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.

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.

Dave