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CRS-7 Launch Update

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Re: CRS-7 Launch Update

#71

Post by VLM »

DavidSJ wrote: post #11
VLM wrote: post #10

Earlier quoted context omitted.

WRT max-Q its a meme that won't go away because the most "interesting" thing on the public PR timelines before the incident was max-q. However dynamic pressure drops off extremely quickly due to altitude (low air pressure) and max-Q was a good while before the incident, so it wasn't a direct issue. It could obviously be an indirect issue if something started to buckle a minute previous or shook loose and for whatever…

> the space-x guys are ... very proud that they did a test flight with a separation near max-q specifically to prove it would work just fine even at max-q… The in-flight abort test for Dragon v2 is scheduled to occur later this year. It hasn't occurred yet. https://en.wikipedia.org/wiki/Dragon_V2#Flight_testing Also note that Dragon v2 was not on this mission and won't fly to space for a while. This was a Dragon v1 m…

You are completely correct that they haven't flown it. When I wrote that, I must have been thinking about the successful pad abort a couple months ago.

Re: CRS-7 Launch Update

#72

Post by 0xffff2 »

drzaiusapelord wrote: post #41
nkoren wrote: post #34

Earlier quoted context omitted.

Rocket physics are actually relatively trivial and, yes, can be fully simulated (and are). Rocket plumbing is always the hard part. Perhaps the threads on some connector got stripped as it was screwed together. Perhaps there was a manufacturing flaw or unexpected bit of corrosion in a particularly vital bolt. Perhaps a bit of contamination in a fuel line caused something catalytic to happen. Perhaps a bit of excess H…

I guess my point is, can we do a full simulation of every screw, material, plumbing, liquid dynamics, weather dynamics, etc and augment those with known fail scenarios and other fuzzy data to build out a real world KSP that predicts fails reliably? We should understand how things like corrosion and condensation work on a rocket engine. Considering the low cost of incredible amounts of CPU power, granular level simula…

>I guess my point is, can we do a full simulation of every screw, material, plumbing, liquid dynamics, weather dynamics, etc and augment those with known fail scenarios and other fuzzy data to build out a real world KSP that predicts fails reliably?

Frankly, no. You're wildly underestimating the complexity of the system.

Re: CRS-7 Launch Update

#73

Post by tbabb »

JshWright wrote: post #29
phkahler wrote: post #21

My thoughts on this. Overpressure in the LOX tank could be due to 1) failure to vent properly or 2) something heating it up. Option 1 is based on the fact that it's constantly evaporating and needs to vent. This seems really unlikely given that it passed all test on the pad 2 minutes before. It also sounds like this was likely ruled out based on Elon's tweet about a "counter intuitive cause". Option 2 sounds like fir…

There are plenty of other scenarios... The IDA is the heaviest thing they have ever carried in the trunk, AFAIK. Maybe its mounting bracket failed and it impacted the top of the second stage, buckling the LOX tank. A suddenly induced crack allowed some LOX to escape (the initial 'puff'), and the suddenly reduced pressure allowed the rest of the LOX to boil off and the tank to BLEVE, causing the catastrophic failure o…

Could the mass of the IDA have introduced unexpected lateral forces that caused the second stage to buckle like a soda can under the aerodynamic pressure? And perhaps simple crushing was the cause of the tank overpressure?

Re: CRS-7 Launch Update

#74

Post by dragonwriter »

drzaiusapelord wrote: post #32
colomon wrote: post #16

Earlier quoted context omitted.

Ugh, now imagining trying to debug a really sneaky bug that costs $100 million every time it triggers...

Stupid question perhaps, but don't we have the ability to 100% simulate the rocket physics and the code it runs on in a simulation environment? Or are they just punching out code, shoving it onto rocket controllers, and testing in the real world? I'm curious as to the QA system used here. I imagine with proper simulation this should have been catchable. I wonder if SpaceX's low cost approach means cutting certain cor…

> but don't we have the ability to 100% simulate the rocket physics and the code it runs on in a simulation environment?

No, we don't. While we can do this very well for the "high level" physics, we can't do it very well for the "low-level" physics such as -- for one example -- the detailed effects of turbulent flows (both outside of the craft and inside of the plumbing), which are usually modeled based on averages of aggregate effects and random models because a detailed deterministic model is impractical (both, IIRC, because doing so at the level we could in theory do is too computationally expensive to do in practice, and because even our theory is pretty limited when it comes to turbulence.)

> I imagine with proper simulation this should have been catchable.

Its possible that there is some level of simulation which would have caught this (we won't know unless they figure out with enough detail what the problem was), but even if it would have been possible, it may not have been cost effective.

Re: CRS-7 Launch Update

#75

Post by 0xffff2 »

Osmium wrote: post #68
grecy wrote: post #60

Earlier quoted context omitted.

If it wasn't in dragon, how was it going to get to the ISS?

Sorry, I wasn't very clear–it is in the Dragon, but it's not in the pressurised 'nose' part (which I believe is the part that's jettisoned in an emergency, but I'm not actually sure about that? perhaps I'm wrong). Instead, it was in the unpressurised 'trunk'. See this image: http://www.nasaspaceflight.com/wp-content/uploads/2014/04/Z8... "Dragon also will use its unpressurized trunk to deliver the first International…

The trunk does come with the capsule during launch abort for Dragon 2. It has fins on it to provide aerodynamic stabilization during the abort.

However, the trunk is later jettisoned, so only the capsule is recovered in the end.

http://www.spacex.com/sites/spacex/files/padabortinfographic...

Re: CRS-7 Launch Update

#76

Post by grecy »

mikeash wrote: post #64
grecy wrote: post #59

Earlier quoted context omitted.

Can Dragon 1 have parachutes?

Yes, and it does on every flight since it's used to return things from the space station back to Earth. However an abort system also needs something to move the capsule away from the (probably exploding) rocket when something goes wrong, which is typically a strong and short-firing rocket on the capsule itself. In this particular case, it sounds like Dragon survived and probably could have been recovered using the pa…

Interesting, thanks.

It would be interesting to know if they can remotely trigger the parachutes - i.e. in this case after it had fallen a ways they could have triggered them - even just to see what would happen.

Re: CRS-7 Launch Update

#77

Post by nether »

drzaiusapelord wrote: post #41
nkoren wrote: post #34

Earlier quoted context omitted.

Rocket physics are actually relatively trivial and, yes, can be fully simulated (and are). Rocket plumbing is always the hard part. Perhaps the threads on some connector got stripped as it was screwed together. Perhaps there was a manufacturing flaw or unexpected bit of corrosion in a particularly vital bolt. Perhaps a bit of contamination in a fuel line caused something catalytic to happen. Perhaps a bit of excess H…

I guess my point is, can we do a full simulation of every screw, material, plumbing, liquid dynamics, weather dynamics, etc and augment those with known fail scenarios and other fuzzy data to build out a real world KSP that predicts fails reliably? We should understand how things like corrosion and condensation work on a rocket engine. Considering the low cost of incredible amounts of CPU power, granular level simula…

no, we can't. we currently do not have the CPU power to do molecular simulations of fluids and solids (beyond the grain level) at large scales, that's why we still have supercomputers working at simplified versions. additionally, we don't have 100% fidelity in knowing environmental conditions, what the weather is doing at that exact point, the exact velocity/temp field of the atmosphere (which is constantly changing) at the molecular scale, which would be essential for a 1:1 simulation.

https://en.wikipedia.org/wiki/Direct_numerical_simulation

Re: CRS-7 Launch Update

#78

Post by mikeash »

grecy wrote: post #76
mikeash wrote: post #64

Earlier quoted context omitted.

Yes, and it does on every flight since it's used to return things from the space station back to Earth. However an abort system also needs something to move the capsule away from the (probably exploding) rocket when something goes wrong, which is typically a strong and short-firing rocket on the capsule itself. In this particular case, it sounds like Dragon survived and probably could have been recovered using the pa…

Interesting, thanks. It would be interesting to know if they can remotely trigger the parachutes - i.e. in this case after it had fallen a ways they could have triggered them - even just to see what would happen.

Yes, it seems likely that the capsule and at least some of the contents could have survived if they had opened the parachutes on descent. Of course, I don't know where it would have landed or how long it would have taken to get a ship out there or.... Anyway, I imagine it just wasn't in the plans for something like this.

Re: CRS-7 Launch Update

#79

Post by emp_zealoth »

JshWright wrote: post #29
phkahler wrote: post #21

My thoughts on this. Overpressure in the LOX tank could be due to 1) failure to vent properly or 2) something heating it up. Option 1 is based on the fact that it's constantly evaporating and needs to vent. This seems really unlikely given that it passed all test on the pad 2 minutes before. It also sounds like this was likely ruled out based on Elon's tweet about a "counter intuitive cause". Option 2 sounds like fir…

There are plenty of other scenarios... The IDA is the heaviest thing they have ever carried in the trunk, AFAIK. Maybe its mounting bracket failed and it impacted the top of the second stage, buckling the LOX tank. A suddenly induced crack allowed some LOX to escape (the initial 'puff'), and the suddenly reduced pressure allowed the rest of the LOX to boil off and the tank to BLEVE, causing the catastrophic failure o…

I can see why you would say BLEVE. But I'm quite curious why there wasn't a huge fireball, at any rate

Re: CRS-7 Launch Update

#80

Post by dlgeek »

imglorp wrote: post #46
dlgeek wrote: post #7

Earlier quoted context omitted.

The manned capsule has a powered abort system, and this one doesn't, so they really don't need to suggest anything (since a failure here would not be reflective of the surviviability of Dragon2). They intentionally disable ("safe") the parachute system during the launch phase, but from the rumors I'm hearing coming out of SpaceX, if they had been enabled, this capsule would have survived.

Maybe all the cargo shots should have these systems enabled to further exercise them. It would have been nice to demonstrate capsule survival in yesterday's event.

Sorry (there was some confusion below):

Dragon 2 has a powered escape system. Dragon 1 just has parachutes for the recovery phase.

You safe the parachutes for the ascent phase because they're dangerous. If they accidentally trigger, you lose the whole rocket due to structural failure from the sudden forces. You'd most likely lose the capsule/chute at this point too.

A chance of recovering the cargo in the event of an incident like this just isn't considered worth it.

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