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SpaceX lands rocket at sea second time after satellite launch

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Re: SpaceX lands rocket at sea second time after satellite launch

#301

Post by mikeash »

dzdt wrote: post #297
LocaX wrote: post #171

Earlier quoted context omitted.

I attended a conference from the head of the CNES (Centre National d'Etudes Spatiales, ~ French NASA) in Paris a week ago and he talked about that. Ariane 6 is going to be built with a cost effective approach and trying to focus on market needs (3D printing of parts, reusability of the first stage, etc.) At first, concerning SpaceX, his group of experts told him that the design of the rocket wasn't going to work and…

Newton's approximation for impact depth [1] gives a way to calculate how thick the barge deck would have to be to survive a high speed impact from the rocket stage. The impactor punches through until it has displaced an equal mass. An empty F9 stage masses about 23,100kg and has a diameter of 3.66m. [2] Steel has a density around 7,700 kg/m^3. Doing the math, the deck would need to be about 29 cm thick to survive a h…

Punch through the deck. Which we already know can happen, the SES-9 landing attempt punched a nice hole in the deck. But you'd need to punch all the way through the hull to even think about sinking the barge, and of course the barge is built with compartments so even that wouldn't do it.

Re: SpaceX lands rocket at sea second time after satellite launch

#302

Post by big_youth »

brianwawok wrote: post #95

Here is the video http://www.space.com/32811-spacex-rocket-landing-jcsat-14-la... Hopefully we won't have the typical hacker news discussion about why the employees chant USA.

http://www.pbs.org/thinktank/transcript1292.html

WATTENBERG: I got to think a lot of illegals add a lot of value to the United States. You have been quoted as saying that you are nauseatingly pro American.

MUSK: Yes, that’s true.

WATTENBERG: What do you mean?

MUSK: Well, I mean, I think the United States is the greatest country that’s ever existed on earth. And I think that it will be difficult to argue on objective grounds that it is not. I think the facts really point in that direction. It’s the greatest force for good of any country that’s ever been. There would not be democracy in the world if not for the United States. We’re obviously falling in the recent few occasions -- maybe three separate occasions in the Twentieth Century -- democracy would have fallen with World War 1, World War 2 and the Cold War, but for the United States.

WATTENBERG: And perhaps the threat of terrorism would be much greater if it were not for the United States.

MUSK: Yeah, absolutely. I think it would be a mistake to say the United States is perfect, it certainly is not. There have been many foolish things the United States has done and bad things the United States has done. But when historians look at these things on balance and measure the good with the bad -- and I think if you do that and -- on a rational basis and make a fair assessment -- I think it’s hard to [unintelligible] that the United States -- is there anything better [speaking over each other]

WATTENBERG: I have a reputation of interrupting my guests. But when they say exactly what I believe, I just let them talk and talk. I think you’re 100 percent right.

MUSK: And -- you know I wasn’t born in America -- I got here as fast as I could.

Re: SpaceX lands rocket at sea second time after satellite launch

#303

Post by castis »

odonnellryan wrote: post #264
thrownear wrote: post #219

Earlier quoted context omitted.

>diminish amazing things.. Sorry. We are living in a period where mediocrity and even complete fraudulent stuff is hailed as profound and "amazing". People with differing opinions matter, and I would say they matter more than ever. And I don't think people love being a contrarian". It is quite easy being a fanboy, but it is hard to go against popular opinion, and be a "contrarian". There is no love in being a contrar…

> Sorry. We are living in a period where mediocrity and even complete fraudulent stuff is hailed as profound and "amazing". Like what? Even the transistor is pretty damn amazing. It's fine to be critical, but let yourself get excited sometimes too.

Check out the history of the person you're replying to. That person doesn't get stoked about anything. It's a shame, really.

Re: SpaceX lands rocket at sea second time after satellite launch

#304

Post by mikeyouse »

Cogito wrote: post #240
mikeyouse wrote: post #20

Earlier quoted context omitted.

Check out the flight profile on Flightclub.io -- I'm not sure how accurate their instantaneous data is but they're showing ~12g acceleration upon landing the booster. Seems more like what I'd expect.

TheVehicleDestroyer (who makes FlightClub) actually commented [1] to say that the 12G is an error due to how he models the deployment of the landing legs. The actual force would have been closer to 5.1G [1] https://www.reddit.com/r/spacex/comments/4htenu/rspacex_jcsa... Ugh sorry, there's a bug of some sort in Flight Club there. There's no way it was that large. A constant deceleration down from terminal velocity ove…

Wow, thanks for the update -- the internet can be damn cool sometimes.

Re: SpaceX lands rocket at sea second time after satellite launch

#305

Post by mikeash »

grondilu wrote: post #281

This success was unexpected. That means that they can recover a stage from a higher speed than previously thought. Does that mean that the recovery of the second stage from LEO may actually be feasible?

Second stage recovery is a whole different beast. Recovering the first stage on a flight like this is a delicate dance because margins are so small, so everything has to go exactly right. The previous attempt (SES-9) didn't quite go exactly right, and made a big boom, perhaps because the engine burns were slightly mistimed.

Recovering the second stage is difficult because it's coming in from a much higher speed. The first stage came in doing about 2km/s. The second stage would come in doing 8km/s or more. That means 16x more kinetic energy to deal with and 64x more heating. You need a proper heat shield, not just clever engine burns. There's much less extra margin to play with as well. The second stage does most of the work but is much lighter, and one pound on the second stage is worth ten pounds on the first stage.

SpaceX definitely believes second stage recovery to be feasible at some point, but not on the current Falcon 9.

Re: SpaceX lands rocket at sea second time after satellite launch

#306

Post by jsrjenkins »

_dark_matter_ wrote: post #182
larrydag wrote: post #174

Earlier quoted context omitted.

Here's a reason why that guy answered it that way. Note these are my definitions but I've heard it before. Scientist: Studies and uncovers mysteries of the universe and natural world Engineer: Applies what scientists discovers

Eh, I think it's simpler than that: Scientist: Unknown outcome (e.g. hypothesis -> experimentation) Engineer: Known (or should be) outcome

Aristotle put it this way:

Science is the knowing of things by their causes. Science is the putting into knowledge what is in reality.

Engineering [which he would call techne, from which we get the word 'technology'] is the art of putting ideas into reality. It is putting what is in our knowledge into the real world.

Thus they are perfectly complementary things, one bringing the world into ideas, the other ideas into the world.

Re: SpaceX lands rocket at sea second time after satellite launch

#307

Post by mikeash »

mattmanser wrote: post #233
hoorayimhelping wrote: post #165

> P.S. Downvotes for this question? Really? There are always people on HN who love being contrarian and trying to diminish amazing things. It's like they hate seeing people excited for something and want to point out that this isn't that big of a deal. We're literally watching things happen for the first time ever, and this person's response is "what's so great about this?" while implying that people who are excited…

This is a new thing, 2-3 years ago downvotes were still rare, these days people treat it like reddit where it means disagree rather than inappropriate. The culture's changed.

Downvoting to express disagreement is sort of officially correct, though:

http://news.ycombinator.com/item?id=117171

Not that I agree with that at all.

Re: SpaceX lands rocket at sea second time after satellite launch

#308

Post by dzdt »

mikeash wrote: post #301
dzdt wrote: post #297

Earlier quoted context omitted.

Newton's approximation for impact depth [1] gives a way to calculate how thick the barge deck would have to be to survive a high speed impact from the rocket stage. The impactor punches through until it has displaced an equal mass. An empty F9 stage masses about 23,100kg and has a diameter of 3.66m. [2] Steel has a density around 7,700 kg/m^3. Doing the math, the deck would need to be about 29 cm thick to survive a h…

Punch through the deck . Which we already know can happen, the SES-9 landing attempt punched a nice hole in the deck. But you'd need to punch all the way through the hull to even think about sinking the barge, and of course the barge is built with compartments so even that wouldn't do it.

I expect the hull is thinner than the deck: it isn't designed to hold up to a rocket blowtorching and landing. But good point about compartments: the barge may well be able to survive a rocket-sized hole punched through it!

Re: SpaceX lands rocket at sea second time after satellite launch

#309

Post by samstave »

Can someone please explain to me how the falcon orients itself during this total process??

Does it use fins, or simply engines and whatever those little jets are that, say, the space shuttle had around its nose...

How does the falcon manage to physically orient its body?

Also, is that process completely autonomous? Is there a remote flight engineer steering this to the barge - or is it completely self-guided

Re: SpaceX lands rocket at sea second time after satellite launch

#310

Post by mikeash »

ck2 wrote: post #259
lfuller wrote: post #253

Earlier quoted context omitted.

One. They're planning on testing manned missions with their Dragon 2 and Falcon Heavy in mid-2017.

Wow are they really ready for human life onboard in a year? Unmanned failure doesn't bring much press. Kill a few people and it will set back the whole program years.

They think they will be ready.

Note that the manned Dragon has an abort capability. If the launcher blows up that doesn't necessarily spell doom for the astronauts.

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