The Reaction Engines Skylon Master Thread (1)

[Carreidas 160]

Also I feel that Skylon would be hard to scale up.

A much bigger Skylon won't happen (although they have increased its size significantly between the C and D designs).

It can scale in numbers quite easily though. If you have the infrastructure to build one Skylon, you can build ten as well.

[Dappa]

F9r >> Skylon:
Even if both receive the necessary funding the technology of Skylon is so sensitive to failures that I have a hard time imagining Skylon succeed.
EVERYthing has to work in order to get ANYthing into LEO.

As is the case with any EELV today, everything has to work in order for it to fly.

On the other hand e.g. an F9r 1st stage might crashland and explode but still have put payload into orbit, earned money for SpaceX.

Which would still mean that the RLV can't be reused, and would probably cost SpaceX more money than it earned them.

On the other hand: an EELV can't return with it's payload in case of any failure before staging, Skylon might just be able to land with an intact payload.

Also I feel that Skylon would be hard to scale up.

Surely a Boeing 747 could never fly, at least that's what a lot of people thought back in 1968. Then 1969 came along, and with it the flight of the 747. I know Skylon is nothing like a 747, but it illustrates that whenever people think that things can't be any bigger, it turns out they can be bigger.

But why would it need scaling up in the first place? If it's large enough, it's large enough.

I would LOVE to see Skylon fly

Me too!

[spectre9]

Skylon has a more realistic method of getting the vehicle back on the ground.

Until large rocket stages are doing VTOL consistently and reliably I think wings have the upper hand.

[A_M_Swallow]

{snip}

But why would it need scaling up in the first place? If it's large enough, it's large enough.

A scaled up Skylon could compete with the SLS for large cargoes.

[Jason1701]

{snip}

But why would it need scaling up in the first place? If it's large enough, it's large enough.

A scaled up Skylon could compete with the SLS for large cargoes.

Every part of that is ridiculous.

[Alpha_Centauri]

{snip}

But why would it need scaling up in the first place? If it's large enough, it's large enough.

A scaled up Skylon could compete with the SLS for large cargoes.

This is fundamentally missing the point. The rationale for Skylon (or any high-turnaround RLV for that matter) is that it changes preconceptions on what are economical activities which is precisely what is holding back space development. Why develop an expensive an uneconomical superheavy lifter which will realistically see little use when you can construct the equivalent mass with multiple launches of an existing launch vehicle in a week or two anyway?

[A_M_Swallow]

{snip}

But why would it need scaling up in the first place? If it's large enough, it's large enough.

A scaled up Skylon could compete with the SLS for large cargoes.

This is fundamentally missing the point. The rationale for Skylon (or any high-turnaround RLV for that matter) is that it changes preconceptions on what are economical activities which is precisely what is holding back space development. Why develop an expensive an uneconomical superheavy lifter which will realistically see little use when you can construct the equivalent mass with multiple launches of an existing launch vehicle in a week or two anyway?

For the standard reason - you use a train carrying 900 people because it is cheaper than 10 trains each carrying 90 people.  Until the proposed manufacture of the supper Skylon can see sufficient cargo/passengers you do not develop a super Skylon.

[Jim Davis]

Surely a Boeing 747 could never fly, at least that's what a lot of people thought back in 1968.

Who, specifically?

Now, there were a number of people who questioned the economics of such a large airliner (and the first few years of operation were very shaky) but I don't recall anyone claiming a 747 could never fly.

[Robotbeat]

Arguments on the Internet are extremely time-consuming...

+1

[anonymous]

Europe’s Next-gen Rocket Design Competition Included Surprise Finalist

http://www.spacenews.com/launch/120713-europe-rocket-design-finalist.html

Astrium Space Transportation and OHB AG will lead two consortia to perform a design of a new heavy-lift launch vehicle for the European Space Agency (ESA) following a bidding competition that included a surprise third bidder in Reaction Engines Ltd. of Britain, ESA Director-General Jean-Jacques Dordain said here July 10.

I found the article very interesting because it discusses ESA's concern about Space X's Falcon 9 and how they are changing their industrial model in an attempt to lower costs. It seems to me that if Space X develops a reusable Falcon 9, it could render Ariane 6 uncompetitive and obsolete, so ESA may be thinking about responding with Skylon.

[Alpha_Centauri]

This is fundamentally missing the point. The rationale for Skylon (or any high-turnaround RLV for that matter) is that it changes preconceptions on what are economical activities which is precisely what is holding back space development. Why develop an expensive an uneconomical superheavy lifter which will realistically see little use when you can construct the equivalent mass with multiple launches of an existing launch vehicle in a week or two anyway?

For the standard reason - you use a train carrying 900 people because it is cheaper than 10 trains each carrying 90 people.  Until the proposed manufacture of the supper Skylon can see sufficient cargo/passengers you do not develop a super Skylon.

As a rail enthusiast actually I'd say that isn't the case which is why in the UK we run a "national metro" rail system that uses more frequent but smaller trains, as this is cheaper/more cost effective than investing in longer platforms. It also more closely matches demand as there is higher demand for turn-up and go services than ones you have to wait an hour for.  Note some significant parallels with the envisioned changes to the space economy here. Train lengthening is a stop-gap when the infrastructure does not allow you to run more trains, it is not usually cheaper/cost effective.

And this is the case even though there are fewer obstructions compared to the launch sector which makes such a comparison irrelevant anyway.  Trains use multiple units, to lengthen a service you just add more carriages.  SLS isn't a modular evolution of an EELV. It is not a capacity enhancement but a whole new infrastructure to research, develop and maintain.  A longer train requires longer platforms and perhaps signalling changes, but much of the rest of the infrastructure used both to build and run that and smaller trains are the same.  This is not the case for ordinary EELV-style launchers and superheavy lifters.  If you think developing and launching the baseline SLS is cheaper than launching an existing EELV ~ 4 more times then I want what you're smoking.

People are complaining that the expectation that even the ordinary Skylon will have enough customers to use up its available flight rate is wildly optimistic (Personally I side with the "build it and they will come" crowd), so as far as i'm concerned by the time the Skylon fleet's capacity is maxed out we'll probably have "the greatest advance in propulsion since the SABRE engine" by then and the question of a heavier version of Skylon will be moot.

[Carreidas 160]

I found the article very interesting because it discusses ESA's concern about Space X's Falcon 9 and how they are changing their industrial model in an attempt to lower costs. It seems to me that if Space X develops a reusable Falcon 9, it could render Ariane 6 uncompetitive and obsolete, so ESA may be thinking about responding with Skylon.

I don't think ESA operates Ariane, that would be Arianespace (not sure though). ESA hitches rides on rockets, whether it's Ariane, Falcon or Skylon.

Arianespace will have to compete with whomever operates Skylon/Falcon. Note that both REL and SpaceX have indicated they're ultimately only interested in building, not operating, spacecraft.

[Alpha_Centauri]

Arianespace operates Ariane day to day, yes, but they do so so on behalf of ESA. It is ESA that is responsible for and funds designing and developing (though industry on behalf of ESA) European launch vehicles. This is not the same as simply hitching a ride on Falcon or Soyuz for example.

There is nothing stopping Arianespace operating Skylon...

Although the fact it was an official competitor for NGL is surprising, the result is not, it seems unlikely ESA would get involved directly in developing Skylon. That said they are probably keen to see Skylon developed in Europe, hence their continued support and interest.

[Carreidas 160]

Arianespace operates Ariane day to day, yes, but they do so so on behalf of ESA. It is ESA that is responsible for and funds designing and developing (though industry on behalf of ESA) European launch vehicles. This is not the same as simply hitching a ride on Falcon or Soyuz for example.

There is nothing stopping Arianespace operating Skylon...

Thanks for clearing that up. I wonder to what extent Arianespace/EADS/others will properly invest in Skylon. Not to sound like a doomer, but would it be possible for them to buy REL and kill the project to eradicate competition, or do EU regulations prevent these kind of things from happening?

Although the fact it was an official competitor for NGL is surprising, the result is not, it seems unlikely ESA would get involved directly in developing Skylon. That said they are probably keen to see Skylon developed in Europe, hence their continued support and interest.

Agreed, ESA's annual budget is around EUR 3bn, too small to pony up (part of the) 10bn or so required for Skylon development. Might they get reduced cost rides in exchange for support, perhaps in the form of expertise, loaning out R&D facilities etc?

[adrianwyard]

I believe this is a new video - a nice edit of previously introduced concepts:
 
http://www.reactionengines.co.uk/vid_skylonops.html

[john smith 19]

I did state my concerns, but you don't find them convincing, which is fair enough.

But let me give some specific scenarios: what if rocket mode Isp turns out to be slightly disappointing (as it was with RS-68) and if that has structural implications (as it did with Delta)? What if the precooler only works efficiently up to Mach 4.5 instead of 5.5? What if it uses more LH2 than expected? What if lower than expected T/W leads to a slower ascent, more drag losses and a need for beefed up TPS? In my opinion all of these could reasonably happen. They could also reasonably not happen. Enough reason for me not to be confident Skylon will work as an SSTO. It could, but I'm not confident.

I am however confident that it could work well as a TSTO, and not too worried about the economic implications. In fact I believe a TSTO RLV with much less ambitious engines than SABRE could be possible (and even the much less ambitious VTVL TSTO RLVs could still be very economical IMO).

I meant there are many TSTO RLV concepts out there, and it is not clear SSTO will be required for a breakthrough in specific launch prices, nor whether SSTO is even possible without including non-chemical power sources. SSTO could indeed be necessary, but I hope it's not, since I'm not confident a chemical SSTO RLV is possible. Hopeful yes, with Skylon a leading contender, but not confident.

Let me see if I can paraphrase your objections.

1) Sklyon is a complex new vehicle with a complex new engine. Either might fail to meet any number of required performance targets making the goal infeasible.

2) Both the vehicle and the engine have a lot of failure modes. Some unique to this design, some generic to other designs. Many of them could stop the vehicle achieving orbit or destroy the vehicle outright.

3)If it was that good they would have got a lot more funding a lot sooner.

4)There are a lot of much more conservative design concepts out there that have had no funding.

5)You don't believe SSTO is possible anyway.

I hate to break this to you but 1 & 2 are pretty much the case with *all* new aerospace projects, and *many* other types of engineering as well. Good engineers set *bands* of values over which a project is viable and outside which it will fail. IIRC Skylon has a 15% margin on its empty weight for this purpose. This is high risk/high reward investment. Not some project to increase the life of the average cell phone battery by 5%.

I'm quite sure there are other tolerance bands on all major engine and vehicle parameters which can be easily updated as information improves and they turn design into implementation. It's probable some factors will come in *better* than designed, allowing some trade off if problems develop, as they do in *real* engineering.

3) & 4) This is an exceptionally difficult area to raise money in for *any* concept. Getting enough to build *any* hardware, let alone flight hardware is hugely difficult.

And let's not forget the last major VC investment driven by the conservative safe-pair-of-hands paradigm. To re-cap the specs.
TSTO
High performance LOX/HC engines
No *powered* landings.
Designed by NASA engineers

c$900m later the Kistler K1 was still a collection of parts and the ex-NASA engineers had run out of money and Barclays VC and several other VC companies developed an acute aversion to certain investment areas (and I'd suspect certain resumes showing certain former employers).

It did however pass the "My uncle Al at NASA says..." due diligence test. Normally  "Uncle Al" says "If it was that good NASA/ESA/JAXA would already be working on it. Anyone aware of how large bureaucratic government institutions who interact closely with a smallish group of govt contractors will know how true that statement is.

 BTW the ESA review was commissioned and paid for *separately* by the BSA from the System Requirements Review which had over 100 guests, not just from Europe but also Japan (presumably with ATREX experience) and South Korea I'm sure most of them were pretty skeptical as well.

5) That's a pretty categorical statement.

You don't have to *believe* SSTO is possible you can verify it for yourself. Classic examples have been the Titan 2 1st stage (30g burnout but mostly because no one ever tried to throttle it), the Atlas 3 (Russian engine but still retained pressure stabilized tanks) and my favorite the Saturn V 1st stage.

Now run the rocket equation with the known Isp of engines like the RD171 or RD181 and factor in this stage (Saturn V 1st stage) was designed to take off with over 100 metric tons of dead weight on top, a 100Kg flight computer and a few 100 Kgs of for the IMU and the GN2 tanks that powered it. As it had 5 engines even if you're preferred option does not throttle you can just shut it down.

For non rocket stages consider the humble drinks can with its 11:1 payload (which can support a stack at least 9 *filled* cans on top) or the dead weight of a 20' ISO container, supporting 2 other containers on top of itself.

Historically the bottom line has been VTOL SSTO gives you roughly 1/3 to 1/4 the *payload* of an ELV and you need to build a *much* bigger vehicle to accommodate the same size of payload.
The argument that it's so *much* cheaper to launch means you can just launch it in 4 launches, has never worked.

Skylon delivers ELV payload fraction in an SSTO concept. Academic to SSTO supporters IRL this seems to have been one of the keys to Skylon surviving and beginning to move to implementation.
 
I'll admit all forms of *reusable* SSTO will be tough but the flat out notion that even *expendable* SSTO is impossible shows either a lack of understanding of basic structures and rocket engined design, or of the forces that control large project funding, or both.

If you have actual *qualitative* reasons that you believe the development team have missed please list them. Otherwise I think we should let this side discussion rest.

[Robotbeat]

Of course expendable SSTO is possible. But it's less efficient from a payload-to-LEO:take-off-mass perspective (1% for SSTO, 4% for TSTO), so it's not desirable. And an SSTO of any sort can pretty much ONLY go to LEO, whereas a TSTO may be able to go to GTO or MEO, etc. So, it'd be generally a poor decision to make an expendable SSTO. And for a reusable one, because of the much greater mass of the recovery hardware, it's basically impossible unless you have a giant leap in technology like Reaction Engines is attempting. Still doesn't mean it's feasible.

Skylon has a "then a miracle happens" moment with their propulsion system. The rest of the vehicle might work. Maybe. (Though I have serious doubts... hypersonics isn't well enough understood for them to be confident in that, yet...) Inlet design is ESSENTIAL (and the inlet looks quite complicated from their animations... not so sure that's terribly realistic) and very difficult. If the pre-cooler gets clogged with ice (hard to see why it wouldn't, although they certainly assert it won't), then it's game over. Managing the liquid hydrogen fuel will probably also be a lot harder than they make it look in their animations. They could have combustion instabilities, or all sorts of other sorts of issues. It's NOT a conservative design because there are a lot of things they are doing which are very, very cutting edge. They may say they have a 15% performance margin, but we don't actually know if that includes the factor of safety for the structure. Also, even if it does, in my experience, every time you add more requirements, your usable material strength decreases.

Need to operate at hard cryogenic temperatures? Whittle down the list of materials or decrease the usable strength. Need to operate at hundreds of fatigue cycles? (Not including flutter.......) Whittle down the list of materials or decrease the usable strength. Needs to operate at very high temperatures? Whittle down the list of materials or decrease the usable strength. Needs to operate for long periods in vacuum with hard UV radiation? Whittle down the list of materials or decrease the usable strength. Needs to have a low enough coefficient of thermal expansion? Whittle down the list of materials or decrease the usable strength. Needs to operate at sea level with possible salt spray? Whittle down the list of materials or decrease the usable strength or increase operational costs. Needs to survive rainfall or possibly a bird strike? Whittle down the list of materials or decrease the usable strength or increase operational costs. Oh, now you have to actually MANUFACTURE the spacecraft? Now you have to worry about work hardening, heat affected zones (from welding), possible need to put the whole thing in the world's largest autoclave to recover the budgeted material strength.

There's a huge list of these sorts of material properties, and you very, very quickly run out of materials that can check all the boxes while remaining lightweight. And not all of these things can be completely foreseen at the powerpoint stage, since in many cases, many materials have never been tested under these sorts of conditions simultaneously or sequentially with the same material sample. And the outcome of such tests can mean your usable specific strength drops in /half/. Totally eating up your factor of safety AND your performance margin.

There's your qualitative assertion. There's absolutely plenty of reason for skepticism for this project.

But I still hope they solve all these problems and get it to work.

EDIT: I forgot a few other driving materials requirements: Avoiding hydrogen embrittlement and having LOx compatible plumbing and valves and tanks.

[mmeijeri]

Let me see if I can paraphrase your objections.

OK. They're not really objections though, I don't at all object to RE working on this or getting some R&D money for the precooler.

1) Sklyon is a complex new vehicle with a complex new engine. Either might fail to meet any number of required performance targets making the goal infeasible.

Yes, but not just that, since that's true of many systems. It's enormously ambitious, with desired capabilities that far exceed the state of the art. There are much less ambitious designs in the same direction that would still be a large step forward. Just saying, not objecting to it.

2) Both the vehicle and the engine have a lot of failure modes. Some unique to this design, some generic to other designs. Many of them could stop the vehicle achieving orbit or destroy the vehicle outright.

Correct. Again, not an objection, just something that causes me not to be confident they'll achieve SSTO. Not confident they won't either of course, and I'm not saying they shouldn't try. I certainly wish them well. Just stating I'm not confident, nothing more, nothing less.

3)If it was that good they would have got a lot more funding a lot sooner.

Not my position. Many good ideas don't get funding.

4)There are a lot of much more conservative design concepts out there that have had no funding.

True, but not the point I was making. There are much more conservative but still innovative designs out there that could make progress with less risk and less money. Doesn't mean RE shouldn't try it their way, just that it's good to know there are alternatives.

5)You don't believe SSTO is possible anyway.

That's not my position. Expendable SSTO is certainly possible, and an SSTO RLV might be too. Then again, there is reason to believe it could turn out to be impossible with all-chemical propulsion, so we can't be confident. That doesn't mean RE shouldn't make that bet, just that I'd start with something simpler. But hey, it's their money and their bet. I certainly wish them well. If they succeed I might live to see things I've given up on, such as manned exploration of Mars.

I hope this clears up some misunderstandings, so I'll wait for your reply to see if any of the issues you raised still apply after this clarification.

[FinalFrontier]

I am getting really tired of the "false until proven true" attitude.  That's not how critical thinking works.

No actually that is how critical thinking as well as the scientific method works.


You are suffering from "favorite vehicle syndrome".

[93143]

I am getting really tired of the "false until proven true" attitude.  That's not how critical thinking works.

No actually that is how critical thinking as well as the scientific method works.

I will repeat:  "false until proven true" is not how critical thinking works.

At best it is a planning formalism, that only works if the negative consequences of an unexpected "true" are vastly outweighed by the negative consequences of an unexpected "false".

More often, it is intellectual laziness, combined with a desire to appear to be a hardheaded skeptic.  Real critical thinking involves assessment of plausibility - how likely it is for a thing to be true, and for what reasons.  The principle of "false until proven true", if followed rigorously, would destroy the philosophical principles underpinning science and even daily life, leading directly to the most extreme form of solipsism.  But of course no one really takes it that far...

The comment was made that until REL have completed flight testing, their engine is just a lump of metals.  This could be useful as a planning formalism, but if the intent is to determine how plausible REL's design is, it is a counterproductive reduction of the current state of our knowledge.