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Old July 18th 19, 12:15 PM posted to sci.space.policy
Jeff Findley[_6_]
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Default SpaceX Capsule Explosion

In article , says...

On 7/17/2019 7:43 PM, Jeff Findley wrote:

The abort system's Super Dracos require *much* higher chamber pressure
than the Dracos, so the system is not pressurized until an abort is
initiated. Why they chose to do it this way, I'm not sure. Perhaps
NASA didn't want super high pressure hypergolic propellant tanks docked
to ISS.


That makes sense...


See above. They burst when the hypergolic system for the Super Dracos
is pressurized, which is only when an abort is initiated.

Jeff


I don't see how that answers my question. I must presume there is
another (helium) valve upstream of the burst disk that holds back the
helium pressure until an abort. It's the helium gas that's doing the
pressurization correct? So I would assume that's implied in Fred's OP.


Yes, there is a valve between the super high pressure helium tank and
the check valve (now burst disk). That's the valve that's opened to
pressurize the propellant tanks for the abort system to operate.

Is helium used for pressurizing both bi-propellants? I would assume so.
But always welcome facts if at hand. I can Google it too if anyone
doesn't already know.


Yes. Both propellants need to be pressurized to about the same pressure
for them to be injected into the engine's combustion chamber at about
the same rate.

Jeff
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