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Comment by jacquesm | Hacker News Reader

Hah, they did it! 3 Landings (2 side boosters and the center core). What a sight!

The third one landed on a drone in the middle of the ocean. Call me crazy but wouldn't that be a moving object?

Insane. All 3 rockets.

The drone ship does what it can to be as stationary as possible but the swell will always move the platform to some extent so the ocean landings are a lot more impressive than the land based ones.

Keep in mind that the boosters flip around and initiate a burn to get back over land. As far as i'm aware, the core maintains a primarily ballistic trajectory and thus lands out in the ocean.

The boostback burn is a hell of a thing too, there was a Space Shuttle contingency plan called RTLS that was essentially the same thing. IIRC one of the commanders described it as "an unholy act of physics". This is quite similar, albeit with much less mass.

Yeah, the major complication with the STS RTLS option is that the Shuttle had to keep the external fuel tank until after the return burn was completed (since the shuttle itself carried no propellant for the main engines).

Scott Manley did a video a few years back explaining how this return profile works (and attempting to fly it in Orbiter)

https://www.youtube.com/watch?v=Iwn3kk-q1YU

Also (IIRC) you wanted the external tank to have as little remaining propellant in the main tank as possible, to facilitate separation without impacting the tank. Which meant that your burn times didn't really change when aborting, which is not a common feature of spacecraft abort systems to say the least.

And there was no way to eject the SRBs early, either. Once those lit, you were in for a ride...

The space shuttle had far more black zones in its launch profile than would have been acceptable in the Saturn program, or any manned program since.

Yeah, the tank had to be empty before it could be dropped (so the RTLS profile actually involved continuing away from the launch site for a while in order to burn off all the fuel without overshooting the return).

I've always been curious as to why that drone is so damn tiny compared to the rocket. Wouldn't make it slightly larger reduce your chances of missing the platform, or are they just that confident about their accuracy?

The drone ship is almost the size of a football field.

Huh, you're right. It's really hard to get a sense of scale.

https://www.teslarati.com/wp-content/uploads/2018/02/OCISLY-...

As someone noted already, the drone ship isn't small. Also, accuracy didn't seem to be a problem in any if the landings, as long as nothing unexpected happened, like fuel running out. Someone ok r/spacex recently compiled a diagram of landing locations: https://i.redd.it/yra4ipgl3ln21.jpg it doesn't look like they need the target to be bigger.

It’s just a practice round for the startup of regular New York to London service.

For anyone searching, the timestamp is 27:30

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