[AR] Re: Skylon and related (was Re: SSTO)
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Wed, 14 Feb 2018 18:47:45 -0500 (EST)
On Wed, 14 Feb 2018, Keith Henson wrote:
In order to get down into the $100/kg to LEO range, the vehicles need
to fly around 1500 times, with two rebuilds (reskins) at 500 and 1000
flights. Can we do something similar with rockets?
Remember, Skylon *is* a rocket for much of its ascent, and it has all the
rocket subsystems and issues, in addition to a bunch of its own. If such
a working life can be done for Skylon, it can be done for a rocket --
quite possibly more easily, because the hardware is simpler (and doesn't
have awkward problems like its own exhaust plumes striking its tail for
much of the ascent).
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).
Compared to rockets, aircraft are cheap to operate.
There are many differences between today's rockets and today's aircraft
other than the mode of propulsion, so it's questionable to infer anything
from this. (And any attempt to do so should include low-ops-cost systems
like DC-X and the Masten vehicles, not just traditional artillery
rockets.) Any system for your requirements is operating in an ops regime
completely different from anything that has ever been done with rockets
before.
For that matter, Skylon would operate in a completely different regime
from anything that has ever been done with aircraft before. Even the
seemingly-familiar phases like takeoff and landing don't seem quite so
familiar when you look at the numbers. As Jeff Greason commented some
years ago, in a slightly different context: "this *isn't* just like an
airplane" even if it still has wings and wheels.
In theory, Skylon has safe abort modes through the entire launch, though
an abort just before rotation is a dicey stopping problem. It's not
highly stressed because it flies up the constant dynamic pressure line.
Neither are rockets, which very quickly move up to a zero dynamic pressure
line. This is better, not worse, in most ways.
Henry
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