[AR] Re: thinking big once more
- From: Alexander Ponomarenko <contact@xxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Thu, 29 Sep 2016 02:33:01 +0200
I had usually heard 2-3x, which would imply something closer to 60-90
bar (9000-14000psi).
That is correct for "normal" SC cycle where only one of the components
is used completely in preburner.
FFSC makes it possible to have lower pump outlet pressure for the same
chamber pressure.
Actually, initially I believed that Musk has selected FFSC exactly for
this goal: to achieve high Isp at relatively high chamber pressure
having "low" pump and preburner pressure => better relaibility (as well
design simplicity, cost etc). Still wondering why they selected champion
chamber pressure.
Alexander
On 09/29/2016 02:22 AM, Jonathan Goff wrote:
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 <mailto:contact@xxxxxxx>> wrote:
> At 3x the chamber pressure, and 5-6x the peak pump outlet pressure of a
Merlin-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 <mailto: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
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