Author Topic: The Reaction Engines Skylon Master Thread (5)  (Read 441511 times)

Offline 93143

  • Senior Member
  • *****
  • Posts: 3039
  • Liked: 292
  • Likes Given: 1
Re: The Reaction Engines Skylon Master Thread (5)
« Reply #80 on: 02/21/2015 11:27 PM »
"Step 1: Get 10 billion investment..."

Umm, no.

Background:  HOTOL was a high-resolution design study resulting in an airbreathing SSTO that looked marginally feasible but not economically interesting, powered by deeply precooled air turborocket engines (Rolls-Royce RB545) with a solution to the icing problem incorporated (no, it's not the same solution SABRE uses).  After the study was essentially completed and the involved parties lost interest, the engine tech got classified, with no indication (even now, after a quarter of a century) of any actual intent to use it.  So to circumvent the classified patents, Bond & co. came up with a modified engine cycle that actually turned out to be superior to the RB545.  They also rethought the airframe concept to eliminate one of the biggest problems with the original design.  It is at this point that REL was formed.

Step 1:  solicit small grants and investments and use them to buy down risk, partnering with industry and academia as appropriate.

Step 2:  land enough investment (millions) to carry out a comprehensive technology demonstration program with the goal of raising SABRE/Skylon's component TRL floor to 4, again seeking out external expertise as appropriate.  This program started in 2009, and one of the more prominent results was the flight-weight precooler hardware tested in 2012.
Step 2a:  simultaneous to Step 2, produce a high-fidelity vehicle design (Skylon D) to anchor the engine design, so as to avoid having to go back and redesign the engine once the vehicle takes shape.

Step 3:  leverage the results of the tech demonstration program to attract sufficient cash (hundreds of millions) to start intensive engine development.  This has apparently happened; the 60M government investment is not a keepalive fund but rather a pump primer for a large effort.  REL has been expanding significantly, and has apparently secured enough funding to forgo a subscale demonstrator (SCEPTRE) in favour of a full-size prototype SABRE.

Step 4:  With a full-size prototype SABRE showing good results on the test stand, get the interested parties to commit to full-scale vehicle development, which may well involve subscale and/or suborbital demonstrator vehicles.

At no point does REL itself ask anyone for a 10 billion investment.

...

As you can see, it is not accurate to claim REL is not doing "incremental development".  It just looks a bit different, because what they're trying to do is different.  It's not REL's fault there doesn't seem to be a commercially useful way to half-ass the idea (leaving aside peripheral stuff like the Valkyrie sounding rocket)...

Quote
Because high speed military aircraft are a lucrative market. And a company that develops the next big thing in aircraft engines will end up with much spare cash for their more speculative R&D.

The precooler tech is tied to hydrogen fuel.  This immediately makes it useless on any existing airframe, creating a very high entry barrier, and greatly complicates the operation of any new vehicle using it.  The difficulties of hypersonic cruise only make this situation worse.  (Remember, existing engine tech is perfectly capable of propelling an aircraft faster than any currently-operational aircraft actually goes.)  Space launch is about the only market with a clear near-term use for the technology.

The U.S. military hates hydrogen, probably because logistics are so important to them.  They don't even like LOX.  I don't know why the USAF is interested in SABRE, but I'd be willing to bet it's not for a fighter.

Non-aerospace applications of the precooler technology are possible, but they will have to wait until the manufacturing process is refined and the price comes down...

Quote
I've just started posting here, but I've been watching REL since they started, and HOTOL before it. And I've been "around" these discussions long before NSF existed.

Yet you don't seem to know much about it, and a lot of what you think you know seems to be wrong.

Science is creating the rocket-equation

No.  The rocket equation could be derived in short order by any reasonably competent engineer who actually bothered to think about the problem.  Tsiolkovsky was merely one of the first people to do so (not the very first; it shows up in earlier sources).  The "science" in the rocket equation is all Newton.
« Last Edit: 02/22/2015 02:12 AM by 93143 »

Offline knowles2

  • Full Member
  • *
  • Posts: 115
  • Liked: 20
  • Likes Given: 50
Re: The Reaction Engines Skylon Master Thread (5)
« Reply #81 on: 02/21/2015 11:46 PM »
I think USAF is interested in SABRE simply because they hate the thought of anyone else having something that outclass anything they are working on at least publicly.

 The last thing they want is the Chinese showing up in 20 years time having developed their own Sabre/Scimitar  engine powered aircraft either independently or stolen from REL and USAF not having any answers . This is good news for REL assuming they can figure out how to get hold of USAF money without to many strings being attach  ;).

Plus with hydrogen being use in cars and in buses and everyday civilian lives there probably some in USAF that thinks it time for their hatred of hydrogen fuel engines to come to an end. Especially as their scramjets projects seems to crash just as often as they manage to fly.
« Last Edit: 02/21/2015 11:48 PM by knowles2 »

Offline 93143

  • Senior Member
  • *****
  • Posts: 3039
  • Liked: 292
  • Likes Given: 1
Re: The Reaction Engines Skylon Master Thread (5)
« Reply #82 on: 02/21/2015 11:58 PM »
Do we think we know enough about SABRE to state categorically that it only works when integrated with a Skylon type of airframe?

SABRE isn't tightly integrated with the airframe like a scramjet is.  All it strictly requires is a source of liquid hydrogen.

The only airframe-integration feature I can think of is the nacelle camber, which is due to the difference between the desired angle of attack and the desired angle of thrust.
« Last Edit: 02/22/2015 12:22 AM by 93143 »

Online Chris Bergin

Re: The Reaction Engines Skylon Master Thread (5)
« Reply #83 on: 02/22/2015 01:30 AM »
Ok guys, this thread is a problem as not a day goes by without report to mods coming in, mainly due to off topic and a few people getting rowdy with each other.

All posts from this point onwards will be on topic and civil.

No excuses.

Offline adrianwyard

  • Full Member
  • ****
  • Posts: 955
  • Liked: 172
  • Likes Given: 220
Re: The Reaction Engines Skylon Master Thread (5)
« Reply #84 on: 02/22/2015 03:37 AM »
Do we think we know enough about SABRE to state categorically that it only works when integrated with a Skylon type of airframe?

SABRE isn't tightly integrated with the airframe like a scramjet is.  All it strictly requires is a source of liquid hydrogen.

The only airframe-integration feature I can think of is the nacelle camber, which is due to the difference between the desired angle of attack and the desired angle of thrust.

That's my understanding too. So what other airframe configurations might make sense? And are there any that are less ambitious/costly than the Skylon vehicle as currently conceived?

Online john smith 19

  • Senior Member
  • *****
  • Posts: 6187
  • Everyplaceelse
  • Liked: 828
  • Likes Given: 5156
Re: The Reaction Engines Skylon Master Thread (5)
« Reply #85 on: 02/22/2015 11:01 AM »
JS19: While technically accurate (VTHL design) we HAVE done this before and its a pretty straight forward engineering problem. Has issue but then again so will designing and building what amounts to a hypersonic zeppelin :)
True. But it never would have worked without those monster RATO packs and the humungous drop tank. :)
Quote
Its always a plus if you can design a vehicle to only handle the "exact" loads it needs and not a bit more. (Henry Ford logic/economics at work :) However that "logic/economics" leads to surviving a crash only to be killed when the "minimum" roof of the car collapse on you :) ) And since every ounce counts/costs going into space...
Sometimes referred to as the "one horse shay" paradign.  :)

I think you are completing misreading John Smith 19's points.  As I read it, he is pointing out that there is a difference between applying well known existing engineering principles to a particular problem (engineering), and developing new processes that require new and deeper understand of fundamental processes (science). The distinction isn't clear cut, but it is there.

Nor is it correct to say that John Smith 19 has consistently denigrated SpaceX.  He has not as far as I can see. He has merely pointed out that SpaceX and REL are approaching things differently and have different goals.  As others have said, it isn't a race.
Your are correct in all points. There was much more I'd written, but it's OT and I'd like to bring it back to SABRE/Skylon.  :(

That's my understanding too. So what other airframe configurations might make sense? And are there any that are less ambitious/costly than the Skylon vehicle as currently conceived?
That's tricky without understanding why they developed this configuration.

The problem is twofold.

The Centre of Pressure shifts a lot over an airframe going from 0-M23-0

The Centre of Gravity shifts a lot because propellant is a much bigger fraction of the vehicle weight than in an aircraft.

A key  problem with HOTOL was with the engines at the back as the tanks emptied you had very little mass to stop the body "flipping" upward, so you needed a huge set of control surfaces (and their actuators) to keep the nose at the right angle. IIRC Bond said "2000 tonne metres" IE a small ship on those control surfaces.

Terrestrial aircraft can get away with the engines at the back (Trident DC-10, Caravelle) because of a) A relatively empty fuselage b) "Wet" wings and c) More "dead" weight in the vehicle to counter balance the weight of the engines in the back.

There are various configurations you could build a SABRE (ideally a pair of SABRES) into but they all face 2 problems.

High pressure LH2 engines (or rather their turbo pumps) scale down badly so you'd want to use full size SABRE engines.

It's not what your sub scale prototype can demonstrate it's what it cannot. Those things can only be demonstrated in the full size vehicle, IE a Skylon. So you're building a Skylon (actually REL are planning 2 flight test Skylons) and  this demonstrator/proof-of-concept/whatever vehicle, so your overall budget goes up.  :(

My instinct is the simplest way to go is with full size SABRES propelling a reduced scale Skylon airframe with narrower, shorter fuselage, no payload bay (and no payload  :( ) and much lower propellant load.

If such a vehicle matches a full sized Skylons aerodynamics and mass properties then its results should be transferable directly to the full size Skylon, shortening the flight programme of the full sized vehicles to lower the overall development budget and "squaring the circle" of using 3 vehicles instead of 2 but still working out cheaper.   :)

IRL my instinct is that being able to scale a design to that way while preserving all the main features is a very big "if" indeed. I suspect the range over which you could scale the airframe while a)Using full size SABRES and b)keeping the various mass properties and aerodynamic coefficients matching the full size vehicle is very limited.

The question is not "can you scale it down" but "do you save so much on the test budget it's worth doing" ?

I suspect the answer comes out "Build a full size Skylon with full size engines and no payload bay (there is room, but only enough is installed to preserve necessary structural stiffness) and smaller tanks," and I think REL have a better idea of the answer, but I don't know what it is.  :(
"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 adrianwyard

  • Full Member
  • ****
  • Posts: 955
  • Liked: 172
  • Likes Given: 220
Re: The Reaction Engines Skylon Master Thread (5)
« Reply #86 on: 02/22/2015 08:15 PM »
I suspect the answer comes out "Build a full size Skylon with full size engines and no payload bay (there is room, but only enough is installed to preserve necessary structural stiffness) and smaller tanks," and I think REL have a better idea of the answer, but I don't know what it is.  :(

Hmmm, you may be right. At first blush, building a half-scale Skylon seems less ambitious, and so more likely to happen, i.e. receive funding. Skylon as currently described is soooo huge that size alone makes the whole project appear impractical. BUT once you've committed to the design of a few square meters of aeroshell/tankage, then manufacturing lots and lots of square meters is not that much more difficult/costly than half as much. This is probably made easier because Skylon has such a regular/recurring shape.

And as you say, smaller and lighter internal tanks give you lots of margin to play with on the test vehicle, and lower loads... And unlike other spacecraft you have the option of loading a small amount of LH2 (and no O2) which again lowers weight and loads.
« Last Edit: 02/22/2015 10:02 PM by adrianwyard »

Offline space_britannia

  • Member
  • Posts: 7
  • UK
  • Liked: 1
  • Likes Given: 0
Re: The Reaction Engines Skylon Master Thread (5)
« Reply #87 on: 02/23/2015 11:36 PM »

The U.S. military hates hydrogen, probably because logistics are so important to them.  They don't even like LOX.  I don't know why the USAF is interested in SABRE, but I'd be willing to bet it's not for a fighter.


I wouldn't be surprised if it's for SUSTAIN ("Marines in Space") - see http://www.popsci.com/military-aviation-space/article/2006-12/semper-fly-marines-space
http://www.popularmechanics.com/military/a5539/plans-for-marines-in-space/
http://www.defenseindustrydaily.com/hypersonic-rocketplane-program-inches-along-0194/

Those stories talk about a 2-stage concept however, and whether with scramjets or sabre (hydrogen fuel issue again), that's going to be one very expensive ride to ditch in the middle of a conflict zone

Offline Asteroza

  • Full Member
  • ****
  • Posts: 483
  • Liked: 53
  • Likes Given: 2
Re: The Reaction Engines Skylon Master Thread (5)
« Reply #88 on: 02/24/2015 02:35 AM »
Do we think we know enough about SABRE to state categorically that it only works when integrated with a Skylon type of airframe?

SABRE isn't tightly integrated with the airframe like a scramjet is.  All it strictly requires is a source of liquid hydrogen.

The only airframe-integration feature I can think of is the nacelle camber, which is due to the difference between the desired angle of attack and the desired angle of thrust.

That's my understanding too. So what other airframe configurations might make sense? And are there any that are less ambitious/costly than the Skylon vehicle as currently conceived?

Probably not , considering it's a tube with wings and you need spheres or tubes ideally for the tankage. Tube with wings is well known, and has low frontal area.

But, as a thought exercise, a squished pancake shape might work. Internally, you have three rows of cylindrical spaces, center with payload bay and fore/aft LOx tanks flanked by full length LH2 tanks. Fit the SABRE equipment near the mid-fuselage edge of the pancake, with a 2D ramp inlet on its side, and exhaust is half an aerospike ramp on its side. That largely preserves the basic Skylon layout (which does well to deal with cg changes), but frontal area drag unfortunately goes up which goes against the partial cruise accelerator profile. The only advantage to that layout is if you were doing something kinky like receiving external heating AKA Laser Skylon, as you could have a better receiver area.

Offline Paul451

  • Full Member
  • ****
  • Posts: 1289
  • Australia
  • Liked: 631
  • Likes Given: 535
Re: The Reaction Engines Skylon Master Thread (5)
« Reply #89 on: 02/24/2015 03:50 AM »
I don't know why the USAF is interested in SABRE, but I'd be willing to bet it's not for a fighter.
I wouldn't be surprised if it's for SUSTAIN ("Marines in Space")

[Such speculation may be off-topic, I'm not sure how strictly to Skylon Chris wants the thread to run.]

There are other applications of the pre-cooler. Improving flight range via greater engine efficiency; higher speed from existing engines without overheating the engine; even reducing the IR signature of engine exhaust (which wasn't one I'd previously considered.) Plus you've got the ongoing interest in fast-turnaround small-sat launchers, a la DARPA XS-1.

(For other Services, you've got improved operations of any large turbine-based engine (increasingly common in non-nuclear ships.))
« Last Edit: 02/24/2015 08:41 AM by Paul451 »

Offline adrianwyard

  • Full Member
  • ****
  • Posts: 955
  • Liked: 172
  • Likes Given: 220
Re: The Reaction Engines Skylon Master Thread (5)
« Reply #90 on: 02/24/2015 06:15 AM »
The projected first flight of Skylon has always been far enough into the future, and the schedule burdened with sufficient unknowns that you can forgive critics for doubting it will ever see the light of day. But it occurred to me that if (big if) investors were to suddenly want to make it happen ASAP we could conceivably see it in the first half of the 2020s rather than the second for a couple of reasons.

Firstly, as REL have rightly pointed out before, the full engine cycle can be thoroughly tested on the ground. This is hugely beneficial, and additional cash would allow more extensive testing to be concluded sooner.

Secondly, the airframe could be prototyped/tested in parallel with the engine or beforehand. No-one's talks about doing this because if the SCEPTRE tests show major problems you won't need the airframe. However, if someone wanted to I suspect you could do subsonic testing of the airframe shape by placing turbojets in the nacelles. Perhaps you could then go supersonic by adding rockets and closing (and testing) the nacelles cones.

Don't ask me where the money and desire to do this will come from, but it's one more reminder that Skylon's problems have more to do with politics and economics than technology or necessarily long dev schedule.
« Last Edit: 02/24/2015 10:51 PM by adrianwyard »

Online john smith 19

  • Senior Member
  • *****
  • Posts: 6187
  • Everyplaceelse
  • Liked: 828
  • Likes Given: 5156
Re: The Reaction Engines Skylon Master Thread (5)
« Reply #91 on: 02/24/2015 09:09 AM »
I wouldn't be surprised if it's for SUSTAIN ("Marines in Space") - see http://www.popsci.com/military-aviation-space/article/2006-12/semper-fly-marines-space
http://www.popularmechanics.com/military/a5539/plans-for-marines-in-space/
http://www.defenseindustrydaily.com/hypersonic-rocketplane-program-inches-along-0194/

Those stories talk about a 2-stage concept however, and whether with scramjets or sabre (hydrogen fuel issue again), that's going to be one very expensive ride to ditch in the middle of a conflict zone
Welcome to the forum and the thread.

Firstly "Force projection" through space has a long history. Bono and Gatlands "Frontiers of Space" looked at delivering 100s of Marines at a time by "ballistic transport" IE near SSTO sub orbital vehicles. That was around 1969.

Reading the links you listed in detail they read like sales pitches for yet another SCRamjet research programme.  :(

AFAIK the CRADA is for SABRE engine cycle only. So the USAFRL can run the numbers (the pressures, temperatures and flows at various parts of the system) through their design codes and satisfy themselves that it it will produce the output they expect.

I do hope they pay attention to what the condition of the inlet air is as the Mojave desert is a little different from Kourou.  :)

It would seem that some in the USAF are starting to think the unthinkable.

"What if we do a vehicle without developing an SCRamjet in it as it does not need an SCRamjet?"

But Skylon is not designed as some kind of assault transport. The problem is you need to secure a landing strip before it arrives with reinforcements (although without LH2 and LO2 on board it can land on quite a poor runway), a chicken and egg situation.  :(

However "responsive" access to space IE launching payloads to monitor or assist in developing theaters of operations in days not years, has been an interest of some parts of the DoD for a long time, XS1 being the latest attempt (although that's gone rather quiet of late).

SABRE/Skylon can deliver such a capability.
BUT once you've committed to the design of a few square meters of aeroshell/tankage, then manufacturing lots and lots of square meters is not that much more difficult/costly than half as much. This is probably made easier because Skylon has such a regular/recurring shape.
Making things smaller in prototype has some history in aerospace to a point, but only to a point. This is why REL were looking for IIRC 250m then worked out that for 15m more they could a full size engine, so why not?

In mfg the hardware you have access to always has some limits on how big a thing you can make on it. For 1 offs you can probably find a way to exceed those limits (again, to a point ) but for repeat production you're looking at a step change in costs as now you've got to buy/build a whole new suite of machines to handle that.

NASA can do a 10m tank, but push it to 15m or 20m? I think you'd have to tear out the current hardware and replace it wholesale.  Obviously it's a question of what you're funded to and how far you think a concept can go when you're planning  your factory.
Quote
And as you say, smaller and lighter internal tanks give you lots of margin to play with on the test vehicle, and lower loads... And unlike other spacecraft you have the option of loading a small amount of LH2 (and no O2) which again lowers weight and loads.
True.

It comes down to a very tricky problem. Can I find a cheaper way to do part of the programe (easing my fund raising problem) that does not mean I have to buy extra hardware (or tests) later, so increasing the overall cost, the problem I'm trying to avoid.

Probably not , considering it's a tube with wings and you need spheres or tubes ideally for the tankage. Tube with wings is well known, and has low frontal area.
Exactly.  Keep in mind that a "tube with wings" has already demonstrated successful reentry about 130 times
Quote
But, as a thought exercise, a squished pancake shape might work. Internally, you have three rows of cylindrical spaces, center with payload bay and fore/aft LOx tanks flanked by full length LH2 tanks. Fit the SABRE equipment near the mid-fuselage edge of the pancake, with a 2D ramp inlet on its side, and exhaust is half an aerospike ramp on its side. That largely preserves the basic Skylon layout (which does well to deal with cg changes), but frontal area drag unfortunately goes up which goes against the partial cruise accelerator profile. The only advantage to that layout is if you were doing something kinky like receiving external heating AKA Laser Skylon, as you could have a better receiver area.
If cost is the issue for a prototype you'd scrap the payload bay. This layout might handle the Cp/Cg shifts well enough to do the whole flight trajectory.

But look what you've lost  :(

This design is reminiscent of the "pye wacket" missile concept for an armed SR71 but AFAIK it has no flight history in other vehicles you can call on to refine the design.

Then you're suggesting some altitude compensation by expansion against the underside, which raises the temperature quite a bit.

And once you've got it working how do you translate the measurement of the flight programme to that of a Skylon?

It's a tough problem.  :(
« Last Edit: 02/24/2015 09:16 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 francesco nicoli

  • Full Member
  • ****
  • Posts: 493
  • Amsterdam
    • About Crises
  • Liked: 226
  • Likes Given: 331
Re: The Reaction Engines Skylon Master Thread (5)
« Reply #92 on: 02/24/2015 09:38 AM »
true that skylon could not land itself to deliver troops in a contested combat zone- it is also too expensive for this.

But may it could
1) deliver into space a specifically designed lander and its squad
2) deliver the specifically designed lander into space, and bring the squad there when it is needed.

in the option 1) it would work as a sort of first stage
in the option 2) it would work as a transport vehicle of its own. however I guess the timeframe for going to LEO, transit the squad in the vehicle stationning there,  and down again, isn't any close to "two hours". Although it would still solve the issue of transportation above unfriendly territory.


Offline Paul451

  • Full Member
  • ****
  • Posts: 1289
  • Australia
  • Liked: 631
  • Likes Given: 535
Re: The Reaction Engines Skylon Master Thread (5)
« Reply #93 on: 02/24/2015 10:13 AM »
2) deliver the specifically designed lander into space, and bring the squad there when it is needed.

The lander-in-orbit would be limited to a single window in a single orbital plane, making it incompatible with the goal of a suborbital ballistic "drop-ship" to allow any point-to-point travel in 90 minutes or so.
« Last Edit: 02/24/2015 10:14 AM by Paul451 »

Offline RanulfC

  • Senior Member
  • *****
  • Posts: 4416
  • Heus tu Omnis! Vigilate Hoc!
  • Liked: 770
  • Likes Given: 32
Re: The Reaction Engines Skylon Master Thread (5)
« Reply #94 on: 02/24/2015 03:38 PM »
There are other applications of the pre-cooler. Improving flight range via greater engine efficiency; higher speed from existing engines without overheating the engine; even reducing the IR signature of engine exhaust (which wasn't one I'd previously considered.) Plus you've got the ongoing interest in fast-turnaround small-sat launchers, a la DARPA XS-1.

Just to note but these were "somewhat" brought up by REL as part of pushing the HE technology as a breakthrough "on-par" with the development of the jet engine itself and unfortunately isn't as "applicable" as REL made it out to be or having all that many "applications" above and beyond its actual use in SABRE.

Deep-Cooling can in fact extend the usable Mach range of a turbine based engine as well as increasing thrust output. But this was shown with previous work including the most recent Mass-Injection-Pre-Compressor-Cooling, and in fact does not require Liquid Hydrogen to accomplish things like a doubling of thrust and Mach number of the turbine engine. Increased engine efficiency is possible but only if the entire engine is run using hydrogen fuel as a standard hydrocarbon engine wouldn't stand to gain much due to the use of multiple fluids. (Which is already an "issue" with standard MIPCC which uses LOX/Water both of which are far more compact and easier to use than LH2)

"Standard" (LOX/Water) MIPCC can extend the Mach number of a standard (F100 for example) low-bypass turbofan from Mach-2 to Mach-4 and double or more the output thrust. Deep-Cooling with LH2 through an HE might extend this to Mach-6 though the extensive "bulk" of the LH2 tankage and system would probably greatly increase the vehicle design and complexity.

Exhaust IR mitigation IS a possible use but again mitigation doesn't "require" the use of liquid hydrogen and again unless the whole vehicle/engine is based on LH2 propulsion the use of an LH2 HE and bypass cooling air system wouldn't be very effective in operational use due to the added complexity and cost.

Last I looked the XS-1 program was specifically avoiding LH2 due to such systems NOT having fast turn around capability of more benign cryogenic systems such as LOX/Kero.

In most operational cases, unless your engine system and therefore your vehicle design overall, is using LH2 for fuel the efficiency isn't all that clear cut a case. Which is I suspect one of the (many) reasons no one is jumping on the REL investment bandwagon :)
What they are doing is directly relatable to GTO (Ground-To-Orbit) launch but doesn't have much broader uses under the current situation.

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

  • Senior Member
  • *****
  • Posts: 4416
  • Heus tu Omnis! Vigilate Hoc!
  • Liked: 770
  • Likes Given: 32
Re: The Reaction Engines Skylon Master Thread (5)
« Reply #95 on: 02/24/2015 03:52 PM »
I wouldn't be surprised if it's for SUSTAIN ("Marines in Space") - see http://www.popsci.com/military-aviation-space/article/2006-12/semper-fly-marines-space
http://www.popularmechanics.com/military/a5539/plans-for-marines-in-space/
http://www.defenseindustrydaily.com/hypersonic-rocketplane-program-inches-along-0194/

Those stories talk about a 2-stage concept however, and whether with scramjets or sabre (hydrogen fuel issue again), that's going to be one very expensive ride to ditch in the middle of a conflict zone
Welcome to the forum and the thread.

Firstly "Force projection" through space has a long history. Bono and Gatlands "Frontiers of Space" looked at delivering 100s of Marines at a time by "ballistic transport" IE near SSTO sub orbital vehicles. That was around 1969.

Earlier than that actually :)

@1958 the Army did some research on delivering troops and/or supplies to the front lines by sub-orbital ballistic missile delivery. Specifically the "Redstone" IRBM:
http://www.popsci.com/blog-network/vintage-space/riding-rocket-battlefield

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

  • Senior Member
  • *****
  • Posts: 4416
  • Heus tu Omnis! Vigilate Hoc!
  • Liked: 770
  • Likes Given: 32
Re: The Reaction Engines Skylon Master Thread (5)
« Reply #96 on: 02/24/2015 04:40 PM »
2) deliver the specifically designed lander into space, and bring the squad there when it is needed.

The lander-in-orbit would be limited to a single window in a single orbital plane, making it incompatible with the goal of a suborbital ballistic "drop-ship" to allow any point-to-point travel in 90 minutes or so.

Just to make sure everyone's on the same page, the actual SUSTAIN/Hot Eagle requirements had the vehicle being capable of P2P travel OR being put into orbit as a "standby" measure for "drop" at any point up to several days later.

The conflicting requirements of those two mission parameters were something that was never addressed and would drive a "vehicle" design that would be very costly to meet both requirements.

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

  • Senior Member
  • *****
  • Posts: 4416
  • Heus tu Omnis! Vigilate Hoc!
  • Liked: 770
  • Likes Given: 32
Re: The Reaction Engines Skylon Master Thread (5)
« Reply #97 on: 02/24/2015 06:49 PM »
Do we think we know enough about SABRE to state categorically that it only works when integrated with a Skylon type of airframe?

SABRE isn't tightly integrated with the airframe like a scramjet is.  All it strictly requires is a source of liquid hydrogen.

The only airframe-integration feature I can think of is the nacelle camber, which is due to the difference between the desired angle of attack and the desired angle of thrust.

That's my understanding too. So what other airframe configurations might make sense? And are there any that are less ambitious/costly than the Skylon vehicle as currently conceived?

That's my understanding too. So what other airframe configurations might make sense? And are there any that are less ambitious/costly than the Skylon vehicle as currently conceived?
That's tricky without understanding why they developed this configuration.

The problem is twofold.

The Centre of Pressure shifts a lot over an airframe going from 0-M23-0

The Centre of Gravity shifts a lot because propellant is a much bigger fraction of the vehicle weight than in an aircraft.

A key  problem with HOTOL was with the engines at the back as the tanks emptied you had very little mass to stop the body "flipping" upward, so you needed a huge set of control surfaces (and their actuators) to keep the nose at the right angle. IIRC Bond said "2000 tonne metres" IE a small ship on those control surfaces.

Terrestrial aircraft can get away with the engines at the back (Trident DC-10, Caravelle) because of a) A relatively empty fuselage b) "Wet" wings and c) More "dead" weight in the vehicle to counter balance the weight of the engines in the back.

There are various configurations you could build a SABRE (ideally a pair of SABRES) into but they all face 2 problems.

High pressure LH2 engines (or rather their turbo pumps) scale down badly so you'd want to use full size SABRE engines.

It's not what your sub scale prototype can demonstrate it's what it cannot. Those things can only be demonstrated in the full size vehicle, IE a Skylon. So you're building a Skylon (actually REL are planning 2 flight test Skylons) and  this demonstrator/proof-of-concept/whatever vehicle, so your overall budget goes up.  :(

My instinct is the simplest way to go is with full size SABRES propelling a reduced scale Skylon airframe with narrower, shorter fuselage, no payload bay (and no payload  :( ) and much lower propellant load.

If such a vehicle matches a full sized Skylons aerodynamics and mass properties then its results should be transferable directly to the full size Skylon, shortening the flight programme of the full sized vehicles to lower the overall development budget and "squaring the circle" of using 3 vehicles instead of 2 but still working out cheaper.   :)

IRL my instinct is that being able to scale a design to that way while preserving all the main features is a very big "if" indeed. I suspect the range over which you could scale the airframe while a)Using full size SABRES and b)keeping the various mass properties and aerodynamic coefficients matching the full size vehicle is very limited.

The question is not "can you scale it down" but "do you save so much on the test budget it's worth doing" ?

I suspect the answer comes out "Build a full size Skylon with full size engines and no payload bay (there is room, but only enough is installed to preserve necessary structural stiffness) and smaller tanks," and I think REL have a better idea of the answer, but I don't know what it is.  :(

But, as a thought exercise, a squished pancake shape might work. Internally, you have three rows of cylindrical spaces, center with payload bay and fore/aft LOx tanks flanked by full length LH2 tanks. Fit the SABRE equipment near the mid-fuselage edge of the pancake, with a 2D ramp inlet on its side, and exhaust is half an aerospike ramp on its side. That largely preserves the basic Skylon layout (which does well to deal with cg changes), but frontal area drag unfortunately goes up which goes against the partial cruise accelerator profile. The only advantage to that layout is if you were doing something kinky like receiving external heating AKA Laser Skylon, as you could have a better receiver area.
If cost is the issue for a prototype you'd scrap the payload bay. This layout might handle the Cp/Cg shifts well enough to do the whole flight trajectory.

But look what you've lost  :(

This design is reminiscent of the "pye wacket" missile concept for an armed SR71 but AFAIK it has no flight history in other vehicles you can call on to refine the design.

Then you're suggesting some altitude compensation by expansion against the underside, which raises the temperature quite a bit.

And once you've got it working how do you translate the measurement of the flight programme to that of a Skylon?

It's a tough problem.  :(

Very good discussion of various flight issues and body type trade offs. Couple of points:

Just a correction JS19 but the "Pye Wacket" lenticular missile was being designed for the XB-70, not the SR-71 :)

-An alternative Skylon design by the Centre for Future Air-Space Transportation Technology (cFASTT,)at the University of Strathclyde  has already come out suggesting various changes to enhance the "basic" design by REL.
http://www.strath.ac.uk/fastt/
https://www.facebook.com/cFASTTstrath/photos_stream?ref=page_internal
http://www.rocketeers.co.uk/node/3129
http://strathprints.strath.ac.uk/48572/1/Wuilbercq_R_et_al_Pure_Robust_multi_disciplinary_design_and_optimisation_of_a_reusable_launch_vehicle_Jun_2014.pdf

-As noted the main reason for the current suggested design of the Skylon is to reduce the aerodynamic variables that are associated with changes in CP/CG over the flight trajectory. However the design functions end up so that the basic design is almost "required" to be along certain lines. The engines are going to end up either under the airframe or on the wings, beyond that your airframe choices, due to the aim to reach minimum hypersonic (Mach-5) speed ends up being similar to Boeing Model 1074-xxxx (sometimes called the "Hyperdart") interceptor design. (Which was designed around the Mach-4.5 hydrocarbon/H2O2 propellant SERJ engine) Reference: http://www.secretprojects.co.uk/forum/index.php/topic,11580.0/all.html?PHPSESSID=2f9apo98c9kqtupnof6cmqo6u5

Which dates from the mid-60s hence the "needle" nose instead of the more common "shovel" nose you'd see today.

Much as I like the idea of a lenticular design ("Pye Wacket" see: http://www.rimworld.com/dsp/pyewacket.html, and http://aviationtrivia.blogspot.com/2010/05/in-1947-researchers-at-wright-patterson.html) as noted it doesn't lend itself well to hypersonic accelerator designs though it HAS been suggested in the past. (LM among others patented several designs for supersonic and hypersonic models in the 60s such as this: http://www.freepatentsonline.com/3066890.pdf, but you'll note how difficult fitting LH2 tanks into such a design would be. Moving the engines towards the outer sections and the tankage towards the middle induces intake issues and mounting the engines above or below the vehicle with a lenticular design offers none of the normal intake/exhaust compression/expansion advantages that a more dedicated (and normal layout) design would. And as noted higher drag and therefore heating would be an issue.

In the end the basic shape that REL has chosen for the baseline Skylon so they can have something to anchor their work in is what you're going to end up with in a very close approximation unless you have some compelling reason to go with a more radical airframe design. And the reason would have to be VERY compelling given the amount of data the "baseline" design has available.

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?

Online john smith 19

  • Senior Member
  • *****
  • Posts: 6187
  • Everyplaceelse
  • Liked: 828
  • Likes Given: 5156
Re: The Reaction Engines Skylon Master Thread (5)
« Reply #98 on: 02/24/2015 10:47 PM »
Very good discussion of various flight issues and body type trade offs. Couple of points:
Thank you.
Quote
Just a correction JS19 but the "Pye Wacket" lenticular missile was being designed for the XB-70, not the SR-71 :)
Oops. My memory playing tricks with me. I conflated the SR71 with the missile.
Quote
-An alternative Skylon design by the Centre for Future Air-Space Transportation Technology (cFASTT,)at the University of Strathclyde  has already come out suggesting various changes to enhance the "basic" design by REL.
http://www.strath.ac.uk/fastt/
https://www.facebook.com/cFASTTstrath/photos_stream?ref=page_internal
http://www.rocketeers.co.uk/node/3129
http://strathprints.strath.ac.uk/48572/1/Wuilbercq_R_et_al_Pure_Robust_multi_disciplinary_design_and_optimisation_of_a_reusable_launch_vehicle_Jun_2014.pdf

-As noted the main reason for the current suggested design of the Skylon is to reduce the aerodynamic variables that are associated with changes in CP/CG over the flight trajectory. However the design functions end up so that the basic design is almost "required" to be along certain lines. The engines are going to end up either under the airframe or on the wings, beyond that your airframe choices, due to the aim to reach minimum hypersonic (Mach-5) speed ends up being similar to Boeing Model 1074-xxxx (sometimes called the "Hyperdart") interceptor design. (Which was designed around the Mach-4.5 hydrocarbon/H2O2 propellant SERJ engine) Reference: http://www.secretprojects.co.uk/forum/index.php/topic,11580.0/all.html?PHPSESSID=2f9apo98c9kqtupnof6cmqo6u5

Which dates from the mid-60s hence the "needle" nose instead of the more common "shovel" nose you'd see today.
Given the advances in supersonic and hypersonic flow heating analysis is the "needle nose" even plausible today?
Quote
In the end the basic shape that REL has chosen for the baseline Skylon so they can have something to anchor their work in is what you're going to end up with in a very close approximation unless you have some compelling reason to go with a more radical airframe design. And the reason would have to be VERY compelling given the amount of data the "baseline" design has available.
Indeed. Once  you consider the full list of constraints a design must meet the options are quite limited.  :(
"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 Paul451

  • Full Member
  • ****
  • Posts: 1289
  • Australia
  • Liked: 631
  • Likes Given: 535
Re: The Reaction Engines Skylon Master Thread (5)
« Reply #99 on: 02/24/2015 11:41 PM »
and in fact does not require Liquid Hydrogen [...]
Exhaust IR mitigation IS a possible use but again mitigation doesn't "require" the use of liquid hydrogen

Neither does Bond's heat exchanger. Indeed the major testing has not been with LH on the cold-side of the He-loop. LH is a requirement for Skylon because of the hypersonic operating environment where they need around 1000C cooling (as would most hypersonic applications, for the same reason.) Outside of that operating environment, you pick the coolant to suit the application.

The key to Bond's idea is a) that it's frostless, b) that it's fast, and c) that it's both hot- and cold-side agnostic. The first lets you use where you can't use other heat-exchanges, the second means it acts almost like a thermal-superconductor (it will near-instantly cool the hot-side close to the temp of whatever is on the cold-side), the last means it's flexible for more applications. A bonus is that it's ridiculously light as a side-effect of (b).

[I do like how now I'm arguing that REL understands their pre-cooler well enough to model applications, while you're arguing that they've been a little premature/overenthusiastic...]
« Last Edit: 02/25/2015 02:36 AM by Paul451 »

Tags: