On 7/19/2019 2:43 PM, JF Mezei wrote:
On 2019-07-19 12:05, David Spain wrote:

presume the only method to relieve the pressure is through combustion,
but there may also exist a pressure relief valve that vents off the
helium without need to run the engines. Without hard data this is just a
WAG but not a SWAG.


You can vent off the Helium between the Helium tank and the
Fuel/oxydizer tanks. But the pressure inside the later tanks can't be
vented otherwise you are venting uncombusted NTO and MMH which may
combust if they meet after having been ventet and remain highly toxic if
they don't meeet to combust.


You close the Helium pressurization valve, and de-press through another
valve and coupling perhaps one at the top of the helium tank.

The NTO and MMH would be drained via separate plumbing connections,
which already must exist to fuel it anyway.

Then you purge the system with helium to remove the trace elements of
NTO and MMH from the pressurization lines. Yeah if you do it together
you stand back, otherwise you do them singly with lots of venting to
allow it do disperse.

I can make up a lot of stuff too w/o data it's a WAG (Wild Ass Guess)
but not a SWAG (Silly Wild Ass Guess).

Dave