Alex,
If the chamber pressure of Raptor is 300bar / ~30MPa / ~4500psi, wouldn't
that imply a much higher high-side pressure for the oxygen and the fuel
component that goes into the preburner? I don't know what sort of multiple
of chamber pressure is typical for the pump outlet pressure on FFORSC
engines, but I had usually heard 2-3x, which would imply something closer
to 60-90 bar (9000-14000psi). Could someone who actually knows turbopumps
chime in?
Raptor's chamber pressure is 20-30% higher than most of the RD-170 family
engines.
~Jon
On Wed, Sep 28, 2016 at 3:09 PM, Alexander Ponomarenko <contact@xxxxxxx>
wrote:
At 3x the chamber pressure, and 5-6x the peak pump outlet pressure of aMerlin-1D
Note also that with FFSC cycle one of the two flow paths in power head is
running with oxidizer rich preburner and turbine, with estimated preburner
pressure ~45 MPa and LOX pump exit ~50 MPa.
This makes it pretty close to the RD-170 family in terms of reliability
and outcome from possible failures within the engine.
Alexander
On 09/28/2016 10:51 PM, Jonathan Goff wrote:
Henry,
I also wonder about the probability of unsurvivable engine failures with
Raptor. At 3x the chamber pressure, and 5-6x the peak pump outlet pressure
of a Merlin-1D while being in the same general package, we're likely
talking about a 3-6x increase in worst case P*V energy available to do
antisocial things. Not sure if that means anything, but it at least
suggests to me that anti-fraticide protections might be more challenging
and heavier for Raptor.
Or maybe SpaceX will get it working without an hitch, who knows.
~Jon
On Wed, Sep 28, 2016 at 2:36 PM, Henry Spencer <hspencer@xxxxxxxxxxxxx>
wrote:
On Wed, 28 Sep 2016, Eric Robbins wrote:
Interesting design choice, it would seem that for a certain number of
engines N that the chance of at least 1 engine failing approaches 100%.
The key question is not really the probability of an engine failure --
the question is the probability of an *unsurvivable* engine failure.
Rockets with more than 3-4 engines often can survive a single engine out,
provided it doesn't fail violently and destructively enough to knock out
others. Four of the Saturns survived (and completed their missions) with
engines out. For that matter, one Falcon 9 had a moderately violent
first-stage engine failure in flight, and made it to orbit.
I wonder what N is? I can't imagine it being 3 digits, I would not be
surprised if it were around 40-50.
It depends greatly on the reliability of the individual engines. With a
good engine like the RL10, it could easily be in three digits. (Back in
the 80s, when Hughes was studying its Jarvis launcher concept, they had a
problem with availability of suitable engines. They looked seriously at a
first stage with about 200 [!] RL10s.)
Henry
