[AR] Skylon and related (was Re: SSTO)
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Tue, 13 Feb 2018 15:47:25 -0500 (EST)
On Tue, 13 Feb 2018, Keith Henson wrote:
...Skylon development is still forecast to cost tens of billions and
there is no plan for a less-expensive demonstrator first. (Which puts
Skylon in the "need not be taken seriously" category, in my opinion, since
nobody is going to spend that kind of money on an unproven concept.)
Let's turn this around. What would it take for someone (governments
most likely) to fully develop Skylon?
The last time this happened was nuclear weapons during WW II. So it
would take the moral equal of a war of survival.
Arguably the last time it happened was Apollo -- same story, a major
battle in the Cold War.
However, I think the question is poorly framed. Almost certainly, there
is *nothing* that would make governments (or somebody) set out to fully
develop *Skylon* in response to a perceived crisis-level threat. There is
no convincing argument (convincing to skeptics, not just true believers)
that Skylon is the One And Only Way to achieve cheap launch. There's a
lot of new technology there -- as witness the price tag -- and no way
would a General Groves type bet his whole project on Skylon succeeding.
Such a project would certainly pursue multiple approaches, not just one.
The Manhattan Project put major effort into *four* different methods of
uranium enrichment, and three or four different types of nuclear reactor
for plutonium production, although not all of these got as far as
full-scale plants. And those weren't even all the choices pursued --
several more enrichment/reactor technologies got lesser levels of effort.
Being generous, Skylon might be the gaseous-diffusion equivalent: looked
like the best method overall, but there were nasty technical problems to
be solved, so it couldn't be the only choice. Mass-spectrometer
enrichment looked much more simple and certain, just difficult to scale up
to the level needed, so it got pursued too (eventually assisted by thermal
diffusion), and it produced the first uranium bomb cores. And in fact
most of the early bomb cores came from water-cooled graphite reactors
producing plutonium, even though that required a lot of work to develop
implosion bombs (much trickier, much less well understood at the start).
Gaseous diffusion ended up contributing nothing at all to the war effort,
although when they finally got it working afterward, the mass-spectrometer
and thermal-diffusion plants were closed down, and uranium became the bomb
fuel of choice wherever it was suitable.
Less charitably, Skylon might be the gas-centrifuge equivalent. GC had
some important advantages, and the Manhattan Project built a GC pilot
plant, but they eventually concluded that the technology was too far from
practicality then, and scaled the GC effort back to long-term R&D. (And
in fact it's now the method of choice, but that took decades to happen.)
...needs about $100/kg to LEO. I don't think rockets can reach that
number...
If Skylon can, almost certainly rockets can do even better. A reusable
TSTO burning LOX and some cheap hydrocarbon should be rather easier to
develop, and there's no reason operations couldn't be scaled up to the
same launch tempo.
If I recall correctly, Kistler was hoping to get its LOX/kerosene TSTO
flying with a total under a billion (counting the pile they'd already
burned through by putting too much trust in dinospace subcontractors).
They may have been too optimistic, but then, they were rather farther
along than Reaction Engines is with Skylon.
The LOX costs almost nothing compared to the fuel, and "There's nothing
magic about rubber wheels rolling on a runway that's gonna make it cheap
to operate." (Mitch Burnside Clapp).
Henry
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