Just to check my understanding of what you are saying, that follows only if
the payload mass to empty stage mass fraction is small, right? So if you
had an SSTO that arrived on orbit as 50% payload then the performance
difference would be much smaller.
Of course, as Bill showed a while back you could also use that same
technology base to make an even better two stage to orbit vehicle. But
eventually, when we have "sufficiently advanced" technology
(indistinguishable from magic), an SSTO will the better architecture. We
could save fuel or increase payload using drop tanks on 747s, for example,
but we don't.
(I could see an alternate history where we did, though. Halfway to China,
drop the tanks into the Pacific for someone to fish out and bring back for
reuse!)
Thanks!
-David Summers
On Sat, Mar 16, 2019 at 6:30 PM Rand Simberg <simberg@xxxxxxxxxxxxxxx>
wrote:
And as with any SSTO, Skylon would suck for off-nominal (higher
inclination/altitude) missions.
On 2019-03-16 16:24, Evan Daniel wrote:
The original presentation for the SpaceX BFR called for $500/kg tothe
Mars surface, including LEO refueling, with the capital cost of the
transit ship being a very large fraction of that. They didn't break
out the numbers in detail to give a LEO payload cost estimate, but I
infer it was much lower than $500/kg.
Numbers since have gone up, and sizes and flight rates down, but I
think if you asked SpaceX to project out to those volumes you'd see
numbers below $100/kg to LEO. I don't think Skylon is unique in that
fashion.
One can, of course, believe or not believe either set of projections.
But, I think it's (at least) as reasonable to suppose that SpaceX
could hit that target with a BFR style architecture as to believe that
Skylon can hit its target.
Evan Daniel
On Sat, Mar 16, 2019 at 6:23 PM Henry Spencer <hspencer@xxxxxxxxxxxxx>
wrote:
On Fri, 15 Mar 2019, Keith Henson wrote:
Reaction Engines is the only company that projects a cost to orbit low
enough for power satellites to make sense. They think they can get
cost down to a hundred dollars a kg to LEO...
The cynical observer would say that they are the only ones whose
projected
startup costs are so colossal that they *must* project far ahead, to a
very high flight volume, to make their case close. Less-challenging
approaches should do better, not worse, given the same assumptions...
but
they don't need such rosy assumptions, so they generally don't project
so
far beyond the current market.
(Max Hunter used to suggest that cost plots should always show the
marginal cost of a single added flight, as a way to hint at bulk
prices
without having to justify massive market expansion, but few do it.)
Henry