flying; after about 90 seconds, it can
tolerate a second engine shutdown. Even
if an engine explodes, says Mueller, the
others will not be affected.
Of course, SpaceX goes to great lengths
to prevent such a scenario. Part of the
Merlin’s qualification testing involves
feeding a stainless steel nut into the fuel
and oxidizer lines while the engine is
running—a test that would destroy most
engines but leaves the Merlin running
basically unhindered. Every Falcon upper
and lower stage is test-fired in Texas
before it’s cleared to fly. “It’s very
common to do component and system-
level testing…. That’s very typical in
aerospace, ” says Alan Lindenmoyer of
Houston’s Johnson Space Center, who
has been working with SpaceX since 2005
as manager of the agency’s Commercial
Crew and Cargo program. “But to
actually put a vehicle together and do
system-level testing of the rocket is not.
That’s a level of rigor you don’t typically
see.” On the pad at Cape Canaveral,
Florida, the rocket undergoes an
additional brief firing a few days before
launch. And just before liftoff, for a few
moments after the engines are lit, their
performance is analyzed by the Falcon’s
computers before hold-down clamps are
released and the rocket is allowed to rise.
The Merlin engine itself has undergone a
number of improvements, including
reducing the number of parts and
increasing its power and efficiency.
According to Mueller, the 140,000-pound-
thrust
Merlin
1D,
designated
the
production model for Falcon 9, has the
highest thrust-to-weight ratio of any
rocket engine ever made.
Significantly, the Merlin engines—like
roughly 80 percent of the components for
Falcon and Dragon, including even the
flight computers—are made in-house.
That’s something SpaceX didn’t originally
set out to do, but was driven to by
suppliers’ high prices. Mueller recalls
asking a vendor for an estimate on a
particular engine valve. “They came
back [requesting] like a year and a half in
development and hundreds of thousands
of dollars. Just way out of whack. And
we’re like, ‘No, we need it by this
summer, for much, much less money.’
They go, ‘Good luck with that,’ and kind
of smirked and left.” Mueller’s people
made the valve themselves, and by
summer they had qualified it for use with
cryogenic propellants.
“That vendor, they iced us for a couple of
months,” Mueller says, “and then they
called us back: ‘Hey, we’re willing to do
that valve. You guys want to talk about
it?’ And we’re like, ‘No, we’re done.’ He
goes, ‘What do you mean you’re done?’
‘We qualified it. We’re done.’ And there
was just silence at the end of the line.
They were in shock.” That scenario has
been repeated to the point where,
Mueller says, “we passionately avoid
space vendors.”
In a few cases, SpaceX has even been
able to advance the state of the art. For
the Dragon’s heat shield, the company
chose a material called PICA (phenolic
impregnated
carbon
ablator),
first
developed for NASA’s Stardust comet-
sample-return spacecraft. Rejecting the
prices they were getting from the
manufacturer, they took advantage of
help from NASA’s Ames Research Center
to make it themselves. According to
Mueller, SpaceX’s material, called PICA-
X, is 10 times less expensive than the
original, “and the stuff we made actually
was better.” In fact, says Musk, a single