The Reaction Engines Skylon Master Thread (1)

[flymetothemoon]

And, Elon Musk was obviously addressing an air-breathing, vertical ascent rocket stage in his talk, not SKYLON. I doubt he even has read anything about REL. He didn't even understand the tradeoff between gravity losses and a winged vehicle. Apparently, he's too busy to keep abreast of what the competition is doing. His argument against an air-breathing rocket falls flat on its face when you realize he's reasoning from a viewpoint of ignorance.

It just shows that even a genius like Musk can be wrong based upon ignorance.

Yes it seems clear he is talking about staged and vertical.

Not so sure about your non-sequitur here though. If he is talking about staged / vertical / wingless then presumably, if he has done the maths, he is absolutely correct. So, "right", rather than "wrong", would be the word I would use for that.

He even says he could be wrong (presumably *still* talking about staged / vertical / wingless). Being a "genius", I am sure if he looked at Skylon / Sabre and saw that it works he would have a different view about that approach.

Science / scientists always update their views given new scientifically proven information. I am quite certain Elon Musk would. Granted, if their whole careers are based on some outdated notions, some scientists fight hard or die before they get there.

[Jim]

It just shows that even a genius like Musk can be wrong based upon ignorance.

There is nothing that proves him wrong.  Skylon is not a reality.

[Tass]

It just shows that even a genius like Musk can be wrong based upon ignorance.

There is nothing that proves him wrong.  Skylon is not a reality.

Nothing that proves his conclusions wrong, but his premises are certainly wrong. As such if his conclusions turn out to be right it would only be by accident.

[grondilu]

Skylon is not a reality.

It is, at least in computer simulations.   And those simulations represent reality pretty much as well as our physical laws do.

Otherwise you deny the very pertinence of mathematics as an abstract yet effective representation of reality.  I'm not sure such a denial is compatible with modern epistemology.

You can say "Skylon is not a reality" if you mean that it is not yet a physical, functional device.  But if you put such a sentence just after "there is nothing that can prove him (E. Musk about Skylon) wrong", then you suggest that only physical things and empirical evidence are a source of knowledge.  Which is not true.


PS.  A rocket capable of going into orbit, re-entering the atmosphere and landing vertically on his feet is not a reality either.

[Rugoz]

It just shows that even a genius like Musk can be wrong based upon ignorance.

Why should he care about skylon? Its far from certain that it will be built and if it will there's nothing he could do about it anyway.

And to be honest I don't see much genius in musk, he's a good businessman but its not like the world has been waiting for paypal, tesla motors. Whether spacex will be "revolutionary" remains to be seen.

[Jim]

It is, at least in computer simulations.   And those simulations represent reality pretty much as well as our physical laws do.

Otherwise you deny the very pertinence of mathematics as an abstract yet effective representation of reality.  I'm not sure such a denial is compatible with modern epistemology.

Wrong.  computer simulations can not accurately predict whether Skylon will be viable system

[Jim]

PS.  A rocket capable of going into orbit, re-entering the atmosphere and landing vertically on his feet is not a reality either.

Between current vehicles and DC-X, this has been approximated. 
Anyways, the rocket made into orbit with a payload, the rest is gravy.

[john smith 19]

It just shows that even a genius like Musk can be wrong based upon ignorance.

That's a little harsh. Musk is running a very complex operation and wearing 2 big hats. He has to prioritise his time. The trouble is media reporters at such events will expect him to be current on all launchers, both current and in design.

skylon is a long way from mainstream. I'd suggest Musk's concerns right in terms of competition are more to do with ULA(getting on the DoD, USAF and NRO launch lists) , OSC (antares). Even Stratolaunch is likely quite a long way down his "to watch" list. In house he's watching Grasshopper and the Dragon LES develop (as CTO) while as CEO he'd be wanting to get some non NASA launches up the hill while getting the next ISS Dragon launched.

I doubt he'll be worrying about Skylon until at least a full size Y vehicle was making orbit.

It's a good principle to not worry about stuff until you've got a solid reason to. While I believe in time Musk will have something to worry about  from REL its still a ways down the road.

[aero]

It is, at least in computer simulations.   And those simulations represent reality pretty much as well as our physical laws do.

Otherwise you deny the very pertinence of mathematics as an abstract yet effective representation of reality.  I'm not sure such a denial is compatible with modern epistemology.

Wrong.  computer simulations can not accurately predict whether Skylon will be viable system

People have accepted computer simulations as representing reality since the days of analog computers. Sure, the math is accurately represented but typically the coefficients are not known well enough. The details (math and data) are where the devil hides and there be demons!

It's to bad that one can't just simulate it, build it and fly it. But no, very extensive test programs are needed before a vehicle can be flight rated, and data from those test programs are fed back to the simulation bringing it into accurate alignment with the real vehicle. Once that is done it is possible to use the simulation to investigate the impact of small changes on the vehicle but belief in the absolute accuracy of the simulation is one road to disaster. There are many such roads for a program as extensive as Skylon development.

[grondilu]

People have accepted computer simulations as representing reality since the days of analog computers. Sure, the math is accurately represented but typically the coefficients are not known well enough. The details (math and data) are where the devil hides and there be demons!

True.  But still, if a simulation shows that success is one of the possible outcomes, I can not agree with a statement saying that Skylon does not make physical sense.

If Skylon did not make physical sense, all simulations would predict failure, wouldn't they?

[BobCarver]

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.

[Elmar Moelzer]

Well, I think that he was not that far off with what he said. Skylon is a very big and complex vehicle with a very large development cost that will only provide marginal cost improvements over his own proposed TSTO RLV and will be more limited in terms of scaling it up to larger payloads, etc.
It might also be that he was more referring towards Stratolaunch (and interpreting the question being targeted at his former cooperation with them).

[flymetothemoon]

Ha! Fair point. Stratolaunch is 'air-breathing', 'hybrid' and another stage. I couldn't quite imagine what he was talking about, but if he was talking about that, his answers fit.

Also, for reasons we knew very shortly after this, Stratolaunch was at the front of his mind right then and he might have suspected people had heard something...

[sanman]

There's no way that Falcon could compete in the intercontinental travel market, which is where the real money is for REL in the nearer term, before Skylon. Unless of course Musk feels that his hyperloop can span between continents.

Heck, if the Sabre engine can just be used for rapid intercontinental travel then it will have fulfilled most of its promise. After that, the money for follow-on development into Skylong would probably be easy to come by.

[BobCarver]

Skylon is a very big and complex vehicle with a very large development cost that will only provide marginal cost improvements over his own proposed TSTO RLV and will be more limited in terms of scaling it up to larger payloads, etc.

Not according to Alan Bond in The Three Rocketeers:

[BobCarver]

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.

[93143]

Sure, the math is accurately represented but typically the coefficients are not known well enough.

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.

Skylon... will only provide marginal cost improvements over his own proposed TSTO RLV

You can't say that.  Neither of them is anywhere near reality right now.  SpaceX in particular don't seem likely to have a particularly good handle on the operational details; they're still experimenting with the basic concept.  REL have been planning their system for far longer, and have just now cleared the biggest single technical hurdle, but even they could encounter unexpected difficulties.

There's no way that Falcon could compete in the intercontinental travel market, which is where the real money is for REL in the nearer term, before Skylon. Unless of course Musk feels that his hyperloop can span between continents.

Heck, if the Sabre engine can just be used for rapid intercontinental travel then it will have fulfilled most of its promise. After that, the money for follow-on development into Skylong would probably be easy to come by.

Skylon comes first.  The A2 is considerably more difficult; unlike Skylon, it relies on technologies below TRL 4.  The engines are more difficult, at least partly because they need to have a much longer service life with much higher reliability.

[Matt32]

Brief article on non-space applications of SABRE technology here:

http://www.flightglobal.com/news/articles/spaceplane-air-cooling-technology-could-revolutionise-aero-engines-379772/

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.

[Elmar Moelzer]

Also, for reasons we knew very shortly after this, Stratolaunch was at the front of his mind right then and he might have suspected people had heard something...

Yepp

You can't say that.  Neither of them is anywhere near reality right now.  SpaceX in particular don't seem likely to have a particularly good handle on the operational details; they're still experimenting with the basic concept.  REL have been planning their system for far longer, and have just now cleared the biggest single technical hurdle, but even they could encounter unexpected difficulties.

I was talking from Musks perspective.

There's no way that Falcon could compete in the intercontinental travel market, which is where the real money is for REL in the nearer term, before Skylon.

I am sure that Musk was strictly talking about the LEO and GTO markets.

[Elmar Moelzer]

Not according to Alan Bond in The Three Rocketeers:

Watching the video, I still cant see how the Skylon will scale to put larger payloads into orbit. The F9 can be scaled to the falcon heavy. You cant cluster several Skylons... That is what I was referring to.