The Reaction Engines Skylon/SABRE Master Thread (6)

[Rocket Science]

Perhaps you should look a little deeper into its history

https://en.wikipedia.org/wiki/Bell_P-59_Airacomet

The engine is a copy of the Power Jets W2B/23

AFAIK the US had no indigenous jet engine projects anywhere close to flight weight when they were informed the Gloster existed.

John, I guess we are two nations separated by a common language as we are in full agreement once again!

[CameronD]

What's more practical in having three sets of heavy engines instead of one set of engines?

Actually starting to build something that might fly instead of Powerpoints forever. (Something which has little to do with the number of engines.)

On that basis, perhaps REL do indeed have a perfect design??  After all, there can't possibly be anything wrong with a design that only exists on Powerpoint.. and if you do just happen you notice something screwy (perhaps a design parameter or three), it takes only a minute or two to edit it.  Science Fiction folks do this all the time.

[knowles2]

Thank God for China, rescuing this thread from whining about SpaceX:

Looks like they're developing their own version of Skylon.

And good for them, as Europe is too timid to fully fund such a huge sum for the full-up space plane and Reaction Engines refuses to come up with a more practical, gradual plan to develop a reusable orbital vehicle.
http://www.spaceflightinsider.com/organizations/china-national-space-administration/china-develop-hybrid-spaceplane-cheaper-space-travel/

From a nation that has trouble developing it own indigenous jet engines, we shall see but I won't be placing my money on seeing this take off.

That could have been said of America, which did not have an indigenous jet engine development programme before the British brought a sample to them.

But even with many many samples  of Russian engines, China is still behind The West and Russia in jet engine developments and being able to research, design and build it own engines completely from scratch.

[john smith 19]

What's more practical in having three sets of heavy engines instead of one set of engines?

Actually starting to build something that might fly instead of Powerpoints forever. (Something which has little to do with the number of engines.)

For a proper "Powerpoint Project"  No hardware is built

REL have built quite a lot of hardware up to the pre cooler and precooler test system, contra rotating turbines and assorted nozzle test rocket engines and heat exchangers in various technologies.

Perhaps you might like to check some of the roundup slides on their presentations?

On that basis, perhaps REL do indeed have a perfect design??  After all, there can't possibly be anything wrong with a design that only exists on Powerpoint.. and if you do just happen you notice something screwy (perhaps a design parameter or three), it takes only a minute or two to edit it.  Science Fiction folks do this all the time.

The difference is that when REL get funding they make stuff and do things, not issue another video about it.

Nor have they issued a video and then announced "Oh we can't do this but the next version will work" either.

[Rocket Science]

I try not to scoff at people that try to break new ground. History has taught us that many pathfinders were laughed at from the Wrights to Goddard and now we laud their efforts. The road of aerospace projects is riddled with forgotten individuals who sweated blood and tears and have been forgotten except for by a few.  PowerPoint comments are best reserved for wasteful government agencies that have promised a lot and delivered little to the taxpayers. Individuals that take on an aerospace project should be commend for their efforts and be allowed to prove their concept with a healthy dose of skepticism by the observers. Many X programs that might be viewed as a failures in terms of not meeting the original objectives, have still provided valuable research data increasing the knowledge base.

[john smith 19]

PowerPoint comments are best reserved for wasteful government agencies that have promised a lot and delivered little to the taxpayers.

Or in the case of the X30 and X33 delivered nothing at a total cost of $2Bn+

Individuals that take on an aerospace project should be commend for their efforts and be allowed to prove their concept with a healthy dose of skepticism by the observers.

Whenever REL have had the funds they have proved their assertions. And there have never  been too few sceptics (often with very little awareness of the subject they are talking about) to tell them they can't do it. 

Many X programs that might be viewed as a failures in terms of not meeting the original objectives, have still provided valuable research data increasing the knowledge base.

Actually that's exactly the objective of properly conducted X programmes. To fill in the design equations and charts of engineering handbooks.  It's only when they are meant to act as prototypes for operational vehicles that things usually ended badly. 

[Robotbeat]

PowerPoint comments are best reserved for wasteful government agencies that have promised a lot and delivered little to the taxpayers.

Or in the case of the X30 and X33 delivered nothing at a total cost of $2Bn+...

...delivered a lot more than Reaction Engines so far. Fabricated tanks (which had problems, but still). Even test-fired the linear aerospike. If that's your standard of "nothing," than Reaction Engines has delivered much less than nothing. Though luckily for not as much money as for X-33.

I'm not opposed to RE or Skylon, but they just don't seem to have a fire in their belly, a willingness to find a "minimum viable product" that can be built upon now without waiting decades to find someone desperate enough to sink enormous funds without any flying precursor.

It's as if SpaceX were founded, but refused to do anything but subcomponent tests of Raptor. Never flying Falcon 1, 9, cargo or crew or Heavy but just holding out hope that a few guys in California knew enough about rocketry to be worth sinking billions into for a totally unproven concept.

Now I don't know if the Chinese are serious or not. Time will tell. But at least there's a hope of something really actually flying.

[RanulfC]

AJ/RD/GE/etc don't propose aircraft. They are catering to an existing market. They anticipate that aircraft developers will keep developing newer models and will go looking for engines to power those models, so they try to push the technology further in the direction they think that market is going (more power, better fuel economy, lower maintenance costs) and sometimes they pick correctly and are selected, and sometimes they fail and have to scramble to catch up. But the basic aircraft design is never the engine manufacturer's. Not in large airliners, not in supersonic fighters, not cargo planes, not rocket launchers, not missiles.
Skylon is REL's design. Solely and utterly. Even moreso, it's mainly Bond's design.
There is no "market" of Skylon-type vehicle developers that is going to go looking for a suitable engine to power their future designs. Skylon is REL, REL is Skylon.
There's no comparison with engine companies. Hence this continual reference to conventional aircraft development makes no sense.

Er, no. In many cases this is so but strangely enough when engine manufacturers are going out to push the envelope or try and market a 'new' engine that was not a straight out development of an existing engine they quite often put them on notional or concept vehicles for marketing purposes. Aerojet did it for the RSX, Marquardt did it for their LH2 powered Supercharged-Ejection Ram Jet engine and did a much more detailed design or their H2O2/JP4 engine. Usually how detailed they get is how interested they are in selling the design, especially for a "non-standard" engine concept.

So just to be clear, you're comparing REL's development model with companies which never actually sold their product?

Do you have a successful comparison?

So we're clear you DO know who Marquardt was, right? (https://en.wikipedia.org/wiki/Marquardt_Corporation) You know the folks who built and sold THOUSANDS of different models of wind-tunnels, pulsejets, ramjets and rocket systems to every major manufacturer and military service in the US?

My comparison is that EVERY engine manufacturer occasionally goes out on a limb and more often than not they make changes to the market/industry. REL is starting OUT with a non-standard engine that address what people have considered "problems" with air-breathing launch and they are not the first to do so by any means.

[edit: Although it's interesting that in order to get even close, you had to go to VTO-boosters, even though the original analogy was the REL is acting like an aircraft-engine company.]

I didn't HAVE to bring up "VTO-boosters" to get close, specifically I brought up the SERJ because it is pretty close to what REL wants to get out of the SABRE. Lars-J brought up the Merlin, after I'd listed both air-breathing and rocket engine makers in effect working with airframe makers to bring product to market NOT running the show. The reason for bringing up rocket engine makers is, rather obviously, because rockets are involved not because they are the only thing that comes 'close' to any performance parameters.

Randy

[RanulfC]

I don't see why you have a hard time understanding my position, or think that my two statements contradict each other. If REL just wants to build and sell SABRE, they could find great success (or failure) just like many other engine manufacturers. But if they want specifically SKYLON built, then they need to take control and become the prime contractor selling it to customers.

This unwillingness to start and lead the "consortium" needed to get Skylon built is why I (and many others) for a long time assumed that REL simply wasn't interested in seeing it be built, that REL simply wanted to live off government research funding where they didn't have to produce much of anything. I've changed my mind on this - mostly - But it still appears that REL lacks that final killer instinct to make Skylon happen, by any means necessary.

I'm not having a hard time understanding your position, what's hard is trying to wrap my mind around why you think the two statements are NOT contradictory since you admit they are based on a your bias' and assumptions rather than actual business practice or history

Lets review: REL has always been attempting to sell the SABRE concept as a viable combined cycle engine for earth-to-orbit flight. In general there is and always has been a significant bias towards the assumption that any type of air-breathing engine was impractical for such operations and on top of this the principles had a very visible previously 'failed' project using a similar engine concept who's issues needed to be addressed in order to allow a focus on the engine cycle not the failed LV proposal. In addition people were questioning not only the engine cycle itself but the overall ability of any LV to reach orbit with any payload, specifically because REL was stating it could be done in a single-stage, air breathing vehicle.

So in order to address all the above REL spent time outlining and defining a notional vehicle that, using the SABRE could perform as they suggested with the performance they assumed could be derived from the SABRE in a conservative overall design. Hence Skylon. Every use of the Skylon in PR, media and written works has highlighted the performance and possibility of the SABRE specifically and the Skylon only generally. Specific enough to showcase the possibilities of the SABER but not enough to constitute a fully designed and ready to build vehicle.

This is on purpose. Yet as you note you and many others made the assumption that REL was specifically trying to get the Skylon built but as they have consistently said they are aiming at building the SABRE and Skylon is only there to provide a platform for that purpose. Skylon COULD provide the basis for SABRE powered SSTO vehicle it has been shown that as a basic concept and given close approximations of the assumed performance of the SABRE engine it would actually work which is the basic point of the whole exercise by REL.

The other false assumption is that REL could simply "sell" it's engine to a customer when it's very clear that, (and I've already noted that) in general there are no "makers" of air-breathing LVs out there to sell to. This isn't because it is known and proven that an air breathing launch vehicle isn't possible. In fact almost every major airframe maker at some point HAS done preliminary design work and (sometimes very detailed) studies into building such vehicles for almost 50 years and the consensus has always been they are quite possible with the right propulsion system.

But there's a couple of catches; First REL has to prove the engine performance. Second there are some design constraints that make the SABRE 'different' to use for an LV propulsion system that most past designs have not taken into consideration. Again, that's what Skylon is for in showing how those differences effect the airframe design and suggesting solutions or methods of addressing those effects. Simple.

The disconnect is that you had an erroneous original conclusion that while you have modified you still hold. REL never intended to sell Skylon, though thanks to the work done by REL it actually might be the basis of the real Skylon LV. But once SABRE is proven its quite possible that whomever they partner with on actual development of "Skylon" will toss all of RELs work in favor of their own design. More likely they will fold REL's Skylon into their own work and proceed from there. Much more likely is that once SABRE is proven REL will in fact have 'customers' looking to buy their SABRE's for their own designs but I wouldn't be that surprised to see the work done on Skylon itself to be included in those designs. SSTO, TSTO, whatever as already note the work REL has done IS applicable even if it's not strictly the current REL "design" of Skylon.

Randy

[RanulfC]

Thank God for China, rescuing this thread from whining about SpaceX:

Looks like they're developing their own version of Skylon.

And good for them, as Europe is too timid to fully fund such a huge sum for the full-up space plane and Reaction Engines refuses to come up with a more practical, gradual plan to develop a reusable orbital vehicle.

What's more practical in having three sets of heavy engines instead of one set of engines?

Three engine TYPES does not equate to three actual engines as I noted. The only thing different in a general description of the SABRE and what was printed is the inclusion of a ramjet and how often have we seen the SABRE described in print WITH one? (Or worse adding SCramjets? )

Thank God for China, rescuing this thread from whining about SpaceX:

Looks like they're developing their own version of Skylon.

And good for them, as Europe is too timid to fully fund such a huge sum for the full-up space plane and Reaction Engines refuses to come up with a more practical, gradual plan to develop a reusable orbital vehicle.
http://www.spaceflightinsider.com/organizations/china-national-space-administration/china-develop-hybrid-spaceplane-cheaper-space-travel/

From a nation that has trouble developing it own indigenous jet engines, we shall see but I won't be placing my money on seeing this take off.

That could have been said of America, which did not have an indigenous jet engine development programme before the British brought a sample to them.

Lockheed L-1000 was in development already before we saw a British jet. (http://www.tailsthroughtime.com/2010/06/probably-one-of-most-obscure-yet.html) Wasn't as good and was eventually developed into a more standard jet engine but it was on-going already.

Randy

[knowles2]

PowerPoint comments are best reserved for wasteful government agencies that have promised a lot and delivered little to the taxpayers.

Or in the case of the X30 and X33 delivered nothing at a total cost of $2Bn+...

...delivered a lot more than Reaction Engines so far. Fabricated tanks (which had problems, but still). Even test-fired the linear aerospike. If that's your standard of "nothing," than Reaction Engines has delivered much less than nothing. Though luckily for not as much money as for X-33.

I'm not opposed to RE or Skylon, but they just don't seem to have a fire in their belly, a willingness to find a "minimum viable product" that can be built upon now
It's as if SpaceX were founded, but refused to do anything but subcomponent tests of Raptor. Never flying Falcon 1, 9, cargo or crew or Heavy but just holding out hope that a few guys in California knew enough about rocketry to be worth sinking billions into for a totally unproven concept.

[/quote]

The difference here is that Reaction engines haven't got any billionaires on hand who is willing to stump up the money for the project, let alone one willing to go bankrupt to get Sabre and Skylon flying, they have been living on scraps of research grants for years.

I have no doubt in my mind if Reaction engines had someone willing to sink half a billion a quid into the company they would have at least ended up with an engine that works and was ready to fly and perhaps a prototype vehicle using the engines to fly. They have already aired ideas for smaller vehicles that would test the engines. But Skylon is pretty much the minimum viable product that is capable of launching satellites into space or doing anything useful up there. Anything smaller and you lose a lot capabilities, why not reducing costs all that much. 

Musk took all of the early risks of Space X on himself, building the engine and Falcon 1, he then convince his friends , a lot of them billionaires and millionaires to fund Falcon 9 launch.

Personally I'm still surprise they are quoting 12bn pounds for Skylon, which seems to me way overpriced. I think it may well be worth their time and effort to recalculate that cost using Space X approach.

I suspect RE had two billion quid they would have gotten a working engine and least a prototype vehicle fly of some sort flying at least to sub orbital or even orbital, an the manufacturing facility ready to build a larger, more capable vehicles.

[Rocket Science]

PowerPoint comments are best reserved for wasteful government agencies that have promised a lot and delivered little to the taxpayers.

Or in the case of the X30 and X33 delivered nothing at a total cost of $2Bn+...

...delivered a lot more than Reaction Engines so far. Fabricated tanks (which had problems, but still). Even test-fired the linear aerospike. If that's your standard of "nothing," than Reaction Engines has delivered much less than nothing. Though luckily for not as much money as for X-33.

I'm not opposed to RE or Skylon, but they just don't seem to have a fire in their belly, a willingness to find a "minimum viable product" that can be built upon now without waiting decades to find someone desperate enough to sink enormous funds without any flying precursor.

It's as if SpaceX were founded, but refused to do anything but subcomponent tests of Raptor. Never flying Falcon 1, 9, cargo or crew or Heavy but just holding out hope that a few guys in California knew enough about rocketry to be worth sinking billions into for a totally unproven concept.

Now I don't know if the Chinese are serious or not. Time will tell. But at least there's a hope of something really actually flying.

Absolutely, we got more bang for the X-33, from rocket engine to cryopumping issues and composite tank data. Of course the agency PowerPoint program I had in mind was  the 9B NASA Constellation; however we did get a tower and a really neat large scale model rocket launch...

[Paul451]

Yet as you note you and many others made the assumption that REL was specifically trying to get the Skylon built but as they have consistently said they are aiming at building the SABRE and Skylon is only there to provide a platform for that purpose.

Perhaps because every time someone suggested an alternative (especially TSTO), they were jumped over by the true-believers who insisted that Skylon was the one-true-design, perfect in every way, and anything else was madness and ignorance.

I mean, where have you been for the last 5 threads?

Do you have a successful comparison?

So we're clear you DO know who Marquardt was, right?

Bankrupt.

and a really neat large scale model rocket launch...

It's amazing how big you can make fireworks.

[Rocket Science]

Yet as you note you and many others made the assumption that REL was specifically trying to get the Skylon built but as they have consistently said they are aiming at building the SABRE and Skylon is only there to provide a platform for that purpose.

Perhaps because every time someone suggested an alternative (especially TSTO), they were jumped over by the true-believers who insisted that Skylon was the one-true-design, perfect in every way, and anything else was madness and ignorance.

I mean, where have you been for the last 5 threads?

Do you have a successful comparison?

So we're clear you DO know who Marquardt was, right?

Bankrupt.

and a really neat large scale model rocket launch...

It's amazing how big you can make fireworks.

All you need is " We the people's" money...

[john smith 19]

...delivered a lot more than Reaction Engines so far. Fabricated tanks (which had problems, but still). Even test-fired the linear aerospike. If that's your standard of "nothing," than Reaction Engines has delivered much less than nothing. Though luckily for not as much money as for X-33.

I'm not opposed to RE or Skylon, but they just don't seem to have a fire in their belly, a willingness to find a "minimum viable product" that can be built upon now without waiting decades to find someone desperate enough to sink enormous funds without any flying precursor.

It's as if SpaceX were founded, but refused to do anything but subcomponent tests of Raptor. Never flying Falcon 1, 9, cargo or crew or Heavy but just holding out hope that a few guys in California knew enough about rocketry to be worth sinking billions into for a totally unproven concept.

Now I don't know if the Chinese are serious or not. Time will tell. But at least there's a hope of something really actually flying.

Absolutely, we got more bang for the X-33, from rocket engine to cryopumping issues and composite tank data. Of course the agency PowerPoint program I had in mind was  the 9B NASA Constellation; however we did get a tower and a really neat large scale model rocket launch...

None of which was essential to meeting the only core requirement of the X33 programme which was demonstrate SSTO or near SSTO performance of a vehicle. BTW X33 was a 1$Bn programme and that was expected to deliver a complete flight vehicle on that budget. LM sucked down the whole budget and delivered nothing close to a flight vehicle.

REL identified designing and making the pre-cooler as the unknown element in the SABRE design so that's what they went for. 

That's what you do when your goal is to make something work, not suck up as much government money as possible to ensure your core ELV business is protected.

[john smith 19]

Perhaps because every time someone suggested an alternative (especially TSTO), they were jumped over by the true-believers who insisted that Skylon was the one-true-design, perfect in every way, and anything else was madness and ignorance.

SABRE is an engine designed to accelerate a vehicle from runway to orbit. It is also designed to be testable on the ground. Either it will meet those performance specs or it does not, before you have to install it in a vehicle and fly it.

Either you want an engine that can go from runway to orbit or you do not.

If you want runway to orbit you need a SABRE cycle. If you do not then whatever it is is not a SABRE cycle. REL are probably the lead developers on those as well with the Scimitar. Call it whatever you want, but it's not a SABRE.

If you've got a fully orbital capable engine not to build an SSTO round it only makes sense if you're too scared to do the design. Given REL have spent some time and effort on doing such a reference design for you it would an epic failure of nerve not to. 

It's just a series of logical questions.  It's a question of what a prospective customer wants and do they understand what they are getting. Saying you want TSTSO and SABRE is simply illogical.

I'm quite sure there is plenty about Skylon that has deliberately been left low resolution so the vehicle consortium can impose their own mark on the design but I also expect it would take a lot of effort to come up with a design that looked radically different that can do the job as well as Skylon is expected to.

Once you understand the massive CoG and CoL shifts during the M0-M23-M0 flight path and you want an easily controlled vehicle the Skylon configuration is tough to beat.

[Rocket Science]

...delivered a lot more than Reaction Engines so far. Fabricated tanks (which had problems, but still). Even test-fired the linear aerospike. If that's your standard of "nothing," than Reaction Engines has delivered much less than nothing. Though luckily for not as much money as for X-33.

I'm not opposed to RE or Skylon, but they just don't seem to have a fire in their belly, a willingness to find a "minimum viable product" that can be built upon now without waiting decades to find someone desperate enough to sink enormous funds without any flying precursor.

It's as if SpaceX were founded, but refused to do anything but subcomponent tests of Raptor. Never flying Falcon 1, 9, cargo or crew or Heavy but just holding out hope that a few guys in California knew enough about rocketry to be worth sinking billions into for a totally unproven concept.

Now I don't know if the Chinese are serious or not. Time will tell. But at least there's a hope of something really actually flying.

Absolutely, we got more bang for the X-33, from rocket engine to cryopumping issues and composite tank data. Of course the agency PowerPoint program I had in mind was  the 9B NASA Constellation; however we did get a tower and a really neat large scale model rocket launch...

None of which was essential to meeting the only core requirement of the X33 programme which was demonstrate SSTO or near SSTO performance of a vehicle. BTW X33 was a 1$Bn programme and that was expected to deliver a complete flight vehicle on that budget. LM sucked down the whole budget and delivered nothing close to a flight vehicle.

REL identified designing and making the pre-cooler as the unknown element in the SABRE design so that's what they went for. 

That's what you do when your goal is to make something work, not suck up as much government money as possible to ensure your core ELV business is protected.

I would have loved to have seen that 9B spent on SKYLON on a joint R&D program between the air forces of both US and the UK...

[Hanelyp]

I have to agree with Paul that using a Sabre cycle engine for the first stage of a 2STO launcher is not a stupid idea.  Sabre is designed to deliver SSTO performance, but that does not eliminate using the engine on a booster stage as a viable concept.  A launcher that can cruise to "launch" point, shotput to altitude at hypersonic speed, and the booster then cruise back to a runway, has some operational advantages.  Like all rocket launchers, staging tends to improve the payload/GTO ratio, though that's not the best metric for a design's economics.  Vs. a rocket booster return to start point is easier.  Whether the economic case closes for SSTO or 2STO launchers based on the engine is harder to see from where I stand.

[Lars-J]

I have to agree with Paul that using a Sabre cycle engine for the first stage of a 2STO launcher is not a stupid idea.  Sabre is designed to deliver SSTO performance, but that does not eliminate using the engine on a booster stage as a viable concept.  A launcher that can cruise to "launch" point, shotput to altitude at hypersonic speed, and the booster then cruise back to a runway, has some operational advantages.  Like all rocket launchers, staging tends to improve the payload/GTO ratio, though that's not the best metric for a design's economics.  Vs. a rocket booster return to start point is easier.  Whether the economic case closes for SSTO or 2STO launchers based on the engine is harder to see from where I stand.

Exactly. What makes SABRE unique is the air breathing phase. Once you are above the atmosphere (or cease collecting O2), then it is no different than a normal rocket engine. And that is where staging - if one wanted to do it - would make sense.

[RanulfC]

Yet as you note you and many others made the assumption that REL was specifically trying to get the Skylon built but as they have consistently said they are aiming at building the SABRE and Skylon is only there to provide a platform for that purpose.

Perhaps because every time someone suggested an alternative (especially TSTO), they were jumped over by the true-believers who insisted that Skylon was the one-true-design, perfect in every way, and anything else was madness and ignorance.

I mean, where have you been for the last 5 threads?

Here Arguing that while it's "non-optimum" it's not only a consideration but, (and I've said this consistently) that the Skylon design itself while it is technically an SSTO vehicle is specifically a TSTD (Two-Stage-To-Destination) design as it's based on the idea of equaling EELV satellite delivery capability. That requires delivery to GTO and Skylon can't do it alone so needs a stage/transfer-vehicle/what-have-you.

Do you have a successful comparison?

So we're clear you DO know who Marquardt was, right?

Bankrupt.[/quote]

After being quite lucrative over decades and it actually still exists IIRC so my point stands.

SABRE is an engine designed to accelerate a vehicle from runway to orbit. It is also designed to be testable on the ground. Either it will meet those performance specs or it does not, before you have to install it in a vehicle and fly it.

Either you want an engine that can go from runway to orbit or you do not.

Rather simplistic actually. It keeps being said that if you want an engine for a TSTO you want the Scimitar and not the SABRE because of the mistaken belief that "if you want to go to orbit need SABRE, if you're not going all the way you don't" which is, pardon me BS.

If you want runway to orbit you need a SABRE cycle. If you do not then whatever it is is not a SABRE cycle. REL are probably the lead developers on those as well with the Scimitar. Call it whatever you want, but it's not a SABRE.

SABRE isn't a single niche engine no matter what people think though that's what REL WANTS the simple and very obvious truth is it's not that limited of an engine cycle. SABRE is capable of air-breathing up to around Mach-5 pretty easily followed by rocket powered flight, technically up to orbital speed but that should be noted that includes every Mach number short of that speed as well. Note the main difference between SABRE and Scimitar is the latter is designed for extended CRUISE at hypersonic speed while the former is designed as an acceleration engine.

"Runway-to-Orbit" is NOT about the engine, as I've often pointed out the SERJ and several other combined cycle engine system are perfectly capable of performing the same mission and have been since the mid-50s. The major problem is they almost all got caught in the two main traps of thinking at the time, (and currently if we are being honest) liquid-air-cycle and SCramjets as "requirements" for operation. "Runway-to-Mach-10-and-500,000ft" would be something that SABRE could and would do as well as orbital flight so trying to say a SABRE is ONLY good for runway-to-orbit and nothing else is simply a bias on the part of the person saying it.

There's optimum and then there's good-enough either of which SABRE is perfectly capable of handling and still being SABRE.

If you've got a fully orbital capable engine not to build an SSTO round it only makes sense if you're too scared to do the design. Given REL have spent some time and effort on doing such a reference design for you it would an epic failure of nerve not to. 

That statement actually hurts my brain because it points up a lot of misunderstandings about what REL has done, what they are proposing, and what their goals are. In reverse order; TSTOs have proven advantages over SSTO designs when directly compared and vice-versa so the 'call' to go one way or the other is a business, engineering, and operations decision. Not something you base on optimum use of a specific engine design. RELs "efforts" have amounted to what would be a very preliminary study of a possible airframe that can maybe do "this" with an assumed performance of "this" from the propulsion system. REL has gone a bit further due to being biased towards an SSTO design but because they are not in fact airframe designers/makers they have missed some obvious areas. Any actual airframe designer/engineer/maker is going to take the "Skylon" design under consideration and then do actual trade studies to define a REAL design capable of doing what the overall business/market/user requires.

The REL "Skylon" has a leg up in the preliminaries because of the work REL has done but they didn't do the work to actually DESIGN an airframe, they did the work to define something that by using SABRE engines that meet expectations could do "this" operationally. Someone who's going to make an actual Skylon vehicle will do a lot more detailed and in-depth work which may or may not validate RELs assumptions and combine that with marketing and operational inputs which may not in fact recommend an SSTO design at this time or a different airframe configuration.

Again I'd be highly surprised if the actual "Skylon" design gets built as it has some issues that need more work, but the work REL has already done address some general known issues relating to hypersonic, high altitude, and trans-orbital flight, just not to the level that Skylon would be considered an "actual" design in it's present form.

More in the next post because addressing the assumptions in the rest is going to be a bit long... And "I" said that so you've been warned

Randy