5 ms·

Anyone knows how the landing is guided? Is it just really precise GPS/altimeter or does it use computer vision?

pfdietz 2y ago
I'd imagine a combination of inertial and GPS, combined with a Kalman filter. Inertial handles short term estimation; GPS correcting drift in the inertial system. But they could roll in other information sources at the end.
- imglorp 2y ago
  For the centimeterish precision needed to hover into the chopsticks, they also have the opportunity to use signals from the tower area for final alignment. I'm thinking riding a beam like aviation ILS. Just speculating but it would be easy to implement. Optical/camera alignment is probably out of the question due to fire and smoke.
  - pfdietz 2y ago
    The arms themselves could have sensors on them. Inductive loops sensing the presence of the stainless steel structure? Also, I doubt centimeter scale precision would be needed; the arms have some compliance in them, I'm sure, as well as the ability to control how far in they swing.
    - imglorp 2y ago
      Yeah really - it's half centimeter nav according to BG. Ctrl-f for centimeter: https://arstechnica.com/space/2024/10/spacex-catches-returning-rocket-in-mid-air-turning-a-fanciful-idea-into-reality https://arstechnica.com/space/2024/10/spacex-catches-returni... Surveying GPS can do that with WAAS and a bunch of integration time and extra receivers, but not in real time: https://www.gps.gov/systems/gps/performance/accuracy https://www.gps.gov/systems/gps/performance/accuracy So that's why I think they need to have a high resolution, close range, 3d positioning method for the final seconds.
mt_ 2y ago
I would bet in the traditional sensors.
dotnet00 2y ago
Likely a mix of GPS, inertial guidance, vision and radio/laser beacons/ranging.
generuso 2y ago
Falcon-9 relies on GPS and a couple of altimeters. (Filtered, as others have already said, with the help of data from the inertial sensors.) Compared to Falcon-9, Starship/Superheavy additionally has a command link from the ground. Whether it is used to coordinate the movement during the catch is not publicly known, but it is easy to imagine how this could be useful.

I'd imagine a combination of inertial and GPS, combined with a Kalman filter. Inertial handles short term estimation; GPS correcting drift in the inertial system. But they could roll in other information sources at the end.

imglorp 2y ago
For the centimeterish precision needed to hover into the chopsticks, they also have the opportunity to use signals from the tower area for final alignment. I'm thinking riding a beam like aviation ILS. Just speculating but it would be easy to implement. Optical/camera alignment is probably out of the question due to fire and smoke.
- pfdietz 2y ago
  The arms themselves could have sensors on them. Inductive loops sensing the presence of the stainless steel structure? Also, I doubt centimeter scale precision would be needed; the arms have some compliance in them, I'm sure, as well as the ability to control how far in they swing.
  - imglorp 2y ago
    Yeah really - it's half centimeter nav according to BG. Ctrl-f for centimeter: https://arstechnica.com/space/2024/10/spacex-catches-returning-rocket-in-mid-air-turning-a-fanciful-idea-into-reality https://arstechnica.com/space/2024/10/spacex-catches-returni... Surveying GPS can do that with WAAS and a bunch of integration time and extra receivers, but not in real time: https://www.gps.gov/systems/gps/performance/accuracy https://www.gps.gov/systems/gps/performance/accuracy So that's why I think they need to have a high resolution, close range, 3d positioning method for the final seconds.

mt_ 2y ago

I would bet in the traditional sensors.

dotnet00 2y ago

Likely a mix of GPS, inertial guidance, vision and radio/laser beacons/ranging.

generuso 2y ago

Falcon-9 relies on GPS and a couple of altimeters. (Filtered, as others have already said, with the help of data from the inertial sensors.) Compared to Falcon-9, Starship/Superheavy additionally has a command link from the ground. Whether it is used to coordinate the movement during the catch is not publicly known, but it is easy to imagine how this could be useful.