Author Topic: The Reaction Engines Skylon Master Thread (5)  (Read 420686 times)

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1340 on: 03/16/2016 07:42 PM »
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.
The cross range capability is a result of the Skylon design, not the SABRE engine.

But a pre cooled engine gives you the T/W to allow such a design to take off from a runway.

It took me years to find a report that would finally state what a SCRamjet T/W was.  ONce I saw "2:1" It thought, "how did they ever get funding to pursue this?" Yet $Bn have been spent.  :(
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Online RanulfC

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1341 on: 03/16/2016 09:12 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.

Right off the bat let me say that there have been a LOT of combined cycle rocket-air-breathing engine concepts over the years that have performance similar to the SABRE and they have been suggested for use in booster stages of a TSTO system NOT because they can't fly all the way to orbit but because a TSTO system nominally has more payload and engineering margins than an SSTO. The concept and practice of "using" the air and not "fighting" it is a well known possible path of development for spaceflight. (Trust me, this is one I've argued for years :) ) In reality though they have never been as simple as just using all rockets despite any obvious disadvantages and the real struggle is to get any of them to an operational or demonstrable flying status in order to actually PROVE the advantages. Skylon/SABRE is no different really and must ("justifiable" or not) therefor prove itself and it's advantages.

The "case" is a lot more complex than you make it out to be. First of all there is a difference between "orbit" and "destination" that is often ignored in these comparisons. Far more often than not the former is not the latter. The adage that once you're in orbit you are half way to anywhere is often cited as a truism but really we don't currently USE LEO as much as that was assumed when that was said. GTO/GEO and escape trajectories, serviced by multi-stage, direct ascent vehicles has become the default method instead of LEO rendezvous, fueling, and orbital assembly. The latter is more conducive to SSTO operations because SSTOs rarely can service both systems while TSTOs have the excess capability to do so. Skylon does not change this operational fact. (See below)

Second your assumed "assumption" is not correct as the reason the analogy of current VTO TSTO is used for comparison is that they exist and the data is well known. Similar comparisons have been done with just about every proposed concept for getting from the surface to orbit because that data is so well known and available and Skylon is not any special case. Lastly the suggestion, (not assumption) is that a TSTO system would have higher engineering margins and payload mass than an SSTO system FOR THE SAME DESIGN POINTS. Which is admittedly something that tends to get forgotten in the conversation.

Why do you assume at all that something must be "thrown away"? Staging is dropping off excess mass to increase efficiency of the overall system. That CAN mean "expending" some portion of the system, (which isn't either 'bad' nor unheard of since every transportation system 'expends' fuel to operate after all :) ) and there are viable and logical trade-offs where that may apply, but dropping off the excess mass of the booster stage and continuing the mission profile with a more efficient second stage that is fully reusable is as valid an assumption as not.

And in fact operationally the Skylon is a two stage 'to-destination' vehicle with the Skylon only attaining orbit while it requires a second stage, (Skylon Upper Stage, SUS) to deliver it's designed payload to the proper (GTO/GEO) orbit or beyond. (This tends to be where the statement that the Skylon was designed to carry "EELV" class payloads breaks down. In general that payload class is somewhere between 8mt to 10mt to GTO, but closer to 18mt to 20mt to LEO. Best case for Skylon is between 15mt and 18mt to LEO and that has to include the SUS mass for GTO/GEO payloads) The SUS can be used either as an expendable or reusable stage depending on the payload destination requirements. You'll note the various payload capabilities listed in the Skylon Users Manual and various propulsive requirements for each*

REL decided on going SSTO rather than TSTO for reasons they have often given HOWEVER that in no way invalidates the use of the SABRE in TSTO applications nor do any of those reasons REL gives do so.

I keep pointing out that SABRE is perfectly capable of performing the most common HTL air-breathing booster mission; Ground take-off, Orbital plane and Trajectory adjustment or "cruise" mode to selected "launch" point, "launch" with acceleration to above Mach-5 in air-breathing mode, powered pull-up and switching to pure rocket mode for climb outside the atmosphere, release second stage, perform controlled reentry and powered return to take off site for turn around. REL has base lined the Skylon as an SSTO vehicle and operations mode but even they admit that TSTO operations even with the Skylon design has operational and payload advantages. It would be more advantageous if the Skylon were actually designed for the TSTO booster role but that's not the way they are aiming and the reasons given are viable either way for the assumptions made.

AFRL has been looking at both SSTO and TSTO designs using various propulsion systems and for various applications for decades and they are interested in the SABRE as a power plant for an HTL-TSTO booster application which, while different operationally from the path that REL chose it's no less valid and it certainly can't be argued as being 'wrong' either. Frankly, if they can keep from trying to slap some SCRamjets on the design somewhere it has a much higher chance of reaching testing which would benefit REL to no end than if REL had insisted that the SABRE can ONLY be used on SSTO designs and crocked the whole deal. REL doesn't have an issue with the decision really, so why should we?

Randy
*REL itself, while rightly pointing out that the Skylon is DESIGNED for SSTO operations and is more "efficient" at that design point given it's design assumptions, explains that the Skylon AS DESIGNED is capable of and could be used as the suborbital first stage of a two-stage mission. It's right there in the Skylon Users Manual cited earlier. Page 8-9 give orbital figures while page 10 is for suborbital deployment. Note in either case for anything other than LEO all payloads have to include propulsion to deliver to their required destination. As noted above that's somewhere around 15mt to 18mt for Skylon delivery to orbit but the guide points out that Skylon can deliver up to it's maximum STRUCTURAL load of 30mt in a suborbital, two stage launch with payload supplied propulsion.  :)
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?

Online RanulfC

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1342 on: 03/16/2016 09:23 PM »
You have mentioned "single engine possibility" more than once now.

It should be pointed out that it was the rear-heavy design failure of HOTOL - which became a "means for lifting hydraulics into orbit" (huge canards to compensate CoM issues) - which principally drove the twin-engined Skylon design.
True.

For a demonstration vehicle what is essentially a winged nacelle would be possible.

To preserve the CoG protecting features you'd need to put it on top of the payload bay, like a sort of V1 cruise missile.

But that would leave the issue of how  you open the bay to get the payload out. 

The latter is a slightly closer to Skylon so might shorten the test programme of the real Skylon, while the former is likely to be cheaper.

Both would probably make the test programme more expensive overall.

Two things; While it's awkward, "under" is also possible, but more importantly would you want a 'demonstrator' to have payload? It's nice but... You could also go with a more integrated engine/body design which REL has avoided due to this being rather difficult to get "just right" without extensive testing BUT it something that any airframe manufacturer could do within a budget. The basic Skylon design is the way it is to avoid as much airframe design work as possible, (REL keeps telling everyone they design engines with airframes as a side-line to have something to put those engines on after all :) ) but once you go beyond that requirement there's a lot of ways to do the design itself.

In the end you have to make a decision what exactly the 'demonstrator' is demonstrating. If it's engine operations over the flight regime an actual payload isn't needed. If it's going to be demonstrating that the entire concept of both the engine cycle flight operations is possible then you are pretty much designing a actual sub-scale vehicle with certain capabilities which can include payload deployment. (This was the concept behind the GTX which could "deliver" 300kg to orbit or carry test instruments, but was also to demonstrate the engine concept) There are variations in between but not as much as you'd think.

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 93143

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1343 on: 03/16/2016 09:31 PM »
Shuttle has a problem because of margins.  Mass to orbit was not just the payload at 50klb (round numbers) but the 250klb orbiter.  So if the orbiter came in too heavy at 5%, that means the payload loses 12.5klb mass.  that is why they had to increase the performance of the system.  For SSTO, it is worse.

Not this SSTO.  The vehicle's projected mass at MECO minus the payload is less than four times the payload, not much worse than the Shuttle orbiter and significantly better than the orbiter+ET.  This is after industry-standard mass growth margins.

The engineering challenge of developing an SSTO is so astoundingly far beyond the engineering challenge of TSTO. Not just twice as hard, but orders of magnitude.

The whole point of SABRE is that it makes this not true any more.  Insisting otherwise without any actual math as backup (as people like to pop in here and do now and then) is cargo cultism - associating the difficulty with the label rather than with the technological requirements.

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REL is at least doing one form of iterative development: subscale component testing. It also seems like they are happy to have other players use their technology on lower risk iterations, ironically unlike many of their defenders here.

Quite so.  But they apparently see no need to take that detour themselves; they've been doing risk reduction on the SSTO and pushing it pretty much exclusively, because they think it's a reasonable thing to do if the engine works.

The technical risk involved in doing TSTO first is probably lower.  But the cost may very well not be - these are still high-performance flight vehicles, after all - and the commercial payoff is dubious.

Quote
Engineering margins.

Last I heard, the airframe was being designed to a safety factor of 1.5, the same as a commercial airliner.
« Last Edit: 03/16/2016 10:50 PM by 93143 »

Online RanulfC

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1344 on: 03/16/2016 09:41 PM »
A strapon booster for existing/future LV is one possibility.
No it's not. This was a running theme of WIlliam Escher.  It's a bad notion given the poor T/W of airbreathers (although SABRE's is excellent by turbofan standards).

Oh it's still possible, just not likely :) T/W can be adjusted in a lot of jet engines by various means. Some more operationally viable than others, but in context you could get a much higher T/W from the SABRE with enough work. The main issue is why you'd want to though as it would degrade capability in other areas enough that it probably wouldn't be a SABRE anymore.
And it should be pointed out that he did say "future" LVs too which could be interesting to explore. The main issue with current LVs is they don't deal well with horizontal operations and you'd avoid VTO operations with the base line SABRE so what if any advantage would there be?

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.
The cross range capability is a result of the Skylon design, not the SABRE engine.

Really? What's the cross-range on an Atlas-V or Delta-IV? :)

No that's actually because the SABRE is an air-breathing engine which allows them to MOVE the launch point around to where they need it. I probably should have been more explicit though.

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But a pre cooled engine gives you the T/W to allow such a design to take off from a runway.

You and I have discussed this before and it's NOT just pre-cooling that allows such operations. The SERJ could do it just fine without. With enough "bits" added, (pre-cooling was included in all of Escher's "Spaceliner" class air-breathing propulsion engines except some H2O2 prototype design concepts) you get a T/W which allows VTOL operations which was unattainable for most jet-type engines alone. No where near a rockets but a lot of the combined cycle engines used both rockets and air-breathing in various combinations in the same engine anyway.

It's a design toss-up decision that is based on what your assumptions are from the start. Frankly I don't see SABRE working that way operationally efficient enough to warrant and would stick to HTOL operations to take advantage of the cycle.

Quote
It took me years to find a report that would finally state what a SCRamjet T/W was.  ONce I saw "2:1" It thought, "how did they ever get funding to pursue this?" Yet $Bn have been spent.  :(

But EVENTUALLY (so the theory says) you can go as fast as you want to with a SCRamjet engine which is WHY the bucks keep flowing in. Of course as everyone well knows "I" can't see any way that justifies trying to fly around in an atmosphere at speeds above Mach-5 for any length of time but then again I'm not an advocate of SCRamjets anyway :)

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 Jim

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1345 on: 03/16/2016 10:57 PM »


Quote
Engineering margins.

Last I heard, the airframe was being designed to a safety factor of 1.5, the same as a commercial airliner.

That is not the same.  Engineering or design margin is in addition to the safety factor. If they design has something wrong or under calculated, they might not have 1.5 safety factor

Offline Jim

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1346 on: 03/16/2016 10:59 PM »
Shuttle has a problem because of margins.  Mass to orbit was not just the payload at 50klb (round numbers) but the 250klb orbiter.  So if the orbiter came in too heavy at 5%, that means the payload loses 12.5klb mass.  that is why they had to increase the performance of the system.  For SSTO, it is worse.
Not this SSTO. 

Yes, this SSTO and all others.  They are more sensitive to mass increases than other LVs, especially first stages.
« Last Edit: 03/16/2016 10:59 PM by Jim »

Offline 93143

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1347 on: 03/17/2016 01:08 AM »
Engineering or design margin is in addition to the safety factor. If they design has something wrong or under calculated, they might not have 1.5 safety factor

I may have trimmed my post too much.  In any case it doesn't sound like the post I was responding to meant anything especially specific by the term...

REL claims that Skylon D1 uses "a mass margin philosophy consistent with AIAA guidelines", and one of their old papers calculated C1's truss structure mass using both a safety factor of 1.5 and a 15% mass growth allowance.  They're not just using bare calculated part masses in their presentations.  And there's a modest payload margin (~6.5% as of two years ago) on top of the structural margins.

Yes, this SSTO and all others.  They are more sensitive to mass increases than other LVs, especially first stages.

The point wasn't about "other LVs", and nobody mentioned first stages.  You were taking STS as an example, noting that the bulk of the mass that had to make orbit was not payload, and then said that "For SSTO, it is worse".

Well, technically this one is, a little, if you only compare it to the orbiter.  But a better comparison might be to the orbiter+ET, since that's the hardware unit that reaches orbit (basically) and thus trades 1:1 with payload.  It's also a better functional match to Skylon.  And it turns out that the payload of Skylon D1 (15,000 kg) is a larger fraction of the projected total orbited mass (73,435 kg) than the payload of STS was if you include the ET.  Even if you don't, it's fairly close.
« Last Edit: 03/17/2016 04:02 AM by 93143 »

Offline TrevorMonty

Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1348 on: 03/17/2016 01:24 AM »
A strapon booster for existing/future LV is one possibility.
Does anybody know what type performance increase 2 1xsabre boosters would give Vulcan assuming they separate at Mach5.

SABRE has a projected thrust-to-weight ratio of around 14. That's double the F119 engine, for example, which itself it higher than most commercial engines.

But rocket engines are up around 80-100. (The record is either Merlin 1D (180:1) or one of the Russian engines.)

[edit2: to clarify that. It means that if your SABRE-booster and fuel masses 14 times the mass of the engine, the booster will only be able to hover, it won't add any lift. If it masses more than 14 times the engine, the boosters will actually be hanging off the core stage, merely adding to the weight.]

SABRE's Isp is massively better than any rocket during its air-breathing mode, but for a vertical launch that precisely when you are most willing to sacrifice Isp for thrust. (The amount of fuel you burn in your first three minutes is much less important than the amount consumed in the last three minutes, because the fuel burnt in the last three minutes has to be carried during the rest of the flight.)

Skylon can cope with low thrust/weight because it gets lift from aerodynamic surfaces to compensate for gravity losses. And that long horizontal climb is where you need high-Isp.

[edit1: added the parenthesised comments]
Figured where I went wrong, I was looking at its rocket phase (LoX/LH) thrust of 440lkbs not airbreathing thrust which is considerably less.

Offline Paul451

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1349 on: 03/17/2016 03:11 AM »
To preserve the CoG protecting features you'd need to put it on top of the payload bay, like a sort of V1 cruise missile.
But that would leave the issue of how  you open the bay to get the payload out.

Belly doors, obviously. (Loading would be via an elevator-pit.)

but dropping off the excess mass of the booster stage and continuing the mission profile with a more efficient second stage that is fully reusable is as valid an assumption as not.

If you're using SABRE, then you've got that backwards. You'd have a reusable first stage (the Skylon-derivative), with an expendable all-rocket, vacuum-optimised upper-stage.

The cross range capability is a result of the Skylon design, not the SABRE engine.
No that's actually because the SABRE is an air-breathing engine which allows them to MOVE the launch point around to where they need it.

JS19's point was that any air-launch system has the same cross-range, rapid deployment ability; not just a SABRE-based launcher.

Offline Hanelyp

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1350 on: 03/17/2016 03:57 PM »
If you use a Skylon derived first stage in a TSTO system, the second stage would be all rocket vacuum optimized, not necessarily expendable.

Online adrianwyard

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1351 on: 03/17/2016 05:16 PM »
To preserve the CoG protecting features you'd need to put it on top of the payload bay, like a sort of V1 cruise missile.
But that would leave the issue of how  you open the bay to get the payload out.

Belly doors, obviously. (Loading would be via an elevator-pit.)

Bear in mind that even with the SABREs on the wingtips there's concern over the vacuum-expanded plume heating the rear fuselage. So a V1-style configuration could melt the aft?

If you really need a single SABRE config, then perhaps something D21-like could work? You'd have to run the cooled air around or through the tanks, and managing center of mass would be trickier. You might need the same dual LOX and H2 tanks that Skylon has in order to be able to drain fore/aft strategically. Sounds like too many compromises vs. the standard Skylon.
« Last Edit: 03/17/2016 05:16 PM by adrianwyard »

Offline Vultur

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1352 on: 03/17/2016 05:36 PM »
The engineering challenge of developing an SSTO is so astoundingly far beyond the engineering challenge of TSTO. Not just twice as hard, but orders of magnitude.

The whole point of SABRE is that it makes this not true any more.  Insisting otherwise without any actual math as backup (as people like to pop in here and do now and then) is cargo cultism - associating the difficulty with the label rather than with the technological requirements.

I'm not sure this is even true of pure-rocket SSTOs anymore, and I'm pretty sure it won't be in 5 years.

SSTO-level mass fractions have been done before. SpaceX has demonstrated engines with sufficient TWR, and they're working on VTVL recovery and reusability. In 5 years, they should have the capacities needed to build a pure-rocket VTVL SSTO (they won't, because it doesn't fit their plans, but they could).

A pure-rocket SSTO would still have less payload than a TSTO, and would be harder, but not I think orders of magnitude harder.

EDIT:
The "case" is a lot more complex than you make it out to be. First of all there is a difference between "orbit" and "destination" that is often ignored in these comparisons. Far more often than not the former is not the latter. The adage that once you're in orbit you are half way to anywhere is often cited as a truism but really we don't currently USE LEO as much as that was assumed when that was said. GTO/GEO and escape trajectories, serviced by multi-stage, direct ascent vehicles has become the default method instead of LEO rendezvous, fueling, and orbital assembly.

True. I think SSTOs would have a much stronger case if we had space tugs.

However, with electric propulsion now being available to raise satellite orbits...
« Last Edit: 03/17/2016 05:45 PM by Vultur »

Offline SICA Design

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1353 on: 03/18/2016 01:10 PM »
video from SABRE – The Next Leap Forward in Powered Flight
15th March 2016, Aerospace and Transport Technologies Research Priority Area, Faculty of Engineering, Nottingham University.

(I've not seen it yet, but passing on the link)

Almost inaudible - a shame...

Online adrianwyard

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1354 on: 03/18/2016 01:56 PM »
The audio has had a strong noise-gate filter applied, so the gaps between words are dropped to low volume. I bet it would be easier to understand if that were removed - assuming it's not in the original recording.

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1355 on: 03/18/2016 07:45 PM »
Belly doors, obviously. (Loading would be via an elevator-pit.)
I had not thought of this. More or less SOP for bombers though.
Quote
If you're using SABRE, then you've got that backwards. You'd have a reusable first stage (the Skylon-derivative), with an expendable all-rocket, vacuum-optimised upper-stage.
Yes that makes more sense. The days when avionics was so heavy/expensive to only use 1 set is long over.
Quote
JS19's point was that any air-launch system has the same cross-range, rapid deployment ability; not just a SABRE-based launcher.
Not quite. In principal you could get the cross range on a Skylon shaped vehicle with rockets, because Skylons aerodynamics are better than the Shuttle (not having slab sides on your fuselage is probably quite helpful here), but you'd take a big hit on payload because of the extra reaction mass that vehicle would take which SABRE gets from the air.
"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 #1356 on: 03/18/2016 08:32 PM »
If anyone from REL reads this.....please please provide some advertising of the talks you're going to give in advance - e.g. a list on your website.  Quite a few people mentioned this to me recently and it is *the* most basic form of public relations you could engage in.  I mean giving the talk itself is many times harder than entering an item onto an REL web page so what's the problem?

Another issue is please consider recording the audio for these things. again this is not so hard with modern technology - a mobile phone with an external battery would make the whole thing easy and reliable - it can sit on the presenter's desk or in their pocket. 

Think how you manage to talk to 50 people in a lecture theatre but 100s or 1000s over a period of months on the internet. Of all those people the number that can help you is small so you have to maximise the reach of each chance you get to state your case. Some of us are such fools we want to spend our spare time helping you so help us please.
« Last Edit: 03/18/2016 08:56 PM by t43562 »

Offline Radical_Ignorant

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1357 on: 03/19/2016 07:34 AM »
...And unfortunately Sabre is not very scalable. Nor down (engine reasons) nor up (infrastructure reasons) except single engine possibility.

You have mentioned "single engine possibility" more than once now.

It should be pointed out that it was the rear-heavy design failure of HOTOL - which became a "means for lifting hydraulics into orbit" (huge canards to compensate CoM issues) - which principally drove the twin-engined Skylon design.

Yes. I'm fully aware of this. I just think Skylon idea for them is more like basic math which proves: yes, this makes sense, so let's not waste time wondering what could be done if engines were ready. We now know something very useful can be done so let's focus our super tiny resources on engine development.
But there is lot of different shapes of working planes. I won't pretend I know anything about aerodynamics, but I believe if they were bigger and have time to focus a little bit on anything else than engine development, they, or other air frame developers, could came with other solutions. Maybe this one is optimal, but those others could be little more expensive per kg of cargo delivered while much cheaper per vehicle.

Offline Radical_Ignorant

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1358 on: 03/19/2016 08:20 AM »

proof of concept and tech demonstrator [...] but I suspect it wouldn't save much development.

This is, IMO, one of the most destructive myths in aerospace. The belief that developing directly to the end goal is going to be cheaper than passing through three or four operational stepping-stones.

Reality is the opposite. Unless what you are developing is completely mundane and your designers, engineers, technicians and ops people are all experienced in that technology, it will always cost less to pass through multiple iterative stages before even attempting the final design. (Indeed, before attempting to design the final design.)

(It's the same "one is less than two" mentality.)

REL is at least doing one form of iterative development: subscale component testing. It also seems like they are happy to have other players use their technology on lower risk iterations, ironically unlike many of their defenders here.

In short if you don't push envelope you don't have benefits. You much prefer Space X way of pushing it in small steps. But then we have Space X and they won't stop doing it, so duplicating their way is doing what other does and makes no sense if you are not established player on the market.

That's silly. It's their method you'd be copying, iterative development, not the product.

Can you go to investors and tell them: hey I need few hundred millions and I'll do things like Space X is doing except I'm much late into the game

Versus going to investors and saying: hey I need a ten billion (probably) and I'll (try to) develop something that no-one (including me) has ever done before, and without doing any risk-reducing steps? Oh, and because I'm developing directly to the end-goal, you won't see any return for twenty years. Oh, and it involves sustained high-mach flight, which has been traditionally horribly expensive. Oh, and it involves a hybrid engine, which has traditionally been horribly expensive. Oh, and we're not airframe designers, so we'll need to outsource that anyway, but don't worry, this computer model says my design is perfect.

[edit: typos]

I believe here you nailed core point of our disagreement. But first - please don't suggest that I'm against risk reducing steps. I'm aware it can fail, I'm aware of costs.
Please consider that in Europe there is no something like NASA or DARPA which will pay for tech demonstrators. So you'd need to have some private willing to pay for most of development for something not usable. I just can't imagine such a thing. That's the very reason why you have those gov agencies. We don't have them.
Secondly, there is what Zurbin is arguing against: let's do multiple middle steps. Let's push the final goal so far away that till this time will come, everything will change. How many projects with approach let's-first-develop-demonstrator were never continued because of, "nah, we are not interested in this anymore" from politicians.
However I think I now understand much better your point. Shuttle seems to be good example of rushed development which failed in most of goals because it was first iteration of new technology. So thanks for making your stance clearer for me.

Offline Paul451

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1359 on: 03/19/2016 11:43 AM »
Please consider that in Europe there is no something like NASA or DARPA which will pay for tech demonstrators.

That's precisely why trying to jump directly to a multi-billion Pound/Euro design seems so unlikely.

And I'm not talking about "tech demonstrators", I'm talking about productive versions that reduce the development costs for each step.

Secondly, there is what Zurbin is arguing against: let's do multiple middle steps. Let's push the final goal so far away that till this time will come, everything will change.

How's that worked out for Zubrin so far? He's now notorious for handwaving any problems in his own proposals while attacking any alternatives, to the point that I doubt anyone except a few rusted-on fanbois¹ take him at all seriously any more.

The most he's achieved is to reduce support for other technology development programs.

¹ Of course, one of those fanbois now owns his own rocket company. But ironically he practices the iterative development method I prefer.

How many projects with approach let's-first-develop-demonstrator were never continued because of, "nah, we are not interested in this anymore" from politicians.

Far fewer than have overpromised and underdelivered, and consumed way too much money chasing a technological mirage before being cancelled.

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