[AR] Re: clustering big rockets
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Sun, 27 Dec 2015 17:33:11 -0500 (EST)
On Sun, 27 Dec 2015, John Dom wrote:
SLS is ... a way of maintaining employment at MSFC and some of the major
shuttle contractors...
I wrote new, in the sense that the SLS version should (incl. SRBs) for
the first time in 45 years re-enable NASA to fly Saturn V 140 t to LEO
missions. Enabling planning of large post STS space projects.
There is no fundamental difficulty in planning big projects using only
medium launchers. ISS weighs a lot more than 140t, and went up one piece
at a time -- just like factories, dams, ships, etc. on Earth.
Also, remember that planning and execution are two different things. The
problem with huge launchers has never been the lack of plans for them, but
rather the lack of approved, funded payloads for them. That's why the
Saturn V died when Apollo wound down -- it wasn't due to lack of *ideas*
for other uses for it. (No, NASA did not conspire to kill it to avoid
competing with the Shuttle -- NASA struggled for years to keep Saturn V
production going, or at least preserve the option of restarting it, and
gave up only after hope was absolutely dead.)
Why not go for more powerful liquid motors or more of them instead...
Because the US has no suitable large liquid engines.
Can say, Atlas V or Delta IV liquid first stage engines be clustered (not
unlike SpaceX actually does) so SRBs/strapons become unnecessary?
The Atlas V first-stage engine is Russian; a US production line would be
needed, and that wouldn't be easy to set up (even assuming that relations
with Russia improve), and the engines from it would be expensive. The
RD-180 is an impressive engine, but not simple to build. If you accept
that, this certainly would work, especially if you build the RD-170 (more
or less two RD-180s in one package) instead -- that being what powered the
Energia first stage (its "strap-ons").
The Delta IV first-stage engine is the RS-68, which unfortunately burns
liquid hydrogen (suboptimal for a first stage because of bulky tanks and
poor engine T/W) and is not really quite big enough. Clustering them is
not unthinkable -- when I sketched Brown Bess, my idea for an Ares
alternative, that's what I used -- but is clumsy and probably costly.
Although the Russians have plenty strategic launchers, they kept a lot
of them liquid propelled like the recent Topol-Ms.
It took the Russians a long time to develop high-performance solids --
although some of their sub-launched missiles now are solids -- and they
were never as sold on them as the US military was. (I conjecture that the
US military might not have gone into solids quite so enthusiastically if
they had understood quite what they were getting into: the technology was
new and seemed to avoid most of the military headaches of liquids, and it
took a while for people to realize that it had its own problems.)
The huge Russian Energiya rocket ... carried no SRBs. The Energiya
boosters (or parallel stages) were, like its ME liquid propelled... In
principle they could have been recovered by parachute (over land?).
NASA would have preferred liquid-fuel boosters for the shuttle, but the
estimated development cost was always too high, so they went with solids
as a temporary expedient (which gradually became permanent).
One alternative that *almost* made the cut (as George noted) was a single
liquid booster based on a Saturn V first stage. There were two of those
sitting around surplus, and building a few more wouldn't have been too
hard then. Add wings, landing gear, jet engines, and a cockpit (!), and
you get the "Flyback F-1", the world's biggest rocketplane. But it would
have pushed the shuttle development funding peak a little bit over OMB's
$1G/yr cap, and so no go.
I wonder why the French did not go for cooperation on this 5 times more
powerful Energiya: 100 t to LEO...
Lack of payloads. The French wanted rockets that would have customers.
By comparison Saturn V was 140 t to LEO capable.
Not really. That's the partially-fueled S-IVB/Apollo combination in
parking orbit, but that's *after* the first S-IVB burn, so you can't
directly convert that to payload unless the payload is capable of doing a
similar burn. In theory, using all three stages and burning the S-IVB
dry, a Saturn V could put about 119t in LEO... except that a payload that
heavy would crush the S-IVB during the first-stage burn. To get maximum
LEO payload with an unmodified Saturn V, you use only the first two stages
and the payload is about 100t, e.g. Skylab.
To get more, either build a new third stage -- stronger, and perhaps
powered by RL10s for their higher Isp -- or stick with two stages but give
them upgraded engines (F-1A and J-2S) and tank stretches. The latter is
probably preferred, since if you were continuing/resuming Saturn V
production, you'd want the engine upgrades and tank stretches anyway.
Henry
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