JF Mezei wrote on Sat, 4 May 2019
17:50:29 -0400:

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.


Who led you to believe that? This stuff is dirt simple to find out,
SO WHY DON'T YOU ONCE IN A WHILE?


1000psi is much much higher.


Gee, did you take off your shoes for that one?


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?


That depends on things we don't know. It will be stored at the
highest pressure reasonable in order to minimize the size of the
required helium tanks (and don't assume there's just one; there are
two propellant tanks per pair of engines and four pairs of engines).


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).


Neither do we. We know how much propellant each pair of engines has,
from which we can calculate the volume of the propellant tanks. From
those tank volumes you can calculate how much helium it takes to bring
those tanks to 1,000 psi when empty. Then you hit the unknowns, since
how much pressure a helium cOPV needs to carry depends on the volume
of the COPV. But by all means, you break out your crayon and do those
calculations.


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.


Which part of my telling you this was one possible failure mode was it
that escaped you?


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


Of course not. The tanks would have to be stupidly heavy if you did
that.


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 ?


They're called 'throttle valves' at that point, not 'regulators'. The
pressure the fuel is delivered at is relatively constant, no matter
how fast you deliver it to the combustion chamber.


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn