Doubtful if SKYLON will every be SSTO. Last I heard it only breaths air up to Mach 5. The rest is rocket. SKYLON would have to be built extremely light while providing for TPS, Takeoff/landing gear, wings, Sabre engines. This is beyond the state of the art.
You’re not very well informed (no reason you should be. Winged vehicles on mars are pretty much non-starters). Starting with the fact Skylon is the vehicle. SABRE is the engine, or more accurately the engine cycle. It’s a combined cycle and under William Eschers taxonomy it’s a “Deeply pre-cooled air-turbo rocket.”
In air breathing mode SABRE’s Isp is about 6x that of an SSME, at about 1/2 the Pch. That’s about 2600secs above Raptor’s target Isp (382 if Wikipedia is to be believed
) In rocket mode it has about the same as the SSME, so about 70secs above Raptor.
That Isp allows you the ability to buy the mass of the wings and go for HTOL. For people used to the rocket equation it’s a difficult engine to simulate so they struggle with figuring out that what is and is not possible. Reaction estimate that saves them about a 100tonnes of LOX. It’s not the cost it’s the mass saved (and all the structure to carry it) that makes Skylon possible.
As for the vehicle structural fraction again that Isp buys you a reasonable one of 25% of GTOW. For reference the highest “Fuel fraction” (which is what aircraft use) I could find was Steve Fossett’s Virgin Atlantic Global Challenger at 84% IE Structure and payload is 16% of GTOW.
The Radian assisted launch kerolox SSTO spaceplane in Advanced Concepts needs one of 11% to make it work. The SkylonSABRE threads moved to “Commercial” several years ago.
Landing gear can be an issue but like many things there is what’s common practice and there’s what is SoA. Both the B58 and B70 had remarkably light landing gear for their size, mostly due to engine performance limitations. Neither was designed with the benefit of CAD/CAM. Reaction also located tech from other industries that can lighten the mass still further. This is a known issue since the days of the Boeing RASV study. Boeing reckoned they could do it on a fixed price contract to the USAF in the 80’s.
Reaction are moving to a complete ground test of their engine (something basically impossible for SCramjet engines) within the next 2 years. When fully funded Reaction has delivered what it has promised when it has promised it. This is because Reaction basicall does engineering, not science. They are not still trying to figure out how to do combustion in a high speed airstream, which still seems to be a less-than-fully-solved issue with SCramjets.
SABREs T/W ratio is pretty poor by rocket engine standards at 15:1, but that’s 50% better than any gas turbine aeroengine I’m aware of, which might explain why Rolls Royce and the investment are of Boeing have invested in Reaction. Reaction has an architecture specifically for hypersonic aircraft but no one seems that interested in it (or are not talking publicly about it).
Perhaps you should reconsider what you know about this design?
– I am better informed than you know. I know that SKYLON is the vehicle. I know that Sabre is the engine and that it is a deeply pre-cooled air-turbo rocket. I am also familiar with Bill Escher’s taxonomy.
– I know the performance characteristics of this cycle, having modeled similar cycle for the Air Force in the early 1990s. Your numbers seem about right. I believe our installed (including inlets and fairings) thrust to weight was about 10.
– My team and I have designed and sized dozens of airbreathing access to space vehicles for the Air Force from 1980s to 2010. These include TSTO, SSTO, HTO, VTO, airbreathers and rockets. Compound engine cycles LACE, ACES, RBCCs, TBCCs, ATRs. Note: Adam Dissel (current president of Reaction Engines Inc. USA) worked on some of these studies early in his career.
– Bottom line to all of these studies:
– SSTO might be possible, but will be risky and expensive.
– The simplest and lightest empty weight airbreathing SSTO was a VTO rocket/scramjet design.
– The simplest and lightest empty weight rocket SSTO was a hydrogen-hydrocarbon-LOx tri-propellant rocket.
– TSTO reusable rockets are possible with less risk and expense.
– I have included one of my briefings.
– I have not seen any studies or work which would cause me to change our conclusions.
– Perhaps you should consider being a little more polite. :^)
John