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Space

SpaceX Blast Investigation Suggests Breach in Oxygen Tank's Helium System (reuters.com) 79

Posted by msmash from the take-note dept.
Weeks after a SpaceX rocket exploded inexplicably, engineers at Elon Musk's company have traced the flaw to its source. Space today released the initial results of its investigation, in which it says that a breach in helium system in the Falcon 9's liquid oxygen system caused the sudden flare up. From a Reuters report: SpaceX, owned and operated by technology entrepreneur Elon Musk, was fueling a Falcon 9 rocket on the launch pad in Florida on Sept. 1 in preparation for a routine test-firing when a bright fireball suddenly emerged around the rocket's upper stage. "At this stage of the investigation, preliminary review of the data and debris suggests that a large breach in the cryogenic helium system of the second stage liquid oxygen tank took place," SpaceX said in a statement posted on its website. No one was hurt in the explosion, which could be heard 30 miles (48 km) away from SpaceX's launch pad 40 at Cape Canaveral Air Force Station. The cause of the accident is under investigation.
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SpaceX Blast Investigation Suggests Breach in Oxygen Tank's Helium System More

SpaceX Blast Investigation Suggests Breach in Oxygen Tank's Helium System

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  • Huh. (Score:3)

    by Ecuador ( 740021 ) on Friday September 23, 2016 @03:50PM (#52949229) Homepage

    Huh, that doesn't say much, it is only the location of the problem, not the cause. So they say they currently don't have an explanation for the breach but are "investigating a range of possibilities". Is it me or does it look like they are looking into things like projectiles fired towards the rocket?

    • Nope. Putting bits back together after a violent explosion is hard.
      Some parts of the jigsaw will have simply burned away, others will never be found.
      This is a first step in finding "what"...by finding "where".
      Once you've got where, then what, off we go to "why"...

    • I think it's you

    • Re: (Score:1)

      by Anonymous Coward

      Who knew helium is flammable?

    • Helium cooling for liquid hydrogen fuel? Why does this sound so old school rocketry to me? My Estes solid fuel rockets sound more advanced, and I did that in the 1960s.

      This is really the best SpaceX can do? I love rockets, I have loved space exploration since I was a kid back in the 60s, but I just don't see Elon Musk as the right way to stellar exploration. It seems like the oligarchy's means to the stars, not something for everyone like the Apollo program.

      If we are going to put a national effort into goin

      • Why does this sound so old school rocketry to me? My Estes solid fuel rockets sound more advanced, and I did that in the 1960s.

        This is pretty funny. Of course SpaceX is more sophisticated than Vernon Estes and his toy rockets.

        The helium is for pressurizing the tank so that the turbopump can receive fuel at a very high volume. In addition, ullage motors cause a small G force on the rocket before the main engine activates in microgravity, so that the fuel or LOX rather than the helium is at the bottom of the

      • SpaceX doesn't use liquid hydrogen fuel

        There are multiple private venture rocket companies, including the very successful ULA. The reality is there is a large and growing market for commercial satellite launches. I think that is fantastic.

      • Is your sig from first hand experience or what?

        Hydrogen wasn't even mentioned in TFS, in fact it says 2 or more times the helium was for cooling OXYGEN.

        Furthermore, if you do any half assed research you would know that the engines run on RP-1, which is basically kerosene, also known in generally similar chemical compositions with minor additive changes as jet fuel, and #1 diesel fuel. Much more energy dense than hydrogen as a fuel.

        • Re:Huh. (Score:5, Interesting)

          by Rei ( 128717 ) on Friday September 23, 2016 @09:47PM (#52951237) Homepage

          The helium isn't used for cooling; it's a pressurant. It's lower mass to make a small COPV and have that store your pressurant in it than to have the whole LOX tank be strong enough to withstand the pressure.

          It's always bothered me, the concept of having a COPV sitting around in LOX, though. Ignoring the thermal cycling, LOX and epoxy aren't exactly fast friends. We don't make LOX tanks out of composites because composites tend to become impact sensitive in LOX (there've been some attempts, but it's still an active reseach field, not a "solved problem"). Not sure there's that much difference between making your whole tank out of composites vs. having a composite tank inside of one. I don't know what SpaceX does, if anything, to try to protect them, but the general concept has always concerned me.

      • Well.. feel free to start your own space-company based on your superior technology! ;-)

    • No conspiracy here. The conspiracy folks can go over to here [af.mil] and figure out why the base is now fighting its third fire in a week.

    • Jeff Bezos was in Seattle at the time...
    • Its just you.

  • Hindiburg all over again (Score:1, Funny)

    by Anonymous Coward

    Shoulda used hydrogen, which won't, explode because it's mostly, water.

  • "...the cryogenic helium system of the second stage liquid oxygen tank..." makes it sound like they use liquid helium to refrigerate the LOX. Is that really how it works?

    • Re:Am I reading this right? (Score:5, Informative)

      by Ellis D. Tripp ( 755736 ) on Friday September 23, 2016 @03:58PM (#52949297) Homepage

      I would ASSume that the helium is used to pressurize the fuel and oxidizer tanks. Would be stored as a liquid to save space...

      • Re: (Score:2)

        by Rei ( 128717 )

        It's not stored as a liquid, but as a compressed gas in a composite overwrapped pressure vessel (COPV) located inside the LOX tank. And yes, it is used as a pressurant.

    • Re: (Score:1)

      by Anonymous Coward

      They use helium to pressurize LOX and keep the LOX flowing as its exhausted.

    • Re: Am I reading this right? (Score:1)

      by Anonymous Coward

      Helium is used to fill the space in the LOX tank as the LOX is consumed during launch.

    • Re:Am I reading this right? (Score:5, Informative)

      by Mysticalfruit ( 533341 ) on Friday September 23, 2016 @04:01PM (#52949325) Homepage Journal
      No. The helium is used to pressurize the liquid oxygen tank and provide back pressure to the engines. Basically it's the gas that's used to shove the LOX down the fuel lines to the engines as fast as possible.

      Also when you're listening to the com loop when you hear "Engine chilldown has begun, they're pumping through the engine.

      The prior mishap was caused by one of the struts that holds these tanks to the inner walls failing.
      This failure was caused by the tank itself bursting.

      I'm suspecting they're going to have to reengineer the COPV helium tanks to be a bit tougher.

    • Re: (Score:1)

      by Altanar ( 56809 )
      They use the helium to pressurize the oxygen tank. In low gravity with no engines ignited, the liquid oxygen just sloshes around, floating everywhere. They need the liquid oxygen to be at the back of the tank in order to reignite the engine for later burns. Having the tank pressurized with helium pushes the liquid oxygen down to the back.

      • Re:Am I reading this right? (Score:5, Informative)

        by Arnold Reinhold ( 539934 ) on Friday September 23, 2016 @04:31PM (#52949515) Homepage
        That's not quite how it works. In zero g, just adding Helium pressure to a tank won't accomplish much. You either have to use some kind of pressurized bladder to force the liquid down (ok for thrusters, too big a weight penalty for the main engine fuel and oxidizer) or supply a small acceleration, say from auxiliary thrusters, to settle the liquid to the bottom of the tank prior to ignition. Then He pressure can push the liquid into the main pumps which, in turn, provide enough pressure to force the liquid into the engine against its internal pressure.

        • That's not quite how it works. In zero g, just adding Helium pressure to a tank won't accomplish much. You either have to use some kind of pressurized bladder to force the liquid down (ok for thrusters, too big a weight penalty for the main engine fuel and oxidizer) or supply a small acceleration, say from auxiliary thrusters, to settle the liquid to the bottom of the tank prior to ignition. Then He pressure can push the liquid into the main pumps which, in turn, provide enough pressure to force the liquid into the engine against its internal pressure.

          Ullage motors are used to force the propellants to the bottom of the tank...mostly

          • Re: (Score:3)

            by AaronW ( 33736 )

            Wikipedia [wikipedia.org] has a good description of Ullage motors. Basically they provide a small thrust to force the liquid fuel to the aft portion of the tank prior to firing the main engine to prevent bubbles in the supply.

    • No, the liquid Oxygen is delivered as liquid on trucks, and stored in large tanks at the pad as liquid. The Helium would be cooled to LOX temperature by virtue of being inside a tank full of the stuff. This would lower the pressure of the stored helium, allowing you to put more in the tank, but it's not cold enough to liquefy.

      One possible failure mode is something preventing the Helium from cooling down, in which case it could overpressure the tank and it blows up. That could be a problem with getting th

      • Re: (Score:2)

        by Rei ( 128717 )

        The weird thing, if it is the COPVs, is... there was so much attention focused on them after CRS-7. It'd be weird if this was the cause. And extremely frustrating, too, as they're not manufactured in-house. SpaceX surely tests the tanks, so they too would bear some responsibility for it getting past their test procedures, if this is the cause. Personally (as I mentioned elsewhere in the comments), having a composite vessel sitting in liquid oxygen always strikes me as a dangerous situation to begin wit

        • if we were good at maintaining LOX-composite compatibility, we'd be making the stages themselves out of composites rather than aluminum.

          I get that LOX plus composites are an un-good mix. But even with passivation, are aluminium and LOX really that much better? There's still a nerve-twanging amount of free energy in there.

  • It was a fire that spread really really quickly.

    • Re: (Score:2)

      by tomhath ( 637240 )
      ...and caused a Rapid Unscheduled Disassembly (TM) of the rocket.
    • Yes, yes, we all learned the difference between deflagration and detonation the first time we blew up the school chemistry lab. It is, after all, one of the prime purposes of chemistry labs.
  • Good news is that it was not a fault of the ground system and the launch pad so launching from Pad 39 where the falcon heavy is supposed to launch from is an option. The bad news is that it's a second stage issue with the falcon rocket again. This second mishap will make it much harder to qualify the rocket for manned NASA missions and for critical payload Air Force missions.

    • Re: (Score:1)

      by Anonymous Coward

      Good news is that it was not a fault of the ground system and the launch pad

      Not proven. It could have been an issue with the ground system that cause the He tank rupture, either from something as obvious (thus unlikely) as bumping the stack to some trickier like an unregulated pressure surge or flow resonance during the filling process.

      • Re: (Score:1)

        by Anonymous Coward

        Or anything anywhere rupturing with enough force to fling something through the tank.

        Honestly, I don't know that they've found anything other than which tank ruptured first. That is not a root cause unless it can be proven that it did so due to faulty design, construction, or material of the He tank.

        Ever since they started asking the public about a ping prior to the fire, my money has been on a projectile directed to the rocket by a competitor or nation state. There are many billions of dollars or even the

  • Although SpaceX asserts that this is not related to the CRS-7 mishap, it's the same system. On CRS-7 it came loose and released the helium through a broken tube, bursting the second stage nonexplosively (until it self-destructed). This time, it looks like the same tank, a carbon-overwrapped pressure vessel, ruptured. Carbon + LOX + heat of compression from the pressure of the burst = explosion.

    This system also leaked during the 2014 Orbcomm misison, delaying the launch by several months.

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