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The accident investigation team concluded that one of the three composite overwrapped pressure vessels (COPVs) inside the second stage liquid oxygen (LOX) tank
by hoorayimhelping 10y ago
The accident investigation team concluded that one of the three composite overwrapped pressure vessels (COPVs) inside the second stage liquid oxygen (LOX) tank failed. Specifically, the failure was likely due to the accumulation of oxygen between the COPV liner and overwrap in a void or a buckle in the liner, leading to ignition and the subsequent failure of the COPV.
The investigation team identified several credible causes for the COPV failure, all of which involve accumulation of super chilled LOX or SOX in buckles under the overwrap. The corrective actions address all credible causes and focus on changes which avoid the conditions that led to these credible causes. In the short term, this entails changing the COPV configuration to allow warmer temperature helium to be loaded, as well as returning helium loading operations to a prior flight proven configuration based on operations used in over 700 successful COPV loads. In the long term, SpaceX will implement design changes to the COPVs to prevent buckles altogether, which will allow for faster loading operations.
SpaceX is targeting return to flight from Vandenberg's Space Launch Complex 4E (SLC-4E) with the Iridium NEXT launch on January 8.
Are COPVs a universal thing in rocketry? Or has SpaceX actually loaded fuel into its rockets over 700 times?
- schiffern 10y agoIt's true that COPVs are rather common in aerospace (being the lightest pressure tank technology available). > Or has SpaceX actually loaded fuel into its rockets over 700 times? This. SpaceX has done development test cycles, and for each launch performs stage acceptance tests at McGregor Texas and both "wet dress rehearsals" (now generally skipped) and static fires at their launch pads. All of these operations involve loading and unloading helium and LOX.
- deleted 10y ago[deleted]
- astrodust 10y agoGiven the nature of carbon-fiber composite manufacturing where it's usually applied in layers, is the risk of a tiny bubble a lot higher when it's subjected to repeated heating/cooling cycles?
- apendleton 10y agoNot 100% sure, but each stage has multiple COPVs and there are two stages per vehicle, plus each vehicle is loaded multiple times (minimum two, for the static fire and the actual launch, and possibly more than that), so 700 occurrences of an individual COPV being loaded over the history of SpaceX (with ~30 total launches) is not totally ridiculous.
- mikeash 10y agoI believe it's a minimum of 3 loads per vehicle, as they're also tested at McGregor, Texas before being shipped to the launch site. Launch scrubs after propellant loading would add more, as would R&D testing. They've done almost 30 Falcon 9 launches now. If there are 4 per vehicle and 3 loads per launch, that's about 360 loads just from that.
- bewaretheirs 10y agoThe design which failed in September has three COPVs just in the second stage LOX tank - for a picture, see http://spaceflight101.com/falcon-9-amos-6/wp-content/uploads/sites/104/2016/09/9420707_orig.jpg; http://spaceflight101.com/falcon-9-amos-6/wp-content/uploads... there are additional helium COPVs in the (much larger) first stage LOX tank.
- dgritsko 10y agoLink not working, FYI.
- mikeash 10y agoAh, I just assumed it was 3 in S1 (as mentioned in another comment) and 1 in S1 (pulled out of my rear). If it's 6 per vehicle, that would mean at least 540 fills, not counting scrubs and R&D tests. For the broken link, there's just a stray semicolon at the end. Working version: http://spaceflight101.com/falcon-9-amos-6/wp-content/uploads/sites/104/2016/09/9420707_orig.jpg http://spaceflight101.com/falcon-9-amos-6/wp-content/uploads...
- JshWright 10y ago
- lmm 10y agoIf there are 3 in the first stage alone, and they static fire the stages before launching, I can see that adding up.
- Symmetry 10y agoSome sort of gas injection system is essentially universal in rocketry since you need something to maintain tank pressure as you use the fuel in the tank. The helium vessels aren't always COPVs, sometimes it comes from outside the tank, and some rockets use something called autogenous pressurization where propellant is heated to gas to take up that extra space. And some rockets manage without pressurization entirely though I believe only very low performance ones. SpaceX hasn't flow anywhere close to 700 flights but a lot of testing would involve fuel loading so the 700 figure sounds high but not unreasonably high to me.