Author Topic: The Reaction Engines Skylon Master Thread (5)  (Read 419798 times)

Offline Ravenger

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1300 on: 03/10/2016 12:57 PM »
Quote
Far too soon for engine testing, component testing  yes.

Thought it was probably too good to be true.  ::)

Let's hope we get some decent info from REL soon.
« Last Edit: 03/10/2016 03:26 PM by Ravenger »

Offline RanulfC

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1301 on: 03/10/2016 02:24 PM »
I still see no reply to the very informative post of 93143. Any one with better numbers? let's have a polite discussion on how much off the design must be not to deliver. We all want to see the calculations of those claiming the margins are really small.

While it would nice to have such a conversation there are at least two criteria for that to happen;

1) You need the numbers, the ACTUAL numbers to base such a conversation on. The numbers provided by 93143 are the best estimates available from the estimates and assumptions that REL has done so far which is all well and good. But they are still not actual performance figures. If we compare actual, historical numbers... Which was one of the "points" since we can't, no one has designed, built, or operated an SSTO (either horizontal or vertical take off nor by power plant type) so the only available numbers are estimates from previous designs.

2) Everyone has to at least agree on some basic factors to have any chance of discussing the original subject. Which by the way was that "TSTO designs give greater design margins than SSTO designs" which is in fact TRUE and verifiable through historic reference and experience.

Despite John Smith 19 confusing "airplanes" with "spacecraft/spaceplanes" and using the old saw that the former are "SSTO" (which ignores SO many operational and design differences as to have no meaning) so "obviously" having the latter SSTO is the only thing that makes sense, and attacks describing all TSTO designs as "failures" of design-and-engineering, etc, etc the basic fact does not change a bit.

Probably the main question or point of discussion would be how applicable is the SABRE engine design to use on a TSTO vehicle? SABRE on the Skylon is specifically designed for SSTO operations, but we already know from LAPCAT that a similar engine-cycle is applicable to high-speed, in-atmosphere flight so it's not really that much of a stretch to see SABRE being adapted to booster use only even though it is probably less of an efficient use of the system.

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 RanulfC

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1302 on: 03/10/2016 02:28 PM »
There's a new article about Skylon and Sabre at The Verge website:

http://www.theverge.com/2016/3/8/11174670/rel-skylon-spaceplane-announced-jet-engine-rocket-propulsion

One bit of info was new to me:

Quote
"The company plans to test the engines this year"

This is exciting news if true.

Far too soon for engine testing, component testing  yes.

Really? I was under the impression that REL was planning on testing a "bread-board" SABRE engine system this year. Yes it could be considered "component-testing" but it is testing the components together AS a system in order to refine function and efficiency.

And frankly they need to.

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 Star One

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1303 on: 03/10/2016 03:50 PM »

There's a new article about Skylon and Sabre at The Verge website:

http://www.theverge.com/2016/3/8/11174670/rel-skylon-spaceplane-announced-jet-engine-rocket-propulsion

One bit of info was new to me:

Quote
"The company plans to test the engines this year"

This is exciting news if true.

Far too soon for engine testing, component testing  yes.

Really? I was under the impression that REL was planning on testing a "bread-board" SABRE engine system this year. Yes it could be considered "component-testing" but it is testing the components together AS a system in order to refine function and efficiency.

And frankly they need to.

Randy

I am with you on this not sure why the OP thinks they are that far behind.

Offline Hankelow8

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1304 on: 03/10/2016 04:08 PM »

There's a new article about Skylon and Sabre at The Verge website:

http://www.theverge.com/2016/3/8/11174670/rel-skylon-spaceplane-announced-jet-engine-rocket-propulsion

One bit of info was new to me:

Quote



"The company plans to test the engines this year"

This is exciting news if true.

Far too soon for engine testing, component testing  yes.

Really? I was under the impression that REL was planning on testing a "bread-board" SABRE engine system this year. Yes it could be considered "component-testing" but it is testing the components together AS a system in order to refine function and efficiency.

And frankly they need to.

Randy

I am with you on this not sure why the OP thinks they are that far behind.

They have a massive amount of detailed design work to undertake before  work can start on construction.

I seem to recall Reaction Engines stating engine testing would not start until late 2018/2019


Offline francesco nicoli

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1305 on: 03/10/2016 04:11 PM »
SpaceX president yesterday declared that first stage reusability would cut prices of max. 30%, meaning a per-kg cost of 2800$. still sure there is no business case for Skylon? even being very pessimistic, it approaches a cost of 1500/2000 $/kg, and the optimistic figure says 600....

Offline chipguy

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1306 on: 03/10/2016 04:58 PM »
SpaceX president yesterday declared that first stage reusability would cut prices of max. 30%, meaning a per-kg cost of 2800$. still sure there is no business case for Skylon? even being very pessimistic, it approaches a cost of 1500/2000 $/kg, and the optimistic figure says 600....

First of all you have to recognize the *difference* between price and cost. You are using the terms
interchangeably above.

If SpaceX is already offering substantially lower prices than competitors then how should it apply the
cost reduction benefit of first stage re-usability? Smart business practice is to split the cost reduction
bonus between some price reduction, like up to 30%, and increased launch services gross margins to
pay for R&D and build financial resources. Any price reduction is basically an experiment to test TAM
demand elasticity. Putting a toe in the water is sensible rather than leaping in and generating demand
you can't meet and leaving money on the table for the demand you do fill.

Holding back some of the cost reduction also provides flexibility in case a new lower cost competitor,
perhaps using Skylon if it completes development and performs as advertised, appears.

Offline Hauerg

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1307 on: 03/10/2016 05:14 PM »
SpaceX president yesterday declared that first stage reusability would cut prices of max. 30%, meaning a per-kg cost of 2800$. still sure there is no business case for Skylon? even being very pessimistic, it approaches a cost of 1500/2000 $/kg, and the optimistic figure says 600....
Skylon is so far away from flying that "current" reusable pricing will be irrelevant.
(I like it to be successful, though.) 

Offline RanulfC

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1308 on: 03/10/2016 06:40 PM »
They have a massive amount of detailed design work to undertake before  work can start on construction.

I seem to recall Reaction Engines stating engine testing would not start until late 2018/2019

I think there's some confusion between engine-testing and engine-system testing :)

As I understood it they need to test the various components in a basic configuration (hence the "bread-board" type layout) in order to refine the overall design requirements and system functionality. It won't be an "engine" but the systems of the engine run as a unit to define the design of the actual engine.

They were supposed to run the configuration this year so they could have a basic prototype engine by late 2018/2019.

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 Hankelow8

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1309 on: 03/10/2016 07:12 PM »
They have a massive amount of detailed design work to undertake before  work can start on construction.

I seem to recall Reaction Engines stating engine testing would not start until late 2018/2019

I think there's some confusion between engine-testing and engine-system testing :)

As I understood it they need to test the various components in a basic configuration (hence the "bread-board" type layout) in order to refine the overall design requirements and system functionality. It won't be an "engine" but the systems of the engine run as a unit to define the design of the actual engine.

Just to clarify my position on this.

Testing of various components will progress over the next couple of years and then a "non-flight" proof of concept engine will be tested. If the testing proves successful I think they will endeavour to bring an airframe manufacture on board. I still think a first  flight will not happen until around 2028.
Skylon is a post Ariane 6 launcher. It just cannot operate in such a low launch  per year environment.

I expect by the end of the next decade the number of launches per year will be at a totally different level with a responsibility of companies to keep space clear of "trash" . There will be all sorts of large structures in orbit from power generation beamed down to earth, manufacturing in zero gravity and more, all needing service and supply. this is Skylons home ground.

My personal view of course!.



« Last Edit: 03/10/2016 07:52 PM by Hankelow8 »

Offline RanulfC

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1310 on: 03/10/2016 07:24 PM »
SpaceX president yesterday declared that first stage reusability would cut prices of max. 30%, meaning a per-kg cost of 2800$. still sure there is no business case for Skylon? even being very pessimistic, it approaches a cost of 1500/2000 $/kg, and the optimistic figure says 600....

Actually there is no business "case" for Skylon because of the simple fact there is no Skylon... Yet :)

I'll have to look up the exact quote but as chipguy notes there's a difference between price and cost and which one the "30%" actually applies to AND how SpaceX is applying it.

In general, (all "things" being equal etc :) ) a SSTO vehicle is supposed to be cheaper to operate than a TSTO vehicle due to the factors of only a single vehicle, monolithic maintenance and operations costs, etc. That's why all other transportation systems (supposedly) are "Single Stage" vehicles rather than multiple stages. ("Supposedly" because really all transportation is composed of a "system" of moving the payload from place to place and "technically" more often than not you use several "vehicles/stages" to get it from point A to point B but we don't want to get to confusing or push any analogy to far... Because...)

However, space launch has never been something you can directly "analog" with any other transportation system we have because of numerous factors inherent in it. People tend to default to aviation as an analog because it is a) the "newest" transport system we have, and b) because its the easiest to make comparisons with in general. (Planes and rockets both "take-off" and "land" and in between they "fly" and both carry passengers and cargo, etc. If you really wanted to be more accurate they would compare with ships and water travel because they both pretty much require both a source and destination to be effective and if you "stop" a ship is sits on the water and floats like a rocket does once in-orbit, but as I said NONE of our other transportation systems really are an effective analog in anything but really general terms)

"Space is hard" is a truism and that's when the base line is using multiple stages to get the payload where you want to go. It gets harder with only a single stage and the basic idea that operating and maintaining that single stage will be "cheaper" than doing so with multiple stages tends to not be as true as it would seem. A lot of the assumptions involved are not based on actual data but on extrapolations of other transportation systems and again the analogies (and data) are not as clear cut as it would appear. The fact that most of the data points come from aviation experience do not in fact increase the viability of the data as much as is supposed.

Leaving aside the main point of one being a currently operational, partially reusable system transitioning to a fully reusable (is the hope) system at a later date, while the other is still in the design stage. The Falcon-9 is a Vertical Take-Off, Two-Stage-To-Orbit system whereas the Skylon is a Horizontal Take-Off, Single-Stage-To-Orbit* system and the two vehicles are going to have vastly different flight regimes and well as operations and maintenance schemes. The capabilities are different as well and direct comparison or the use of the former to "prove" any data points on the latter is questionable at best.

Randy
*Technically you COULD do some comparison between Falcon-9 and Skylon as when you get right down to it both are actually "Two-Stage-To-Destination" vehicles in that both require a second stage to deliver the payload to the proper destination and Skylon therefore has to include margin to allow bringing said stage all the way to orbit in it's "payload" but that's a nit and, again, mostly not indicative of comparable capability. But it IS fun to occasionally bring up to tweak people with :)
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 93143

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1311 on: 03/10/2016 10:41 PM »
The general theory on how much ISP you can get out of a certain engine setup is pretty well understood, yes. But getting there can be very expensive and time consuming if you lack the experience and especially if it's a high ISP.

The argument was that a "slight shortfall" in performance could zero the payload.  A staged-combustion hydrolox engine coming in at 380-400 seconds is not a "slight shortfall".

Hydrolox engine design is much better understood than it was when the 455 s target was established for the SSME, and the design tools are much better.  Furthermore, the SABRE's lower pressure as compared with the SSME would vastly ease the design even if it didn't have hugely more benign turbomachinery environments due to the cycle layout.  Not to mention that the SABRE 4 concentric nozzle design allows the designers to simply ignore sea-level performance and optimize for vacuum; as far as I can tell from the numbers, REL have not attempted to take advantage of this by raising the target Isp.

It would take a 0.7% loss of trajectory-averaged Isp - roughly 3 seconds vac, more than what the SSME saw - just to wipe out the 986 kg performance margin, assuming the vehicle eats up its entire mass growth allowance.  The RS-68 saw a bigger shortfall, but I believe that was because of a known injector design flaw they haven't bothered to fix, and in any case it's still in the range where if SABRE suffered a similar but unfixable shortfall, a reasonable vehicle scale-up could restore the lost payload.

Note also that my numbers so far all assume no vehicle redesign, either to lighten the structure or to replace lost payload with extra propellant.  If you replace lost payload with propellant instead of with nothing (there is headroom in the airframe design), the numbers look even better.

Large reductions in airbreathing effective Isp are perhaps less unlikely, but the design is vastly less sensitive to airbreathing performance (note that Skylon C1 was considered viable even with the SABRE 3, which seems to have had an estimated airbreathing Isp approximately half that of the SABRE 4).  Dry mass could be a problem too, but again my numbers suggest healthy margins, particularly if they're not cheating on the mass growth allowance...

As of two years ago, the SABRE programme was estimated to cost close to $6B, most of that after demonstrating a full-scale prototype on the test stand.  That doesn't sound to me like they plan to just sling together a first cut and call it a day.

I still see no reply to the very informative post of 93143. Any one with better numbers? let's have a polite discussion on how much off the design must be not to deliver. We all want to see the calculations of those claiming the margins are really small.
You need the numbers, the ACTUAL numbers to base such a conversation on. The numbers provided by 93143 are the best estimates available from the estimates and assumptions that REL has done so far which is all well and good. But they are still not actual performance figures.

What?

If we had actual performance figures, there would be no room for said conversation.  The whole point is that we don't; the viability of the design is not known yet and depends on how close they can get to their estimates.  The question is: how much margin for error in those estimates do they have?  If my math is right, it seems they have quite a bit...

Actually there is no business "case" for Skylon because of the simple fact there is no Skylon...

That's not how that works.  You build a business case for something you're considering doing in the future, in order to determine whether or not you should.  If there's no business case for Skylon, no business will build it because it would be a pointless money pit.  The business case comes first; the product comes later.

To be fair, the business case is kinda wobbly right now due partly to the technical unknowns; it should firm up considerably as development progresses (assuming it goes well), which is one reason REL aren't asking for $15B up front...
« Last Edit: 03/11/2016 01:09 AM by 93143 »

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1312 on: 03/11/2016 01:14 AM »
1) You need the numbers, the ACTUAL numbers to base such a conversation on. The numbers provided by 93143 are the best estimates available from the estimates and assumptions that REL has done so far which is all well and good. But they are still not actual performance figures. If we compare actual, historical numbers... Which was one of the "points" since we can't, no one has designed, built, or operated an SSTO (either horizontal or vertical take off nor by power plant type) so the only available numbers are estimates from previous designs.
True. Hopefully this situation will be clearer by the end of the year.
Quote
2) Everyone has to at least agree on some basic factors to have any chance of discussing the original subject. Which by the way was that "TSTO designs give greater design margins than SSTO designs" which is in fact TRUE and verifiable through historic reference and experience.
Agreed, for VTO ELVs. But the evidence for Shuttle is much less conclusive. Both engine systems failed to meet their performance targets. One did not compensate for the other.
Quote
Despite John Smith 19 confusing "airplanes" with "spacecraft/spaceplanes" and using the old saw that the former are "SSTO" (which ignores SO many operational and design differences as to have no meaning) so "obviously" having the latter SSTO is the only thing that makes sense, and attacks describing all TSTO designs as "failures" of design-and-engineering, etc, etc the basic fact does not change a bit.
Quote
Not so. I think the fact that all other transport systems are "single stage," in the sense they use one vehicle to do one job is strongly suggestive that is the way to go. The reality (until now) is that has not been possible. The question is will it always be so? I don't believe it is a law of nature.
Probably the main question or point of discussion would be how applicable is the SABRE engine design to use on a TSTO vehicle? SABRE on the Skylon is specifically designed for SSTO operations, but we already know from LAPCAT that a similar engine-cycle is applicable to high-speed, in-atmosphere flight so it's not really that much of a stretch to see SABRE being adapted to booster use only even though it is probably less of an efficient use of the system.
Certainly possible. What's odd is why would you would still call it SABRE, given so much of the design would be thrown away?

Logically they should just ask (and pay) REL to design an engine for the part of the flight regime they believe it can safely cover and buy a rocket to cover the rest.  :(
"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 #1313 on: 03/11/2016 01:15 AM »
As I understood it they need to test the various components in a basic configuration (hence the "bread-board" type layout) in order to refine the overall design requirements and system functionality. It won't be an "engine" but the systems of the engine run as a unit to define the design of the actual engine.

Just to clarify my position on this.

Testing of various components will progress over the next couple of years and then a "non-flight" proof of concept engine will be tested.
I'm guessing where your post starts and ends as you seem to be having trouble with quoting.

You don't appear to be aware that component design and testing has been underway (funds permitting) since the late 90's

the 2014 NISSIG presentation

Look at slide 15.

You will see they have been developing test components and mfg methods for some time. Not just Powerpoints or CFD models but actual working hardware, at full size wherever possible to avoid scale effects and to allow them to drop that part directly into the full scale engine.

You might like to revise your estimate of how soon that test model will be ready.
"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 93143

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1314 on: 03/11/2016 01:21 AM »
I think he's talking about the "dissected rabbit" engine, which was ruled out when they got enough money to go full-scale right away but may have been ruled back in when their major investor pulled out, or when BAE bought into the project.  (I can't remember, and right now I should do some actual work instead of digging for that information...)

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1315 on: 03/11/2016 01:31 AM »
LOX-LH2 rocketry is a sufficiently mature tech that a large shortfall is ISP seems unlikely, even with the novel pump arrangement.  Which, presuming their engineers have done their jobs right, leaves substantial performance margins before complete loss of payload. 
The design of the SSME was off it's predicted Isp by about 3 secs. Note this was only the 2nd staged combustion engine built in the US and the first (and only) LH2 engine. That's 0.66% for a first of a kind (SC of LH2) design.  This suggests the rocket part at least is fairly well understood.
Not necessarily. Don't exactly know what you mean by "first LH2 engine", probably first LH2 staged combustion engine.
Correct. And you managed to reason that out without using the context of the early part of the sentence IE the first SC engine using storable propellants. This situation will change with the new Blue BE4 engine of course.
Quote
But if you look at the development effort you'll see that it had several years of delays and huge cost overruns in development.
As to hitting the ISP: they had to at all cost to make the whole thing viable, 10s less ISP and there goes your payload.
In total they lost 5 secs across the solid and liquid systems, which lead to a payload "scrub" (of the whole orbiter) to lower mass by 15%. They never achieved the target payload in the payload bay of 65 000lb.

STS demonstrated that any Vertical Takeoff system is very sensitive to Isp
"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 Hankelow8

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1316 on: 03/11/2016 08:22 AM »
As I understood it they need to test the various components in a basic configuration (hence the "bread-board" type layout) in order to refine the overall design requirements and system functionality. It won't be an "engine" but the systems of the engine run as a unit to define the design of the actual engine.

Just to clarify my position on this.

Testing of various components will progress over the next couple of years and then a "non-flight" proof of concept engine will be tested.
I'm guessing where your post starts and ends as you seem to be having trouble with quoting.

You don't appear to be aware that component design and testing has been underway (funds permitting) since the late 90's

the 2014 NISSIG presentation

Look at slide 15.

You will see they have been developing test components and mfg methods for some time. Not just Powerpoints or CFD models but actual working hardware, at full size wherever possible to avoid scale effects and to allow them to drop that part directly into the full scale engine.

You might like to revise your estimate of how soon that test model will be ready.

The vast majority of Reaction Engines design and testing has been on the heat exchanger.

Although  Detailed design work on all the other components designed for SABRE has been ongoing for some time, I think they now have started to crank up this work, you only have to look at their job adverts over the last 12/18 months to see they now really mean business on a full scale engine development.

One cannot underestimate the task in development. They are developing a joint rocket and jet engine, a world first for the UK again.

While I would love to see a non-flight SABRE on test next year, I cannot see that happening until 2018/2019.
Only time will tell on this JS.
« Last Edit: 03/11/2016 08:24 AM by Hankelow8 »

Offline RanulfC

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1317 on: 03/14/2016 05:58 PM »
I still see no reply to the very informative post of 93143. Any one with better numbers? let's have a polite discussion on how much off the design must be not to deliver. We all want to see the calculations of those claiming the margins are really small.
You need the numbers, the ACTUAL numbers to base such a conversation on. The numbers provided by 93143 are the best estimates available from the estimates and assumptions that REL has done so far which is all well and good. But they are still not actual performance figures.

What?

If we had actual performance figures, there would be no room for said conversation.  The whole point is that we don't; the viability of the design is not known yet and depends on how close they can get to their estimates.  The question is: how much margin for error in those estimates do they have?  If my math is right, it seems they have quite a bit...

If their math is correct then your math is probably correct to their estimates... Which still doesn't eliminate the possibility that everyone's math isn't going to be met by actual performance. Doubtful but the chance is non-zero to a significant degree. Hybrid engines specifically are tricky beasts to get working as various SERJ and other air-breathing hybrid engines showed.

But lets' all be honest, what we REALLY want is to but this entire argument to bed for good, which requires the real numbers and yes that would leave LITTLE (come on, you know as well as I do how much people love to argu.... er, discuss this stuff :) ) room for discussion.

Quote
Actually there is no business "case" for Skylon because of the simple fact there is no Skylon...

That's not how that works.  You build a business case for something you're considering doing in the future, in order to determine whether or not you should.  If there's no business case for Skylon, no business will build it because it would be a pointless money pit.  The business case comes first; the product comes later.

To be fair, the business case is kinda wobbly right now due partly to the technical unknowns; it should firm up considerably as development progresses (assuming it goes well), which is one reason REL aren't asking for $15B up front...

To be totally honest the "business case" exists but the Skylon is not technically firm enough to apply to that case. That would be the normal commercial launch business "case" but Skylon isn't at the point yet, (as you note) where it can be realistically compared to the current providers. Skylon IS a "product" under the circumstances and it has to be brought to a point where enough technical and operations unknowns are retired to be able to build an applicable business and operations plan specifically for Skylon.

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 RanulfC

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1318 on: 03/14/2016 06:37 PM »
1) You need the numbers, the ACTUAL numbers to base such a conversation on. The numbers provided by 93143 are the best estimates available from the estimates and assumptions that REL has done so far which is all well and good. But they are still not actual performance figures. If we compare actual, historical numbers... Which was one of the "points" since we can't, no one has designed, built, or operated an SSTO (either horizontal or vertical take off nor by power plant type) so the only available numbers are estimates from previous designs.
True. Hopefully this situation will be clearer by the end of the year.

Please, yes! :)
 
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2) Everyone has to at least agree on some basic factors to have any chance of discussing the original subject. Which by the way was that "TSTO designs give greater design margins than SSTO designs" which is in fact TRUE and verifiable through historic reference and experience.
Agreed, for VTO ELVs. But the evidence for Shuttle is much less conclusive. Both engine systems failed to meet their performance targets. One did not compensate for the other.

The Shuttle was specifically a 1.5STO design with the SRBs being "augmentative" rather than an actual stage. It was a design compromise that was well known but un-avoidable under the circumstances. HAD the Shuttle been designed as an actual TSTO or any number of "improved" boosters (and no, the ASRBs were no where near enhance enough to make up for the short-falls) concepts had been built they would have compensated for the SSME short-falls.

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Despite John Smith 19 confusing "airplanes" with "spacecraft/spaceplanes" and using the old saw that the former are "SSTO" (which ignores SO many operational and design differences as to have no meaning) so "obviously" having the latter SSTO is the only thing that makes sense, and attacks describing all TSTO designs as "failures" of design-and-engineering, etc, etc the basic fact does not change a bit.
Not so. I think the fact that all other transport systems are "single stage," in the sense they use one vehicle to do one job is strongly suggestive that is the way to go. The reality (until now) is that has not been possible. The question is will it always be so? I don't believe it is a law of nature.

Quite a few people believe the same way but the plain fact is that no other transportation system has to do what ground-to-orbit transport does and while operationally single-stage has obvious advantages both technically and operationally the minimum we've found to work currently is 1.5STO. If Skylon is fully verified then that could (should) change but there is in fact no guarantee even if Skylon works TECHNICALLY that it won't be OPERATIONALLY as much a game-changer as assumed.

I probably wouldn't go as far as calling it a "law of nature" but pushing payload "uphill" from the surface of the Earth to orbit two-stages sharing the load puts more mass into place than a single stage vehicle does. And those two stages have higher overall margins than the single vehicle can have because they are split between two vehicles.

The main draw/claim for SSTO versus multiple stages in simple terms is that while the SSTO has lower margins and payload to destination, it is cheaper to operate and build since it's only a single vehicle. The idea being that it would be more like all the 'other' transportation systems and therefor even with less payload and possibly a higher cost it could fly more often and OVERALL would deliver more payload and lower operations costs over time. This hasn't been shown yet and is based on a lot of un-proven assumptions based on OTHER transportation systems which don't operate at all like space launch. Will this always apply? Probably not but at this point Skylon is in the same situation as Space Tethers where all the assumed number make them look wonderful but they haven't actually gotten to the point where those numbers are solid enough to assume they are true without significant added assumptions.

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Probably the main question or point of discussion would be how applicable is the SABRE engine design to use on a TSTO vehicle? SABRE on the Skylon is specifically designed for SSTO operations, but we already know from LAPCAT that a similar engine-cycle is applicable to high-speed, in-atmosphere flight so it's not really that much of a stretch to see SABRE being adapted to booster use only even though it is probably less of an efficient use of the system.
Certainly possible. What's odd is why would you would still call it SABRE, given so much of the design would be thrown away?

Logically they should just ask (and pay) REL to design an engine for the part of the flight regime they believe it can safely cover and buy a rocket to cover the rest.  :(

The main point of SABRE is it's a combined air-breather/rocket which means it can cover a larger portion of the trajectory than a single system. You'll note in most combined-cycle studies the AF has had used the first stage to reach speeds low-hypersonic speed (Mach 5-6) and then used rockets to push the stage out of the atmosphere to a point where the second stage needs little or no streamlining and/or the engines can be vacuum optimized.

It would also allow the design to have loiter and significant cross-range launch capability which is another thing the military loves for an "on-demand" launch system.

Randy
« Last Edit: 03/14/2016 06:41 PM by RanulfC »
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 Radical_Ignorant

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1319 on: 03/15/2016 10:15 PM »
Often in this thread there is assumption: if they would go two stage everything would be easier and better. This is reasoning from analogy to VTO rocket Launch Vehicles.
The case is: if they go TTO then nor Skylon nor Sabre has any sense. All concept is build around using air, not fighting with it, what makes it unique and first phase super efficient - and since engines are the same then what you can throw away? Airframe? How much fuel is used in first phase? How much mass could be shaved?
This is two phases to orbit in one stage to orbit.
« Last Edit: 03/15/2016 10:18 PM by Radical_Ignorant »

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