The Reaction Engines Skylon Master Thread (1)

[Andrew_W]

Mark, I was wondering if you could clarify the different versions, C1 at 275 tonnes is obviously earlier, and D1.5 latest at 325 tonnes, is C2 at 345 tonnes an initial version of the D1 series?
 It's the C2 that's described on Wiki and on the REL pdf "Skylon users Manual".

Thanks again for your time.

[Downix]

On the other side of the argument the main reason our structure masses are lower than conventional civil aircraft of comparable dimensions is the truss frame structure - like an airship.

That's the bit I think makes the difference to your numbers compared to other SSTO, but you can use such a truss frame structure irrespective of what form of engine you're using.

Not quite.  I worked on a truss for aerospace applications myself, and the form of engine actually does make a great deal of difference in the weight of the final product.  Some engines have stronger lateral motion than others, some have more occilation demands, some push, some pull.  A truss system optimized for one engine will not work with another due to how you optimize the truss support.  If you know precisely how the engine works, you can reduce a good portion of the support weight, and some engine configurations enable more reductions than others.  I do not have details on SABRE, but I do know that when using a J-58, I could eliminate a good 400 kg in support structure thanks to the truss I made, and that if I used another engine in the same space, I would have not have been able to eliminate as much weight, so even if I'd gained some thrust, the weight penalty would have eliminated any gains.

[Andrew_W]

No doubt you're correct Downix, but debating the finer points you mention might be premature given that many of the characteristics of the Sabre engines hasn't been determined, maybe it's Sabre that would require the heavier truss frames, after all, it operates in two modes and so will perhaps have the wider variation in loadings?

[Downix]

No doubt you're correct Downix, but debating the finer points you mention might be premature given that many of the characteristics of the Sabre engines haven't been determined, maybe it's Sabre that would require the heavier truss frames?

Precisely, we can't know.  However, those within the Skylon group can and do know.  I was just pointing out how his point can work using my own experience for it.

Incidentally, grown to love working with isoform truss systems.  It is astounding how much weight you can eliminate with them.

[Andrew_W]

The other thing about Skylon that is overlooked is their plans to turn a 450s H2/O2 rocket engine around in 2 days, this is a big deal, as such a quick turn around on a high Isp engine would revolutionize the economics of any reusable launch system with that feature.

[Downix]

The other thing about Skylon that is overlooked is their plans to turn a 450s H2/O2 rocket engine around in 2 days, this is a big deal, as such a quick turn around on a high Isp engine would revolutionize the economics of any reusable launch system with that feature.

Actually the next-stage SSME was to be capable of 60-hour turnaround times.  It is not that difficult to imagine Skylon, utilizing the same kinds of systems, achieving even faster turnaround times with their engine.

The Shuttle still had other systems not as capable of such rapid turnaround, but the overall processing time, had the full strength of the logistical upgrades been applied, would have been reduced to a matter of weeks rather than months.

[NotGncDude]

The other thing about Skylon that is overlooked is their plans to turn a 450s H2/O2 rocket engine around in 2 days, this is a big deal, as such a quick turn around on a high Isp engine would revolutionize the economics of any reusable launch system with that feature.

Actually the next-stage SSME was to be capable of 60-hour turnaround times.  It is not that difficult to imagine Skylon, utilizing the same kinds of systems, achieving even faster turnaround times with their engine.

That's a bit of a leap of faith.

[Andrew_W]

I know this is getting off topic, (but still to do with H2/O2 engine turn around - which is pertinent to Skylon). When I asked about it at Rand Simberg's place I got this about the SSME's

pennypincher Says:
June 7th, 2011 at 3:25 pm

The engines are still inspected quite frequently and that requires their dismounting in many cases.

The basic problem with the Orbiter maintenance is that it was NOT DESIGNED to be easily maintained. Not that it couldn’t have been, but that it wasn’t. The components were “supposed” to have very long life, and so the design features needed to allow them to be removed and replaced without enormous labor were not included. Imagine that 99% of your car engine parts lasted a long time, but the 1% that failed often were buried in the heart of the engine and you had to diassemble the whole engine to get at it. The 99% that works doesn’t help the average much….

All of this could be corrected in a second generation reusable system, applying lessons learned — as long as it were being designed by an organization which viewed high operating cost as a bug, rather than a feature.

So maybe engines with fast turnarounds are practical.

[maximlevitsky]

I know this is getting off topic, (but still to do with H2/O2 engine turn around - which is pertinent to Skylon). When I asked about it at Rand Simberg's place I got this about the SSME's

pennypincher Says:
June 7th, 2011 at 3:25 pm

The engines are still inspected quite frequently and that requires their dismounting in many cases.

The basic problem with the Orbiter maintenance is that it was NOT DESIGNED to be easily maintained. Not that it couldn’t have been, but that it wasn’t. The components were “supposed” to have very long life, and so the design features needed to allow them to be removed and replaced without enormous labor were not included. Imagine that 99% of your car engine parts lasted a long time, but the 1% that failed often were buried in the heart of the engine and you had to diassemble the whole engine to get at it. The 99% that works doesn’t help the average much….

All of this could be corrected in a second generation reusable system, applying lessons learned — as long as it were being designed by an organization which viewed high operating cost as a bug, rather than a feature.

So maybe engines with fast turnarounds are practical.

I have a feeling you have just hit a nail on its head.
And its so sad that shuttle is dismissed instead of being replaced with 2nd gen system.

I bet a 2nd gen shuttle could have being really cheaper to operate that conventional launch systems has that goal really being set.

But lets hope that Skylon replaces it and starts real space age.

[Downix]

The other thing about Skylon that is overlooked is their plans to turn a 450s H2/O2 rocket engine around in 2 days, this is a big deal, as such a quick turn around on a high Isp engine would revolutionize the economics of any reusable launch system with that feature.

Actually the next-stage SSME was to be capable of 60-hour turnaround times.  It is not that difficult to imagine Skylon, utilizing the same kinds of systems, achieving even faster turnaround times with their engine.

That's a bit of a leap of faith.

Not really, there's a paper on it in L2.  But the jist is, they learned lessons in why the SSME was so maintenance heavy, and they have been over the years replacing/redesigning the components to no longer require as much maintenance.  The Turbopumps, for example, only need removal once every 10th flight now.  They had it down to only three systems left with heavy maintenance, and the next upgrade to the SSME was to address those issues.  With the 2007 Block IIA upgrades, they put in a new system to monitor the status for operational support in place, the Health Management System.  Once they put the new nozzle, combustion chamber, and valves in place along with the turbopump nozzle alterations, the system will be very rugged and much simpler to maintain, and thanks to the HMS there is now real-time information in regards to system state, so they no longer need to completely disassemble big complex systems in order to verify if a system needs maintenance anymore.

The Block III SSME will be an incredible machine, higher performing and longer life.  The irony in having the program ready just as the shuttle is winding down.

[Downix]

I know this is getting off topic, (but still to do with H2/O2 engine turn around - which is pertinent to Skylon). When I asked about it at Rand Simberg's place I got this about the SSME's

pennypincher Says:
June 7th, 2011 at 3:25 pm

The engines are still inspected quite frequently and that requires their dismounting in many cases.

The basic problem with the Orbiter maintenance is that it was NOT DESIGNED to be easily maintained. Not that it couldn’t have been, but that it wasn’t. The components were “supposed” to have very long life, and so the design features needed to allow them to be removed and replaced without enormous labor were not included. Imagine that 99% of your car engine parts lasted a long time, but the 1% that failed often were buried in the heart of the engine and you had to diassemble the whole engine to get at it. The 99% that works doesn’t help the average much….

All of this could be corrected in a second generation reusable system, applying lessons learned — as long as it were being designed by an organization which viewed high operating cost as a bug, rather than a feature.

So maybe engines with fast turnarounds are practical.

You've almost hit it on the head.  The issue is not that 1% fail, but that 1% fails, and they never knew *which* 1% failed, hence a full engine disassembly.  In 2007, they outfitted the SSME's with a new Health Monitoring System which enables them to dissect component health in real-time, so now they knew exactly which parts needed to be replaced and when they did, rather than a complete disassembly. Block III would have pushed this even further, replacing the last of the 1970's era Shuttle components with new, modern, more rugged components.

[Cinder]

Taking the risk of a total bonehead suggestion but..  Would these be any use to Skylon?  For the truss framing perhaps?
http://www.bainitesteel.com/default.asp
The zip below is the powerpoint the jpg comes from.

[RobLynn]

Taking the risk of a total bonehead suggestion but..  Would these be any use to Skylon?  For the truss framing perhaps?
http://www.bainitesteel.com/default.asp
The zip below is the powerpoint the jpg comes from.

While Bainitic steels are cheap, there are higher specific strength materials out there in all temperature ranges.

Polyimide (eg RP46) carbon fiber composites might be the best bet, with strength to weight 2-3 times that of best metals, good burn resistance and useable up to about 350°C for a few hundred hours (ascent+reentry life of vehicle).  For hot areas some selection of nickel superalloys, Titanium Aluminide, carbon carbon composites, or maybe pyrosic (glass + silicon carbide fiber composite).

[Hempsell]

SKYLON C1 configuration was the last fully worked through design and the one evaluated by ESA and the System Requirements Review. Its mass breakdown is:

SKYLON C1 MASS BUDGET

ITEM                                                            Mass Estimate*   % of ToM

Dry Vehicle Mass (including all dry margins)          42,647 kg      15.5
Fluids including residuals and fluid margins             9,489 kg        3.5
Usable LH                                                           64,956 kg      23.6
Usable LOX                                                       147,934 kg      53.7
Payload (Target Payload 12,000 kg)                      10,275 kg        3.7

Mass at roll start                                                275,000 kg

C1 is now over 15 years old and clearly needed to be updated to reflect the results of the technology work and changing market conditions.  The start of the design revision process was to re-examine the payload requirements leading to an increase in target mass to 15 tonnes, a larger payload centre of mass variation, and a change to the payload bay dimensions.  We also went into much more detail on the payload interfaces.  We wanted to get public comment thorough the “User Manual” on the new payload provisions before we committed major effort on D1 so we scaled C1 by 1.25 (=15/12) to get to C2; hence 345 tonne take off mass.  It is not a worked through design but gives us a vehicle we can use to illustrate SKYLONS potential and try things out before we get the D1 configuration.

I have a confession: in the User Manual table 1 I am not sure all dimensions were scaled properly by the cube root of 1.25 and I have also found out that when I have asked designers how long SKYLON is they sometimes give the dimension to the tail fin end and sometimes to the OMS engine exit so you may find different length figures doing the rounds.

D1 will be a fully worked through design.  It is currently at 325 tonne ToM but that may change.

If you make SKYLON a pure rocket using the simplistic assumptions of SI =4500 m/s and you need 9500 m/s then the end of burn mass need to be 12%.  You will see on SKYLON it is nearly 23% and removing the compressors and pre-coolers does not get you anywhere near the required 12% so I am sceptical of the view that just using SKYLON’s structure technology alone without some other “magic” gets to a pure rocket solution.

Even if a pure rocket is feasible it will be in the 1000 tonne class (where most rocket SSTO studies end up) the 12% gives an end of burn mass of 125 tonnes.  Take off 15 tonnes of payload and 10 tonnes for consumable fluids leaves you with a 100 tonne dry mass vehicle - double SKYLON’s dry mass and correspondingly more expensive to develop.  The SABRE engine is not just a mass saver it is also a development cost saver.

[Jim Davis]

If you make SKYLON a pure rocket using the simplistic assumptions of SI =4500 m/s and you need 9500 m/s then the end of burn mass need to be 12%.  You will see on SKYLON it is nearly 23% and removing the compressors and pre-coolers does not get you anywhere near the required 12% so I am sceptical of the view that just using SKYLON’s structure technology alone without some other “magic” gets to a pure rocket solution.

Mr. Hempsell,

I think the reasoning goes along these lines:

Skylon has an overall O/F ratio of 2.27. A rocket has an O/F ration of 6. Therefore you can place 75% more propellant into a Skylon vehicle if it is a pure rocket. This brings the end of burn mass down to about 14.5% even before mass savings from lower engine mass, lower landing gear mass (due to vertical takeoff), lower dynamic pressure, etc. Since structural mass scales with propellant volume and not propellant mass that should be a wash.

Changing the subject:

Even if the British government had £10 billion burning a hole in its pocket that they wanted to spend on RLV development is it likely that they would hand REL a contract of that size? Wouldn't they be more likely to contract with BAE Systems and Rolls-Royce who would come up with their own design(s) which may bear little resemblance to Skylon and SABRE and which may or may not use REL heat exchangers?

Thanks for gracing these boards. It is much appreciated.

[baldusi]

Skylon has an overall O/F ratio of 2.27. A rocket has an O/F ration of 6. Therefore you can place 75% more propellant into a Skylon vehicle if it is a pure rocket. This brings the end of burn mass down to about 14.5% even before mass savings from lower engine mass, lower landing gear mass (due to vertical takeoff), lower dynamic pressure, etc. Since structural mass scales with propellant volume and not propellant mass that should be a wash.

Skylon uses the oxygen on air as oxidizer when in the atmosphere. So the O/F ration of the tanks is not the O/F of the engines. In that sense, it "cheats" at the rocket equation. If I'm not mistaken, most hydrolox rockets have O/F between 3.5~6. I don't know if the stoichiometric mixture of H2/LOX is 6 or 8, but you'd be surprised how many engines run fuel rich. An interesting question for Mr. Hempsell would be exactly how are the mixtures in the different phases of the engine.

Changing the subject:

Even if the British government had £10 billion burning a hole in its pocket that they wanted to spend on RLV development is it likely that they would hand REL a contract of that size? Wouldn't they be more likely to contract with BAE Systems and Rolls-Royce who would come up with their own design(s) which may bear little resemblance to Skylon and SABRE and which may or may not use REL heat exchangers?

I guess that if they pass the critical tests of the SABRE engine, something akin to Airbus would be formed, and the whole continent will make it a flag program. You'd probably see all the usual suspects one way or the other, in proportion to the money invested by their home country (so you could count on Thales Aliena, BAE, EADS, etc.) They will probably invest "small amounts" for a more serious studies phase for five years. And after that, they will barter a big conglomerate, akin to Arianespace or Airbus, but obviously with a higher participation of the UK. Ironically, if BAE wouldn't have sold it's Airbus share, it would probably be the perfect vehicle for this development. But what I say is pure speculation.

[Lampyridae]

The other thing about Skylon that is overlooked is their plans to turn a 450s H2/O2 rocket engine around in 2 days, this is a big deal, as such a quick turn around on a high Isp engine would revolutionize the economics of any reusable launch system with that feature.

Actually the next-stage SSME was to be capable of 60-hour turnaround times.  It is not that difficult to imagine Skylon, utilizing the same kinds of systems, achieving even faster turnaround times with their engine.

The Shuttle still had other systems not as capable of such rapid turnaround, but the overall processing time, had the full strength of the logistical upgrades been applied, would have been reduced to a matter of weeks rather than months.

There will probably be a similar learning curve with Skylon. It'll be some time before flight rates get to needing the "2 day turnaround" stage.

The engines are in quite accessible locations, and the vehicle itself is not so huge as to require a VAB to service. No crawler, no pad, no range evacuation, no barges, just use regular hangars... VTVL is really the way to go to cut costs. Even if pure rocket solutions were mass-competitive, then there would still be these extra costs.

[simonbp]

As adrianwyard points out the black TPS is actually a reinforced high temperature glass (such Pyrosic from Pyromeral Systems)

Skylon: The British Black-Glass Zeppelin That Will Ride Columns of Steam to Outer Space In An Inventive New Fashion!

Sounds rather steampunk/Isambard Kingdom Brunel-ish if you phrase it like that...

[Downix]

As adrianwyard points out the black TPS is actually a reinforced high temperature glass (such Pyrosic from Pyromeral Systems)

Skylon: The British Black-Glass Zeppelin That Will Ride Columns of Steam to Outer Space In An Inventive New Fashion!

Sounds rather steampunk/Isambard Kingdom Brunel-ish if you phrase it like that...

Needs more brass fittings!!

[Lampyridae]

As adrianwyard points out the black TPS is actually a reinforced high temperature glass (such Pyrosic from Pyromeral Systems)

Skylon: The British Black-Glass Zeppelin That Will Ride Columns of Steam to Outer Space In An Inventive New Fashion!

Sounds rather steampunk/Isambard Kingdom Brunel-ish if you phrase it like that...

Needs more brass fittings!!

Built by a league of extraordinary gentlemen!