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SpaceX Blast Investigation Suggests Breach in Oxygen Tank's Helium System (reuters.com)
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.
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?
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I honestly can not tell if this is a joke, or authentic stupid. Both are equally likely.
I would ASSume that the helium is used to pressurize the fuel and oxidizer tanks. Would be stored as a liquid to save space...
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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.
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.
Yes Francis, the world has gone crazy.
Oh the outsourced humanity!
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.
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 the LOX into the tank, bubbles around the He tank, etc. Or it could be something simple like a flow valve fracturing. They have all the telemetry data, so I can only speculate.
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.
Bruce Perens.
Wikipedia 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.
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Well actually the Zeppelin company wanted to use He for the Hindenburg, but the USA wouldn't let them have it. (at the time the USA was the sole supplier.