The Reaction Engines Skylon/SABRE Master Thread (6)

[RanulfC]

I don't think you understand how this works. YOU made the claim, with no evidence to back it up. I challenged it.

Actually "I" made the claim and as I've noted above the 'evidence' is pretty plain. Specifically that neither Musk nor Bezos have actually 'considered' air-breathing engines or propulsion or winged vehicle during their design process.

But since you asked, here is what Musk has said about air breathing launch vehicles: http://shitelonsays.com/transcript/elon-musk-lecture-at-the-royal-aeronautical-society-2012-11-16   (search in page for 'reaction engines')

Sure:
"With respect to air breathing hybrid stages, I have not seen how the physics of that makes sense. There may be some assumptions that I have that are incorrect, but really, for an orbital rocket, you're trying to get out of the atmosphere as soon as possible because the atmosphere is just as thick as soup when you're trying to go fast, and it's not helped by the fact that the atmosphere is mostly not oxygen." It's 80% nitrogen. So, mostly what you're air breathing is chaff, not wheat, and having a big intake is like having a giant brake. The braking effect tends to overwhelm the advantage of ingesting 20% oxidizer. You could just make the boost stage 5% to 10% larger and get rid of all the air breathing stuff and you're done."

Lets start with the obvious, he was asked about REL and the SABRE and he admits he has assumptions that may be incorrect. He then compounds the issue by pointing to most of the rather wrong assumptions as the reasons he does not consider air breathing for orbital launch. He then points to simply building a bigger 'rocket' stage and not bothering with the atmosphere at all.

Well what about REL specifically? Actually he never goes into any detail which is likely as he doesn't consider it much:
"This is using an air breathing engine? When I looked at the numbers it didn't seem too compelling compared to having a slight increase in the size of the first stage. So if you're going to add a whole bunch of complexity, it needs to really pay off and, at least using the numbers I've seen, I have a hard time seeing how it does pay off - but I could be wrong about that. If there is really a big advantage then it would be worth investigating, but it would have to be a big advantage. I would be reluctant to add essentially some sort of jet engine on top of the rocket engine problem."

Note he could be wrong and admits it but since he doesn't know any details, (or care) it's not something he's going to consider. (And again note he has ONLY considered numbers he's been given/seen which in no way sounds like what goes on in official 'trades' or studies, just his own work)

And specifically about Skylon:
"Don't know it well enough. In the past, whenever I've done the basic math on an air breathing stage, it doesn't seem to make sense, but I could be wrong about that and I always look to figure out how I can better understand things. I think it's maybe easier to just increase the size of the boost stage than to add an air breathing stage."

And as long as you're only looking at rockets just making the stage bigger will always win in the end. Bias all the way. (Oh he's 'done-the-math' alright but the question of worth is WHAT math because there are many different ways and formulas to use depending on the overall mission profile. As noted he's probably never done anything BUT the 'basic' math which will invariably lose to the 'basic' math of a pure rocket powered, multistage launch vehicle which is where he was always going in the first place)

You seem so very sure he's wrong. Do you have facts or just your simple faith to guide you?

Pot, kettle, black? You are so convinced that Skylon is the way forward, that anyone who did 'due diligence' on it must have selected it, and the only way one could explain them not selecting that path is by not doing 'due diligence'. 

I know we are in a post-facts society, but at least TRY to step out of your bubble.

What you said Mr. Kettle/Potter

Seriously, I'm going to point out that the POINT was that Musk did NOT do any 'due-diligence" work on air breathing as he had already decided it wasn't a viable option so assuming his 'opinion' on Skylon or SABRE is any more relevant than anyone else's is a stretch. He didn't, Bezos didn't and they both are quite obvious in their opinions which SHOULD make anyone who stops to think for a moment actually DOUBT their opinions as they quite obviously, (and in Musk's case ADMITED) don't know enough to offer a viable opinion on the subject.

As everyone should be aware by now I personally don't think that Skylon and SSTO is the way forward even WITH SABRE working as advertised for a number of reasons, most of which are not in fact technical The problem I have is the assumption of "due diligence" by someone when there is in fact no evidence of that being the case and then that assumption being used to justify inflating opinions over those who not only have the means, knowledge and ability to actually DO "due diligence" calculations which show the original opinion may in fact have been wrong.

Randy

[john smith 19]

My view has always been that it has been the cost of moving mass to space that has blocked our ability to expand humanity out into space.  Essentially that it doesn't matter what the technology is, the entire cost to move a kg of mass to space has to drop substantially over time.

A very reasonable PoV.

Unfortunately it has not happened. And it's likely it won't happen with semi reusable systems either.   

"National pride" had nothing to do with it.  NASA is the majority owner of the ISS, and if it didn't take steps to create a cargo resupply system to take over for after the end of the Shuttle, the ISS may not have continued.  And remember that the SpaceX Dragon is the only vehicle that could replace the down-mass need from the ISS, so it's not like there were valid alternatives available to ensure redundant services.

Note that was a design decision taken by Orbital.

I've never had an issue with the UK supporting the Skylon.  I've only had an issue with the claim that the Falcon 9 development was state supported.

I'd suggest a much stronger case could be made for state support for Orbital's Antares  rocket. That didn't seem to have a test flight planned before going operational. That was entirely funded by NASA IIRC.

You've actually touched on the core of the issue here.  The other COTS participants didn't continue building their proposed capabilities because there wasn't a market outside of the ISS to target.  And "revolutionary" or not, their hardware solutions would have worked just fine, but they were not as cost competitive as Orbital and SpaceX - and money is the deciding factor in a competitive environment.

And yet SNC with Dream Chaser still seems to be pushing on....
It was ATK that pulled the plug on Liberty.

So I'd say it's more a question of wheather you're a public company or not that decides this. IE the sole determiner is corporate structure.

But would the UK, or even ESA as a whole benefit from such an approach? Hell yes.

Here in the U.S. we have a thing called "pork politics", which is government spending that is based on politics, not need.  My hope would be that the money spent on the Skylon would result in a net add to the GDP of the UK, but that would only happen if there was a "demand" for it's capabilities.

Hopefully there is, but just because something is "revolutionary" doesn't mean that there is.

My $0.02

The difference between Skylon and every other concept or LV to date is that it is designed to be sold to other operators.

So as long as someone wants to buy it it would enrich the UK economy.

Ideally one of those operators would supply it's services to HMG or (radical notion here) HMG could actually operate it themselves.

I would have thought that should the U.K. ever come round to that sort of support for Skylon it would be in the form of a PPP like the one that funded Skynet. They would contract for so many Skylon launches/year so much responsive  availablity with the excess capacity being available for commercial sale and a consortium would then be formed to privately purchase the Skylon's and operate the launch company, which is how Skynet is managed.

That would allow REL to approach merchant banks and other institutions for further funding.

I just really want them to launch from Ascension.

Doubtful. I'm not sure it's got the length or the strength for it. Kourou remains pole position. It's about 2 deg closer to the equator.

[john smith 19]

"Intact Abort" is a built in and design feature and is not limited to any type of design, especially in space launch. And no even if both stages run on different propellants "intact abort" can be designed in.

True, but the fact that AFAIK no TSTO offers it suggests it's extraordinarily difficult to design in, let alone retrofit to an existing system.

Staging IS in fact a 'complication' but is a very proven and effective technique and would be more so in a fully reusable TSTO design.

I would say the way SX does staging is more reliable than the usual pyrotechnics system but it is something that has to work. I think

Again that's the main "wings-and-wheels" argument which is questionable for space launch purposes. If you assume you need them then they are great, if you don't they have less value than it would seem.

Historically if you've got a design with low Isp (and all rocket engines hae low Isp relative to air breathers) you'd want to get up to speed and altitude ASAP. Historically a rocket powered HTOL SSTO gives you the same issues of structural mass fraction as a VTOL and the needed mass of wings.  No surprise such an idea would be rejected early on.

Which just demonstrates SSTO is very tricky without either a really low structural fraction or a really good engine or both. SABRE lets you evaluate how good an engine it will be before you have to build the airframe.

Having them makes you 'safer' only under certain circumstances and for certain values of 'safer' since you have to dump propellant AND find a suitable place to set down within gliding range as compared to a VTOL spot of flat ground.

IRL either system would have pre planned locations to go to during their trajectories. But Skylon is designed to be statically stable and not need engine restart. It will probably need LOX dump and LH2 dump to safe the vehicle before emergency landing but that's basically 2 valves, or even none if they just shut off ignition and let the propellants stream through the engine.

Which is nice and all but kind of hard to understand since most international flight certification organizations have come right out and said that no "launch vehicle" is going to be certified in that manner because they are NOT aircraft. The only possible exceptions are aircraft used as carrier vehicles for launching vehicles which specifically applies to the carrier AIRCRAFT because it IS an aircraft. Carried launch vehicles, (such as Spaceship 2 for example) are NOT planned to be given aircraft like certifications in the foreseeable future.

It's got wings and it will be breathing air during the part of the flight when it's under any regulators jurisdiction. Since SABRE gives "virtual staging" benefits I think a case could be made. I'd wonder how the combines cycle systems you've mentioned would have been dealt with. 

Actually ANY launch system has 'range' requirements this isn't as restrictive as most people think either. Skylon is no different as it has to have cleared airspace corridors and ground track, though like most space launch systems it will get away with much of this by going over water. Every transportation system has such limitations imposed by public safety and good sense.

True

The public tends to allow variance over time as the system improves but for the most part space launch is always going to require more separation and a bigger buffer zone.

And let's be honest the fact the failure rate has never dropped below about 4% for ELV's has not helped.

If you want to launch more people or cargo you can always use multiple pads and that actually reduces your range overhead by splitting it up among multiple users per day.

If you can justify it at that price point.

AFAIK the current systems launch what's needed, but unless that price point falls a lot the market will never expand.

Launch CAPACITY isn't the problem though it is the general requirements and economics that are holding back space development. Find a reason to launch more and the capability will be there.

At the relevant $62-100m+ point, not the $6m mark.

[Paul451]

It will probably need LOX dump and LH2 dump to safe the vehicle before emergency landing but that's basically 2 valves, or even none if they just shut off ignition and let the propellants stream through the engine.

Que? I can see how you can shut off an engine, I can see how you let propellants flow, but how do you do both simultaneously?¹

_{¹ Outside of a spark-plug pulse engine like a petrol ICE.}

[re: intact abort] the fact that AFAIK no TSTO offers it suggests it's extraordinarily difficult to design in, let alone retrofit to an existing system.

It's not really a design difficulty, let alone an "extraordinary" one. It's more of a chicken and egg situation. On a TSTO, cargo-LAS reduces your payload, as would any LAS system, so you can only offer it for smaller payloads. Additionally, most recovered payloads would then require virtually a full break-down and rebuild after such an abort in order to re-certify them, and the existing launch insurance industry doesn't have a mechanism to determine losses in such cases. Hence you might as well let it burn, claim the loss and buy a new satellite.

There might be a market for cargo-LAS for self-insured, very expensive, one-off designs, where the owner is willing to pay extra for an additional chance of recovery if the launch fails, but none have had sufficient budgets to be the first to fund the development of a bespoke recovery system just for that single payload.² And there are too few such payloads for existing launchers to be motivated to develop it out of their own pocket, unless someone else paid them to. And (AFAICT) there's no way for a third party to offer a cargo-LAS that's compatible with all launchers, hence no way for them to tap into even those handful of potential customers.

Skylon inherently allows flyback.³  So even if there's a small percentage of self-insuring customers who care, it's there as an option. That might prompt the insurance industry⁴ to develop a mechanism for assessing partial losses for re-certification, which solves the chicken'n'egg problem for conventional payloads...

<sub>² Even for monsters like JWST, no-one would seriously suggest creating a LAS. But if there was an existing standard off-the-shelf option, with known properties, NASA might be willing to pay a premium to avoid losing a $9 billion payload.

³ But only in a very narrow range of failures. You have to get a clean shut-off of both engines simultaneously, still have control of aerodynamic surfaces or both aero-surfaces and RCS, fully functioning electrical/GNC system and landing gear, and no structural damage that preclude re-entry, atmospheric flight, and landing.

⁴ The insurance issue will apply to Skylon, there's no model to assess the cost of payload re-certification as a claimable loss. But for irreplaceable payloads there will be customers (mainly government) who would love one-extra-chance at recovery, even if there's no insurance to pay for re-cert.</sub>

[oddbodd]

_{³ But only in a very narrow range of failures. You have to get a clean shut-off of both engines simultaneously, still have control of aerodynamic surfaces or both aero-surfaces and RCS, fully functioning electrical/GNC system and landing gear, and no structural damage that preclude re-entry, atmospheric flight, and landing.}

Actually, I'm pretty sure (from one of the presentation videos) that the Skylon design is supposed to allow for powered flight with a single engine just like a commercial airliner. It's the main reason the tail rudder is so large, so as to counter-act the turning force of the remaining working engine. This of course assumes that whatever failed didn't degrade the vehicle to the point that flight of any kind was impossible.

[Star One]

Nothing really new, but I thought it was an interesting summary of the UK government thinking on space.

http://spacenews.com/britain-endorses-esa-promises-increased-export-credit-support-for-industry/

They are blaming Reaction Engine and EU for the slow release of government funds for Sabre engine development, but that pretty normal for this government, everyone but themselves are to blame.

Already posted in here several days ago.

[knowles2]

Nothing really new, but I thought it was an interesting summary of the UK government thinking on space.

http://spacenews.com/britain-endorses-esa-promises-increased-export-credit-support-for-industry/

They are blaming Reaction Engine and EU for the slow release of government funds for Sabre engine development, but that pretty normal for this government, everyone but themselves are to blame.

Already posted in here several days ago.

Must have missed it amongst all the bickering about how seriously Musk and Benzo have look at Reaction engines and Sabre/Skylon.

[Coastal Ron]

"National pride" had nothing to do with it.  NASA is the majority owner of the ISS, and if it didn't take steps to create a cargo resupply system to take over for after the end of the Shuttle, the ISS may not have continued.  And remember that the SpaceX Dragon is the only vehicle that could replace the down-mass need from the ISS, so it's not like there were valid alternatives available to ensure redundant services.

Note that was a design decision taken by Orbital.

And NASA would have been thrilled to have a redundant down-mass capability.  But that doesn't change the calculus for why NASA created the COTS/CRS program.

I'd suggest a much stronger case could be made for state support for Orbital's Antares  rocket. That didn't seem to have a test flight planned before going operational. That was entirely funded by NASA IIRC.

As with SpaceX, NASA only paid for a small part of the cost of a demonstration mission, and DID NOT fund the development of Antares through the COTS program.

And yet SNC with Dream Chaser still seems to be pushing on....
It was ATK that pulled the plug on Liberty.

So I'd say it's more a question of wheather you're a public company or not that decides this. IE the sole determiner is corporate structure.

Lots of debate about what makes a company "Old Space" vs "New Space".  The definition I use is that "New Space" is willing to risk their own money, whereas "Old Space" would rather risk Other People's Money.

The difference between Skylon and every other concept or LV to date is that it is designed to be sold to other operators.

I really don't care what the business model is, I only care about what the customer pays to move mass to space.  And while selling a Skylon may make economic sense to the UK, the added cost a service provider has to take into account for their pricing may not make the Skylon anymore cost effective than other transportation options.

So as long as someone wants to buy it it would enrich the UK economy.

As Airbus investors will gladly tell you, unless you can sell ENOUGH of your product you may actually LOSE money in the whole venture.  That is certainly the outlook for the A380.  So your statement is not a reflection of reality.

[high road]

I'd suggest a much stronger case could be made for state support for Orbital's Antares  rocket. That didn't seem to have a test flight planned before going operational. That was entirely funded by NASA IIRC.

As with SpaceX, NASA only paid for a small part of the cost of a demonstration mission, and DID NOT fund the development of Antares through the COTS program.

Can you tell me what the 42% of the development programme that was paid for by the government was used for? This might be semantics, but 42% or 47% are not 'small parts' to me. If you want to put the 'state supported' marker nearer to the 100% mark, fine. Arguing about that is as pointless as arguing about the color of 'the dress'.

page 95 in the aformentioned final report: http://www.google.be/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0ahUKEwi98-aX_s_QAhXGWhoKHYFqA0YQFgguMAI&url=http%3A%2F%2Fwww.nasa.gov%2Fsites%2Fdefault%2Ffiles%2Ffiles%2FSP-2014-617.pdf&usg=AFQjCNHlDAikuHiJ3Ud5oNKCBAdOhR5OAQ&sig2=Xq3m2hu4XXoAomdLxW-vgA&bvm=bv.139782543,d.d2s

And yet SNC with Dream Chaser still seems to be pushing on....
It was ATK that pulled the plug on Liberty.

So I'd say it's more a question of wheather you're a public company or not that decides this. IE the sole determiner is corporate structure.

Lots of debate about what makes a company "Old Space" vs "New Space".  The definition I use is that "New Space" is willing to risk their own money, whereas "Old Space" would rather risk Other People's Money.

Well, newspace seems to be a little less than half as happy to spend 'other people's money' as oldspace. But it is indeed a good thing that they invest their own money. Now how would doing exactly the same thing for Skylon be different than doing it for SpaceX? Other than that Skylon would likely be one of the participants that don't make it to the end, like most COTS participants. IIRC, expectations weren't that high for SpaceX at the start, having never succefully launched a rocket and all. Live and be surprised.

[Coastal Ron]

Can you tell me what the 42% of the development programme that was paid for by the government was used for? This might be semantics, but 42% or 47% are not 'small parts' to me. If you want to put the 'state supported' marker nearer to the 100% mark, fine. Arguing about that is as pointless as arguing about the color of 'the dress'.

You can find the answer to your question on that same page, above the chart - "low- Earth orbit transportation systems", which are the Dragon and Cygnus spacecraft systems.  Which is what the milestone payments clearly show.

Have you looked at the milestone payment schedule that I referenced?  I'm not sure how much clearer it can be to show that no funds were paid for development of the Falcon 9 or the Antares.

Well, newspace seems to be a little less than half as happy to spend 'other people's money' as oldspace.

You are apparently referencing the chart in that NASA report, but since "Old Space" would not risk any of their own money, then the 42% "New Space" would risk would be infinitely more than the 0% "Old Space" would risk.

And since I've (again) been able to show that no NASA money went to developing the launch systems (i.e. the Falcon 9 and Antares), private investment covered 100% of the risk.

Now how would doing exactly the same thing for Skylon be different than doing it for SpaceX?

Elon Musk used his own money to start SpaceX, and was able to attract outside investment.  On top of that, SpaceX was able to convince customers to pay them launch deposits, which they were able to use for development also.  Add on top of that the profit they likely made from other services, and you can see that if the service you plan to provide has enough demand, that you can bootstrap yourself without direct government subsides.

Other than that Skylon would likely be one of the participants that don't make it to the end, like most COTS participants. IIRC, expectations weren't that high for SpaceX at the start, having never succefully launched a rocket and all. Live and be surprised.

Failure is always an option, but for NASA they always had backups for the COTS program.  Remember it was originally Rocketplane-Kistler that won the COTS contract, not Orbital, and Orbital was only awarded their COTS contract after Rocketplane-Kistler failed to complete mandatory financial milestones.  If SpaceX would have failed NASA would have backfilled with one of the other runners up, such as Boeing or Lockheed Martin.

But SpaceX did succeed, and along the way it continued to win launch services contracts from commercial companies, which was really the secret to it's early success - they found customers willing to hand them money before they had proved they could provide the service.

Why can't Skylon find customers for it's product/service and get them to fund Skylon development?

[john smith 19]

As with SpaceX, NASA only paid for a small part of the cost of a demonstration mission, and DID NOT fund the development of Antares through the COTS program.

I don't think I said they did, although I'm unaware of any other customer that Orbital had planned for the Antares concept.

Lots of debate about what makes a company "Old Space" vs "New Space".  The definition I use is that "New Space" is willing to risk their own money, whereas "Old Space" would rather risk Other People's Money.

I'd suggest a big part of that is they don't have stockholders and a stock price to manage.

I really don't care what the business model is,

Perhaps you should investigate it a bit more.

While the model is one mfg / one operator (and they are basically branches of the same company) you won't get anywhere near the level of cost sharing needed to radically lower $ per unit mass to orbit.

Making that system an ELV, or at best semi reusable, will not lower that price below the cost of the expendable stages and the refurb cost of the first stage, and that only happens after a substantial number of launches of a semi reusable system.

That is of course if the operator agrees to lower the price it offers to its customers.

I only care about what the customer pays to move mass to space. 

Then you need to understand what drives those prices.

And while selling a Skylon may make economic sense to the UK, the added cost a service provider has to take into account for their pricing may not make the Skylon anymore cost effective than other transportation options.

Skylon's mfg and economics have been scrutinized by third party consultancies to test wheather their business model is viable.

I'm unaware of any other company that's had their plans have any level of outside study.

So as long as someone wants to buy it it would enrich the UK economy.

As Airbus investors will gladly tell you, unless you can sell ENOUGH of your product you may actually LOSE money in the whole venture.  That is certainly the outlook for the A380.  So your statement is not a reflection of reality.
[/quote]
The UK economy would be enriched by the money earned (and spent) by the workforce hired to build it.

As for you point about selling enough that's the situation with all normal products that don't use the cost model of weapon systems IE where the whole R&D programme cost is dropped on the first batch made.

[high road]

Can you tell me what the 42% of the development programme that was paid for by the government was used for? This might be semantics, but 42% or 47% are not 'small parts' to me. If you want to put the 'state supported' marker nearer to the 100% mark, fine. Arguing about that is as pointless as arguing about the color of 'the dress'.

You can find the answer to your question on that same page, above the chart - "low- Earth orbit transportation systems", which are the Dragon and Cygnus spacecraft systems.  Which is what the milestone payments clearly show.

Have you looked at the milestone payment schedule that I referenced?  I'm not sure how much clearer it can be to show that no funds were paid for development of the Falcon 9 or the Antares.

I did, but during this discussion, it seems that there's no clear view whether NASA paid for 'an ISS supply system' with or without the rocket that gets that supply system up there. The report you mentioned mentions Falcon 9 as part of the hardware being developend by SpaceX to meet their COTS milestones, page 20 to 23, including review by NASA, which doesn't exactly come for free.

Yes, SpaceX did the development and NASA paid them when they met milestones. That's exactly the programme that would be great for Skylon and other desings that would attempt to compete.

Note the graph with alternative supply capabilities on page 18. Maybe no more downmass, but that could have been done by working together with the other ISS partners. So it's not like there were no alternatives to meet NASA's need to supply ISS. But no domestic commercial ones, which is the goal of COTS.

Well, newspace seems to be a little less than half as happy to spend 'other people's money' as oldspace.

You are apparently referencing the chart in that NASA report, but since "Old Space" would not risk any of their own money, then the 42% "New Space" would risk would be infinitely more than the 0% "Old Space" would risk.

Now that's where you enter my territory:

Statistical nonsense alert: Even if NASA covered 99.99% of the cost, newspace would still have an 'infinitely higher risk' than oldspace, and would bear 'all the risk'. While in reality, the remaining value at risk becomes a lot lower, as investors only need to fund the development towards the next round, and receive a known prize upon completion of that round. The value at risk of every round is same as the value of the prize. This part has a lower probability of default.

The value at risk to the completion of the project is the remaining cost of each round above each prize. Earlier phases have a lower value at risk, but a much higher probability of default as there is a possibility that you might not make it to the end.

So a research programme that with prizes that cover a higher percentage of the early costs and less of the final phase, would attract more investors than a programme that covers a stable percentage of the costs along the way.

(Let's ignore for the sake of simplicity the risk to NASA: that no organization is able to complete the programme in an acceptable amount of time).

Edit: Warning: if you respond to this in a way that does not make statistical sense, I'll be forced to explain this with numbers. Very few people on this forum like crunching the numbers on financial issues ;-)

Now how would doing exactly the same thing for Skylon be different than doing it for SpaceX?

Elon Musk used his own money to start SpaceX, and was able to attract outside investment.  On top of that, SpaceX was able to convince customers to pay them launch deposits, which they were able to use for development also.  Add on top of that the profit they likely made from other services, and you can see that if the service you plan to provide has enough demand, that you can bootstrap yourself without direct government subsides.

Why can't Skylon find customers for its product/service and get them to fund Skylon development?

I'm right there with you that Skylon should not be the only design that should be able to profit from this hypothetical programme.

SpaceX has repeatedly stated that Falcon 9 would not have been possible, or only much later, if it hadn't been for NASA's help. It's public knowledge that SpaceX was struggling to find more investors. It probably would have struggled on to get Falcon 1 flying if NASA hadn't stepped in. Because finding investors is a lot harder if your only hardware is still a lot of development away. Unless of course if you can show that the government is going to put up a part of the bill at various stages along the development process, doesn't let you achieve milestones easily (so investors know their money isn't hemorraging out without actual progress), and promises to buy the service at the end.

So Skylon, being far more excentric than Falcon 9, has even more trouble to find investors, for exactly the same reasons as SpaceX was struggling. And they will have an easier job to find more investors if they can profit from a similar programme than SpaceX. Wether they'll be succesful depends as much on the technical issues with their design, the team that has to see the project through, and their ability to attract funding.

[Paul451]

Yes, SpaceX did the development and NASA paid them when they met milestones. That's exactly the programme that would be great for Skylon and other desings that would attempt to compete.

There would still be the difference that is, as near as I can tell, the whole point of the current dispute between you/JS19 and Ron/Chris.

NASA is paying SpaceX to develop a specific service that NASA has a current need for. Cargo and later crew. NASA didn't care what form the service provider took, hence companies bid everything from Orbital's ATV-like Cygnus to SpaceX and t/Space's almost-crew-capsules, to SNC's Dreamchaser mini-spaceplane. The form is irrelevant.

The UK Govt would be paying REL just to develop Skylon. Not "a program to create a domestic capability to launch government payloads to LEO", but Skylon for the sake of Skylon. The form is the point.

The latter would be much closer to the development of Ariane, Concord, or any military jet-fighter or warship.

The latter may be a valid role for government, but it's not how COTS/CCDev worked.

SpaceX has repeatedly stated that Falcon 9 would not have been possible, or only much later, if it hadn't been for NASA's help.

Prior to COTS, NASA provided certain technical expertise. Particularly the NASA-funded Fastrac program which created a new generation of rocket engineers with recent experience of building a new generation of engines. Just as the UK had the HOTOL program. Although Fastrac was a vastly smaller program, obviously.

In essence, Musk hired NASA's version of "Alan Bond" to develop Merlin-1a. For REL, the main difference being that the engineers themselves owned the company.

Because finding investors is a lot harder if your only hardware is still a lot of development away.
So Skylon, being far more [eccentric?] than Falcon 9, has even more trouble to find investors, for exactly the same reasons as SpaceX was struggling. And they will have an easier job to find more investors if they can profit from a similar programme than SpaceX. Wether they'll be succesful depends as much on the technical issues with their design, the team that has to see the project through, and their ability to attract funding.

This is why many of us have suggested for years that REL was making a mistake in focusing so tightly on Skylon. (And got shouted down for our efforts.)

It would have been like SpaceX had started with Musk's proposed Mars vehicle. Intending to start with development of a giant methalox engine. (You'll recall, SpaceX had a development path from F1, to F5, to F9, to F9H, to F9-1E & F9H-1E, to FX, to FXH, and finally FXX. So they would have actually been trying to start with Merlin-2 and FXX.) Today, Musk would be bankrupt and SpaceX would be yet another corpse on the pile of failed aerospace wannabes.

Even today, with their iterative development, with their NASA contracts, with their order book backed up with commercial payloads, there's a lot of justified skepticism of Musk's ITS proposal. Now imagine he had started with ITS. That's effectively what REL is.

(What's interesting to me is that the main suggestions that were so authoritatively dismissed by you, JS19 and others is exactly what we're seeing evolve now. A D-21 type SABRE flight demonstrator. A TSTO as a stepping stone development. Etc.)

[high road]

I've lost count of how many times I repeated this: I don't think the UK should fund Skylon exclusively. I'm only opposing that Skylon can only succeed if it was fully funded by the UK. And I've been applauding the intermediate steps you mention as well. In fact, I don't think I have even considered anything beyond the full size SABRE engine... Which is why there's usually a few months between my posts in this thread.

Don't confuse all the people arguing here ;-)

[lkm]

Yes, SpaceX did the development and NASA paid them when they met milestones. That's exactly the programme that would be great for Skylon and other desings that would attempt to compete.

There would still be the difference that is, as near as I can tell, the whole point of the current dispute between you/JS19 and Ron/Chris.

NASA is paying SpaceX to develop a specific service that NASA has a current need for. Cargo and later crew. NASA didn't care what form the service provider took, hence companies bid everything from Orbital's ATV-like Cygnus to SpaceX and t/Space's almost-crew-capsules, to SNC's Dreamchaser mini-spaceplane. The form is irrelevant.

The UK Govt would be paying REL just to develop Skylon. Not "a program to create a domestic capability to launch government payloads to LEO", but Skylon for the sake of Skylon. The form is the point.

The latter would be much closer to the development of Ariane, Concord, or any military jet-fighter or warship.

The latter may be a valid role for government, but it's not how COTS/CCDev worked.

Speaking for my part my contention is simply that when the state makes a policy decision that benefits an industry, that industry has received support from the state, the reasons behind that policy being irrelevant . And that is not necessarily a bad thing.
Furthermore I contend that the COTS/CCDEV policy benefited the commercial space industry, and that was not a bad thing.

Statement of William H. Gerstenmaier Associate Administrator for Space Operations
In 2005, NASA established the Commercial Crew and Cargo Program Office at Johnson Space Center. The objectives of the Program, which oversees the COTS projects, is to further the implementation of U.S. space policy with investments to stimulate the commercial space industry, facilitate U.S. private industry demonstration of cargo and crew space transportation capabilities with the goal of achieving safe, reliable, cost-effective access to LEO, and create a market environment in which commercial space transportation services are available to Government and private sector customers. NASA believes the eventual availability of safe, reliable and economical service to LEO through the private sector will help NASA achieve the Nation’s space exploration goals following retirement of the Space Shuttle, thereby allowing NASA to focus on developing new space transportation capabilities to support exploration beyond LEO.

Finally I contend that in part the objective of said policy was explicitly to benefit said industry, again not a bad thing.

SpaceX has repeatedly stated that Falcon 9 would not have been possible, or only much later, if it hadn't been for NASA's help.

Prior to COTS, NASA provided certain technical expertise. Particularly the NASA-funded Fastrac program which created a new generation of rocket engineers with recent experience of building a new generation of engines. Just as the UK had the HOTOL program. Although Fastrac was a vastly smaller program, obviously.

In essence, Musk hired NASA's version of "Alan Bond" to develop Merlin-1a. For REL, the main difference being that the engineers themselves owned the company.

And that REL had no mega millionaire to fund them through the research stage.

Because finding investors is a lot harder if your only hardware is still a lot of development away.
So Skylon, being far more [eccentric?] than Falcon 9, has even more trouble to find investors, for exactly the same reasons as SpaceX was struggling. And they will have an easier job to find more investors if they can profit from a similar programme than SpaceX. Wether they'll be succesful depends as much on the technical issues with their design, the team that has to see the project through, and their ability to attract funding.

This is why many of us have suggested for years that REL was making a mistake in focusing so tightly on Skylon. (And got shouted down for our efforts.)

It would have been like SpaceX had started with Musk's proposed Mars vehicle. Intending to start with development of a giant methalox engine. (You'll recall, SpaceX had a development path from F1, to F5, to F9, to F9H, to F9-1E & F9H-1E, to FX, to FXH, and finally FXX. So they would have actually been trying to start with Merlin-2 and FXX.) Today, Musk would be bankrupt and SpaceX would be yet another corpse on the pile of failed aerospace wannabes.

Even today, with their iterative development, with their NASA contracts, with their order book backed up with commercial payloads, there's a lot of justified skepticism of Musk's ITS proposal. Now imagine he had started with ITS. That's effectively what REL is.

That's a bit of a tortuous analogy. To make it work you're equating a 15mt ETO launcher with an integrated super heavy launch system designed to put hundreds of people on Mars. If that's the equivalent of Skylon what does that make the A2 or an equivalently sized Skylon Heavy? An O'Neil Cylinder?

(What's interesting to me is that the main suggestions that were so authoritatively dismissed by you, JS19 and others is exactly what we're seeing evolve now. A D-21 type SABRE flight demonstrator. A TSTO as a stepping stone development. Etc.)

I think you're reading far too much into very little. The SABRE UAV has been part of REL's program for as long as we've known about it, that's at least five years and their engine development program is proceeding as planned.
REL hasn't published anything about moving to a TSTO development pathway, what's changed is increased interest in SABRE from third parties and those third parties being interested in TSTO and REL's new commercially minded management is saying to them we're happy to take your money .
What you're actually saying is some people outside of REL agree with some other other people outside of REL, and thus you are pleased.
The reality is that their last conference paper detailed plenty of Skylon development work and until they actually publish something to the contrary we should assume that their plans haven't changed.

[RanulfC]

Thought I posted this but it never appeared, lost in the Twilight Zone I'm guessing

(Paul451, I think there may have been one to many "sub" on those notes )

It will probably need LOX dump and LH2 dump to safe the vehicle before emergency landing but that's basically 2 valves, or even none if they just shut off ignition and let the propellants stream through the engine.

Que? I can see how you can shut off an engine, I can see how you let propellants flow, but how do you do both simultaneously?¹

_{¹ Outside of a spark-plug pulse engine like a petrol ICE.}

Typical rocket/jet in that even with the engine off you can still 'dump' fuel through the feed system, further it is supposed to have propellant dump and vents installed. The key is a method of keeping the turbopumps running (or maintaining gas pressure in the propellant tanks) to force the propellant out through the engine injectors, it's suggested you only do one propellant at time though

[re: intact abort] the fact that AFAIK no TSTO offers it suggests it's extraordinarily difficult to design in, let alone retrofit to an existing system.

It's not really a design difficulty, let alone an "extraordinary" one. It's more of a chicken and egg situation. On a TSTO, cargo-LAS reduces your payload, as would any LAS system, so you can only offer it for smaller payloads. Additionally, most recovered payloads would then require virtually a full break-down and rebuild after such an abort in order to re-certify them, and the existing launch insurance industry doesn't have a mechanism to determine losses in such cases. Hence you might as well let it burn, claim the loss and buy a new satellite.

There might be a market for cargo-LAS for self-insured, very expensive, one-off designs, where the owner is willing to pay extra for an additional chance of recovery if the launch fails, but none have had sufficient budgets to be the first to fund the development of a bespoke recovery system just for that single payload.² And there are too few such payloads for existing launchers to be motivated to develop it out of their own pocket, unless someone else paid them to. And (AFAICT) there's no way for a third party to offer a cargo-LAS that's compatible with all launchers, hence no way for them to tap into even those handful of potential customers.

What he said essentially Now if we talks various reusable TSTO concepts a good number of them require intact abort as much as any SSTO. They have to as they are fully reusable as well. Need to be careful when trying to compare what CAN be done with what IS done as there are underlying reasons that are more often than not, NOT for technical or design difficulty reasons.

Which is nice and all but kind of hard to understand since most international flight certification organizations have come right out and said that no "launch vehicle" is going to be certified in that manner because they are NOT aircraft. The only possible exceptions are aircraft used as carrier vehicles for launching vehicles which specifically applies to the carrier AIRCRAFT because it IS an aircraft. Carried launch vehicles, (such as Spaceship 2 for example) are NOT planned to be given aircraft like certifications in the foreseeable future.

It's got wings and it will be breathing air during the part of the flight when it's under any regulators jurisdiction. Since SABRE gives "virtual staging" benefits I think a case could be made. I'd wonder how the combines cycle systems you've mentioned would have been dealt with.

Previously it wasn't, dealt with I mean It has only been recently anyone even seriously suggested applying anything but very general guidelines derived from aircraft regulation to launch vehicles. The whole reason that has been shut down is because launch vehicle traffic and air traffic simply are not compatible in regular use. One or the other has the be the 'priority' supported system and that is pretty much always going to be the launch vehicle rather than an aircraft which means that aircraft operations will always be placed second to a launch vehicle flight. Given the larger depth and breadth of aircraft operations this is unacceptable as a regular operation parameter so the decision was made to separate air craft and launch vehicles by regulation.

This wasn't some whim either as it is pretty clear that no launch vehicle will in fact be ABLE to fully meet aircraft certification requirements. Aircraft have to meet those ALL THE TIME, not just in "some" parts of the flight and as we've noted many times an LV simply can not do so and still be an LV. (Note this does not actually mean that the vehicle can't have a general 'air worthiness' certification but its actually unlikely due to the FAA and most aeronautical certification agencies being leery of the issues connected to the vehicles NOT being aircraft but having more than one operating mode and environment)

Part of this is why you have anything with a "rocket engine," (within certain performance parameters) is a "launch vehicle" as a regulatory rule. Their operation and capabilities are different enough from any other aircraft power plant that trying to tie them to current air craft power plant regulations would severely restrict their use DUE to those regulations. (Imagine SABRE being required to meet noise abatement standards from runway to 20,000ft no matter WHERE it launches from)

There are ways around this of course, (getting back to the "previously" mentioned Combined Cycle concepts ) the easiest and most direct is not using commercial airports or such to launch from which was never actually a 'plan' but often illustrated to give the impression Space Travel would soon be as easy as Air Travel but this stuff also showed things like the ROMBUS launching from an east coast airport so I never understood how someone could NOT understand this wasn't a practical way of operation.

Along with this many of the early CC propulsion (such as the SERJ) was specifically aimed at military applications which did not require meeting "civilian" standards and could be operated from places where their individual 'quirks' were less of an issue. And in fact many of the early CC propulsion systems were originally (and specifically) high performance AERO propulsion systems rather than launch or space systems. (Again SERJ is an example as it was originally proposed and designed for a VERY high performance interceptor AIRCRAFT rather than a launch vehicle)

Those CC systems that were more directed towards actual 'space launch' were suggested to offer 'airplane-like' operations and were assumed to operate under a certification authority system in a similar manner but would not in fact be considered or certified as aircraft whether they had wings or not.

The public tends to allow variance over time as the system improves but for the most part space launch is always going to require more separation and a bigger buffer zone.

And let's be honest the fact the failure rate has never dropped below about 4% for ELV's has not helped.

No lets be even MORE honest, the place I grew up didn't have anything bigger than an oversized 'private aircraft' airport which never hosted any significant traffic routes or air travel service. To reach one of those you had to travel by car, train, or bus about 70 miles in any one direction so the only aircraft we tended to see/hear were small private planes and agricultural support aircraft. (Firebombers weren't even stationed there during major fires) Having said that I have spent the rest of my life (from 18 to 38) living and working on/right next to military air bases servicing every type of aircraft the US military has on a regular 24/7/365 basis. Often the runways are literally right outside the door to the place I work and/or sleep/eat/etc. And saying the military has a BIT more of a 'flexible' attitude towards what's "acceptable" as a risk than the general population is an understatement. (We 'bombed' ourselves a couple of years ago when a aircraft emergency caused it to jettison it's payload while trying to fly back to the runway, shut down the road near the landing point for about an hour and that was it)

These guy do NOT have "launch vehicles" anywhere near inhabited areas or allow close proximity to people or buildings and it is NOT because of the 'failure' rate. (IIRC even combining the LV and Missile stats the success rate is a good bit higher) No the reason is they launch vehicles are very damaging even if they work perfectly! Huge noise signature, heat pulse and pressure waves among other things mean you simply can NOT operate them within certain distances of buildings and people that are not protected from those effects. SABRE is actually going to be a 'bit' tamer than say the Merlin but not as much as say a commercial high-bypass turbofan engine.

The failure rate hasn't helped but even if it was 0 (zero) you would still have a large number of issues that would preclude a close integration of the public and launch services. So I'm pretty sure that operationally "spaceports" will remain more isolated and closed off than airports even if the former stared out as the latter in the first place

If you want to launch more people or cargo you can always use multiple pads and that actually reduces your range overhead by splitting it up among multiple users per day.

If you can justify it at that price point.

That's part of the point in that your 'fixed' range costs are actually lower and therefor your overall price per launch DOES go down and it works much better than the "launch from the middle of nowhere and avoid range costs" concept. And lets face the simple fact if there WERE more demand there could easily be more launches and while in the main demand is driven by price, increased demand will always engender more competition to meet that demand which invariably lowers price.

AFAIK the current systems launch what's needed, but unless that price point falls a lot the market will never expand.

Not at all, unless you assume the current "market" (uses of space) is all there will ever be and therefore is the only market you are concerned with. There is a bit of a 'backlog' even with the current market though it would take a great expansion of "need" (the proposed LEO satellite constellations for example) to begin to expand that enough to require increased launch capability or pacing. It's arguable that current providers COULD in fact lower their prices if they feel the need to do so but mostly choose not to because they are 'comfortable' with the current pricing situation. Similarly their customers are mostly agreeable to the current price schemes when all is said and done and they don't have any firm plans to greatly 'expand' should the price drop significantly because for the most part their business and long range planning are not very flexible nor would they benefit greatly from either a significantly lower price or more available launches. (While they would welcome the former it is not an important enough factor to make a deciding factor in most cases, and it would not significantly impact their NEED to launch payloads which is the main driver)

And that is what will drive the race for lower launch service prices; a larger overall NEED for launch services which will be seeking lower launch costs BECAUSE they need to launch more payloads. In transportation as long as there is only a limited need or market prices remain high and competition is very narrow but once need/market expand then prices go down as availability goes up.

But transportation growth has always depended greatly on being a system of moving 'payload' from one place to another not just one-way delivery and space has no 'destinations' and limited utility so it has never been capable of using existing Earth-bound systems to build upon to increase market and throughput. And that goes right back to why 'space' has to be developed to find new markets that both increase traffic and the need to transport payloads between Earth and space. Of course to do that we need to do research and development which is very expensive at the current price point so lowering prices would definitely help but it won't be enough to expand the CURRENT market significantly enough to pay the whole way itself. Lowering price will help but it's a limited game with the current market what we need is that AND expanded and new markets, opportunities and uses at the same time.

]quote]
Launch CAPACITY isn't the problem though it is the general requirements and economics that are holding back space development. Find a reason to launch more and the capability will be there.

At the relevant $62-100m+ point, not the $6m mark.[/quote]

People have been pointing out various 'price-points' where "space" will explode with development for decades and it not only keeps changing it's pretty obvious that as presented it also not true.$5,000 dollars a pound to orbit, $1,000, $500, $100, take your pick all have been said to be the 'point' where things will break out. Unfortunately there appears to be no actual justification to those assumptions because they seem to be based on the assumption that not only will the number of payload 'customers' increase but the actual market and use of "space" will skyrocket with various needs. The uses and new markets vary but most are centered around increased human access which is questionable as there is a very steep infrastructure and capability curve that must first be invested in to accomplish that. Then there is various industrial and resource programs but those not only require the infrastructure investment most of those are only theoretical with little or no research and development at this point which will be required to be invested and proven FIRST before we could move onto the infrastructure deployment phase.

There is a very good reason the most likely to 'succeed' business plans are pretty much based on servicing and hopefully expanding the CURRENT market rather than the more speculative markets. Like most transportation systems servicing a known market segment more efficiently and less expensively will ALWAYS be the safest way to establish a niche from which to expand but in the case of space there is a limit currently as to how much expansion is available from market and unlike historical, terrestrial transportation 'bootstrapping' is much more difficult and expensive due to the utter lack of pre-existing markets/destinations to tap into. You have to build it all FIRST and the price point where that becomes significantly easier it likely too low (or to hard to reach in the near term) to justify explosive rapid development. Don't get me wrong, ANY price reduction starts the process, but it has to be a big enough competitive market to KEEP prices reducing while demand goes up AND the necessary infrastructure is built up from scratch. So far that last part is the thing that most scenarios skip over in their rush.

Randy

[RanulfC]

This is why many of us have suggested for years that REL was making a mistake in focusing so tightly on Skylon. (And got shouted down for our efforts.)

It would have been like SpaceX had started with Musk's proposed Mars vehicle. Intending to start with development of a giant methalox engine. (You'll recall, SpaceX had a development path from F1, to F5, to F9, to F9H, to F9-1E & F9H-1E, to FX, to FXH, and finally FXX. So they would have actually been trying to start with Merlin-2 and FXX.) Today, Musk would be bankrupt and SpaceX would be yet another corpse on the pile of failed aerospace wannabes.

Not a good analogy as it is more like jumping straight into a fully re-usable F9 (F5 actually since he hadn't started out with the F9 in the first place) LV which you will note SpaceX still doesn't have. It also probably wouldn't look like the F9 as we know it either and while Musk probably wouldn't be broke he certainly wouldn't have built up SpaceX the way he has in the way he has over the same period.

In fact it's a major point that you can NOT really 'compare' SpaceX and REL since the former designed a lower cost but still rather 'vanilla' TSTO expendable launch vehicle that is slowly morphing towards a semi-re-usable TSTO LV and the latter started from the premise of a fully reusable SSTO vehicle using a specific engine cycle (which in fact was their main focus rather than the vehicle itself) which is probably going to morph into a semi-or-fully reusable TSTO vehicle. One is self financed and due to the conservative and conventional design has achieved a segment of the launch market while still progressing towards the 'ultimate' goal, (which is Mars and not surface-to-orbit transport or lowering cost there of but is a 'nice' to have on the way which is why ITS and not continued evolution of the F9 design which in fact may not be made "fully" reusable in the end) the other has constantly had to see out investment and support while slowly developing and proving the propulsion system which is the key and heart of the company while using a notional vehicle to help refine the design and operation of that propulsion system.

Had REL been able to attract an "angel" investor with the ability to sink as much money into it as Musk's done with SpaceX we'd probably have seen a SABRE powered LV flying by now and while it probably wouldn't have been Skylon, (as much as REL feels that is the most efficient use of their engines in the end they are not designing or building the LV as they are JUST the engine maker and they have already proven they can live with compromise) we at least would not be having so many people doubting that SABRE will even work let alone work as advertised

Even today, with their iterative development, with their NASA contracts, with their order book backed up with commercial payloads, there's a lot of justified skepticism of Musk's ITS proposal. Now imagine he had started with ITS. That's effectively what REL is.

Only if he'd stared with the idea that the Raptor was the minimum engine he would build since to make it an 'analog' you have to have some comparable areas and since REL is all about the ENGINE rather than the vehicle. People get hung up on how much 'focus' REL has on Skylon but they really don't as their focus has always been more on SABRE than the Skylon. They put together Sklon so they had an airframe to work around for SABRE operations and design but while they are biased towards SSTO as they see it being the most efficient use of the engine they obviously are willing to compromise to get it flying. There's a very GOOD reason Musk has continued to tap dance around the rather obvious "capability" inherent in the ITS spaceship stage, he's rightly concerned with the numerous folks who are going to be unable to see beyond the fact it MIGHT be an SSTO vehicle rather than the ITS spaceship which is what he and SpaceX are focused on. Similarly people tend to obsess on Skylon (both pro and con) in RELs case simply because it supports or undercuts their own bias' on the subject of SSTO and never mind the engine which is the entire point.

REL defined Skylon as a really 'best-case' example of an end product to launch EELV-class payloads with a single stage HTAL vehicle and then proceeded to refine and developing the SABRE engine/cycle towards supporting that design choice. If the SABRE works as well as they think it will then something like Skylon could be built with some pretty robust margins. If SABRE doesn't work that well or the airframe can't be afforded or built within those margins then quite obviously some changes in design will have to be made, ("F1, to F5, to F9, to F9H, to F9-1E & F9H-1E") as the design and vehicle itself move ahead, but that WAS the plan from the beginning. In RELs, (and a lot of other peoples you will notice) thinking SSTO makes the most economic, design, and operational sense for an efficient surface-to-orbital vehicle. So that is what they designed to but they are obviously willing to consider other approaches should those they partner with (and investors) feel that isn't the case. They will continue to argue their side but I'm pretty sure if it comes down to it they will in fact build whatever engine system is needed as that IS the job they have chosen for themselves.

(What's interesting to me is that the main suggestions that were so authoritatively dismissed by you, JS19 and others is exactly what we're seeing evolve now. A D-21 type SABRE flight demonstrator. A TSTO as a stepping stone development. Etc.)

The engine demonstrator as far as I can see was never going to be anything but a single engine test vehicle so I don't see what's changed other than they finally came up with an illustration. It looks "D21-ish" but considering it has to carry LH2 in sufficient quantizes to actually TEST the engine during flight I really doubt that's what it's going to end up looking like in the end. (Though considering it a proven Mach-4 design it would make sense to pursue it as closely as they can to save design time and effort)

And I think you may have missed how much the afore mentioned people have been arguing AGAINST TSTO as a stepping stone While REL has always said it wasn't the most efficient use of the SABER they have never dismissed it as a possible option. And really their 'opinion' is the one that matter I'd say

Randy

[Paul451]

It would have been like SpaceX had started with Musk's proposed Mars vehicle. Intending to start with development of a giant methalox engine. (You'll recall, SpaceX had a development path from F1, to F5, to F9, to F9H, to F9-1E & F9H-1E, to FX, to FXH, and finally FXX. So they would have actually been trying to start with Merlin-2 and FXX.) Today, Musk would be bankrupt and SpaceX would be yet another corpse on the pile of failed aerospace wannabes.

Not a good analogy as it is more like jumping straight into a fully re-usable F9 [...] LV [...]

No. The development cost of the first version of F9 was estimated to be around $300m. (And even that took outside investment and the promise of a cargo contract with NASA. Remember Musk was rich, but he wasn't a billionaire.)

The development cost for Skylon is estimated in the high billions to low tens of billions, depending on who you ask.

The technological and cost comparison is with ITS (or Falcon-XX in Musk's original plan).

(F5 actually since he hadn't started out with the F9 in the first place)

I'm not sure what you're referring to here. It seems like you are saying that SpaceX didn't have a plan to develop F9 when they were developing F1, planned only as far as F5. If so, that's wrong. The first iterative path they released was the chain I mentioned in my comment: Merlin 1, then F1, F5, F9, F9H (as it was then known), then develop Merlin 2. Redo F9 as a single engine vehicle, F9H as three engines on three cores. Then develop a new 3-engined large vehicle, called FX. Then a three core FXH. Then a single 9-engine monster called FXX.

In fact it's a major point that you can NOT really 'compare' SpaceX and REL since the former designed a lower cost but still rather 'vanilla' TSTO expendable launch vehicle

Which is why I specifically didn't compare to F9.

Within two paragraphs you've gone from telling me that the correct analogy is F9 (or F5), then immediately telling me that, no, my comparison to F9 is inaccurate...

[Paul451]

People get hung up on how much 'focus' REL has on Skylon but they really don't as their focus has always been more on SABRE than the Skylon. They put together Sklon so they had an airframe to work around for SABRE operations and design but while they are biased towards SSTO as they see it being the most efficient use of the engine they obviously are willing to compromise to get it flying. [...]
REL defined Skylon as a really 'best-case' example of an end product [...]
[...] but that WAS the plan from the beginning.

REL have proposed a design for the GTO upper-stage for Skylon. They've proposed a design for a freakin' human passenger pod for Skylon. But in 27 years they haven't provided a single suggestion of an alternative launch vehicle to Skylon. Not a napkin sketch. Haven't made so much as a hint of an alternative launch vehicle design that SABRE is also suitable for.

No. You don't get to pretend that Skylon is just a "fill in the blank" for the engine.

And I think you may have missed how much the afore mentioned people have been arguing AGAINST TSTO as a stepping stone

I really haven't.

[lkm]

I found several papers not by REL but about Skylon related issues.


A paper on the atmospheric response to large scale reusable launch vehicle use based on Skylon.
http://onlinelibrary.wiley.com/store/10.1002/2016EF000399/asset/eft2171.pdf;jsessionid=1B7858A9DD26B51D197FA5A6814938D8.f04t04?v=1&t=iwi25d7t&s=58b70fa89498d5126a7659f23187d3f15b1e29d7

A paper about Skylon's approach to safety and certification.
http://www.saturnsms.com/wp-content/uploads/2016/06/Quinn_Varvill_SABRE_Enabling-Single-Stage-to-Orbit-Safely_final.pdf

An interesting paper on the economic value of reusability.
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160013370.pdf