Author Topic: The Reaction Engines Skylon Master Thread (5)  (Read 419999 times)

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #20 on: 02/19/2015 11:51 AM »
Claiming, no. Acting, yes. They are designing payloads and space stations and Mars missions around the size/capacity of the Skylon payload bay.
Another new member who's appeared from nowhere. Welcome to the forum.

Actually you have REL's process backwards.

They run these projects to ensure that a)The existing Skylon iteration is big enough to accommodate potential customers or b)What size or other part of it needs to be re-sized to to accommodate them. Skylon is on the "D" level of its iteration so it's actually been through 4 major design cycles, although C was the first public design.
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(Not to mention a hypersonic passenger plane.)
Then why mention it? It's a separate project that was sponsored by the EU.
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And Bond rejects out of hand any suggestions that Skylon may not be the optimal design (as John echoes, above). If you were an "airframer", would you get mixed up with an engine company which behaves like that? Or wait until they fail and just licence the engines from whoever buys the IP, and develop your own clean-sheet design?
What a delightful plot for a James Follet novel.  :)

IRL Engine makers make engines and airframers make airframes. The situation is somewhat analogous to that still paper airplane the "SR72." do you expect LM to wait till Aerojet fails and buy up their IP as well?
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To me, it's like some who wants to develop the world's first jet engine. So far they have one compressor fan. But they've not only designed the rest of the engine, and designed the entire airliner around that engine, and insisted it's the only possible design, but they are proposing new airport designs based around the door spacing on that proposed airliner for the proposed engine for which they have (after 20 years) only built a single compressor fan.
Your PoV would make a lot more sense if there was someone out there saying "no, that's not how a partially air breathing HTOL SSTO should be built."

Except there is no one arguing that and the Skylon design makes good sense. In fact when NASA looked at combined cycle vehicles using TBCC they came up with a remarkably similar vehicle
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But you dare suggest they are being a bit premature...
{sigh} Why is this idea so prevalent in aerospace?

Two is more than one, so therefore it must cost twice as much to develop an aircraft to carry freight between cities and a truck to ferry between individual customers and the airfreight terminals than to develop a single vehicle which can fly between cities but land directly on the customers' driveways. Must. Because two is more than one.
Perhaps because the launch problem isn't like your rather elaborate metaphor?

You might like to study the real 2 stage vehicles proposed under the original Shuttle programme. Or you might like to glance through the thread I started on the idea of a "Triamese" shuttle.
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and the testing around hypersonic separation.

Only if they were stupid.

When Chris is suggesting smaller stepping stones, when that's the entire premise of his argument, why would you assume he would be suggesting the hardest possible version of TSTO?
You clearly know his mind better than we do. Perhaps you could explain his thinking?
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #21 on: 02/19/2015 12:07 PM »
I'm not an expert on any of this so feel free to correct me, but wouldn't it make more sense to develop a TSTO Skylon in such a way that the skylon makes a suborbital hop and, once outside the brunt of the atmosphere, open the cargo bay and deploy an upper stage to which the payload is attached?

In fact, hasn't something similar to this concept been proposed in this study by Mark Hempsell?

It'd certainly be less complicated than staging inside the atmosphere at hypersonic velocities IMO.
Yet another new forum visitor. You really are coming out of the woodwork today.  :) Welcome.

Your line of reasoning leads to the logical conclusion that the simplest process is to not stage at all does it not?

I'm not sure where you're reading about sub orbital staging in the paper you cited.  Hempsell in a previous thread mentioned REL had looked at this. REL studies indicated a sub orbital flight could put 30 tonnes into LEO if the payload could supply sufficient delta V to circularise it's orbit.

IIRC no one they've been talking to said they really need this and further studies showed that the window between doors open, payload deployment and doors closed before re entry began was tight. With no one actually asking for it and little margin for error they deleted it as an option from the latest issue of the Skylon user manual.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline Krevsin

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #22 on: 02/19/2015 12:41 PM »
Your line of reasoning leads to the logical conclusion that the simplest process is to not stage at all does it not?
Not really. In the "suborbital + kick stage to orbit" TSTO method, your primary carrier doesn't need to have quite as thin a mass margin than in a fully SSTO vehicle. It gives you more room to work with.

The only reason it goes above the atmosphere is to avoid the trouble with staging at hypersonic velocities while in the thick atmosphere.

I'm not sure where you're reading about sub orbital staging in the paper you cited.
Sorry, my bad. What I mostly meant with the study was that it contained the "fluyt" stage which could be scaled down from a GEO/Lunar transfer stage to a orbital circularization stage.

Of course, the down side of all this kick stage mallarkey would be a smaller space for payload in the cargo bay, but given the larger mass fraction thus allowed, the cargo bay would have (probably) been expanded somewhat. I'm unsure on this.

IIRC no one they've been talking to said they really need this and further studies showed that the window between doors open, payload deployment and doors closed before re entry began was tight. With no one actually asking for it and little margin for error they deleted it as an option from the latest issue of the Skylon user manual.
Those were some issues that I have also considered, but given the fact that Skylon is a reusable system, in case of running the margin too close for comfort, the people launching could easily simply opt not to deploy the payload and simply return Skylon to the ground, with the payload intact, and try again after adressing any issues which might have cropped up.

So, while the deployment window is short, I believe it is manageable.


The real issue with this TSTO concept I've outlined (at least from what I can tell) lies in getting the Skylon back to its launch site, as that would probably require prohibitive amounts of fuel so two facilities, one for launch and one for landing would most likely be required. Which would probably run the infrastructure maintenance bill through the roof.

Yet another new forum visitor. You really are coming out of the woodwork today.  :) Welcome.
Thanks.  :)
I've been registered here a while, but I mostly prefer to lurk as I often feel like I don't really have anything to add to the conversation.
« Last Edit: 02/19/2015 12:46 PM by Krevsin »

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #23 on: 02/19/2015 02:45 PM »
Not really. In the "suborbital + kick stage to orbit" TSTO method, your primary carrier doesn't need to have quite as thin a mass margin than in a fully SSTO vehicle. It gives you more room to work with.

The only reason it goes above the atmosphere is to avoid the trouble with staging at hypersonic velocities while in the thick atmosphere.
You're operating under a very big misunderstanding.

Thin mass margins apply to vertical take off SSTO's and all rocket HTOLs.

Skylon is neither. Air breathing to Mach 5.5 raises the average Isp to something like 5x what you get from an all rocket design and hence a much bigger payload mass fraction. Roughly speaking SABRE costs 20 tonnes to buy 100 tonnes off the LOX mass budget.  Being HTOL it also avoids needing SABRE thrust to be > than it's T/O mass. They can be about 1/3 that and (like ordinary conventional aircraft) get the job done.

That does 2 things. 1) Gives a mass fraction in the possible range for an HTOL SSTO and 2) Gives a payload fraction as good as an ELV of the same GTOW. This has never happened before. SSTO proponents have always expected to take a payload reduction and make up for it with more launches.  Skylon does not need to do this.

2) matters when you have to raise funds since why would people pay for a system that cannot at least match what a TSTO does already?
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Sorry, my bad. What I mostly meant with the study was that it contained the "fluyt" stage which could be scaled down from a GEO/Lunar transfer stage to a orbital circularization stage.

Of course, the down side of all this kick stage mallarkey would be a smaller space for payload in the cargo bay, but given the larger mass fraction thus allowed, the cargo bay would have (probably) been expanded somewhat. I'm unsure on this.
Flyt can't fit in the cargo bay in one piece. It's designed to work only in vacuum. The Skylon Upper Stage is designed to take payloads from LEO to GTO before returning and is now included in the budget.
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Those were some issues that I have also considered, but given the fact that Skylon is a reusable system, in case of running the margin too close for comfort, the people launching could easily simply opt not to deploy the payload and simply return Skylon to the ground, with the payload intact, and try again after adressing any issues which might have cropped up.

So, while the deployment window is short, I believe it is manageable.
I'll quote what Hempsell, who was with REL at the time, had to say.

Advanced Concepts / Re: The Reaction Engines Skylon Master Thread (4)
« on: 10/17/2014 04:23 PM »

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Quote from: lkm on 10/17/2014 03:19 PM

    With regards to Skylon forming  part of a military weapons platform, the Skylon user manual does detail the suborbital deployment of payloads of up to 30mt at Mach 20. Couldn't a module be designed to rack launch a load of HTV-2 like prompt global strike weapons using that mission mode?
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Sorry; sub-orbital deployment is off the menu and is not in the latest issue of the Users' Manual.  There were problems making the reentry work and, as there was no identified use for it, we gave up trying to find a solution.  We found the very low orbit deployment worked better for maximising the payload.

A further point is that the front payload mounting interface is now designed for a maximum of 17 tonnes so at the moment that is the biggest payload that can be carried regardless of where it is deployed.

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The real issue with this TSTO concept I've outlined (at least from what I can tell) lies in getting the Skylon back to its launch site, as that would probably require prohibitive amounts of fuel so two facilities, one for launch and one for landing would most likely be required. Which would probably run the infrastructure maintenance bill through the roof.
Yes and no. In air breathing mode Skylon is about 150 tonnes lighter, so a conventional runway could handle the landing.  Skylon is also a pretty good glider. The wings look too small but that's because the body is so big and so empty. It's a lot more aerodynamic than the Shuttle was. REL expect the D revision to have transatlantic range in air breathing mode. LH2 is qutie expensive at around $8.29/Kg but that would still mean a fully fueled fly back would be less than $500k.

The real problem is likely to be takeoff noise from the down range airport. Even 150 tonnes lighter and substantially throttled back a Skylon on takeoff will be very loud.  :(
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Yet another new forum visitor. You really are coming out of the woodwork today.  :) Welcome.
Thanks.  :)
I've been registered here a while, but I mostly prefer to lurk as I often feel like I don't really have anything to add to the conversation.
SABRE/Skylon is now in it's 5th thread. There's been a lot of discussion and a lot of ideas have come up (sometimes on several occasions). The site search function is very useful for finding out if something has come up before. Sadly it seems there's no way I can find to search a whole thread, rather than 1 page at a time.  :(

Electromagnetic catapult launch, catapult launch up a mountain, landing on a shallow water pool (to spread the load) have all come up already. 

Happy reading.
« Last Edit: 02/19/2015 03:09 PM by john smith 19 »
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline Krevsin

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #24 on: 02/19/2015 02:56 PM »
I see. Well, thanks for the info.

Offline RanulfC

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #25 on: 02/19/2015 03:48 PM »
The people working on Skylon have been working on the idea for decades.  They are certainly dedicated and well-meaning, and they have some competence.  But they have been working on theory and small components.  They don't have experience in system integration.  They haven't built real flight hardware.  They haven't seen a system from concept through to all the inevitable compromises necessary to make a practical system.

I don't have a biography to hand of each one of them but I suggest that it's a sweeping statement to say that they have no experience in system integration.  At the very least some of them are veterans of Blue Streak and others of the aerospace industry.

But that goes for almost any aerospace start-up. Among its employees you would expect to see some veterans from other aerospace firms - but that does not mean that the "organizational experience" as a whole translates to this new organization. 

In other words SpaceX was "unproven" until they actually flew something successfully. (That would be the F9 btw :) )

Got it.
They are an engine company not an airframe company.   Let the airframe company use its great institutional experience for its part of the work.

That's fine, but this engine company is making projections about the performance and economic viability of the complete system, including engines and airframe.

??? And your point? Engine companies have done that before, quite often and often with "notional" airframes to boot rather than ones that have been actually researched. Pratt-&-Whitney, GE, Mardquart to name a few. Some of them have published "studies" that made claims to those factors for everything from SCramjets to StrutJet systems. Occasionally they will actually "quote" airframe manufacturers but more often than not (since involving them costs money) they will "interpret" data from other airframes and or "other" source material.

There'd be no shame in their saying "we don't know yet".

Isn't there? After all, yourself being an example, there are people who are taking them to task FOR "not-knowing" what they are talking about when they DO talk about subjects and methods they have experience with :)

They are making, (as I pointed out many "engine" companies do) educated projections based on available knowledge and assumed performance with some very deep margins for the assumptions involved.

Actually, that demonstrates my point quite well.  DC-X never progressed to an operational vehicle.  It was never more than a sub-scale technology demonstrator.  Working on DC-X wouldn't give any experience with the very difficult transition from technology demonstration to a system that is economically successful as an operational system.

And "worked on" isn't the same as being in charge.

Actually what it "demonstrates" is you don't even have a firm grasp on what you mean to say and therefore keep moving the goal posts as you argue :)

The DC-X was, if you'll recall a "SSTO-Rocket-Powered-subscale demonstrator vehicle with NO intention other than demonstrating several ancillary "functions" of such a vehicle not any of the "substantive" functions thereof.

It "proved" that VTVL and fairly "quick" operational turn around were possible on a vehicle that faced nor addressed none of the substantial challenges to actual operational flight.
"Learning" experience here was consistent with operations and data acquisition for an LH2 rocket engine over the lifetime of the program and various issues and questions relating to those operations. Directly applicable to what amounts to a rocket powered air/LH2 engine such as Skylon.
(Note: Also applicable was the experience gained from that program which was directly related to the "future development" of a fully operational vehicle as proposed by the manufacturer of the vehicle and this was one of the reasons that led Mr. Hempsell to conclude that with current technology a solely rocket powered SSTO vehicle wasn't viable and turned his interest towards air-breathing designs :) )

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REL is the one who chose to design it for an SSTO vehicle.  They chose to optimize it for that role rather than as part of a reusable first stage of a two-stage launch system, which would be the more conservative choice and give them more margin and require much less in the way of pushing the edge of what technology can do.

And everything gets cheaper when things are smaller.

And they "choose" to do so due to issues with scaling of the engine and LH2 propellant. They also DID run a trade study on a TSTO versus an SSTO vehicle and found that the favored design was an SSTO rather than breaking the design into a fully-TSTO design.
(I should point out that "technically" the Skylon IS a fully-reusable TSTO design since the "target" market is GTO/GEO and not LEO so a "second" stage is needed to complete the mission. A "fully-reusable" baseline TSTO therefore would require a "third" stage of similar design to achieve the stated goal as well)

Further while it IS true that TSTO designs have excess "margin" to allow for possible design and operational changes they also have those margins only to a limited extent as has been shown by the SpaceX Falcon-9 design. Referencing the trades that REL did showed that the "margins" allowed by the current suggested design of the Skylon allow very similar margins while using the SSTO design over the increased complexity and cost of a TSTO design.
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Getting to Mach 5.5 isn't the challenge.  They still have to get to Mach 25 to make orbit.  True, in some ways it's easier if they're only air breathing to Mach 5.5.  But in other ways it's harder.  They have to carry much more oxidizer, and their engine has to work well in both air-breathing and rocket mode.  Going from Mach 5.5 to Mach 25 in rocket mode (with some of that rocket mode in the dense part of the atmosphere at Mach 5.5) means they need a very good mass fraction.

Note that while "you" don't think they have thought of this "issue" the plain fact is they have done a LOT of work on this and have come to the conclusion that a ROCKET BASED rather than some form of turbine-engine based engine design actually fits this criteria. Funny enough that was a conclusion reached by most researchers in the field by the late 1950s. Unfortunately several mis-assumptions crept into the field at that same time which REL have managed to avoid. (Such as a requirement for air-liquification for rocket engine use rather than deep cooling, ramjets being "required" to reach speeds between Mach-3 and Mach-6, and the "need" for SCramjet engines to allow high hypersonic air-breathing flight, etc)

The SABRE is a "good" rocket engine that can be operated "decent" air-breathing engine from a standing start to around Mach-5.5. From there is goes back to being a "good" rocket engine using on-board propellant to go from Mach-5.5 to around Mach-25 and orbit. The rocket equation (modified) shows this has enough performance to allow some pretty hefty mass-margin and a very robust mass-fraction with the given design. Rocket engines, and materials science have come a long way from the 1950s and thankfully REL never even considered using multiple engine types to close their design :)

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Like I said, they don't have exactly the same challenges NASP had, but they have very great challenges, and I think they're at a comparable level of difficulty.  Apparently, others think they are too, which is why others are continuing SCRAMJet research and development.

SCramjet research and development continues because of the "promise" of hypersonic flight within the atmosphere despite the problems and issues of such flight. In 'theory' a SCramjet can fly to beyond Mach-24 and that 'theory' looks really, really good despite some obvious flaws in the full logic chain. (As an example, its obvious that internal airflow within a SCramjet at speeds of around Mach-15 become so hot that even with hydrogen fuel further operation {acceleration} is unlikely. Operations above that speed induce 'plasma' like flow where NO amount of additional fuel will continue operations but that's not ever mentioned when SCramjets research and development is discussed.

"Truth" is that REL is working on and from the point where air-breathing, rocket based, acceleration engines was "going" before it was side-tracked in the 1950s/60s. The "challenges" are significantly less since the vehicle is not designed to nor will it remain in the atmosphere any longer than needed.

"Smaller-is-cheaper" is pretty much an aerospace "law" for intents and purposes and yes it would be "nice" if REL could do a demonstrator first but there is a minimum size for a fully operational SABRE engine and LH2 propellant system capable of supporting the same. And yes its "tricky" because LH2 is required for the deep cooling effect which is the basis of the system, but that's actually a requirement, not a choice. Liquid Hydrogen systems do not as a rule lend themselves to "small" systems in any sort of "operational" use. The only way REL could build a significantly "smaller" system would be to forgo the use of LH2 for a more compact but MUCH less capable propellant and they have already PROVED the engineering of an LH2 heat exchanger system so what would be the point?

REL plans on "demonstrating" a full sized SABRE engine operationally for the full flight duration and then moving on to an actual airframe designed and built with the help of a fully "proven" builder. But in order to do the "testing" necessary for a "full-duration" test of the engine they need to have an idea of what the airframe and its effects on performance will be. Not even REL is expecting the Skylon to turn out EXACTLY as they propose but until an airframe company steps forward and proposes their own idea with accompanying data REL has to make its own way. (And note that while others HAVE proposed different designs REL has not outright rejected those designs)

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline Paul451

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #26 on: 02/20/2015 06:21 AM »
In other words SpaceX was "unproven" until they actually flew something successfully. (That would be the F9 btw :) )

Actually it'd be the F1.

SpaceX actually did the whole incremental development thing. Are still doing it. And I think it explains a lot about their success. Imagine they had tried to jump directly to MCT/Raptor. (Even then, I think they are still skipping necessary stepping stones.)

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #27 on: 02/20/2015 08:06 AM »
I wonder if we can move the discussion on by agreeing on a few things.

1)Reaction Engines Limited is not SpaceX.

2)It's development approach is completely different to that of SpaceX.

3)REL are not going to change their development approach because of anyone's opinion on the matter.

4) SpaceX have built a very fine ELV for (by government cost modelling standards) a very modest budget.

5) To be a valid comparison for Skylon any competitor has to be a) Fully reusable b) Able to deliver at least 15 tonnes to LEO c) Able to deliver at least 6 tonnes to GTO. If a candidate vehicle cannot manage this then it's not a valid comparison.

6)The arguments that "It's never been done before" or "Others have tried and failed" are in fact the reason why startups are started.  Their founders believe something can be done which has either not been done before or where previous attempts have failed. That definition applies to REL, SpaceX, XCOR, Blue and in fact any start up trying to do something that has never been done or never been done successfully before, probably including whatever start ups some of the other posters here are working for.
« Last Edit: 02/20/2015 08:13 AM by john smith 19 »
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline Lars-J

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #28 on: 02/20/2015 08:19 AM »
5) To be a valid comparison for Skylon any competitor has to be a) Fully reusable b) Able to deliver at least 15 tonnes to LEO c) Able to deliver at least 6 tonnes to GTO. If a candidate vehicle cannot manage this then it's not a valid comparison.

You're right. It's not a fair comparison. One is flying, hopefully partially reused soon. The other... is just something on a paper.
 - A) Skylon is not "fully reusable", because it does not exist.
 - B) Skylon can not "deliver at least 15 tonnes to LEO", because it does not exist.
 - C) Skylon can not "deliver at least 6 tonnes to GTO", because it does not exist.

Are you catching my drift? It's always easy to make a paper project look better in comparison to any existing hardware. Reality can be slightly more difficult.  :)
« Last Edit: 02/20/2015 08:20 AM by Lars-J »

Offline Paul451

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #29 on: 02/20/2015 09:14 AM »
4) SpaceX have built a very fine ELV

And REL have built a heat exchanger.

They have not built SABRE and are nowhere near ready to build even a test version of SABRE. They have not built and are not building Skylon. They have built a heat exchanger. Can we agree on that? I think that would move any discussion on much more.

Whereas insisting...

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5) To be a valid comparison for Skylon any competitor has to be a) Fully reusable b) Able to deliver at least 15 tonnes to LEO c) Able to deliver at least 6 tonnes to GTO. If a candidate vehicle cannot manage this then it's not a valid comparison.

...seems to be the very thing that prevents any progress in the discussion.

Chris's post (which started the discussion that so far dominates Part 5) was asking if Skylon might not the best development path for REL's proposed technology. They are trying to jump too many steps ahead of themselves. Hence 20 years and all they have is a heat exchanger. Surely after all this time, we're allowed to ask, "Is this the best path?" Is that question so offensive to you?

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6)The arguments that "It's never been done before" or "Others have tried and failed" are in fact the reason why startups are started. Their founders believe something can be done which has either not been done before or where previous attempts have failed.

REL is trying to develop a fundamentally new type of engine. A radical air-breathing jet engine/rocket hybrid. When you are doing something so untried, so deep in unexplored territory, you don't try to lock down the end design of a vehicle that might use that engine. Simply because you can't. That's all people are saying. That's what you can't seem to move beyond.

REL doesn't and can't know the actual performance of any eventual engine. None exist, and the very concept is so new and untried that there's no reasonable extrapolation from prior technology. Therefore, without that, they cannot possibly design a vehicle yet. So the idea that this early in the process they are designing end-user missions around the size of the payload bay of that vehicle is bonkers.
« Last Edit: 02/20/2015 09:17 AM by Paul451 »

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #30 on: 02/20/2015 10:58 AM »
And REL have built a heat exchanger.

They have not built SABRE and are nowhere near ready to build even a test version of SABRE. They have not built and are not building Skylon. They have built a heat exchanger. Can we agree on that? I think that would move any discussion on much more.
So far the only person arguing that point is you with yourself. Strawman arguments tend to be the starting point for trolls. You might like to keep that in mind.
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Whereas insisting...
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5) To be a valid comparison for Skylon any competitor has to be a) Fully reusable b) Able to deliver at least 15 tonnes to LEO c) Able to deliver at least 6 tonnes to GTO. If a candidate vehicle cannot manage this then it's not a valid comparison.

...seems to be the very thing that prevents any progress in the discussion.
Not at all. This is REL's choice. It's what they are planning to build since they revised the design in 2010. Please note the thread title.
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Chris's post (which started the discussion that so far dominates Part 5) was asking if Skylon might not the best development path for REL's proposed technology. They are trying to jump too many steps ahead of themselves. Hence 20 years and all they have is a heat exchanger. Surely after all this time, we're allowed to ask, "Is this the best path?"
And it has been asked over the last 4 threads. But since you seem so concerned about the design, what's your design for a SABRE carrying vehicle?
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Is that question so offensive to you?
Not in the slightest. The number of posts I've read have enhanced my tolerance of even the most stupid of comments.
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REL is trying to develop a fundamentally new type of engine. A radical air-breathing jet engine/rocket hybrid.
Actually not that radical, in fact much less radial than the LACE concepts running around the National Aerospace project (the original one in the early 60's). Using William Eschers taxonomy it even has a name. A "Deeply pre cooled air turbo rocket."
Trouble was no one could get the frost control to work in the inlet heat exchanger.   :(
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When you are doing something so untried, so deep in unexplored territory, you don't try to lock down the end design of a vehicle that might use that engine. Simply because you can't.
And yet that was exactly what SpaceX did with the F9. There's a difference between Science and Engineering. REL have done Science to do Engineering. Spacex have done Engineering, now they are doing Science. And Science is not predictable
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That's all people are saying. That's what you can't seem to move beyond.
No that's what 2 people are posting. And what other people with more experience in this area are posting is that actually engine companies in the aircraft business do this regularly.


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REL doesn't and can't know the actual performance of any eventual engine. None exist, and the very concept is so new and untried that there's no reasonable extrapolation from prior technology. Therefore, without that, they cannot possibly design a vehicle yet. So the idea that this early in the process they are designing end-user missions around the size of the payload bay of that vehicle is bonkers.
Wow.  ???
Just wow.

That statement alone tells me you have no understanding of the thermodynamics underlying all engines (rocket, Diesel, gas turbine, ram or SCramjet), dating from the mid 1700s, and even less about the changes in computer modelling over roughly the last 65-70 years.  :o

You appear to think engine design (of all types) is stuck in the 1950's, where cut-and-try was the only option.

Thank you for that. It means I won't have to waste a second more responding to you. Good bye.  :)
« Last Edit: 02/20/2015 11:12 AM by john smith 19 »
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline t43562

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #31 on: 02/20/2015 12:38 PM »
4) SpaceX have built a very fine ELV

And REL have built a heat exchanger.

They have not built SABRE and are nowhere near ready to build even a test version of SABRE. They have not built and are not building Skylon. They have built a heat exchanger. Can we agree on that? I think that would move any discussion on much more.

It seems to me that this debate is about the attitude we should all have more than about facts since I can't remember anyone suggesting that REL have built things they haven't built.

I'm interested in what happens assuming they get things mostly right or what they might do if this or that issue turns out to be more difficult  because the alternative is that they go bust and the world is the same as before which is a non-story - why discuss it?

We might as well mention that lots of people have built rockets before but this heat exchanger is exceptional so it speaks for their ability to come up with something unheard of and get it done right.

Offline lkm

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #32 on: 02/20/2015 01:35 PM »
To start off the new thread, here's a summary of my own reasons for being skeptical about Skylon.  Some of these views are probably shared by other skeptics.  Feel free to reply with opposing views; hopefully, this will help clarify exactly where opinions differ and help undecided readers of these forums see both sides and make up their own minds.

First off, I don't think there's a known flaw in Skylon that definitely makes it impossible.  It's not like a perpetual motion machine that violates known laws of physics.  My issue with Skylon is that there are too many unknowns and the proponents of Skylon assume those unknowns will work out, while history shows this is seldom the case.  There are enough unknowns and enough projections that seem very optimistic to me that the odds of Skylon actually achieving its goals seem remote to me.

The people working on Skylon have been working on the idea for decades.  They are certainly dedicated and well-meaning, and they have some competence.  But they have been working on theory and small components.  They don't have experience in system integration.  They haven't built real flight hardware.  They haven't seen a system from concept through to all the inevitable compromises necessary to make a practical system.

I don't think you are fully aware of the background the REL team. Mark Hempsell for example worked on the DCX.
http://forum.nasaspaceflight.com/index.php?topic=19127.msg493088#msg493088

Actually, that demonstrates my point quite well.  DC-X never progressed to an operational vehicle.  It was never more than a sub-scale technology demonstrator.  Working on DC-X wouldn't give any experience with the very difficult transition from technology demonstration to a system that is economically successful as an operational system.

And "worked on" isn't the same as being in charge.

Except that wasn't your point at at, your point was quite clear. That people in REL lacked "experience in system integration", "haven't built real flight hardware", and "haven't seen a system from concept through to all the inevitable compromises necessary to make a practical system". The DC-X clearly meets your original point which had no requirement of being in charge or the end system becoming operational. Other projects that meet that criteria plus your newly added one of operational status are the EJ200, Spey and RB211 which Richard Varvill and John Scott Scott worked on, respectively.



The team at REL has consistently proposed building a large-scale single-stage-to-orbit system.  That shows poor judgement, in my opinion.  SpaceX started with Falcon 1.  Then then moved to a full-expendable Falcon 9.  Now they are working on perfecting reuse of only the first stage.  Along the way, they have learned many lessons and constantly changed their plans, all while retaining their goal of greatly reducing the cost of launch.  I believe that kind of incremental, flexible approach is very effective.  It is the opposite of the REL approach.  With REL going directly for a huge, single-stage-to-orbit system, there is little room to learn operational lessons and change plans.  And Skylon is so much different from existing systems it is very likely to need far more flexibility for lessons learned than Falcon.

SABRE is a SSTO engine, I'm not sure what intermediate stage there can be for engine explicitly designed to take a single stage into orbit. I can't imagine designs cost get significantly smaller by making a smaller version.

REL is the one who chose to design it for an SSTO vehicle.  They chose to optimize it for that role rather than as part of a reusable first stage of a two-stage launch system, which would be the more conservative choice and give them more margin and require much less in the way of pushing the edge of what technology can do.

And everything gets cheaper when things are smaller.
When are you proposing to stage this notional TSTO? Inside the atmosphere so you can use a simpler non rocket mode SABRE losing LOX tanks from the first stage or outside still using SABRE?
 Are you carrying the second stage internally or externally? If externally how are managing the damage that does to the aerodynamics and thermal protection? If internal how are making the vehicle trimable given the damage that does?   
What engine is powering the second stage?
How does any of that make the development of SABRE cheaper? Either you're proposing using the SABRE design as is, or you're suggesting development of a second engine, on top of SABRE, without a pure rocket mode neither of which can be cheaper for REL as an engine developer than just building SABRE.


There have been many programs with similar or lesser optimistic goals that have failed.  The U.S. National Aerospace Plane had far more resources available and a similar level of technological challenge, and it failed.  Note that I'm not saying the details of the technological challenge are similar -- they are not.  But the programs are similar in having a goal that required many unknowns to be overcome and having people with some competence in specific areas convinced they could overcome them.
The technical challenge of airbreathing to Mach 18 is clearly of a vastly higher level than airbreathing to Mach 5.5 and the number of unknowns in geting to Mach 18 in 1984 far greater than achieving Mach 5 thirty years later.

Getting to Mach 5.5 isn't the challenge.  They still have to get to Mach 25 to make orbit.  True, in some ways it's easier if they're only air breathing to Mach 5.5.  But in other ways it's harder.  They have to carry much more oxidizer, and their engine has to work well in both air-breathing and rocket mode.  Going from Mach 5.5 to Mach 25 in rocket mode (with some of that rocket mode in the dense part of the atmosphere at Mach 5.5) means they need a very good mass fraction.

Like I said, they don't have exactly the same challenges NASP had, but they have very great challenges, and I think they're at a comparable level of difficulty.  Apparently, others think they are too, which is why others are continuing SCRAMJet research and development.
I can't help feel that rocketry (successfully putting things in orbit since 1957)  is somewhat better understood that Scramjets ( someday soon we'll reach ten minutes cumulative flight time). Who is seriously researching scramjets for anything other than hypersonic cruise? Also please name these other people who think that the development challenges of NASP in 1984 are of comparable difficulty to the challenges of Skylon in 2015.

The X-33/VentureStar is another launch program that had optimistic goals and failed.  I think that X-33/VentureStar looked far more realistic at its outset, with less of a techonological leap required, than Skylon today.  And yet it failed because of the engineering details in turning the theory into reality.

X-33 didn't fail, it was cancelled due to a change in administration, just as many Clinton era space programs were cancelled by the Bush administration. What many people forget is that the X-33 was just a rocket powered x-plane like the X-15, like the X-15 it had a ton of not flown before technology some of which had teething problems, and like the X-55 if it had flown it would have provided invaluable hypersonic flight data.

Getting into the details of X-33 is off topic, but lets just say that opinions differ about X-33 -- many people believe it was cancelled because the progress up to that point indicated it was not able to meet its projections and wouldn't have been viable.

Many people believe that VentureStar wasn't viable, but I don't think anybody believes the X-33 couldn't have flown and gathered useful data. The X-33 wasn't VentureStar, VentureStar was a powerpoint, X-33 was an active x-plane project with a similar budget and goals to the X-15. The X-15 wasn't a failure because it had no follow on project so why  should the X-33? When the X-15 first flew it didn't have it's intended engine yet because it wasn't ready, so why should the X-33 not have been given the same leeway? Like I said, there was a change in administration, a desire to cancel and repudiate the projects of the previous one, people obliged.

Offline Lars-J

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #33 on: 02/20/2015 03:29 PM »
There's a difference between Science and Engineering. REL have done Science to do Engineering. Spacex have done Engineering, now they are doing Science. And Science is not predictable

This paragraph deserves some kind of award. ;D It should be smooth sailing for REL now, then!  ;)

EDIT: To offer a more substantive response. I don't think the line between science and engineering exists as you think it does. And what scientific breakthroughs have REL done? Their pre-cooler work would be classified by most as an impressive piece of engineering.
« Last Edit: 02/20/2015 04:17 PM by Lars-J »

Offline RanulfC

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #34 on: 02/20/2015 03:53 PM »
In other words SpaceX was "unproven" until they actually flew something successfully. (That would be the F9 btw :) )

Actually it'd be the F1.

SpaceX actually did the whole incremental development thing. Are still doing it. And I think it explains a lot about their success. Imagine they had tried to jump directly to MCT/Raptor. (Even then, I think they are still skipping necessary stepping stones.)

My bad my source list had the F1 flights as "partially successful" :) And actually they didn't as they "developed" everything from scratch and tested it as they built. Which is technically what REL is also planning on doing but which Chris is ignoring :)

Full scale engine is next and THEN maybe a full scale test vehicle. This is really more how aircraft are built than rockets which is of course the main point in their development plans.

But "my" point still stands that by the criteria Chris used, SpaceX was an "unproven" company despite all their "incremental" testing until they actually flew a successful, full-up flight :)

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline Kansan52

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #35 on: 02/20/2015 04:16 PM »
I'm confused.

It has been posted that all that REL has built is a heat exchanger. My understanding is the heat exchanger is the linchpin. The rest of the engine is based on existing technology.

Is that incorrect?

If the heat exchanger is the linchpin idea is correct, then REL is suffering from NBNBR (No Bucks, No Buck Rogers - Bucks meaning money not dollars). Things will be slow due to money issues, not technology issues.

To recap, REL's heat exchanger is the show stopper and REL has accomplished that, the engine is based on known technology working with the heat exchanger (not easy but not necessarily ground breaking), and REL could work faster is they has more money.

That my understanding.

Offline RanulfC

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #36 on: 02/20/2015 05:13 PM »
I'm confused.

It has been posted that all that REL has built is a heat exchanger. My understanding is the heat exchanger is the linchpin. The rest of the engine is based on existing technology.

Is that incorrect?

If the heat exchanger is the linchpin idea is correct, then REL is suffering from NBNBR (No Bucks, No Buck Rogers - Bucks meaning money not dollars). Things will be slow due to money issues, not technology issues.

To recap, REL's heat exchanger is the show stopper and REL has accomplished that, the engine is based on known technology working with the heat exchanger (not easy but not necessarily ground breaking), and REL could work faster is they has more money.

That my understanding.

They (REL) have built and tested a deep-cooled air/hydrogen rocket engine which would "technically" be the "heart" of the SABRE and built and tested a heat exchanger which was tested under simulated supersonic conditions (using the exhaust of a running jet engine into the intake of the HE) which was the 'key technology' to the deep-cooled engine set up. The rest of the engine is pretty much adaption of off-the-shelf technology for turbojet compressors.

Your also correct that the main reason REL's progress has been slow is the lack of funds as what has gone before has been strictly technology development on the basic systems of the SABRE. Next REL plans on building and running a full size SABRE engine to validate their simulation and models.

(Most of which are based on well documented studies and research done since the mid-50s on similar engines cycles though none used the exact set up that REL has pioneered. I'm sad to say that a majority of the work was done in the United States and "abandoned" after the research was side-tracked into SCramjet research based on the false idea that SCramjets were both "required" and the ultimate "air-breathing" acceleration engine. Despite almost 50 years of focused research the SCramjet has yet to live up to even a third of its supposed "potential" and is far less closer to operational use than the SABRE is. They have so dominated the thinking that almost every "air-breathing" space launch concept MUST have them "tacked-on" at some point despite their lack of use in the majority of cases. Worse of course from my "pro-US" perspective is the fact that OUR engineers missed such a fundamental design flaw in their early Rocket-Based-Combined Cycle engine work in that they made a false assumption that "air-fed" rockets required the liqufication of the air prior to injection into the rocket motor. As just about anyone working on the LH2/LOX RL10 could have told them, a rocket greatly benefits from GAS injection of both the hydrogen AND the oxygen rather than liquid! Kudo's to REL but I'm still upset that the US HAD everything up to including an almost flight-weight engine ready for flight testing but circumstances didn't allow it :(  )

I suspect that once the full size SABRE is tested a lot more interest and money will be generated.

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline banjo

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #37 on: 02/20/2015 06:08 PM »
i don't understand the animosity toward REL.  what have they done to offend so?  to me REL brings to mind two things -  the sentiment behind the quote “We choose to go to the moon in this decade and do the other things, not because they are easy, but because they are hard."   and  Concorde.

REL are working really hard on a disruptive idea that they had; one that they think can achieve the same as elon musk's goal of cheap rapid access to space for the benefit of mankind. good for them. that should inspire, not generate a load of naysaying.  what's wrong with you people?

when the space shuttle idea was proffered, did people say 'what's wrong with normal rockets?, we know how to do normal rockets'  were there naysayers arguing for incremental steps?  i don't know.  the result was awesome.   

' what's wrong with normal aeroplanes?'   and then out rolls concorde.  if there were people at the time who tried to undermine the spirit of the project,  i bet they were as awestruck as the rest of us when the result took off in front of them.

the world has been mesmerised by  spacex landing rockets and capsules; by them constructing a BFR,  and then out rolls Skylon sounding like the end of the world.   how is this bad?  if it is difficult, if it takes a long time, are they reasons for REL to give up?  of course not.  the world needs passionate and competent innovators of their ilk.  they should be encouraged.  i wonder if this thread is getting REL down. i hope not.
« Last Edit: 02/20/2015 06:10 PM by banjo »

Offline Lars-J

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #38 on: 02/20/2015 06:22 PM »
i don't understand the animosity toward REL.  what have they done to offend so?  to me REL brings to mind two things -  the sentiment behind the quote “We choose to go to the moon in this decade and do the other things, not because they are easy, but because they are hard."   and  Concorde.

REL are working really hard on a disruptive idea that they had; one that they think can achieve the same as elon musk's goal of cheap rapid access to space for the benefit of mankind. good for them. that should inspire, not generate a load of naysaying.  what's wrong with you people?

Speaking for myself only, here - I have no animosity towards REL. Zero. I really do hope they succeed.

What does rub me the wrong way, however, is how the two main "Skylon evangelists" on this forum (not affiliated with REL but happy to speak on their behalf it seems)  ::) portray Skylon as a "done deal". Discussing it as of it already exists. Denigrating the hard work by done by people trying for the same goal but by different means.

There is also an element of "been there, seen that" skepticism. Skylon is just another in the long line of SSTO-ish launch concepts that were at their own time portrayed as the greatest idea since sliced bread. So some skepticism is warranted, and this is why I post - to counter the outlandish statements made quite frequently. If that is something "wrong with me", then so be it.

Does that make sense?

Offline Impaler

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #39 on: 02/20/2015 06:35 PM »
Siting the Space-shuttle and the Concorde as great beacons of success in this area gives me shudders down my spine.  These two vehicles are emblematic of why the criticism and doubt area valid, the Shuttle was expensive and dangerous, the Concorde could barely close it's business case in a much more established passenger service market.

And in response to JS19, if you want to count the detractors count me too, so were at 3 people now.

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