Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

SpaceX nails triple booster landing after satellite delivery

bbc.com

Post reply on HN
Print view View original

51–60 of 128 posts

Re: SpaceX nails triple booster landing after satellite delivery

#51

Post by jessriedel »

taneq wrote: post #42
bbojan wrote: post #16

Not only that, but apparently they recovered both fairings: https://www.google.com/url?sa=t&source=web&rct=j&url=https:/... So 5 out of 5...

I guess salt water isn't that much of an issue after all?

Yea, I wish we'd get a more detailed explanation of the accounting on this. For all I knew it was totally plausible that fairings would be destroyed by sea water, and it was also plausible there'd be no damage. The part that confuses me is why they would spend so much effort trying to catch them with Mr. Steven if they are in fact serviceable after a swim. Maybe the idea is that salt-water refurbishment-and-reuse saves a bit of money compared to expendable, but mid-air-catch would have saved more but turned out to be too difficult?

Re: SpaceX nails triple booster landing after satellite delivery

#52

Post by pjc50 »

inflatableDodo wrote: post #15
usermac wrote: post #5

I wonder what emergency procedure is in place in case the landing is off-course. Does it blow itself up?

As an addendum to that, if one accidentally lands in my back yard, can I keep it?

Almost certainly not - there's all sorts of precedent from rolled-away cars to high wind incidents that just because something has ended up on your property does not make it yours unless the owner has abandoned or discarded it.

Re: SpaceX nails triple booster landing after satellite delivery

#53

Post by dom96 »

theoh wrote: post #27
amelius wrote: post #23

Earlier quoted context omitted.

How is "booster landing" mapped to a convex optimization problem?

Lars Blackmore, who works for SpaceX, has a page about the techniques that are used here: http://www.larsblackmore.com/losslessconvexification.htm See also: https://www.aa.washington.edu/facultyfinder/behcet-acikmese

Can anyone give a ELI5 (for developers) of how this technique works?

Re: SpaceX nails triple booster landing after satellite delivery

#54

Post by jessriedel »

martythemaniak wrote: post #21

There's a great media thread on reddit where people post their own photos and videos: https://www.reddit.com/r/spacex/comments/bbhz9a/rspacex_arab... Here's a great video of the entire flight and landing of the side boosters in one shot, made with custom tracking software: https://www.youtube.com/watch?v=cEZZkEXAD6Q

For those interested, booster separation is just after the 3:00 mark. The whole separation, flip, and boost-back dance is incredible to watch.

Re: SpaceX nails triple booster landing after satellite delivery

#55

Post by DennisP »

JshWright wrote: post #44
baq wrote: post #41

Earlier quoted context omitted.

the fully reusable falcon heavy can IIRC only lift about 8000kg to LEO. expendable is volume-limited but if you want to lift a concrete block, you can :)

Reusable is 8000kg to GTO, not LEO. LEO performance in fully reusable configurations is 30+ tons.

So assuming 32 tonnes it's $668/kg for the hardware (assuming full payloads).

Probably also have to build in enough slack for occasional failed landings, but we don't know yet what the failure rate will be after the kinks are worked out.

Re: SpaceX nails triple booster landing after satellite delivery

#56

Post by hwc »

narrator wrote: post #46

Can we finally stop having sci-fi films in which the whole outcome of the movie is solely determined on some heroic manual flying of a spaceship while simultaneously using manually aimed weapons like it's World War II?

Also, can we start seeing this kind of re-usable multi-stage rocket used for achieving orbit in fiction?

Re: SpaceX nails triple booster landing after satellite delivery

#57

Post by azernik »

Ajedi32 wrote: post #49
pedrocr wrote: post #31

Earlier quoted context omitted.

According to a reddit thread they've saltwater hardened the fairings and now they can reuse them: https://www.reddit.com/r/spacex/comments/bc8105/arabsat6a_el... The first reuse mission seems to be an internal one though.

That's just speculation, I wouldn't cite it as an authoritative source.

The part that says they're able to reuse these ones is a tweet directly from Elon Musk; he also confirms they were recovered from in the water, not caught in the air.

Re: SpaceX nails triple booster landing after satellite delivery

#58

Post by that_jojo »

pedrocx486 wrote: post #32
qmarchi wrote: post #25

Earlier quoted context omitted.

On this launch, it looks like they offset the timings to reduce the chance of tipping over. If you get time, go look for the first FH booster landings. The timing is almost perfect and the long exposure images looked beautiful.

>On this launch, it looks like they offset the timings to reduce the chance of tipping over. On reddit a lot of people enphasised that it was to avoid interference. Which interference, no one knows.

Incorrect. Gift that you give to me, no one knows,

Re: SpaceX nails triple booster landing after satellite delivery

#59

Post by theoh »

dom96 wrote: post #53
theoh wrote: post #27

Earlier quoted context omitted.

Lars Blackmore, who works for SpaceX, has a page about the techniques that are used here: http://www.larsblackmore.com/losslessconvexification.htm See also: https://www.aa.washington.edu/facultyfinder/behcet-acikmese

Can anyone give a ELI5 (for developers) of how this technique works?

The control parameter space for the rocket is non-convex because, for one thing, it can't be throttled down close to zero thrust. You can think of the parameter space as having a hole in it. An optimal control algorithm might want to make very delicate low-thrust corrections, but that's not possible.

This technique is based on "the idea of relaxing the nonconvex control constraints to a convex set in such a way that the optimal solution to the relaxed problem is guaranteed to be the optimal solution to the original problem."

By "relaxing", what they mean is that the new model (the convex set) actually contains some parameter values that aren't achievable, but OTOH it is geometrically susceptible to being analyzed by an efficient optimization technique. So it's a clever replacement of a hard problem with an easier one. The complex bit, which I don't understand, is how they show that this replacement will always give the same value as if they had solved the (real) hard problem, i.e. that the solution will never actually use the "illegal" parameter values.

Maybe someone else can give more insight.

Re: SpaceX nails triple booster landing after satellite delivery

#60

Post by xfitm3 »

martythemaniak wrote: post #21

There's a great media thread on reddit where people post their own photos and videos: https://www.reddit.com/r/spacex/comments/bbhz9a/rspacex_arab... Here's a great video of the entire flight and landing of the side boosters in one shot, made with custom tracking software: https://www.youtube.com/watch?v=cEZZkEXAD6Q

I never realized there were launch observers in the water - what a great idea!
Post reply on HN