"Step 1: Get £10 billion investment..."
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.
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.
Science is creating the rocket-equation
Do we think we know enough about SABRE to state categorically that it only works when integrated with a Skylon type of airframe?
Quote from: adrianwyard on 02/21/2015 10:43 pmDo 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.
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
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...
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.
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?
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.
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.
Quote from: 93143 on 02/21/2015 11:58 pmQuote from: adrianwyard on 02/21/2015 10:43 pmDo 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?
Quote from: 93143 on 02/21/2015 11:27 pmI 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")
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-spacehttp://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
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.
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.
2) deliver the specifically designed lander into space, and bring the squad there when it is needed.
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.
Quote from: space_britannia on 02/23/2015 11:36 pmI 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-spacehttp://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 zoneWelcome 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.
Quote from: francesco nicoli on 02/24/2015 09:38 am2) 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.
Quote from: adrianwyard on 02/22/2015 03:37 amThat'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.
Quote from: space_britannia on 02/23/2015 11:36 pmBut, 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_internalhttp://www.rocketeers.co.uk/node/3129http://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=2f9apo98c9kqtupnof6cmqo6u5Which dates from the mid-60s hence the "needle" nose instead of the more common "shovel" nose you'd see today.
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.
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