british rocketplane by 2020?

[Antice]

Scramjet's may be useful one day. but nobody has actually combined one with another engine in the way that has been done with ramjets. ramjet turbojet combined cycle was done with the SR71 among others. Scramjet may be a possible future upgrade path, but it may also turn out to be no benefit from using it. mach 5 to 6 has been identified as in the ballpark area for optimal speed prior to changing into rocket mode. If you could make a scramjet upgrade that could bring the vehicle from 26km mach 5 to say 50 km and mach 10 you may have something worthwhile. but as it is it is altitude and not speed alone that dictates the swap to internal LOX for the rest of the climb. it just does not pay to go any faster that low in the atmosphere.

The SABRE engine does not operate as a turbojet under any part of the flight. it is a turborocket. the main combustion chamber is a rocket chamber in design. It's even part of the name. Synergistic Air Breathing Rocket Engine. A turbojet uses the combustor exhaust to drive a single shaft turbine. SABRE does not. The SABRE engine uses a closed helium loop to drive the turbo compressors. A case could be made that it is not truly a turborocket either. but it does share quite a lot in common with them. the use of rocket chambers for the main thrust as well as a pre burner to drive the turbo-compressors. but the pre burner is not used in the same manner. it is rather used as a heating source for the helium loop to get enough power out of the system at low speeds. the pre burner is throttled back as the speed increases to accommodate the higher heat flux from the pre cooler.

I generally do not ignore other concepts. but i do take exception to betting the farm on scramjets. they will be too late to the party to make a difference in the race to achieve a viable RLV. 2STO RLV's are the closest competitors, and they have their own issues to contend with. It all depends on their methodology. There is as many flavours as there are space advocates it seems. So until the 2STO advocates get their stuff together and start getting more serious i will be cheering the guys at REL on. They are at this time the most likely bet to get there first.

[Antice]

I found this a couple of hours ago. A very interesting lecture about Skylon and the SABRE engine in particular.
Linky
I recomend either owning a very speedy line or chosing the download option on the page i linked to. it's a pretty large movie.
Of particular interest in light of the recent scramjet discusions re airbreathing. look at about 18 to 22 minutes into the lecture movie (the full version not the youtube one)
Alan bond demonstrates pretty clearly why airbreathing beyond mach 6 - 7 is going to turn the vehicle into a Single Stage TPS system to orbit.

[RGClark]

I found this a couple of hours ago. A very interesting lecture about Skylon and the SABRE engine in particular.
Linky
I recomend either owning a very speedy line or chosing the download option on the page i linked to. it's a pretty large movie.
Of particular interest in light of the recent scramjet discusions re airbreathing. look at about 18 to 22 minutes into the lecture movie (the full version not the youtube one)
Alan bond demonstrates pretty clearly why airbreathing beyond mach 6 - 7 is going to turn the vehicle into a Single Stage TPS system to orbit.

Thanks for that. Very informative on the Skylon.


Bob Clark

[RGClark]

No Bob, I simply think you have no clue what you are talking about. The X-43 program was looking to develop an engine that could operate from subsonic to hypersonic velocities and save weight by drawing Oxygen from the atmosphere. Great idea and exactly what the SABRE is designed to do. If you actually read and understood the material you would have realized that the SABRE is the engine NASA wanted to develop, only Reaction Engines are 10-20 years ahead of them.

This member of the X-51A team estimates optimistically the time frame to when scramjets can be used as part of the propulsion system to reach space as 15 to 20 years:

Air Force Sees Hypersonic Weapons and Spaceships in Future.
By Jeremy Hsu
SPACE.com Staff Writer
posted: 17 June 2010
05:30 am ET
"Rise of the space planes.
"If scramjet technology advances far enough, it could become part of a system that helps propel unmanned or manned vehicles into space. Space planes might even emerge that can fly into space at just about any time, without launch window constraints.
"A scramjet-powered vehicle would need to rely upon a regular rocket or jet engine to reach Mach 4, so that the scramjet could take over for hypersonic speeds during the first stage to Earth orbit.
"The X-51A scramjet engine would not be enough by itself to allow a vehicle to reach orbit, said Joseph Vogel, hypersonics director and X-51 program manager at Boeing Phantom Works/Defense, during the teleconference. Both Boeing and Pratt & Whitney Rocketdyne formed part of the private consortium that helped design and build the X-51A.
"Any future space-lift system would also need a more energetic hydrogen-based fuel, rather than the JP-7 jet fuel used in supersonic aircraft, Vogel explained.
"I would say that within the next 15 to 30 years — I'll give you the broad side — but probably 15 to 20 years, you could start to see this technology being expanded to the point where you could get aircraft into outer space," Vogel said."
http://www.space.com/businesstechnol...re-100617.html

So you may be right that the Skylon would reach operation before scramjets for space access purposes. Still optimistically you could have two types of hypersonic airbreathing propulsion in operation in short order after the Skylon enters service which would serve to produce competition to drive down the costs of space access.


Bob Clark

[Antice]

True. having competing technologies is good. but we also have to take into account other aspects of space launch. Scramjet's by themselves do not address the heating issues that once mach 6 is passed surpasses that of re-entry.

Alan bond stated pretty clearly that as far as physical materials limits is concerned that any vehicle going that fast in the denser parts of the atmosphere is going to end up as a TPS to orbit launch system. He also admitted that some of the choices in HOTOL was a big mistake. the HOTOL project would at best have delivered a hydraulics system to LEO vehicle. the compensation requirements against the bending moments on the vehicle would have eaten up all the possible payload mass. Moving the engines to the wings solved this tho. a neat solution that required almost no mass increase at all.
Got to love a guy that is willing to stand up in public and admit that they goofed it the first time, then explain what went wrong and how to bypass the problem entirely.

Something else from that lecture: Alan Bond claimed that they were nowhere near the physical limitations for heat exchanger technology. I read that as meaning that they indeed have ideas of how to make even more efficient heat exchangers that could push the speed limit for the engines even further up the temp scale. but unless aeroshell materials that can withstand even higher temps is invented the issue is moot. you can have the best engines in history and not get anywhere if your vehicle melts before you are halfway there. Adding active cooling turns what was a SSTO into a TPS to orbit vehicle instead. This kind of real world physics limitation is hard to beat. not impossible, but don't hold your breath kinda hard.

The problems with SSTO's has always been that the earth is 10% too big for it to work well. Skylon is pushing the envelope so that it becomes possible to get off this ball of dirt. Hopefully they will get all the funds they need once the engines have been demonstrated.

[Garrison]

True. having competing technologies is good. but we also have to take into account other aspects of space launch. Scramjet's by themselves do not address the heating issues that once mach 6 is passed surpasses that of re-entry.

Alan bond stated pretty clearly that as far as physical materials limits is concerned that any vehicle going that fast in the denser parts of the atmosphere is going to end up as a TPS to orbit launch system. He also admitted that some of the choices in HOTOL was a big mistake. the HOTOL project would at best have delivered a hydraulics system to LEO vehicle. the compensation requirements against the bending moments on the vehicle would have eaten up all the possible payload mass. Moving the engines to the wings solved this tho. a neat solution that required almost no mass increase at all.
Got to love a guy that is willing to stand up in public and admit that they goofed it the first time, then explain what went wrong and how to bypass the problem entirely.

Something else from that lecture: Alan Bond claimed that they were nowhere near the physical limitations for heat exchanger technology. I read that as meaning that they indeed have ideas of how to make even more efficient heat exchangers that could push the speed limit for the engines even further up the temp scale. but unless aeroshell materials that can withstand even higher temps is invented the issue is moot. you can have the best engines in history and not get anywhere if your vehicle melts before you are halfway there. Adding active cooling turns what was a SSTO into a TPS to orbit vehicle instead. This kind of real world physics limitation is hard to beat. not impossible, but don't hold your breath kinda hard.

The problems with SSTO's has always been that the earth is 10% too big for it to work well. Skylon is pushing the envelope so that it becomes possible to get off this ball of dirt. Hopefully they will get all the funds they need once the engines have been demonstrated.

I'm wondering, would that greater efficiency allow for lighter engines/ Or more power from the same size engine? Would it in short allow for a higher payload with essentially the same airframe?

[Antice]

I'm wondering, would that greater efficiency allow for lighter engines/ Or more power from the same size engine? Would it in short allow for a higher payload with essentially the same airframe?

I would think so, but the growth in that direction would not be very drastic I'd guess. but every kg counts. I suspect he is hinting more towards the capability to use these precoolers as parts of other engine configurations to improve efficiency and overall power on those. LAPCAT is one such post skylon type of capability growth project at least. It's a much bigger and more challenging project goal than skylon technology wise.

[Frodz]

Something else from that lecture: Alan Bond claimed that they were nowhere near the physical limitations for heat exchanger technology. I read that as meaning that they indeed have ideas of how to make even more efficient heat exchangers that could push the speed limit for the engines even further up the temp scale. but unless aeroshell materials that can withstand even higher temps is invented the issue is moot. you can have the best engines in history and not get anywhere if your vehicle melts before you are halfway there. Adding active cooling turns what was a SSTO into a TPS to orbit vehicle instead. This kind of real world physics limitation is hard to beat. not impossible, but don't hold your breath kinda hard.

That’s one interpretation but then thinking about it, doesn’t the helium loop ultimately require stored hydrogen to function? I’m sure I heard him say that the pre-cooler system draws more hydrogen than is needed for combustion and the overspill gets fed into the bypass ramjets. If the pre-cooler had greater efficiency could you reduce the systems hunger for hydrogen, thereby saving propellant and ultimately hauling more payload? Or am I missing something?

Also did I hear it right when he said the new Sabre 4 design is intended to increase theoretical Veff from 16k/s to nearer 46 km/s implying that it could reach much higher Isp’s?

So I think what is being implied is it’s possible to greatly reduce hydrogen propellant required during the air breathing mode as a way to increase payload.



And to answer some points from earlier,

The Wiki article (http://en.wikipedia.org/wiki/Reaction_Engines_SABRE) about the SABRE engine makes some amazing claims. To quote, "The engine gives good fuel efficiency peaking at about 2800 seconds within the atmosphere. Typical all-rocket systems are around 450 at best, and even "typical" nuclear thermal rockets only about 900 seconds." Are they talking about specific impulse or specific thrust or what? Are they claiming efficiencies in the range of ion engines?

Yes they are talking about specific impulse, but you should take it with a pinch of salt as specific impulses for rockets and air-breathers are not directly compatible. Air breathers like commercial jet engines do tend to have relatively high Isp’s like ion engines (though of course radically different thrust!), it is an artefact of the air being the propellant mass.

That’s kind of the point this rocket has the best of both worlds as it’s air breathing mode can have the performance of a supercharged commercial jet engine, albeit one that can fly much faster, and then switch to a high performance closed cycle once air breathing is no longer more efficient.

2800 seconds Isp for a turbojet, while relatively high, is certainly not beyond the realms of possibility. It’s a lower Isp than for a turbofan but then a turbofan cannot work at higher speeds.

Then there is the matter of the helium powered turbopumps re-cycling waste heat. Why not do the same using the hydrogen fuel? The helium system just seems like extra mass.

Because the material they want to use for the pre-cooler would be damaged by the hydrogen stream, without the helium loop the pre-cooler (a significant part of the engine) would be less efficient and heavier. So the helium loop is required, turbopump or not, so getting as much efficiency out of it is the best idea.

[TrAI]

That’s one interpretation but then thinking about it, doesn’t the helium loop ultimately require stored hydrogen to function? I’m sure I heard him say that the pre-cooler system draws more hydrogen than is needed for combustion and the overspill gets fed into the bypass ramjets. If the pre-cooler had greater efficiency could you reduce the systems hunger for hydrogen, thereby saving propellant and ultimately hauling more payload? Or am I missing something?

Also did I hear it right when he said the new Sabre 4 design is intended to increase theoretical Veff from 16k/s to nearer 46 km/s implying that it could reach much higher Isp’s?

So I think what is being implied is it’s possible to greatly reduce hydrogen propellant required during the air breathing mode as a way to increase payload.

Yes, the cooling loop uses the hydrogen for cooling. As I understood it it was an inescapable problem with precooled engines that they use more hydrogen for sinking the heat then for powering the engine, and that they actually had improved the efficiency over the earlier hydrogen cooling loop used in the HOTOL study. I should think that an increase in efficiency would mean less hydrogen is used, but how much that affects the total fuel use, I am not sure, but I should think some increase is likely.

Also, it seems to me that the amount of excess hydrogen draw depends largely on the speed of the craft, as the higher speeds would mean more heat. so I would think that if they could make the ram-burners more efficient at a wider speed range, some gain could be got there too, I believe the predicted max eff of the SABRE ram-burners being somewhere between Mach 3 and 4.

But it seems to me that the priority should be on getting the system to work, further improvements can be done when the concept is realized. Firstly to reduce development time, secondly to reduce cost, and thirdly I should think that experience with the actual engine in use will help in testing such improvements.


As a more general observation, it is interesting to look at the work they have done on how the Skylon might actually be used, the Fluyt and the Troy look nice and practical, not like some of the streamlined sci-fi stuff, but like something that actually could get the job done, and may be adapted to other mission profiles relatively easily due to modularity. Of course, the Skylon itself looks rather like something from some sci-fi story, but in that case the shape have a practical purpose, it being designed for atmospheric flight.

And there are those mysterious engine system studies the project name document(27kiB PDF) mentions but that doesn't seem to be mentioned anywhere else...

[Frodz]

Just had a look over at Reaction Engines and found this pdf from 2007, turns out what I thought about the hydrogen consumption is exactly what Bond was on about.

http://www.reactionengines.co.uk/dow...60_188-196.pdf

Further, it is demonstrated that the precooler is a major source of thermodynamic irreversibility within the engine cycle and that further reduction in entropy can be realised by increasing the heat transfer coefficient on the air side of the precooler. If this were to be achieved, it would improve the payload mass delivered to orbit by the Skylon launch vehicle by between 5 and 10%.

Very interesting pdf that, worth a read.

But it seems to me that the priority should be on getting the system to work, further improvements can be done when the concept is realized.

Undoubtedly true, but it is interesting to see how far (theoretically) the technology can go.

And there are those mysterious engine system studies the project name document(27kiB PDF) mentions but that doesn't seem to be mentioned anywhere else...

After some digging I think I found the answer, many of them were related to the above studies you mention.

For example on this site, http://www.ukrocketman.com/space/index.shtml - (interesting insiders view on the STERN project) it mentions,

Reaction Engines is developing 2 classes of rocket engines; the air breathing rocket engines (Sabre, SCIMITAR and STERN), and the bi-prop rocket engines (SERAPH and SANGRAIL).

After some more digging SANGRAIL appears to be an engine studied for use on a type of Earth return capsule for mars missions.

This pdf discusses some aspects and briefly touches on Excalibur,

http://www.astronist.demon.co.uk/spa...ys_to_Mars.pdf

We need a reusable launcher (Skylon), an in-space boost stage, and a
capsule for return from interplanetary space. Hempsell has designed an Earth
return capsule called Excalibur; superficially it resembles an Apollo/Orion
capsule, but is in fact very different from them, as the JBIS papers describing it illustrate.

I had the paper references but now I can’t find where I bookmarked the page!

SERAPH mentioned above is the proposed Mars Ascent Vehicle's LOx/CO engine found near the end of the Troy pdf.

SERPENT could be the nuclear mars engine referred to in the Three ways to Mars pdf above.


As for the rest on that list;
SOMA is pretty straight-forward from the description, and STRICT I believe is the other engine referred to on the ukrocketman site as part of the STERN tests.

SAPPHIRE though I have no clue!

[Antice]

I've been trying to find some info about the SAPPHIRE project on the net, but google is no help there.
STRICT and STERN is basically about the same technology. The plug nozzle upgrade that they want for the SABRE engine.

I've been thinking about those numbers given in the 2007 PDF about how improved heat exchangers could in theory give a 10% increase in payload... that would entail a 20% or more reduction in Hydrogen use during air breathing mode since it is not a 1 for 1 when it comes to mass savings. it's more like 2 for 1 or even 3 for 1 since we are talking about very early in the flight savings. That is no small fuel efficiency increase indeed.

I'm looking into and trying to convert some Isp numbers so that they match up. And i have noticed my flaw in reasoning when i tried to do calculate the airbreathing mode with the rocket equation. The problem is that when air breathing Isp is not a static value, but a dynamic one that changes along with the speed and altitude of the vehicle. and it changes a LOT.
According to wikipedia the N s/kg measure is specific impulse from mass, and is equal to effective exhaust velocity (Veff). we can therefore divide it by g to derive Isp in sec.
The Data given for ISP in the skylon manual is as follows.
Air breathing: 35000 N s/kg = 3569sec (this is probably a rounded average value)
Rocket mode: 4500 N s/kg = 458sec (vacuum level)
SSME (Shuttle) 452.5 sec 4423m/s (vacuum level)
turbofan jet engine: 3000sec or 29000m/s

This is were we stand today at least. and this is with SABRE 3 since SABRE 4 is not ready yet. they are still waiting for it in order to finish the D1 version. I wonder where you got the 16000m/s Veff from. boosting the Veff to 46000m/s that I've not seen any source for would in practice mean an comparative ISP of almost 4700sec. now that is high. Ofc. some of this enhanced fuel mass efficiency increase compared to jet engines is actually due to the higher specific energy of hydrogen. it's energy density however, is lower than for hydrocarbons, so in effect one has traded tank volume for mass efficiency. witch is fine for a SSTO since the greater tank volume helps lessen the heat of reentering.

[Garrison]

I've been trying to find some info about the SAPPHIRE project on the net, but google is no help there.
STRICT and STERN is basically about the same technology. The plug nozzle upgrade that they want for the SABRE engine.

I've been thinking about those numbers given in the 2007 PDF about how improved heat exchangers could in theory give a 10% increase in payload... that would entail a 20% or more reduction in Hydrogen use during air breathing mode since it is not a 1 for 1 when it comes to mass savings. it's more like 2 for 1 or even 3 for 1 since we are talking about very early in the flight savings. That is no small fuel efficiency increase indeed.

I'm looking into and trying to convert some Isp numbers so that they match up. And i have noticed my flaw in reasoning when i tried to do calculate the airbreathing mode with the rocket equation. The problem is that when air breathing Isp is not a static value, but a dynamic one that changes along with the speed and altitude of the vehicle. and it changes a LOT.
According to wikipedia the N s/kg measure is specific impulse from mass, and is equal to effective exhaust velocity (Veff). we can therefore divide it by g to derive Isp in sec.
The Data given for ISP in the skylon manual is as follows.
Air breathing: 35000 N s/kg = 3569sec (this is probably a rounded average value)
Rocket mode: 4500 N s/kg = 458sec (vacuum level)
SSME (Shuttle) 452.5 sec 4423m/s (vacuum level)
turbofan jet engine: 3000sec or 29000m/s

Those numbers seem like magic when you compare them to pure rockets, heck even the NERVA2(Nuclear Engine for Rocket Vehicle Application) was only projected to be have these ISP values:

825 s (vacuum)
380 s (sea level)

And the NERVA numbers are far superior to any chemical rocket ever built.

[Antice]

Yeah. The numbers do look like magic compared to rockets. and I suspect that is why some people remain sceptical of the SABRE concept. Careful reading of the
A Comparison of Propulsion Concepts for SSTO Reuseable Launchers document available on the REL website is a must before one can even start to understand how they are going to accomplish this. It's not just the precooler that makes it possible. it's also the highly efficient brayton cycle with an extreme temperature gradient between the hot and cold side of the cycle. A lot of original thought has gone into SABRE. I'm really looking forward to seing this baby move the last steps into a practical functional engine.

[Garrison]

Yeah. The numbers do look like magic compared to rockets. and I suspect that is why some people remain sceptical of the SABRE concept. Careful reading of the
A Comparison of Propulsion Concepts for SSTO Reuseable Launchers document available on the REL website is a must before one can even start to understand how they are going to accomplish this. It's not just the precooler that makes it possible. it's also the highly efficient brayton cycle with an extreme temperature gradient between the hot and cold side of the cycle. A lot of original thought has gone into SABRE. I'm really looking forward to seing this baby move the last steps into a practical functional engine.

And there is an element that people have gotten their hopes up for plans like Venturestar, the X-30, heck even the STS and been disappointed. They just can't bring themselves to believe that something truly revolutionary could really be about to come to fruition.

[Frodz]

The problem is that when air breathing Isp is not a static value, but a dynamic one that changes along with the speed and altitude of the vehicle. and it changes a LOT.

http://www.reactionengines.co.uk/dow...56_108-117.pdf

At the end, by the looks of it it matches Skylon's air breathing flight-profile.

This is were we stand today at least. and this is with SABRE 3 since SABRE 4 is not ready yet. they are still waiting for it in order to finish the D1 version.

If you notice the updated User Manual on the Reaction Engines website is the C2 specification, not the old C1 version. For example the quoted mass to LEO for C2 is 15,000 kg, larger than C1’s 12,000 kg and the same as the D1. I think the C2 is an interim D1 specification and its performance based on “known” SABRE 4 capabilities.

Hence I think some information out there on the SABRE/Skylon specs is in fact a synthesis of different specifications.

I wonder where you got the 16000m/s Veff from. boosting the Veff to 46000m/s that I've not seen any source for would in practice mean an comparative ISP of almost 4700sec. now that is high.

Starts around 40:50 on the video you posted. Note, this is the Isp at mach 5 and if you look on the Isp profile I posted above at mach 5 the engine would be well below it’s peak of 3600 s and at around ~1600 s Isp, the 16000m/s Veff on the video appears consistent with that (16,000/9.8). So basically what he is saying is that they want with SABRE 4 to at least maintain the peak Isp over the higher mach numbers.

Ofc. some of this enhanced fuel mass efficiency increase compared to jet engines is actually due to the higher specific energy of hydrogen.

Hmm, good point, isn’t the exhaust relatively faster though which would help to balance that out?

Those numbers seem like magic when you compare them to pure rockets, heck even the NERVA2(Nuclear Engine for Rocket Vehicle Application) was only projected to be have these ISP values:

825 s (vacuum)
380 s (sea level)

And the NERVA numbers are far superior to any chemical rocket ever built.

As I said above, you cannot directly compare air breathing engines to closed cycle ones based on Isp, look at the wiki page,

http://en.wikipedia.org/wiki/Specific_impulse

It’s not magic, it’s just how the property is calculated.

In fact SABRE’s values are quite standard for Turbofans, there are some which have much higher Isp’s, and even then it’s only a peak value which it will sustain for something like a minute at most. After all, although many of it’s components are different, it is effectively doing much the same thing as a (very high speed) Turbofan. Indeed come to think of it SABRE is actually conceptually very simple, it’s a conventional rocket with the business end of a high-performance turbofan strapped on the front!

It is essentially this “high-performance” bit (the precooler/helium cycle etc) that makes this engine viable for SSTO’s. I think it is far less mystical than a lot of people believe, the “tricks” the RE lot have used to make the engine work seem to have a lot of people confused.

[Antice]

There is plenty confusion about what SABRE is. far to many confuse it with other concepts that they have heard about. I've seen it confounded with ram/scramjet's, LACE and even in some cases ACE. When people confuse it thus i tend to chalk it up to people not bothering to read the materiel presented propperly... Something that I have noticed is a pretty endemic tendency among Internet airmchair "engineers" in general.

[Garrison]

http://www.reactionengines.co.uk/dow...56_108-117.pdf

It’s not magic, it’s just how the property is calculated.


In fact SABRE’s values are quite standard for Turbofans, there are some which have much higher Isp’s, and even then it’s only a peak value which it will sustain for something like a minute at most. After all, although many of it’s components are different, it is effectively doing much the same thing as a (very high speed) Turbofan. Indeed come to think of it SABRE is actually conceptually very simple, it’s a conventional rocket with the business end of a high-performance turbofan strapped on the front!

It is essentially this “high-performance” bit (the precooler/helium cycle etc) that makes this engine viable for SSTO’s. I think it is far less mystical than a lot of people believe, the “tricks” the RE lot have used to make the engine work seem to have a lot of people confused.

Yes I know that, I was simply pointing out that anyone familiar with the ISP figures for ordinary rocket engines might be taken aback by the raw numbers for the SABRE, it wasn't meant to be taken seriously, or to imply that i don't believe them. I thought that was pretty clear but apparently not.

[Frodz]

Yes I know that, I was simply pointing out that anyone familiar with the ISP figures for ordinary rocket engines might be taken aback by the raw numbers for the SABRE, it wasn't meant to be taken seriously, or to imply that i don't believe them. I thought that was pretty clear but apparently not.

Ah sorry, no it didn't seem clear to me, as I'm sure you're aware many people do make similar comparisons genuinely complaining that SABRE sounds unrealistic!

It's a useful general comment anyway for someone who does actually think the stats for SABRE seem incredulous for a rocket engine.

There is plenty confusion about what SABRE is. far to many confuse it with other concepts that they have heard about. I've seen it confounded with ram/scramjet's, LACE and even in some cases ACE.

Yeah I know, LACE/ACE is understandable given that is is effectively an evolution of that design but the ramjet confusion shows that they haven't actually read anything about what SABRE does. "oh look, it has ramjets, it must be some sort of ramjet/turboramjet engine!"

When people confuse it thus i tend to chalk it up to people not bothering to read the materiel presented propperly... Something that I have noticed is a pretty endemic tendency among Internet airmchair "engineers" in general.

Yeah, reading all those pdf's on the website is essential. A lot of the Reaction Engines public relations bumf stresses their innovations, which is understandable, but there's far less talk of how the overall engine design conforms to already well-established principles and hence is easily one of the most feasible SSTO concepts around. IMO they would do better in the PR stakes stressing many of the similarities with existing engine concepts like the Turbofan and showing why their design is a natural evolution of that that can be used in rockets.

Oh well, that's the opinion of an internet armchair PR agent........

[Antice]

found this yesterday. i tried to trace back to the original news article refered to but was unable to find the correct one.
In any case. it's interesting to note the level of confidence mr Bond displays in regard to skylon happening once the engines have been proven. It may not be the skylon REL has proposed that happens, but he fully expect some sort of vehicle to result from this within 10 years after engine completion.

[Garrison]

found this yesterday. i tried to trace back to the original news article refered to but was unable to find the correct one.
In any case. it's interesting to note the level of confidence mr Bond displays in regard to skylon happening once the engines have been proven. It may not be the skylon REL has proposed that happens, but he fully expect some sort of vehicle to result from this within 10 years after engine completion.

That's interesting because I came across something that took me by surprise(apologies if everyone else already knows about it); Lockheed Martin didn't give up on RLV's after the X-33 debacle:

Reusable Rocket Test

With a working SABRE would REL be looking for a partner in the aerospace industry to build a vehicle around it, be it the Skylon or something else?

[RGClark]

That's interesting because I came across something that took me by surprise(apologies if everyone else already knows about it); Lockheed Martin didn't give up on RLV's after the X-33 debacle:
Reusable Rocket Test

I'm fairly sure this is for a reusable first stage booster for an expendable upper stage:

Plans for future re--usable space launch X-plane hatched.
Posted by Guy Norris at 3/31/2009 3:41 PM CDT
"Concept models of the fly-back winged booster and a similar winged booster with a rocket-powered payload module carried piggy-back, were revealed at the National Space Symposium. The models bore a strong resemblance to the scaled model booster flight tested by Lockheed Martin early in 2008. These tests, conducted in New Mexico, were primarily to investigate guidance and control concepts for the two-stage to orbit vehicle which will be autonomously controlled at speeds for up to Mach 6 for the first-stage and up to Mach 9 and beyond for the second-stage."

http://www.aviationweek.com/aw/blogs...entId=blogDest

Bob Clark

[Antice]

That's interesting because I came across something that took me by surprise(apologies if everyone else already knows about it); Lockheed Martin didn't give up on RLV's after the X-33 debacle:

Reusable Rocket Test

With a working SABRE would REL be looking for a partner in the aerospace industry to build a vehicle around it, be it the Skylon or something else?

REL will only accept a partner that is free of ITAR issues according to most of the interviews I've seen where such questions were asked. But selling SABRE engines to a company that wants them for making a 2STO. yeah i expect that they will be willing to do that. it would be a pop up/fly forward type 2STO then. those avoid a lot of the staging issues by doing it on a suborbital jump out of the atmosphere. SABRE is just about the only engine that could enable those as well as SSTO. that is the big issue with pop up flyback boosters. you really are a good portion of the way to orbit when you finally stage..
But i think skylon makes more sense than a 2STO. staging adds so much extra groundwork that the extra payload may not be worth it. the SUS REL has proposed would be sufficient to allow exploiting any extra potential gained with staging. The SUS can be mated to the payload at the customers facilities (the customer uses a clean-room for building their payload in the first place) then shipped in a sealed container to the launch facility.
Getting rid of the expensive launch prep facility at the launch site is a pretty important economic issue you know. not all payloads need a clean-room facility.

It is a given however that REL are going to need multiple partners in order to realize skylon. they are not planning on building it on their own AFAIK.
But they may actually end up doing just that. Big industry players are being somewhat reticent towards buying into skylon for some reason.

[Garrison]

REL will only accept a partner that is free of ITAR issues according to most of the interviews I've seen where such questions were asked. But selling SABRE engines to a company that wants them for making a 2STO. yeah i expect that they will be willing to do that. it would be a pop up/fly forward type 2STO then. those avoid a lot of the staging issues by doing it on a suborbital jump out of the atmosphere. SABRE is just about the only engine that could enable those as well as SSTO. that is the big issue with pop up flyback boosters. you really are a good portion of the way to orbit when you finally stage..
But i think skylon makes more sense than a 2STO. staging adds so much extra groundwork that the extra payload may not be worth it. the SUS REL has proposed would be sufficient to allow exploiting any extra potential gained with staging. The SUS can be mated to the payload at the customers facilities (the customer uses a clean-room for building their payload in the first place) then shipped in a sealed container to the launch facility.
Getting rid of the expensive launch prep facility at the launch site is a pretty important economic issue you know. not all payloads need a clean-room facility.

It is a given however that REL are going to need multiple partners in order to realize skylon. they are not planning on building it on their own AFAIK.
But they may actually end up doing just that. Big industry players are being somewhat reticent towards buying into skylon for some reason.

May be the old problem of 'not made here', or just concerns about what Skylon would do to to their existing infrastructure and product range. To find a partner or partners they may have to look to some of the newer players in the industry with less baggage. Though REL have said they do have some private investment that their keeping close to their chest so who knows? From a bigger picture perspective it's good to see that Lockheed are least looking to new technology and new approaches, especially after getting burned so badly with the X-33.

[Antice]

May be the old problem of 'not made here', or just concerns about what Skylon would do to to their existing infrastructure and product range. To find a partner or partners they may have to look to some of the newer players in the industry with less baggage. Though REL have said they do have some private investment that their keeping close to their chest so who knows? From a bigger picture perspective it's good to see that Lockheed are least looking to new technology and new approaches, especially after getting burned so badly with the X-33.

It's definately good to see that there are more than newspace/alt.space companies looking into reusability. It's about time that we started to see more serious attempts at breaking this very tough nut. All the lethargy have given REL a real whooper of a leg up on the competition tho. Unless there are some very black projects out there we don't even know about at all.

[Garrison]

It's definately good to see that there are more than newspace/alt.space companies looking into reusability. It's about time that we started to see more serious attempts at breaking this very tough nut. All the lethargy have given REL a real whooper of a leg up on the competition tho. Unless there are some very black projects out there we don't even know about at all.

The USAF might have something lurking in the shadows behind the X-37B but I do agree that barring that REL are out in the lead here. It's all about getting the cost per kilo down for launching, without that all the lofty deep space goals will either be abandoned or wind up as nothing more than PR stunts for whichever country carries them out.

[RGClark]

The import of the Dr. John C. Whitehead article Single Stage To Orbit Mass Budgets Derived From Propellant Density and Specific Impulse is that it shows that for a rocket SSTO even though hydrogen has a higher Isp than kerosene its low density means that it's actually easier to make a rocket SSTO using dense fuels such as kerosene:

Single Stage To Orbit Mass Budgets Derived From Propellant Density and Specific Impulse.
John C. Whitehead
32nd AIAA/ASME/SAE/ASEE Joint Propulsion Conference
Lake Buena Vista, FL July 1-3, 1996
http://www.osti.gov/bridge/servlets/...ble/379977.pdf

This result very well may also apply to a partial airbreathing system such as Skylon that uses airbreathing propulsion in the first part of the trip, switching to rockets in the later part. The key reasons why dense hydrocarbon-fueled rockets can supply multiple times greater payload in the same size vehicle than a hydrogen-fueled one is that their engine T/W ratio is twice as good and their propellant weight to tank weight ratios are 3 times as good as hydrogen, resulting in major reductions in vehicle dry mass.
These factors should also apply to a partially airbreathing system, and an example from the past strongly implies this is the case. Back in the fifties the Air Force wanted a long range reconnaissance craft. Based on the fact that hydrogen has a higher Isp the belief was the vehicle should be hydrogen fueled. The vehicle proposed by Lockheed under this top secret "Suntan" program was the CL-400:

LIQUID HYDROGEN AS A PROPULSION FUEL,1945-1959.
Part II : 1950-1957
8. Suntan
Lockheed CL-400.

http://history.nasa.gov/SP-4404/ch8-3.htm

Notice the similarity to the Skylon with the long thin fuselage and the engines on the ends of the wings. The main difference would be the lack of a tail section on the Skylon, probably because the engines need to gimbal for the flight to space which can also be used for vehicle control in the air.
However, note that the range given on this page is only 4,000 km, for a mission radius of 2,000 km for missions returning to the starting point. This is for a vehicle 160 feet long. But the smaller kerosene-fueled SR-71 at only 100 feet long has a range of 4,800 km:

Lockheed
SR-71 Blackbird
Strategic Reconnaissance.
http://www.aerospaceweb.org/aircraft/recon/sr71/

Indeed the legendary Kelly Johnson soured on the Suntan program when he found despite hydrogen's higher energy content that its use would result in such short range:

LIQUID HYDROGEN AS A PROPULSION FUEL,1945-1959
Part II : 1950-1957
8. Suntan
Suntan Fades.
http://history.nasa.gov/SP-4404/ch8-12.htm

Another key advantage of a kerosene-fueled version is that fuel can be carried in the wings, as with the SR-71, but not in a hydrogen-fueled version:

Suntan fades.
"Ordinarily, range can be extended by adding more fuel or improving the fuel consumption of the propulsion system for a given thrust. Johnson could see a range growth of only a paltry 3 percent or so from adding more fuel. ". . . we have crammed the maximum amount of hydrogen in the fuselage that it can hold. You do not carry hydrogen in the flat surfaces of the wing," he explained.42 Johnson turned to Perry Pratt for estimated improvements in the 304 engine and his answer was equally pessimistic: no more than 5 or 6 percent improvement in specific fuel consumption could be expected over a five-year period. The very low growth estimates were compounded by operational logistics problems of liquid hydrogen. As Ben Rich asked: 'How do you justify hauling enough LH2 around the world to exploit a shortrange airplane?'"
http://history.nasa.gov/SP-4404/ch8-12.htm

So both for the rocket propulsion and the airbreathing propulsion components dense propellants provide better performance despite hydrogen's greater Isp. For this reason I suggest Reaction Engines do a trade study on replacing the hydrogen with kerosene or other hydrocarbon.
Hydrogen does have advantages for the Skylon system in that it has greater cooling capacity for the heat exchangers and it is lighter so requires lower wing weight. Still, careful trades would be required to see if these advantages are enough to counteract the advantages of dense propellants for a SSTO.


Bob Clark

[djellison]

So both for the rocket propulsion and the airbreathing propulsion components dense propellants provide better performance despite hydrogen's greater Isp.

Care to make your brush a little broader? If what you say is true - where are there ANY LOX/LH2 LV's at all.

[Garrison]

The import of the Dr. John C. Whitehead article Single Stage To Orbit Mass Budgets Derived From Propellant Density and Specific Impulse is that it shows that for a rocket SSTO even though hydrogen has a higher Isp than kerosene its low density means that it's actually easier to make a rocket SSTO using dense fuels such as kerosene:

Single Stage To Orbit Mass Budgets Derived From Propellant Density and Specific Impulse.
John C. Whitehead
32nd AIAA/ASME/SAE/ASEE Joint Propulsion Conference
Lake Buena Vista, FL July 1-3, 1996
http://www.osti.gov/bridge/servlets/...ble/379977.pdf

This result very well may also apply to a partial airbreathing system such as Skylon that uses airbreathing propulsion in the first part of the trip, switching to rockets in the later part. The key reasons why dense hydrocarbon-fueled rockets can supply multiple times greater payload in the same size vehicle than a hydrogen-fueled one is that their engine T/W ratio is twice as good and their propellant weight to tank weight ratios are 3 times as good as hydrogen, resulting in major reductions in vehicle dry mass.
These factors should also apply to a partially airbreathing system, and an example from the past strongly implies this is the case. Back in the fifties the Air Force wanted a long range reconnaissance craft. Based on the fact that hydrogen has a higher Isp the belief was the vehicle should be hydrogen fueled. The vehicle proposed by Lockheed under this top secret "Suntan" program was the CL-400:

LIQUID HYDROGEN AS A PROPULSION FUEL,1945-1959.
Part II : 1950-1957
8. Suntan
Lockheed CL-400.

Notice the similarity to the Skylon with the long thin fuselage and the engines on the ends of the wings. The main difference would be the lack of a tail section on the Skylon, probably because the engines need to gimbal for the flight to space which can also be used for vehicle control in the air.
However, note that the range given on this page is only 4,000 km, for a mission radius of 2,000 km for missions returning to the starting point. This is for a vehicle 160 feet long. But the smaller kerosene-fueled SR-71 at only 100 feet long has a range of 4,800 km:

Lockheed
SR-71 Blackbird
Strategic Reconnaissance.
http://www.aerospaceweb.org/aircraft/recon/sr71/

Indeed the legendary Kelly Johnson soured on the Suntan program when he found despite hydrogen's higher energy content that its use would result in such short range:

LIQUID HYDROGEN AS A PROPULSION FUEL,1945-1959
Part II : 1950-1957
8. Suntan
Suntan Fades.
http://history.nasa.gov/SP-4404/ch8-12.htm

Another key advantage of a kerosene-fueled version is that fuel can be carried in the wings, as with the SR-71, but not in a hydrogen-fueled version:

Suntan fades.
"Ordinarily, range can be extended by adding more fuel or improving the fuel consumption of the propulsion system for a given thrust. Johnson could see a range growth of only a paltry 3 percent or so from adding more fuel. ". . . we have crammed the maximum amount of hydrogen in the fuselage that it can hold. You do not carry hydrogen in the flat surfaces of the wing," he explained.42 Johnson turned to Perry Pratt for estimated improvements in the 304 engine and his answer was equally pessimistic: no more than 5 or 6 percent improvement in specific fuel consumption could be expected over a five-year period. The very low growth estimates were compounded by operational logistics problems of liquid hydrogen. As Ben Rich asked: 'How do you justify hauling enough LH2 around the world to exploit a shortrange airplane?'"
http://history.nasa.gov/SP-4404/ch8-12.htm

So both for the rocket propulsion and the airbreathing propulsion components dense propellants provide better performance despite hydrogen's greater Isp. For this reason I suggest Reaction Engines do a trade study on replacing the hydrogen with kerosene or other hydrocarbon.
Hydrogen does have advantages for the Skylon system in that it has greater cooling capacity for the heat exchangers and it is lighter so requires lower wing weight. Still, careful trades would be required to see if these advantages are enough to counteract the advantages of dense propellants for a SSTO.


Bob Clark

These vehicles were/are all designed to operate at high Mach numbers, not surprising that they share some similarities in the aerodynamics. Look at the SST's designed in the 60's and 70's, they all have a similar layout. As for the rest, once again you know better than Alan Bond et al, they are clearly just idiots who have missed your brilliant insight, what's their decades of experience versus your Googling skills... How about you keep your crackpot nonsense in your own threads and keep it out of those dedicated to real projects with real engineering?

[RGClark]

These vehicles were/are all designed to operate at high Mach numbers, not surprising that they share some similarities in the aerodynamics. Look at the SST's designed in the 60's and 70's, they all have a similar layout. As for the rest, once again you know better than Alan Bond et al, they are clearly just idiots who have missed your brilliant insight, what's their decades of experience versus your Googling skills... How about you keep your crackpot nonsense in your own threads and keep it out of those dedicated to real projects with real engineering?

In no way am I suggesting Bond et.al. don't know what they are doing. When in the 50's a long range reconnaissance aircraft was being considered the obvious assumption to make then was that it should be hydrogen fueled since hydrogen has the highest energy per mass of any fuel. Most of the smartest guys in aircraft design then made that assumption. It was only after a careful study of all the physical characteristics of a hydrogen fueled vehicle was done, was it realized you could get better performance just by using kerosene. This is primarily just because of hydrogens very low density (you can fit 10 times as much kerosene as hydrogen in the same size tanks.) This is not my conclusion. It's the conclusion of Kelly Johnson, widely regarded as the greatest aircraft designer who ever lived.
In regards to the design of the Skylon, if you look at REL's article A Comparison of Propulsion Concepts for
SSTO Reusable Launchers you'll note they assume these SSTO's have to be hydrogen-fueled since that was what was proposed for most other earlier SSTO designs. This suggests they never did the trade studies to compare a kerosene-fueled version of the Skylon to the hydrogen-fueled version. Keep in mind then the conclusion that for a pure rocket a kerosene-fueled SSTO would provide better performance than a hydrogen-fueled one came from experts in the industry who actually did make those trade comparisons. Since this is also true for an airbreathing aircraft, it is likely to be true for a SSTO that uses both airbreathing and rocket propulsion, such as the Skylon. However, this can't be known for sure until those careful trade comparisons are made.


Bob Clark

[danscope]

This won't be known " Untill one flies" . Have any of these "skylon" things Ever flown? No? Point taken.