In article ,
says...

On 2019-05-04 17:05, Jeff Findley wrote:

Those were numbers for the space shuttle, not Super Draco.

OK, had been lead to believe that Super Dracos were same ballpark as the
OMS engines on Shuttle. 1000psi is much much higher.

No you weren't. When I posted the shuttle RCS/OMS info, I said that the
because the thrust of Super Draco is so high the flow rate also had to
be high. So that necessitates higher pressure in the propellant tanks.

They're similar overall, but in some of the details, they're quite
different.

Assuming (for simplification) the fuel has to be at 1000psi, roughly
speaking at what PSI would helium tank need to be such that at end of
engine firing, there would still be 1000psi in the fuel tanks?

are we talking 1500psi, 2000 psi ? 5000psi ? (I have no ideas of size of
tanks involved and how much helium needs to be displaced as fuel tanks
empty to combustion chamber).

Depends on the details of the design. Plumbing, control valves, check
valves, and etc. will all cause a pressure drop from the tanks to the
combustion chamber. This is all internal flow type engineering that a
mechanical engineer would perform. That's the high level summary.
Trying to dig down into details isn't something we're going to be able
to do on a forum like this.

This another reason why I hate idle speculation. You're essentially
trying to reverse engineer the entire design to come up with pressures
of everything. Good luck with doing what a team of engineers likely
took months or years to do.

Just curious if in case of regulator failure, the fuel tanks may be
overhwelved with intense pressure from helium or whether the maximum
possible helium pressure would be well within reasonable pressure
capability of fuel tank.

Depends on the details of the design. Regardless, it shouldn't go
"boom", hence the investigation. A mechanical engineer wouldn't
knowingly design in a "feature" which could cause the whole system to go
"boom". This entire system is supposed to be fast, reliable, and fail
safe.

Although arguably an abort system which "fails safe" still leaves the
astronauts potentially dead because if the escape system has been
activated, Dragon 2 is potentially trying to escape a fireball caused by
the Falcon going "boom".

Would they design the hypergolic tanks to widthstand worse case scenario
in terms of helium pressure being fed into it ?

Depends on the design. There could be something like a blow off valve
to vent helium in case of over-pressurization of the plumbing. Air
compressors/tanks typically have a blow off valve so that if the
pressure switch for the compressor motor goes bad, the tank doesn't
over-pressurize.

Also pressurized tanks often have similar features designed into them
such that if they are over-pressurized, they'll more benignly vent
instead of exploding violently. Of course if you're venting hypergolic
propellants, you're already having a "bad day".

Again, we have no idea if the tanks had a feature like this or not.
More idle speculation.

Would the thrust level for Super Dracos be determined by the regulator
between helium tank and hypergolic tanks, or are there variable
regulators between hypergolic tanks and the combustion chamber ?

Most likely thrust level is controlled by valves between the propellant
tanks and the combustion chamber. That would give the fastest throttle
response time.

Jeff
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