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Comment by eltoozero | Hacker News Reader

I understood that part of the reason the landing ship can be so small is that the drone ship is actively maneuvering to a spot to catch the booster.

It's announced in the sequence when the drone ship acquires tracking signals from the booster, I'm guessing it's 99% automated other than abort contingencies.

Even if it's only moving 50ft that'd require a radial increase for a fixed landing spot.

But then they also stuck their land-based landings right on the money so it could just be a purely safety related thing.

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I don't think the ship maneuvers at all. Both the ship and rocket are pre-programmed with the landing coordinates, and independently arrange to be at the right spot at the right time. The ship has fancy thrusters, but their purpose is to hold it perfectly still even when the water is moving around a lot.

That's my understanding as well. The ship moves really slow by comparison to the rocket, not much useful moving it can do - it just stays in place despite waves and weather.

The ship is also painted with a radar reflective X that the booster is targeting on the way down. The ship just has massive engines for solid station keeping in rough seas. Like you say they don't use those to move to the booster.

I'm fairly sure it's these things: https://www.thrustmaster.net/out-drive-propulsion-unit/

They were posted about when the ships were first made. And I know spacex had gone a size up from the originals.

Totally what that guy on Gold Rush needs to get his barge up the Yukon. ;)

That's just a tracking signal, not guidance. Both the booster and the drone ship navigate to the same GPS coordinates.

They also have a radar on the ASDS that the rocket locks onto to help it navigate in addition to the GPS. This gives it a much more exact set of coordinates to shoot for so to speak. There was extensive discussion regarding this on r/SpaceX after they managed a virtually perfect bullseye landing several landings ago.

The landing ship is the size of a football field, not something I'd call small by any means. The booster that lands on it is approximately 14 stories high (230ft / 70m).

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