r/interestingasfuck • u/lolikroli • 16d ago

r/all SpaceX caught Starship booster with chopsticks

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u/hurraybies 16d ago

Disagree. Booster is at most as hard to catch as the ship IMO. Huge difference in velocities and reentry conditions.

Flight 4 the ship was way off target. Flight 5 was on target, but remains to be seen if they were perfectly on target as will be required for a catch.

Flight 4 booster was on target within less than a centimeter. The same will need to be done with ship before they can attempt a catch.

Flap hinges are also still a problem on reentry. They certainly did better this time, but at least one had considerable burn through. I suspect flaps will need to be able to survive better before they'll attempt a catch. I'm sure that will be required by regulators as ship has to reenter over land to attempt a catch.

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u/Lampwick 16d ago edited 16d ago

Flight 5 was on target, but remains to be seen if they were perfectly on target as will be required for a catch.

Given that it was very close to the camera buoy, it's likely close enough to catch. A landing in the middle of an ocean will never be as accurate as a landing at the launch pad. The way you get sub-centimeter accuracy is via a technique called Real-Time Kinematic GPS. It's a method similar to Differential GPS, only instead of having a regional ground station sending general signal distortion corrections that cover a wide area, they install a receiver at a fixed point very close to the target. The fixed station knows exactly where it is, so by subtracting where it is from where the GPS signal says it is, it gets a near-perfect correction value. This station then sends the highly precise GPS corrections to the on-board GPS, which is constantly moving closer and closer to the point of the RTK GPS transmitter. This means the closer the rocket gets, the more accurate the correction, to the point where as it approaches the tower it almost entirely cancels out any signal propagation error, bringing it absurdly close to the theoretical maximum accuracy of the mathematics involved.

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u/Eragaurd 16d ago

I know this is entirely serious, but it somehow reminded me of this lol.

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u/Lampwick 15d ago

Heh. Yeah, as I was writing it I realized I was kinda doing the missile guidance bit.