[AR] Re: SpaceX F9 Launch/Update -- Live Link
- From: Henry Vanderbilt <hvanderbilt@xxxxxxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Mon, 28 Dec 2015 08:22:16 -0700
On 12/27/2015 10:47 PM, David Weinshenker wrote:
On 12/25/2015 09:25 PM, Henry Spencer wrote:
Because the US has no suitable large liquid engines. The RS-27A is out
of production and too small, the RS-68 uses the wrong fuel for
high-thrust first-stage engines, and that was basically it for
off-the-shelf engines. And there is reason to fear the cost and schedule
impact of having MSFC and Rocketdyne develop a big new engine. No,
reviving the F-1 would not solve the problem -- as witness the J-2X,
such an effort would almost certainly end up building essentially a new
engine. No, there is no realistic prospect that it wouldn't be an
MSFC/Rocketdyne project.
It turns out (per wikipedia) that Aerojet-Rocketdyne is proposing a new
LOX/kero "AR1" engine of 500k lbf. thrust (which seems to be about what
would be wanted) - USAF analysis thinks it would take "6-8 years to
develop", Ajet-Rdyne is claiming "ready by 2019".
https://en.wikipedia.org/wiki/Aerojet_Rocketdyne#AR1
Aerojet several years ago tried to sell NASA on funding an upgraded
derivative of the refurbed Russian NK-33 engines they'd been selling to
Orbital as the AJ-26, to be used in clusters for alternative SLS liquid
strapons. I'm not sure anyone in the SLS faction was serious about that
though; it looks more to have been a temporary expedient to get the
California delegation on board supporting SLS funding.
I'm pretty sure the AR-1 is descended from that effort, with the Russian
design origins possibly left further behind and certainly downplayed
more. The propellants (LOX-Kerosene), the cycle (staged combustion) and
the size (about 500,000 lbf thrust) are all the same.
The one thing that's constant is that AJR doesn't have enough faith in
themselves or this engine to raise market funding and do it themselves.
They're practically the metaphysical ideal of an old-line (high)
cost-plus government space contractor, and "entrepreneurial" to them
seems to mean spending more money on lobbying for government funding.
In this current push to get paid for an RD-180 replacement, AJR has been
claiming they can do it in 4-5 years for a billion or so. USAF has been
unusually blunt in saying they don't believe this, that they expect both
cost and schedule would eventually double, and they don't want Congress
to fund it. AJR's lobbyists succeeded in getting a couple hundred
million earmarked for the new engine in this year's budget anyway.
My take is, anyone with $2 billion and ten years to spare, go to AJR for
this engine, and it's even-money that $2 billion and ten years later,
they'd tell you "oops, it's taking longer and costing more."
I'd love to see AJR getting entrepreneurial and proving me wrong - to
the extent they've concentrated US liquid-rocket expertise and IP via
buying up Rocketdyne and P&W, they're a national asset. But until they
prove otherwise, it's safer to regard them as a primary producer of cost
and schedule overruns with a secondary line in rocket propulsion.
My own though would be to start with the ~200k lbf. chamber designs
from the H-1/RS-27 (i.e., Saturn 1 / Delta) engine lineage, and
derated F-1 turbopump technology, and assemble a "four-chamber"
engine with a common pump system and mounting structure
(in the Russian style) - total thrust would be 800-900k lbf. -
and the depth of experience with that particular chamber
design lineage might be such that, even now, building similar
units might not require recovering too much "lost art".
This implicitly would be a gas-generator cycle engine, since all the
design sources you cite are, and as such could not serve as a drop-in
RD-180 replacement - the lower Isp would require major vehicle redesign
to increase propellant tankage. (Was an RD-180 replacement what we were
talking about in this thread? perhaps not...)
In terms of a more generic heavy first-stage engine, you'd need to look
at any such project in terms of whether it would be competitive with a
cluster of Merlin 1D's. The Merlin at this point is a *really good*
gas-generator engine, with outrageously good thrust-to-weight and
above-average-for-a-gas-generator efficiency. The main practical
rationale I could see for developing the engine you describe would be if
SpaceX for some reason wouldn't sell you Merlins.
Henry
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