CRS-7 Launch Update • Hacker News Board

Re: CRS-7 Launch Update

#81

Post by JshWright » Mon, Jun 29, 2015, 11:47 PM UTC

emp_zealoth wrote: post #79

JshWright wrote: post #29

Earlier quoted context omitted.

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

Oxygen by itself doesn't burn. If it was just the LOX tank that burst, there wouldn't have been anything to burn. Clearly some sort of FTS destroyed the vehicle (I don't think atmospheric forces could have taken it apart that cleanly and instantaneously), but the FTS system is probably just detcord running down the length of the propellant tanks. If the tanks were 'unzipped' quickly enough, the fuel and oxygen might not have had time to mix to a stoichiometric ratio that supported combustion.

Looking back at a gif of the incident, there was a pretty impressive amount of fire. Initially when the oxygen hit the first stage exhaust, causing the unburnt RP1 to burn (all the 'extra' flame that appears in the exhaust plume), and then there is a fair amount of fire at the front of the vehicle a second or two later (I assume the second stage RP1 tank failed at that point). Finally there is a large cloud and the rocket vanishes. That's the part that I assume is some sort of FTS, and likely blew the rocket apart with enough force that the prop didn't get a chance to mix.

Re: CRS-7 Launch Update

#82

Post by ethbro » Tue, Jun 30, 2015, 1:52 PM UTC

HCIdivision17 wrote: post #65

drzaiusapelord wrote: post #41

Earlier quoted context omitted.

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 think a critical part of his point is that what you build and what you model are neccessarily two different things. You can totally simulate it, and then when the rocket inevitably fails, you can go "aha! This bit deviated from the simulation!" But you can't feed that forward beforehand to prevent the failure, since you can't expect random acts of poor workmanship or crafting. You can only prepare and hope (and you…

This.

Engineering is what hopefully guides reality up the correct branch of a theoretically possible tree.

You can simulate most of each one of those branches. But what are you going to do with a million simulation results? How does that guide your course of action? What do you do differently?

If this was an engineering or assembly defect, the answer is always going to be "Don't do that next time." If it was a design defect, then the part wasn't simulated (unlikely) or our understanding of how it operated in this design was incomplete (more likely).

The trick with rocket science is that the design tolerances are by necessity very tight. Physics dictates this with chemical propulsion. Every part you over-engineer in a weight-increasing way decreases the weight available for payload. And there isn't very much weight there to start with...

Re: CRS-7 Launch Update

#83

Post by kabdib » Sat, Jul 04, 2015, 5:00 AM UTC

kabdib wrote: post #20

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...

I recommend Henry S.F. Cooper's book _The Morning Star_, which is about debugging hardware failures and OS race conditions on a spacecraft orbiting Venus. (There are similar stories about debugging stuff on the various Martian rovers, but Cooper's book is a very good treatment...).

I stand corrected. Written in haste.

Cooper is a wonderful writer, I've got all of his books :-)