[FatalLogic]

It's an interesting comparison. At least, with a carrier you can go around, but I suppose that, for an aircraft landing on a carrier, the moment of irreversible commitment to landing maybe comes a second or two earlier than it does for SpaceX.

I don't know if the SpaceX vehicle is programmed to back off and wait if a big wave rocks the platform, but it could do that, wind permitting (edit: no, it couldn't, apparently, see reply by Denvercoder9). Fuel is limited, but it seems like it should be able to hover for a few seconds and wait for the platform to stabilize if necessary.

Anyway, they're not developing a sea-landing vehicle, so it's understandable if they don't spend so much time thinking about that. It's designed to land on solid ground, I think and the ground doesn't usually move, after all.

[Denvercoder9]

The thrust-to-weight ratio of an empty Falcon 9 is far too high to hover. Burn the engines too long and it'll just ascent again.

[mhandley]

Their F9R test vehicle could hover. Isn't that essentially a mockup Falcon 9 first stage, but with only the centre engine?

https://www.youtube.com/watch?v=ZwwS4YOTbbw

[Intermernet]

I wonder how feasible / useful it would be to have realtime best-guess altitude from accelerometers / bouys / laser line-of-site relays etc to give the rocket up to date info to adjust thrust / vector to the drone-ship.

Or do they already do this?

[jccooper]

Almost certainly they have really good GPS and inertial sensors on both. That should be enough. Any line of sight like laser or visual can't be trusted due to weather.

[izacus]

I doubt that heavy sea conditions are factored into design - I think currently the way to avoid that is simply not to launch when the weather is bad around landing and launch area. That's probably the cheaper and simpler solution.