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Comment by michaelmcmillan | Hacker News Reader

    T+17m: Not a successful landing today.

That sucks. Source: http://www.reddit.com/r/spacex/comments/32jnyd/rspacex_crs6_...

Edit: "Looks like Falcon landed fine, but excess lateral velocity caused it to tip over post landing" @elonmusk

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"Ascent successful. Dragon enroute to Space Station. Rocket landed on droneship, but too hard for survival." -- Elon Musk

https://twitter.com/elonmusk/status/588076749562318849

Update: Photo @ https://twitter.com/elonmusk/status/588082574183903232/photo...

new photo: https://twitter.com/elonmusk/status/588142879245238273

new video: https://twitter.com/SpaceX/status/588143946800463874

I'm a big fan of arrestor lines around the sides. Basically as the stage lands, stand up four outrigger arms with a cable going through them from the corners of the barge. If it falls over then catch it and lower it gently. But easy to armchair, hard to do! That they have arrived exactly where the barge is (or would have been) 3 times now is pretty awesome in itself.

The question is always whether you remove more risk than you add. That's a big part of why it's easy to armchair but hard to do. In this case, for example, I'd bet that the odds of the rocket getting tangled in the lines and ruining a landing are better than the odds of the rocket being saved by the lines.

From my armchair observations, it looks like they just need to tweak some constants in their control algorithm to avoid control-induced oscillation. This is the first time that the rocket has reached the ship while still under control (the first landing attempt ran out of hydraulic fluid and went out of control, and of course the second not-quite-attempt didn't have the ship there so it probably wasn't as obvious what was going on) and I imagine there's a fair amount of "oh, duh, how did I overlook that?" going around SpaceX headquarters now that they've finally seen it in action all the way to the end.

Very easy to armchair -- but it's a fifteen story beer can, so you need a huge arrestor system, and it's pretty fragile except up its axis.

The ultimate goal is to land on a flat pad, so adding stuff now moves away from that goal.

I love the beer can analogy. Agreed it is a really interesting problem. Which I don't doubt SpaceX will solve. I was not impressed with the ULA "lets just catch the engines with a helicopter" idea.

Can't wait to see the recovered barge video.

I would hesitate to say it's going to be easy to fix because I would have thought this would have come up in simulations, BUT... They got this in the bag. It's going to be very exciting on the fist landing, but I think it's a forgone conclusion at this point that what they are trying to do will work.

Pretty standard Kerbal landing - vertical ok, but too much lateral.

Just have to put those legs on struts sticking out the sides to give it a wider base!

Just how bad is salt water for the engines? Cut a hole in the landing barge and hit that, with struts mounted 2/3 of the way up to catch on the sides of the hole.

Actually -- make the hole a steel cavity projecting below the waterline, with smooth sloped sides. Thus a miss hits the cavity side and the rocket slides down. Put thrusters at the top of the rocket to push against the pitch torque when the thing contacts the cavity. Drop your struts from the top of the rocket on to the barge.

Now you've got a lower center of mass and wider "legs". You will for sure bang up the side of the rocket, but so what, it is the engines that you really want to recover. (Hmm, actually it will be the rocket exhaust that hits the well first anyway, does pressure in the well from the rocket exhaust help at all? Might slow down the descent, might increase the pitch torque.)

Water is not very compressible, and it's very cold. Two things that a hot, thin rocket engine probably won't like.

Sure, but for that to be efficient you need aerodynamics based purely on mass and drag coefficient for each part.

Having KSP stock aero in real life would be so amazing. For one, it would solve air transportation - just put a bunch of control surfaces in a circle and you get free lift!

Vertical ok only after you learn 5 m/s is TOO FAST.

That's the Kerbal way. First they hit it from the side because they run out of control fluid (say, electricity, in Kerbal terms); then they landed a-ok but tipped over. Next time they'll probably miscalculate the suicide burn and - because it's SpaceX - fourth time's a charm.

There is an opportunity here for some clever control system design. If the mobile platform is brought into the control system loop, it can move to adjust for excess lateral velocity.

Won't be easy, but if anyone can do it, it's SpaceX.

This barge is in a turbulent ocean, so it's already doing a lot of work just to stay somewhat still. Plus the vision tracking on the rocket is already accounting for the movement of the barge.

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