4 ms·

Great question! Could just be Real-Time Kinematic (RTK) GPS like someone mentioned. Essentially the landing arms know their position very precisely and they mea

by varenc 2y ago

Great question! Could just be Real-Time Kinematic (RTK) GPS like someone mentioned. Essentially the landing arms know their position very precisely and they measure the tiny errors in GPS data, and send that correction data live to the rocket in real-time as it's landing. Once the rocket gets very very close it could also just be using vision systems to zero-in on exactly where the chopsticks are. To speculate more, they could also be using something like ultra-wide band positioning. This relies on the same time-of-flight principle as GPS but instead of using satellites in orbit to provide the precise time information you rely on various nearby ground stations. Would only be useful right at the final approach, the last couple hundred meters, but it's another way they could get very very precise position information. (fun fact: Ultra Wide band positioning is also how iPhones can locate AirTags with centimeter accuracy)

pj_mukh 2y ago
ooooo Yea forgot about RTK GPS. I’ve always found them to be so brittle but that’s because I’m in a city. In the wide open sky, I’m guessing it’s pretty reliable. Vision systems would be pretty useless with the low visibility of the smoke and fire. So I thought maybe it was some kind of radar configuration. Anyways, I’d pay a lot of money to pick the brain of the GNC team here.
- psb217 2y ago
  Why bother with GPS or other "absolute" coordinate systems? Once the rocket's in close, all that matters is relative position and orientation of the rocket with respect to the landing apparatus. Eg, if you had many sensors in known locations on the rocket and many sensors in known locations on the landing apparatus, and you could measure relative positions between all pairs of these sensors, you could get extremely precise relative position/orientation information without beaming information to satellites or whatever.

by varenc 2y ago

pj_mukh 2y ago

ooooo Yea forgot about RTK GPS. I’ve always found them to be so brittle but that’s because I’m in a city. In the wide open sky, I’m guessing it’s pretty reliable. Vision systems would be pretty useless with the low visibility of the smoke and fire. So I thought maybe it was some kind of radar configuration. Anyways, I’d pay a lot of money to pick the brain of the GNC team here.

psb217 2y ago
Why bother with GPS or other "absolute" coordinate systems? Once the rocket's in close, all that matters is relative position and orientation of the rocket with respect to the landing apparatus. Eg, if you had many sensors in known locations on the rocket and many sensors in known locations on the landing apparatus, and you could measure relative positions between all pairs of these sensors, you could get extremely precise relative position/orientation information without beaming information to satellites or whatever.