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It's surprising how much of a disruption this caused to their launch schedule, but it's great that they got to the bottom of the issue before repeating the proc
by brianshaler 10y ago
It's surprising how much of a disruption this caused to their launch schedule, but it's great that they got to the bottom of the issue before repeating the process on any further rockets.
The worst kind of bug is the intermittent one that you can't reproduce or see in logs. With only 35-55 milliseconds of metrics leading up to the event and nearly obliterated evidence, it seemed nearly impossible they would be able to nail down the exact cause.
Critics have pointed out risks in SpaceX's method of loading supercooled fuel. Accidentally forming solid oxygen around carbon fibers from a buckling overwrap is an example of this.
There are benefits, but they will need to find and prevent all these possible edge cases exposed by the new method.
- phkahler 10y agoI find the whole idea of carbon fiber inside a pressurized LOX contain a bit risky. Also, what about all those reports that we're running out of helium? Is that credible threat to ongoing space flight?
- Pharylon 10y agoWe're not really running out, it's just getting more expensive because the government doesn't regulate it's availability anymore since the strategic helium reserve was done away with. It won't be a big deal for (already expensive) rocketry. Buying helium balloons for your birthday will be pricey, though.
- kobeya 10y agoUm, no. We are in fact running out of helium. There's only a certain mount and nobody not even natural processes is making anymore in any significant quantity. And what we do have is rapidly being released into the atmosphere and escaping into space. And given that the nearest natural source of helium is Jupiter, that is a little concerning.
- greglindahl 10y agoNew helium is generated by alpha decay, and it comes up in natural gas wells that happen to be located in areas with natural radioactivity.
- mikeash 10y agoNot much, though. A quick perusal of Wikipedia (buyer beware, etc.) indicates that about 3,000 tons of helium are generated per year through radioactive decay (that's all happening in assorted rocks throughout the Earth's crust, so much of it wouldn't be easy to recover, either) while current production rates are around 9,000 tons per year.
- greglindahl 10y agoA natural gas well has 10s of millions of years of helium accumulation from its local area.
- mikeash 10y agoRight, which means that while it's renewable over geological timescales, it's more or less a fixed reserve in human timescales. Much like oil.
- kobeya 10y agoAvogadro's number is very big: 6e22.
- digerata 10y agoI believe that it's very likely that SpaceX can recover the helium used during operation. The helium isn't expelled from the fuel tanks. Since the 1st stage returns, it could be recovered.
- extrapickles 10y agoIts more of we are running out of cheap helium as the US has been selling off its massive stockpile and its nearly depleted.
- gpm 10y agoThe cost of the physical helium in rocketry is going to remain negligible for a long time. The total cost of materials in a modern rocket is something like 1/2 of a percent of the cost of a launch, and I'm confident saying Helium is a tiny fraction of that. It doesn't matter if it goes up in price by a few orders of magnitudes. We are also still producing it in large quantities (natural gas often contains a lot of helium, which we extract). Rocket's also use a tiny amount of helium percentage wise, simply because there are so few rocket launches. However even if we did somehow run out of Helium entirely, once SpaceX switches to Methane fuel (as they plan to do for the ITS) they won't need it anymore. Currently it's used to pressurize the tanks, but Methane does that for itself. It would mean speeding up development of 'small' methane launch vehicles presumably, but that's it.
- mikeash 10y agoI imagine that there are other ways to accomplish the same goal, as well, such as using other noble gasses. Helium provides the best cost/benefit tradeoff but surely other approaches would be practical if helium becomes unavailable.
- wildcat55 10y agoHow would you pressurize the liquid oxygen needed for the methane to burn? Per the other comment, no other noble gas has a low enough boiling point to remain a gas at LOX temperatures...
- Symmetry 10y agoIf you need to you can heat up the oxygen to increase it's volume until the pressure is correct. I forget the reason that it's easier to do with methane than oxygen but it's possible to do with oxygen too if you really need to. ULA's new ACES upper stage is planned to use autogenous pressurization for both it's oxygen and hydrogen tanks.
- ghostly_s 10y agoHow does the gas get into this void between liner and overwrap? I presume the liner is meant to be impermeable? Or is it only impermeable when properly backed with the overwrap?
- tsuraan 10y agoThe helium COPV is submerged in LO2, so it's the oxygen that's soaking into the wrapping. I think the failure is that the oxygen is soaking into the wrapping before the helium is fully pressurized, and then the metal container expands slightly and crushes the oxygen that soaked in between the metal vessel and the carbon wrapping.
- mikeash 10y agoThis "anomaly" caused hundreds of millions of dollars in losses, and was an unprecedented failure mode. It doesn't surprise me at all that it disrupted the launch schedule for the better part of a year (edit: actually the lesser part of a year, about four months total if they launch soon). If they manage to return to flight this month, it strikes me as rather quick. I wonder if supercooled propellants are really worth it. It seems like a huge risk in exchange for a small performance increase. Hopefully this will be the last vehicle loss they suffer from it.
- andars 10y ago"small performance increase" FT can get 30% more mass to LEO. That is a pretty big performance increase, especially considering that it enables SpaceX to carry the maximum payload of v1.1 in expendable configuration and still land the FT rocket. Even if we assume that half of that performance boost came from the other improvements, 15% is a significant increase.
- ansible 10y agoThat's the seductive side of design tradeoffs with rockets. Shaving just a little weight (especially on the 2nd stage) or squeezing out just a little more performance can have dramatic differences in mass to LEO. The question is how much this will increase overall operational cost. Up until this year or so, it has seemed that SpaceX has been willing to compromise on performance to get lower overall operational cost and reliability. I'm a bit worried that they've started to go the other way with some of the improvements they've made this year.
- krastanov 10y agoIt disrupted the schedule for 3 months, not for "the better part of a year". Otherwise you are making a fair point (but SpaceX seem to believe that it is worth it and that they will iteratively fix all these issues without losing customer trust).
- mikeash 10y agoHuh, I was sure it was in June. Actually September 1st. I guess it just feels longer to me. Thanks for pointing that out.
- asmithmd1 10y agoTo really be sure they got to the bottom of the issue and are not seeing an intermittent issue they should duplicate the failure, but it may not be possible to do this safely. I detect a little bit of hand waving around the source of ignition: "breaking fibers or friction can ignite the oxygen in the overwrap" I would like to see at least this ignition source duplicated.
- ghshephard 10y agoI also found it a little surprising with so much involved that they didn't take the effort to reproduce the failure case, perhaps doing so on a smaller scale than a full vehicle launch if possible.
- snrplfth 10y agoThe problem is that accurately reproducing this failure case is very difficult. You need to replicate the thermal properties of the loading process and the tanks, at the same speed with the same amounts of propellant and helium, effectively meaning that you have to do it with a full-size tank, and with a large amount of pad equipment. This is all extremely dangerous and almost certainly will result, if successful, in the loss of the testing stand.
- lutorm 10y agoIt doesn't specify whether the mechanism proposed to have caused this particular anomaly has been experimentally verified to be able to cause ignition but, even if it had, it would still not prove it was the mechanism that was at work in this particular instance.
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- asmithmd1 10y agoYes, proposing a theory and reproducing a result experimentally doesn't prove anything - but it is the basis of all science.