps much less so when fixed to starlink. So maybe feasible $$$ hardware can make daylight celestial starlink navigation workable. Bringing component costs down seems like it would be much more useful for increasing capabilities / proliferating of lower end loitering munitions. You can already pack redundant navigation systems in more expensive platforms that gets them to area of operations. But being able to replace $20,000 inertial navigation system with $200 board + IR camera makes a lot of somewhat cheap smart munitions much smarter, and mitigates a lot of expensive electronics warfare platforms. Starlink ubiquity does seem to open a lot of indirect strategic applications, i.e. research using starlink transmissions as bi/multistatic illumination source to detect stealth flyers.