SpaceX Moves Past Explosion With New Launch Plans (cnn.com)

SpaceX plans to resume launching rockets as soon as next week, after completing an investigation into a spectacular launch pad explosion that destroyed a rocket and a satellite in September. From a report on CNN: The news comes following an in-depth investigation into the explosion of a rocket from SpaceX's September mission. The company said in a statement Monday the botched launch was due to a failed pressure vessel in a liquid oxygen tank. The vessel buckled, causing liquid oxygen to accumulate. It believes this led to friction, sparks and the explosion. SpaceX conducted the investigation along with officials from NASA, the Federal Aviation Authority, the U.S. Air Force and the National Transportation Safety Board. The Federal Aviation Administration will have to sign off on the report and issue SpaceX a license to launch. SpaceX appears optimistic it will be launching rockets again soon.

Comments

Re:Hope this is true

[Anonymous Coward]

Challenger was launched right before Reagan's SOTA address, which was a massive scheduling fuckup right there. Obviously in those circumstances there would be high-level pressure not to delay the launch, and that was confirmed during the post-crash investigation.

Would be nice...

[Rei]

... to actually get to see a detailed breakdown of the cause of the last explosion, rather than having to piece it together from bits and pieces of what's been said so far.

So far, it seems that there was (expected) supercooled liquid oxygen seeped into the CF reinforcing fibers on the helium COPVs (as was expected), which was just above its freezing point. They then began loading cold helium. Had the oxygen stayed liquid, it would have squeezed out (expected behavior). Rather, the oxygen wasn't able to seep out fast enough, and the increasing pressure caused some of it to solidify, blocking the escape of oxygen from the CF. LOX is inherently unstable in contact with organics, including carbon fibre, and can detonate under high temperatures, high pressures, shocks, etc; it has to be handled gingerly. In this case, the pressure continued to rise as the COPVs filled, until the LOX reached a critical pressure and detonated - thus rupturing the COPV reinforcement, thus the COPVs, thus the second stage and destroying the vehicle.

That's what it sounds like happened. But it'd be nice to get that confirmed or corrected if inaccurate. If this is correct, there's a number of things they could do to remedy it; I'd think the most likely would be to fill the COPVs before loading LOX.

As a side note, I'm really uncomfortable with their plan to make IPS entirely out of carbon fibre. As they're finding out (and has others have found out in the past), it's really difficult to use LOX with composites. And perhaps most importantly, inconsistently difficult. And the failure modes can be catastrophic - instant explosive rupture at the point of failure. Aluminum is not only light, but (by pure coincidence) one of the easiest things to work with LOX, as the oxide layer does a good job protecting the metal (even still, aluminum can detonate in contact with LOX in the right temperature/pressure/shock conditions, but said explosions are only self-propagating under significantly elevated pressure conditions). Also coincidentally, aluminum-lithium is even more resistant to reaction with LOX than lithium-free aluminum alloys. Basically, rocket manufacturers have been "having it easy" working with LOX by virtue of making rockets out of aluminum. You give that up when you go to composites.

But.... it's their rocket company, I guess we'll see how it goes.

Re:Would be nice...

[Rei]

Indeed, and sometimes COPVs designed for other uses have various outer linings or coatings to protect the CF. But this comes with mass penalities. And rocket engineers are anything if not focused on not including any mass that they don't feel that they absolutely have to. And remember, SpaceX had no problem with their COPVs exploding prior to this one event; none of their testing had previously induced an explosion. So it's understandable that they'd have felt that it was fine. But LOX can be a harsh mistress. Not as unpredictable as, say, H2O2, mind you. But reading through past LOX incidents can be enlightening. For example, the Bell X1-D - it ultimately turned out to be that the gaskets had been treated with a softener, and that softener got into the LOX tank - and as soon as the tank started pressurizing, they hit LOX's critical pressure with the chemical and it detonated.

It's worth noting that the prototype ITS LOX tank that they made (also CF) is linerless. No coatings at all, just bare CF. Now, that's a different situation, it's not part of a helium COPV and thus not subject to the exact same failure scenario. But one doesn't have to wrack their brain too hard to come up with other failure scenarios related to transient impact, friction, general heat, bending or shock (all things that can set off LOX reactions). With aluminum, LOX reactions require fairly severe conditions, and generally self extinguish. With CF, that's not the case.

But perhaps I'm too much of a pessimist. I really want SpaceX to prove me wrong here and show that you can make safe, reliable LOX tanks out of CF :)

Re:Would be nice...

[Bruce Perens]

Of course, oxygen is neither "unstable" nor "explosive".

Every year or so, I stand on Pad 34 and someone tells the story of Apollo 1. I remember the day it happened, too. It's one every engineer should hear.