SpaceX - Why Not RS-27A?

SpaceX recently announced plans to develop the
"Falcon 9", with a first stage powered by nine
Merlin engines each producing 85,000 lbs thrust
at sea level for a grand total of 765,000 lbs
of thrust.

Merlin is the first hydrocarbon rocket engine
to be so nearly-fully develop in the U.S. since
the Saturn V F-1. If NASA agrees to abandon
Delta II and its RS-27A engine in favor of EELV,
Merlin will become the most powerful hydrocarbon
engine in the U.S..

No matter what happens to SpaceX long term,
Merlin is a commendable accomplishment.

Still, I have to wonder if it might be easier to
develop a rocket powered by four 200,000 lb
thrust RS-27A engines than to create a nine-
engine cluster of smaller engines. Since Boeing
is disposing of Rocketdyne, RS-27A (which is
already a proven cluster machine) should be
available for commercialization beyond the Delta
family.

So why not use smaller numbers of a proven engine?

- Ed Kyle

Ed Kyle wrote:
Still, I have to wonder if it might be easier to
develop a rocket powered by four 200,000 lb
thrust RS-27A engines than to create a nine-
engine cluster of smaller engines. Since Boeing
is disposing of Rocketdyne, RS-27A (which is
already a proven cluster machine) should be
available for commercialization beyond the Delta
family.

So why not use smaller numbers of a proven engine?

How much does the RS-27A cost? How much does the Merlin cost?

-jake

Jake McGuire wrote:
Ed Kyle wrote:
Still, I have to wonder if it might be easier to
develop a rocket powered by four 200,000 lb
thrust RS-27A engines than to create a nine-
engine cluster of smaller engines. Since Boeing
is disposing of Rocketdyne, RS-27A (which is
already a proven cluster machine) should be
available for commercialization beyond the Delta
family.

So why not use smaller numbers of a proven engine?

How much does the RS-27A cost? How much does the Merlin cost?

No one knows for sure but Rocketdyne and SpaceX
(and since Merlin is still in development, SpaceX
might not know their answer yet). I did run across
one reference to a TRW pintle engine design that was
predicted to cost 50-75% less than standard engine
designs. So if the answer for Merlin is 50%, it
would be cheaper to go with four RS-27 engines than
with nine Merlins. If the answer is 75%, Merlin
would be cheaper for the engines alone, but perhaps
not for the labor to install all of the extra
propellant and control lines, etc.

NASA's Fastrac, comparable to Merlin, was initially
designed to cost about $1.2 million per copy (1999$),
but the effort was shelved when X-34 was cancelled.
Too-high costs were reportedly a factor, so the
engine development effort must have suffered cost
overruns.

I suspect Merlin cost SpaceX more to develop than
originally projected too. If I had to guess at the
cost of each Merlin, and I don't know how you can
realistically figure that cost without knowing how
many will ultimately fly, I could only suppose that
it is in the $2-3 million range.

Note that Falcon 9 is projected to cost $27 million
and Falcon 5 $9 million less. The only difference
between the two rockets is four more Merlin engines
on the Falcon 9.

- Ed Kyle

Why would Musk assemble an engine design team and then not utilize it
to its fullest capacity? Merlin 2 is in development, but Musk has been
slightly burned by the calendar on Merlin 1 development. Better to put
a marker out there with the new RLV structures and then work the Merlin
2 into the mix when available.

It doesn't seem to make sense to purchase the RS-27 when the Merlin 2
is already in development, no matter the cost differential between the
RS-27 configurations and the Merlin 1 configurations. The correct cost
comparison would be between the RS-27 and the Merlin 2. Not much info
on the Merlin 2 has been released, so at this point we can only
speculate.

Daniel Schmelzer wrote:
Why would Musk assemble an engine design team and then not utilize it
to its fullest capacity? Merlin 2 is in development, but Musk has been
slightly burned by the calendar on Merlin 1 development. Better to put
a marker out there with the new RLV structures and then work the Merlin
2 into the mix when available.

It doesn't seem to make sense to purchase the RS-27 when the Merlin 2
is already in development, no matter the cost differential between the
RS-27 configurations and the Merlin 1 configurations. The correct cost
comparison would be between the RS-27 and the Merlin 2. Not much info
on the Merlin 2 has been released, so at this point we can only
speculate.

What we do know is that SpaceX has said it is
developing a rocket that will use nine of the
Merlin 1 type engines. If the company planned
to develop a higher-thrust (RS-27 class?)
engine, why would it waste effort developing a
Merlin 1 hyper-cluster rocket?

- Ed Kyle

"Ed Kyle" wrote in news:1126724563.896377.307370
@z14g2000cwz.googlegroups.com:

Still, I have to wonder if it might be easier to
develop a rocket powered by four 200,000 lb
thrust RS-27A engines than to create a nine-
engine cluster of smaller engines. Since Boeing
is disposing of Rocketdyne, RS-27A (which is
already a proven cluster machine) should be
available for commercialization beyond the Delta
family.

So why not use smaller numbers of a proven engine?

Crap, I typed this up and lost it... here's the quick answers:

1) Rocketdyne has no incentive/reason to build cheap engines for small
companies. It would only risk tarnishing their image as the premium
rocket engine supplier for the US government.

2) Old engines aren't necessarily cheap. Parts for classic cars
initially get cheaper as the tooling is paid for, and later on more
expensive as the materials/processes become obsolete and supplier base
dries up. This is a very real supplier issue in the rocket industry, with
all the old engine designs.

3) To make money, SpaceX needs a small, focused, efficient, in-house
engineering team -- government contractors are brainwashed to prioritize
things besides making a profitable product.

"Ed Kyle" wrote in news:1126749104.484362.172630
@f14g2000cwb.googlegroups.com:

What we do know is that SpaceX has said it is
developing a rocket that will use nine of the
Merlin 1 type engines. If the company planned
to develop a higher-thrust (RS-27 class?)
engine, why would it waste effort developing a
Merlin 1 hyper-cluster rocket?

For the same reason the F-1 wasn't the A-1, B-1, C-1, etc. You crawl
before you run. They will learn from the small engines and develop a
track record they can build on. You can't do it all in one leap,
particularly when you have a new company with a new engineering team.

Beal tried to develop three engines for his 3-stage rocket, with a planned
1st stage of 2Mlbf. They didn't get the bugs out of the 2nd stage engine
before Beal decided to cut his losses. Scaling engines up is not trivial.

Because there are lucrative markets out there that need early dates
certain. He can't promise that his new engine will be ready by that
time, so he's not.

Ed Kyle wrote:


NASA's Fastrac, comparable to Merlin, was initially
designed to cost about $1.2 million per copy (1999$),
but the effort was shelved when X-34 was cancelled.
Too-high costs were reportedly a factor, so the
engine development effort must have suffered cost
overruns.



One thing that will benefit SpaceX is if Delta II gets dropped as a
launch vehicle, as way well happen- that would create a very exploitable
gap on the lower end of the payload market.


I suspect Merlin cost SpaceX more to develop than
originally projected too. If I had to guess at the
cost of each Merlin, and I don't know how you can
realistically figure that cost without knowing how
many will ultimately fly, I could only suppose that
it is in the $2-3 million range.

Note that Falcon 9 is projected to cost $27 million
and Falcon 5 $9 million less. The only difference
between the two rockets is four more Merlin engines
on the Falcon 9.



I'm till interested in their plans to make their boosters recoverable
and reusable, which to me seems a little odd for a vehicle designed for
low cost in its construction, as it means you have to lug the weight of
the recovery gear along with you, eating into your payload, and
overbuild it some for multiple use and the stress of landing after its
mission.
I still think this is about the cleverest reusable booster design I've
ever seen:
http://www.russianspaceweb.com/baikal.html
http://www.buran.ru/htm/strbaik.htm

Pat

Ed Kyle wrote:
Still, I have to wonder if it might be easier to
develop a rocket powered by four 200,000 lb
thrust RS-27A engines than to create a nine-
engine cluster of smaller engines.

One of SpaceX's marketing angles is its capability to fly even with the
loss of an engine. This is easier to achieve with nine engines than
with four.