Musk should not have made a comment since he really didn't know anything about what REL is doing. He has a tendency to express an opinion even when he doesn't have the facts. "Bad assumptions" always equals "invalid opinion." In that sense, he can't be right because he didn't reason properly. He should simply keep his mouth shut when he doesn't know the facts.
It also should be noted that SKYLON will be licensed as an airliner, not a rocket like Falcon. I don't think there's a valid reason for it to carry explosives, while most assume the Falcon will.
Actually, the math is generally simplified. In CFD, for instance, a complete and correct simulation is totally impossible and will remain so until we develop the requisite quantum computing capabilities. This means we have to use approximate modelling techniques to describe turbulence and combustion, not to mention liquid-gas interaction, radiative heat transfer, plasma dynamics... As for accurate equations of state, high-temperature air isn't too tough, but liquids are brutal...I'm not quite so well versed in solid mechanics simulations, but just off the top of my head, FEA models have a tendency to use the linear strain approximation, and composites could get interesting... Wear on rotating joints? I don't even know...
Experimentum solum certificat in talibus.
Brief article on non-space applications of SABRE technology here:Interesting. Given that a) getting Skylon into space will almost certainly be more expensive and take longer than REL are currently anticipating, and b) licensing this technology to existing aeroengine manufacturers would presumably be lucrative, I wonder if we'll actually see RE-designed precoolers flying on airplanes before spaceplanes.
I'm glad to see REL exploring terrestrial passenger vehicles. They should be ready to monetize the technology as quickly as possible by any means available. Even without a SSTO vehicle, it's still an important advancement if they can make it work.
Regardless of vertical versus horizontal takeoff, it still involves carrying the intakes/precoolers/etc, wings, and all the other atmospheric trappings all the way to orbit. That still constitutes the vast majority of the delta-v. Adding that mass still incurs gravity losses, even without the vertical ascent from sea level. Getting everything working that has to work within the necessary margins before money runs out is still extremely challenging. It's not dishonest or wrong to point this out. More than one scheme that could have theoretically worked didn't because money ran out, in many cases because superfluous stuff was put on the critical path (such as composite tanks on the X-33), so it's important that SpaceX has a launch vehicle that's gone to orbit and can continue to do so even if reusability is a bust or partial success.
No-one cares about how much oxidizer you don't have to load onto it.
Also, the wings provide lift...
Quote from: BobCarver on 11/29/2012 03:16 amI have not found any reference to these kinds of problems/solutions on the REL website. This could be a show-stopper for the reusability of the SABRE engine. Mark Hempsell, if you're reading this, has REL a plan for dealing with this problem?check this page.http://www.reactionengines.co.uk/sabre_howworks.htmlclick on the 3rd picture. It's complicated because you're looking at the hardware for 2 different engine modes superimposed on each other. The bit you're worried about is in the bottom left hand corner labelled "pre-burner" like the bit in the SSME whose output drives the main pump turbines.SABRE does not drive any turbine directly with H2 rich superheated steam. All are driven either by Helium or what they are pumping (at different physical conditions to the pumped fluid). This has 2 effects. a) Parts exposed to the H2 rich super heated steam don't experience the multiplying effect of high mechanical stress. Everything happens through heat exchangers (which is why it has so many of them). Keep in mind these are REL's low pressure loss/high heat transfer heat exchangers so the difference between the pre-burner pressure and the main thrust chamber can be less that in the SSME.b)There are no "Criticality 1" seals like the ones on the SSME between the preburner driving the HP LOX pump and the LOX flow. Poor seal design here required He purge gas to be 4x it's design flow, partly contributing to the 270lb GHe tank on each engine.Eliminating such seals, de-coupling fluid heating from turbine drive and using fluid bearings should eliminate most of the major reasons the SSME was taken apart after every flight (although that got better as time went on NASA could have installed many more improvements).Designing in IVHM sensors to both the engine and the structure (with engine data collection as part of the primary test goals from day 1 on the test stand to drive the health models) "SSME The first 10 years" teaches a lot of lessons if read carefully.
I have not found any reference to these kinds of problems/solutions on the REL website. This could be a show-stopper for the reusability of the SABRE engine. Mark Hempsell, if you're reading this, has REL a plan for dealing with this problem?
I'm surprised that liquids are tough to model at anything below thousands of bar, except for Hydrogen.
QuoteAlso, the wings provide lift... and a lot of drag.
he tradeoff comes in with having to stay in the atmosphere so much longer, which is why a slight increase in Isp from airbreathing doesn't help.
It also should be noted that SKYLON will be licensed as an airliner, not a rocket like Falcon. I don't think there's a valid reason for it to carry explosives, while most assume the Falcon will. Given a choice, passengers will prefer a vehicle that isn't carrying a bomb onboard.
It also should be noted that SKYLON will be licensed as an airliner, not a rocket like Falcon.
QuoteAlso, the wings provide lift... and a lot of drag. Rockets leave the atmosphere are quickly as possible to avoid the drag. An air breather needs air. That air also means drag. It is a blessing and a curse. Yes they need less oxidizer because they can use air. In return they loose some of the advantage due to added drag and heaver engines. You gain some, you loose some.
REL has explicitly stated that they're working towards certification airliner-style - as close to airliner certification as they can get given the differences. There is, as you note, no regulatory regime for spaceplanes; they're working on that.
The FAA proposed rules way-back-when and the reaction from commercial was less than joyful. There doesn't appear to have been much movement since; although the FAA is on the hook to provide some guidance, I don't see much progress. In short, given the present and foreseeable situation, REL is not going to get any sort of "certification" for their vehicle, airliner-like or otherwse. While I wish it were otherwise, that appears to be the state of affairs.
IIRC REL is one of 2 companies in the UK looking at some form of winged launch vehicle and I guess between them they can lobby the CAA. Note that REL tend to state worst case assumptions. A 5.5Km runway is for a fully loaded Skylon aborted takeoff. Quite a bit of the test programme would be without significant payload, possibly on LH2 alone during airbreathing tests only. That would require a much reduced runway spec.
To me the alternative envisioned by Musk, i.e. using rockets to break pretty much all the way down to ground, seems much less realistic. This strategy considers Earth more or less like an atmosphere-less planet, which is not very accurate a model.
Two companies looking at a winged launch vehicle? Assuming you're not talking about Virgin Galactic, who's the 2nd?
