[AR] SpaceX fault tolerance (was Re: thinking big once more)
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Sat, 1 Oct 2016 18:50:55 -0400 (EDT)
On Sat, 1 Oct 2016, John Schilling wrote:
"Designing for survivability" means so very much more than having
engine-out capability, that I am not convinced that SpaceX has actually
done any such thing - as opposed to inheriting a too-small engine
manufacturing capability from their previous design and making the best
of it.
Now, John, I think that's a bit harsh. They most certainly haven't
scrubbed their whole design for fault tolerance, let alone starting with
it as a major goal, but the first-stage engine-out capability is not just
a historical accident -- they worked at it. Quoth an old news update of
theirs (10 Dec. 2007), after a picture of the very first Falcon 9 static
firing (with only one engine populated):
"Over the next three to four months, we will gradually add more engines
until reaching the full complement of nine. Once we have all nine engines
and the stage working well as a system, we will extensively test the
'engine out' capability. This includes explosive and fire testing of the
barriers that separate the engines from each other and from the vehicle.
"It should be said that the failure modes we've seen to date on the test
stand for the Merlin 1C are all relatively benign -- the turbo pump,
combustion chamber and nozzle do not rupture explosively even when
subjected to extreme circumstances. We have seen the gas generator (which
drives the turbo pump assembly) blow apart during a start sequence (there
are now checks in place to prevent that from happening), but it is a small
device, unlikely to cause major damage to its own engine, let alone the
neighboring ones.
"Even so, as with engine nacelles on commercial jets, the fire/explosive
barriers will assume that the entire chamber blows apart in the worst
possible way. The bottom close out panels are designed to direct any force
or flame downward, away from neighboring engines and the stage itself.
"All in all, we've found that the Falcon 9's ability to withstand one or
even multiple engine failures, just as commercial airliners do, and still
complete its mission is a compelling selling point with customers. Apart
from the Space Shuttle and Soyuz, none of the existing launch vehicles can
afford to lose even a single thrust chamber without causing loss of
mission."
[A little bit of spin there in that last, since Falcon 9 can't afford to
lose its single second-stage engine, but...]
[Their old news updates may no longer exist on their web site, but this
one can still be found at:
<
https://web.archive.org/web/20080808050505/http://www.spacex.com/updates_archive.php?page=121007>.]
Henry
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