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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 enhanci

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.
teraflop 2y ago
Star trackers do exist and have been used on spacecraft for decades. But unfortunately, looking at the stars can only tell you your orientation in space, not your position. (At least, not to any remotely useful accuracy; you need to travel a huge distance to get a measurable parallax.) Celestial navigation works on the Earth's surface (or the Moon's surface), because being able to determine the orientation of the local horizon (or zenith) is equivalent to determining your latitude and longitude. But that doesn't work for a spacecraft that doesn't have a horizon reference. Of course, if you're orbiting the moon and you can accurately observe the directions to landmarks such as mountains and craters, you can fix your position relative to them. But that's not really what you'd call "celestial navigation".
- saltcured 2y ago
  I'm not trusting my spatial intuition, but shouldn't a theoretical star tracker for solar system use be able to spot the sun and planets and use them for more parallax info? I assume you would need orbital ephemeris info much like we need for GPS satellites. But, given measurements of angles to multiple planets, how well could you estimate your position? Would there a lot of error for your normal vector to the earth's ecliptic plane?
jjk166 2y ago
There are systems for use on Earth, yes. See for example [0]. Such a system would need to be heavily modified for use on the moon given that its path relative to a "static" stellar background would be very different, but nothing a modern computer couldn't handle. [0] https://theaviationgeekclub.com/the-sr-71-astroinertial-navigation-system-aka-r2-d2-was-crucial-in-blackbird-mission-heres-why/ https://theaviationgeekclub.com/the-sr-71-astroinertial-navi...

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.

teraflop 2y ago

Star trackers do exist and have been used on spacecraft for decades. But unfortunately, looking at the stars can only tell you your orientation in space, not your position. (At least, not to any remotely useful accuracy; you need to travel a huge distance to get a measurable parallax.) Celestial navigation works on the Earth's surface (or the Moon's surface), because being able to determine the orientation of the local horizon (or zenith) is equivalent to determining your latitude and longitude. But that doesn't work for a spacecraft that doesn't have a horizon reference. Of course, if you're orbiting the moon and you can accurately observe the directions to landmarks such as mountains and craters, you can fix your position relative to them. But that's not really what you'd call "celestial navigation".

saltcured 2y ago
I'm not trusting my spatial intuition, but shouldn't a theoretical star tracker for solar system use be able to spot the sun and planets and use them for more parallax info? I assume you would need orbital ephemeris info much like we need for GPS satellites. But, given measurements of angles to multiple planets, how well could you estimate your position? Would there a lot of error for your normal vector to the earth's ecliptic plane?

jjk166 2y ago

There are systems for use on Earth, yes. See for example [0]. Such a system would need to be heavily modified for use on the moon given that its path relative to a "static" stellar background would be very different, but nothing a modern computer couldn't handle. [0] https://theaviationgeekclub.com/the-sr-71-astroinertial-navigation-system-aka-r2-d2-was-crucial-in-blackbird-mission-heres-why/ https://theaviationgeekclub.com/the-sr-71-astroinertial-navi...