In article 01609aef-2c20-43b4-a553-9c84cb346892

@m3g2000pre.googlegroups.com, says...



On Jul 12, 7:59 pm, Jeff Findley wrote:

In article ,



says...







Nothing would ever get built if nothing was ever built before it had

been built.



On paper, Sabre has the characteristics required for an SSTO, and Skylo

n

itself isn't designed around unobtanium. So far no show stoppers have

been identified.



On paper.



The show stoppers are the flight rate and reliability of bleeding edge



technologies. In order to make a profit (and pay off development



costs), Skylon will have to fly quite often and have an extremely high



reliability (hardware losses will be very expensive for such a complex



engine/vehicle).



The engine doesn't have any more moving parts than a conventional

aircraft turbine. True, the vehicle is big, but not as heavy as a

747.



Development costs are still high and it's very unlikely that a Skylon

would have the high flight rate of a 747. The 747 needs that high

flight rate in order to justify the high development and operational

costs of its engines.



A more conventional approach to reusable SSTO using VTVL and plain old



liquid fueled rocket engines would be a far more sane approach when you



take into account economics.



How do you get it back? If you put wings on it and land, then the

structure mass eats the whole mass budget.



I said VTVL: vertical take off and vertical landing.



In other words, land the thing like DC-X on liquid fueled rocket engine

power and on vertical landing gear. This approach is simple (no wings

needed) and has been proven to work "in the real world".



That said, even SpaceX didn't use this



approach, instead choosing to build an expendable in order to minimize



development costs and time.



There are no existing markets which would require the high flight rates



needed to justify the development costs for Sabre and Skylon.



I agree entirely with you statement. There is only one projected

market I know about where Skylon makes sense (SBSP) and even for that

market it takes something extreme for the second stage.



Power satellites really need $100/kg to GEO to make economic sense.



Even then I'm not sure they make sense. They've got to compete with all

other alternative sources of terrestrial power. As fossil fuel prices

continue to rise, terrestrial alternatives become more attractive and

investment in them may yield reductions in cost such that space based

power never makes economic sense.



Jeff

--

" Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry

Spencer 1/28/2011