SpaceX Dragon CRS-6 Launch Webcast • Hacker News Board

Re: SpaceX Dragon CRS-6 Launch Webcast

#101

Post by david-given » Tue, Apr 14, 2015, 9:51 PM UTC

delibes wrote: post #31

I never watched one of these before ... T+13 shows Dragon deploying solar panels (really should to be called 'wings' I think). I think a second stage camera shows the Dragon with a some fairing panel spinning away from it. This is amazing!

They also have a camera inside the liquid oxygen tank. You can see it drain away as the second stage engine runs... and then it cuts off. What do you think happens to the remaining fuel? What happens is that it's awesome.

https://www.youtube.com/watch?v=u656se4e34M

And here's extended video of the last section (I think from a different launch):

https://www.youtube.com/watch?v=8HZrrHI34x4

Re: SpaceX Dragon CRS-6 Launch Webcast

#102

Post by Crito » Tue, Apr 14, 2015, 9:52 PM UTC

erobbins wrote: post #93

dandelany wrote: post #55

Earlier quoted context omitted.

> That stage 2 engine nozzle really glows hot! Yes! Amazingly, although the nozzle looks just like a bell-shaped piece of sheet metal, it in fact uses "regenerative cooling" which means the nozzle is full of small pipes which wind back and forth like a radiator. The rocket fuel is passed through these pipes before combustion, resulting in a heat exchange which is doubly beneficial, keeping the nozzle (relatively) coo…

I thought the 2nd stage engine's nozzle extension was radiatively cooled? First stage engines are regen for sure.

Merlin 1C Vacuum had a regeneratively cooled combustion chamber but radiatively cooled expansion nozzle. I'm not sure if Merlin 1D Vacuum differs from this though.

Re: SpaceX Dragon CRS-6 Launch Webcast

#103

Post by Already__Taken » Tue, Apr 14, 2015, 9:54 PM UTC

swamp40 wrote: post #92

david-given wrote: post #65

Earlier quoted context omitted.

Scott Manley did precisely this in KSP the other day, trying to replicate the barge landing: https://www.youtube.com/watch?v=C9I55o8hQgs Admittedly, he also replicated all the other possible failure modes too. Turns out landing on barges is hard.

I wonder how much of the rocket is steel? Perhaps a barge full of Tesla batteries and electromagnets could grab and hold it as it comes in?

If that's the idea then just land it into a big sunken tube filled with netting.

Re: SpaceX Dragon CRS-6 Launch Webcast

#104

Post by TeMPOraL » Tue, Apr 14, 2015, 9:54 PM UTC

david-given wrote: post #68

sounds wrote: post #62

Earlier quoted context omitted.

Just wild guesses here but anyone who has played Kerbal Space Program knows that while docking is no piece of cake, it happens slowly and you can back off and try again until you run out of fuel. Landing on a moving target shouldn't be that hard except you get (almost) zero weight budget, you're relying on atmospheric braking which means intense heat, and at the end you're hoping the engine doesn't malfunction. In ca…

In addition, even one engine on the F9 first stage, throttled down to its minimum, generates way too much thrust for the vehicle to do a gentle landing. They have to do a suicide burn --- they fall towards the launchpad unpowered and then at the last possible moment light up the engine, and hope that when they come to a halt they've landed. There is no margin for error. KSP doesn't really have an equivalent, but you…

> KSP doesn't really have an equivalent, but you can compare it to trying to land on the moon using a solid rocket fuel engine. (The difference with SpaceX is that at least they can turn it off.)

Minmus suicide burn with a Mainsail could probably compare.

Re: SpaceX Dragon CRS-6 Launch Webcast

#105

Post by david-given » Tue, Apr 14, 2015, 9:58 PM UTC

ufmace wrote: post #94

mikeash wrote: post #78

Earlier quoted context omitted.

From what I understand, the reason they don't show it live is because they don't have enough bandwidth to transmit live video from the barge. They get a frame every second or two, and lots of telemetry, but not video.

Which is probably because they don't want to show it live. If they wanted to, I'm sure they could find a way to get enough bandwidth to it. Their PR is very well-run, and not only will they not show a live video for something that they aren't sure is going to go right, they'll also have a plausible technical excuse for why they can't do it. Not that I have anything against running your PR well, just admiring it.

In the early launches, whenever something went wrong the stream would be cut off instantly --- sometimes they'd even leave the connection open but just stop sending frames, which made my video player very sad.

I sympathise: they don't want to be associated with failure. But on the other hand, there were an awful lot of people, including me, who would have been utterly fascinated to see a first-hand view of the failure modes.

I'd still love to see the crash footage.

Re: SpaceX Dragon CRS-6 Launch Webcast

#106

Post by justin66 » Tue, Apr 14, 2015, 10:04 PM UTC

lutorm wrote: post #100

justin66 wrote: post #87

Earlier quoted context omitted.

> Being fired for low performance is okay The problem is that companies following the "fire at least 10% every year in every department" Jack Welch philosophy tend to let some good people go. It's a management philosophy that just assumes that there's no such thing as a really good team, full of worthwhile players. Its an attitude that works better in professional sports, where hyper-competitiveness is more often an…

It's not appropriate for me to comment on company HR policy. All I'm going to say is that my impression of the atmosphere on the software team is not at all "a bunch of coworkers trying to outdo one another to make the cut".

lutorm, I should have put a disclaimer in there. I know nothing about SpaceX policy and so I wasn't trying to cast any aspersions. (and frankly, the 3% figure VieElm mentioned sounds more like attrition than Neutron Jack policy)

Re: SpaceX Dragon CRS-6 Launch Webcast

#107

Post by david-given » Tue, Apr 14, 2015, 10:05 PM UTC

fit2rule wrote: post #84

I have an idea for how to improve the landing of the rocket stage: instead of fold-out landing-legs, why not fold-out wings ? Or, a combination of both - legs with wing-like features - they function as wings until close to touch-down and then feather to support the rocket laterally upon landing?

They'd be on the wrong end of the rocket. The centre of mass is close to the engines, but not that close; the landing legs have to go at the bottom for obvious reasons, but any aerodynamic surfaces have to go near the vehicle's stern, as it moves through the air. Since it's descending vertically, this means the top. This is what the pop-out grid fins way up are for.

Fun fact: if the F9 first stage had traditional fins at the bottom, they wouldn't be able to do this. The vehicle would tumble in the upper atmosphere and end up either nosediving into the ground or breaking up.

Don't believe me? Go get the KSP demo and try it for yourself! The demo is pretty ancient, but it is free: https://kerbalspaceprogram.com/demo.php

Re: SpaceX Dragon CRS-6 Launch Webcast

#108

Post by TeMPOraL » Tue, Apr 14, 2015, 10:06 PM UTC

tsotha wrote: post #97

smeyer wrote: post #83

Earlier quoted context omitted.

Presumably they've tried to estimate that probability and factored it into the 20% probability of not succeeding. (I don't know though, since I haven't seen the calculation.)

Still... you can't assign a probability to something that is, by definition, unknown. "This is just a complete guess..."

But you shouldn't also pretend you have zero information. They hit the barge last time, engineering principles are sound, so those two things alone give you an estimate of "quite likely". Yes, 80% is kind of arbitrary, but it tells you the same story as "quite likely" with an added benefit of being able to plug it into some math that will yield you better results than going with just words.

See "If It’s Worth Doing, It’s Worth Doing With Made-Up Statistics": http://slatestarcodex.com/2013/05/02/if-its-worth-doing-its-....

Re: SpaceX Dragon CRS-6 Launch Webcast

#109

Post by higherpurpose » Tue, Apr 14, 2015, 10:07 PM UTC

tsotha wrote: post #81

baq wrote: post #51

Earlier quoted context omitted.

the original, yes. now they've got experience and say they've got 80% odds for landing one first stage by the end of the year.

How can that make sense? Until they actually get a successful landing they can't be sure they don't have a problem that causes a failure 100% of the time.

I think he's referring to the fact that every time they do one of these they have more experience with everything, therefore with each new launch the chance of failure should be reduced. He said there will be more than one launches until the end of the year. So by then, the chance of success should rise to 80%.

Re: SpaceX Dragon CRS-6 Launch Webcast

#110

Post by ChuckMcM » Tue, Apr 14, 2015, 10:43 PM UTC

michaelmcmillan wrote: post #35

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

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.