[AR] Re: thinking big once more
- From: Alexander Ponomarenko <contact@xxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Wed, 28 Sep 2016 23:09:26 +0200
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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