Author Topic: The Reaction Engines Skylon Master Thread (1)  (Read 328287 times)

Offline adrianwyard

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Re: Skylon
« Reply #320 on: 07/02/2011 05:07 PM »
Annex B of the Users Manual covers a proposed Skylon Upper Stage that can in some cases be recovered and brought back for refueling and re-use:

http://www.reactionengines.co.uk/downloads/SKYLON_User_Manual_rev1-1.pdf

They have an animation of it, including recovery, here:

http://www.reactionengines.co.uk/skylonreview_commercial.html

Online 93143

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Re: Skylon
« Reply #321 on: 07/02/2011 05:40 PM »
Similarly, does suborbital release of the upper stage augment payload to orbit?

Yes.  IIRC it about doubles it from the baseline Skylon, but it dramatically increases the cost (you're expending an upper stage), so it's not worth it unless you really need that much payload in one chunk...

Offline tnphysics

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Re: Skylon
« Reply #322 on: 07/03/2011 04:05 AM »
Well, some payloads ARE their own upper stage, at least if provided with extra propellant (they must have thrusters that can do this job for other reasons).

Other question: What about transferring heat from the heated (post-precooler) helium to the high pressure (pre-turbine) hydrogen via another heat exchanger? The idea is to allow far higher hydrogen outlet temps, and thus allow less of it to be used.

Offline john smith 19

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Re: Skylon
« Reply #323 on: 07/04/2011 08:49 AM »
I've been following this topic and joined to comment on it. I'm new to this forum but have followed RE since their article in Spaceflight in 1989.

Ramjets. In one of their kickoff papers RE make it clear that following the review of HOTOL they decided that any propulsion system would have to be testable on "open" facilities. Jet engines can start from rest and don't need a forced air blower in front of them. So no ramjets, pulsejets or anything close to them.

I'd hoped to reference the paper but the REL website is up the spout.

"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 Hempsell

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Re: Skylon
« Reply #324 on: 07/06/2011 03:26 PM »

Everyone seems on top of upper stages to augment the basic SKYLON capability issue and it encouraging that people can find answers to such questions in the User Manual.  . 

A point on the SKYLON Upper Stage.  The dry mass in the User Manual did not survive a re-examination of the SUS and better figures are in a paper

Mark Hempsell and Alan Bond “Technical and Operations Design of the SKYLON Upper Stage” Journal of the British Interplanetary Society (JBIS) Vol 63 pp136-144 , 2010

Which I am afraid is not on our website.  The figures now are SI 4560 N S/kg EOL mass 1500 kg max fuel load 7500 kg with a GTO payload of 5,309 kg in reusable mode and 7,750 kg in expendable mode.

Re Archibald’s question: we could carry any stage within the mass limits although existing stages will either need an adaptor or need to be adapted to the SKYLON interface.  We hope like the Shuttle before Challenger there will be several competing upper stages.  If you are deploying an expendable stage, and SKYLON only needs to stay up for an orbit or two, then the orbit can be lowered to 190 km altitude.  This raises the carry mass to around 16 tonnes. 

I think I am with tnphysics in that suborbital deployment with an expendable upper stage might make sense if you were using an expendable stage anyway.  I have also wondered (but not explored) whether a Space Station core could use its orbit make up propulsion system to reach orbit after sub-orbital deployment.  It will be interesting to see how often this suborbital mode is used - a subject of several over lunch debates here and hard cash will be changing hands when this is known.

Offline baldusi

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Re: Skylon
« Reply #325 on: 07/06/2011 03:33 PM »
Which I am afraid is not on our website.  The figures now are SI 4560 N S/kg EOL mass 1500 kg max fuel load 7500 kg with a GTO payload of 5,309 kg in reusable mode and 7,750 kg in expendable mode.

That's with 1500m/s or 1800m/s of delta-v deficit? BTW, what would be the maximum payload size?

Offline Hempsell

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Re: Skylon
« Reply #326 on: 07/06/2011 03:35 PM »

Other question: What about transferring heat from the heated (post-precooler) helium to the high pressure (pre-turbine) hydrogen via another heat exchanger? The idea is to allow far higher hydrogen outlet temps, and thus allow less of it to be used.

I am afraid (like your previous proposal) without diagrams I am not quite sure what you mean.  The hydrogen does not drive the main compressor turbine (it did in the old HOTOL RB545 engine).  It does drive its own (i.e. the hydrogen pump) and the He circulation pump; an arrangement that means the engine can be started (which we judged to be an important feature of a operational engine). But this is already after we have exchanged heat with the helium.

Offline Hempsell

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Re: Skylon
« Reply #327 on: 07/06/2011 03:42 PM »
I've been following this topic and joined to comment on it. I'm new to this forum but have followed RE since their article in Spaceflight in 1989.

Ramjets. In one of their kickoff papers RE make it clear that following the review of HOTOL they decided that any propulsion system would have to be testable on "open" facilities. Jet engines can start from rest and don't need a forced air blower in front of them. So no ramjets, pulsejets or anything close to them.

I'd hoped to reference the paper but the REL website is up the spout.



I think the paper you are looking for is

Richard Varvill and Alan Bond “A Comparison of Propulsion Concepts for SSTO Reuseable Launchers”, Journal of the British Interplanetary Society (JBIS),Volume 56, pp. 108-117, 2003

It is on our website Media Library – pdf downloads and it was working just before I posted this. I am sorry if it gave you trouble.

Of course, we do have a bypass ramjet and this cannot be verified by static testing alone, but we are being pessimistic in its performance estimates and we will have a flying test bed to ensure we have it right.

Offline adrianwyard

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Re: Skylon
« Reply #328 on: 07/07/2011 01:27 AM »
Anticipating the Naysayers.

Even as Skylon continues to make good progress on technical issues, it's going to face an uphill battle as it tries to break out of the 'advanced concepts' research category and into the commercial space launch category. Airbreathing SSTO is just not fashionable today, and many would say that's for good reason; we're back to favoring big dumb boosters and capsules. Naysayers could also argue that Skylon has not learned some hard lessons from recent aerospace accidents:

Like the Shuttle, it has cryogenic temp tanks (i.e. potentially ice) upstream of delicate carbon-carbon wing leading edges, the rudder, etc.
Like the Concorde, it has fuel-tanks (and TPS) behind highly loaded tires that can burst and shed debris.
Like Captain Scully's Airbus, it is vulnerable to bird strikes.

And there are always the standard SSTO cautions, notably: small increases in mass can eat all your payload. With Skylon, the TPS/airframe area is so large that any last minute need to redesign it to increase strength or add thermal capacity could leave it unable to reach orbital velocity.

So, having painted a negative picture, what are the responses?

Icing doesn't seem that hard to resolve. Some well-placed thermal cameras on the apron, and a very long-handled broom (or high-tech equivalent) should sort that out. My guess is the hazard drops quickly after takeoff as speed and skin temp increases.

A Concorde-style accident has two elements, runway debris and burst-tire-debris damage. Ensuring a long runway is free of the smallest piece of debris sounds like an arduous task, but compared to the other challenges of reaching orbit,  it's a piece of cake. Perhaps a special vehicle with a scanning laser could head down the runway just before a launch to confirm it's clear. If a tire bursts on its own, then this must trigger an abort. The remaining wheels will have to do all the braking. Sensing this has happened should be easy. 

In the worst case scenario, a burst tire can send high-velocity rubber chunks into a pressurized hydrogen or oxygen tank. Not good. However, the current design has the wheels quite far outboard of the fuselage, so only a fraction of tire bursts would hit the fuselage. Perhaps there is enough room to add guards that would deflect debris heading that way. If really necessary, these guards could be jettisoned after take-off.

Unlike a vertically launched vehicle Skylon travels very fast through a considerable amount of low-altitude air. I'm guessing that any bird strikes at all are a considerable hazard, whether they be to the fore-planes, the nose/front tank, the rudder, wings, or if ingested into an engine. While not a high-tech challenge, this seems to be a tough problem to solve completely.  I'd welcome any ideas on how to address this. Bird-lovers will surely protest its use, but I wonder if an airborne version of http://en.wikipedia.org/wiki/Active_denial_system would be needed to clear the corridor beyond the runway.

And finally, with an upper stage, the Skylon might remain viable even if it's 1.0 version fails to reach orbital velocity.

Apart from the bird-stike hazard, I think I've presented some pretty reasonable responses to these criticisms of the Skylon design. If you were attempting to pitch Skylon as equivalent to a passenger airliner, then having to check the runway is squeaky clean before each takeoff that would indicate a failure, but that's a false analogy, and this class of problem really doesn't detract from the Skylon's potential as a space launch system.

Anyone care to suggest ways of clearing birds out of the way? Or maybe the hazard isn't that great?

Online 93143

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Re: Skylon
« Reply #329 on: 07/07/2011 02:19 AM »
And there are always the standard SSTO cautions, notably: small increases in mass can eat all your payload. With Skylon, the TPS/airframe area is so large that any last minute need to redesign it to increase strength or add thermal capacity could leave it unable to reach orbital velocity.

Actually, since Skylon is an airbreathing SSTO, it's much less sensitive to either mass growth or engine underperformance than a "standard SSTO".

Skylon C1's airframe (without the engines, hydraulics, undercarriage, etc.) weighed 20 tonnes with the nacelles included, or 16 tonnes without.  The payload was supposed to be 12 tonnes, and a D1 that size would likely have met or exceeded that specification.

An airframe design that needs a 60% mass boost to deal with contingencies is a bad design.

Offline Hempsell

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Re: Skylon
« Reply #330 on: 07/07/2011 09:05 AM »
Which I am afraid is not on our website.  The figures now are SI 4560 N S/kg EOL mass 1500 kg max fuel load 7500 kg with a GTO payload of 5,309 kg in reusable mode and 7,750 kg in expendable mode.

That's with 1500m/s or 1800m/s of delta-v deficit? BTW, what would be the maximum payload size?

The GTO figures are for an orbital plane with an inclination the same as the launch site so the apogee insertion requirement (which the spacecraft has to do) depends upon the launch site latitude.  In reality there is a small performance loss in GTO mass as the latitude increases but this is as second order effect, our numbers are calculated from an equatorial site.

The payload envelopes are defined in the User Manual but roughly with a recovered SUS the satellite has a 4.8 m dia by 5.3 m cylinder and in expendable mode (but still with the USIS interface) the length goes up to 8.4m.

Offline tnphysics

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Re: Skylon
« Reply #331 on: 07/08/2011 04:35 AM »

Other question: What about transferring heat from the heated (post-precooler) helium to the high pressure (pre-turbine) hydrogen via another heat exchanger? The idea is to allow far higher hydrogen outlet temps, and thus allow less of it to be used.

I am afraid (like your previous proposal) without diagrams I am not quite sure what you mean.  The hydrogen does not drive the main compressor turbine (it did in the old HOTOL RB545 engine).  It does drive its own (i.e. the hydrogen pump) and the He circulation pump; an arrangement that means the engine can be started (which we judged to be an important feature of a operational engine). But this is already after we have exchanged heat with the helium.

Well, let me describe it in detail.

After the turbine, the helium passes through a heat exchanger that heats the hydrogen. The hydrogen exits this heat exchanger at a certain temperature.

The idea is actually quite simple, at least in theory (though I am sure not in practice). The idea is that some of the helium (instead of entering the turbine) is shunted into another heat exchanger and then into the last He compressor stage. This heat exchanger heats the hydrogen a second time. The hydrogen then enters its turbine in the usual way.

The net result is that some more heat is shunted from the air to the same amount of H2 -> less H2 needed for a given cooling effect ->higher Isp.

Offline tnphysics

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Re: Skylon
« Reply #332 on: 07/08/2011 04:37 AM »
I've been following this topic and joined to comment on it. I'm new to this forum but have followed RE since their article in Spaceflight in 1989.

Ramjets. In one of their kickoff papers RE make it clear that following the review of HOTOL they decided that any propulsion system would have to be testable on "open" facilities. Jet engines can start from rest and don't need a forced air blower in front of them. So no ramjets, pulsejets or anything close to them.

I'd hoped to reference the paper but the REL website is up the spout.



I think the paper you are looking for is

Richard Varvill and Alan Bond “A Comparison of Propulsion Concepts for SSTO Reuseable Launchers”, Journal of the British Interplanetary Society (JBIS),Volume 56, pp. 108-117, 2003

It is on our website Media Library – pdf downloads and it was working just before I posted this. I am sorry if it gave you trouble.

Of course, we do have a bypass ramjet and this cannot be verified by static testing alone, but we are being pessimistic in its performance estimates and we will have a flying test bed to ensure we have it right.


Suppose the ramjet Isp turned out to be better than expected. What would be the improvement in payload?

Offline john smith 19

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Re: Skylon
« Reply #333 on: 07/10/2011 06:28 PM »
Quote
I think the paper you are looking for is

Richard Varvill and Alan Bond “A Comparison of Propulsion Concepts for SSTO Reuseable Launchers”, Journal of the British Interplanetary Society (JBIS),Volume 56, pp. 108-117, 2003

It is on our website Media Library – pdf downloads and it was working just before I posted this. I am sorry if it gave you trouble.

Of course, we do have a bypass ramjet and this cannot be verified by static testing alone, but we are being pessimistic in its performance estimates and we will have a flying test bed to ensure we have it right.


That's it. I found a way into the site after I posted. I'd hoped the layout was not working pending an announcement of the precooler tests.

Concerning the potential heating issues due to interference between canards/fuselage and nacelle/wing I recall that REL has done work on silicon carbide heat exchanger pipes and wondered if they could be adapted into a heat pipe arrangement to spread the leading edge heat load.

While I am aware of at least 1 reentry test of a transpiration cooled nose cone (and none of a heat pipe system) A heat pipe system does have the virtue of keeping the fluids separated in a closed loop and could leverage substantial development over a range of temperatures and industries.

Obviously this is a non starter if the pipes can't handle sodium vapor in the way superalloys can but if they can this could be a rugged reliable solution that eliminates the topping up of a transpiration system.
"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 john smith 19

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Re: Skylon
« Reply #334 on: 07/10/2011 10:09 PM »
Anticipating the Naysayers.

"Like the Shuttle, it has cryogenic temp tanks (i.e. potentially ice) upstream of delicate carbon-carbon wing leading edges, the rudder, etc."
No. Skylon is not a stressed skin design like the shuttle ET or Delta IV. The tanks sit *inside* the fuselage with a layer of PU foam thick enough to prevent O2 condensation (IIRC it's designed to be thick enough to stop *water* condensation on the outside of the tanks).

"Like the Concorde, it has fuel-tanks (and TPS) behind highly loaded tires that can burst and shed debris."
True. Note the Shuttle has never had a tire failure and it's tire technology used Nylon reinforcement dating from the 1970s (very low technology risk). Concorde had one fatal accident in 27 years of operation.

Like Captain Scully's Airbus, it is vulnerable to bird strikes.
More like an SR71. Unlike turbo fans any bird strikes have to hit the inlet spike and bounce around inside the nacelle to hit the heat exchanger or other vulnerable parts. More likely it will be toasted by the spill ramjet in the exit area.

And there are always the standard SSTO cautions, notably: small increases in mass can eat all your payload.
A standard issue with VTOL SSTO. The wings make Skylon a bit less vulnerable in this area.

"With Skylon, the TPS/airframe area is so large that any last minute need to redesign it to increase strength or add thermal capacity could leave it unable to reach orbital velocity."
Like *all* SSTO concepts of any decent size this actually means you'd have to cut the payload or eat into the weight growth margins, which is what the margins are there for.

"A Concorde-style accident has two elements, runway debris and burst-tire-debris damage. Ensuring a long runway is free of the smallest piece of debris sounds like an arduous task, "
It's a routine part of aircraft carrier operations where a skirmish line walks the deck looking for foreign object damage FOD. the spaceport operator would probably automate it with basically a giant vacuum cleaner.

In the worst case scenario, a burst tire can send high-velocity rubber chunks into a pressurized hydrogen or oxygen tank.
Again only after it's penetrated the fuselage. Note the skin is designed to give on impact and "pressurized" in this case is likely to be in the range 10-20 psig, which REL will be aiming to keep as low as possible.
Concorde flew for 27 years without a fatal (or even major) accident *despite* the close proximity of engines to wheels.

"Not good. However, the current design has the wheels quite far outboard of the fuselage,"
Also the wheels are in parallel with the engines, leaving any shedding rubber possibly hitting the back of the fuselage. This leaves the nose wheels.

"so only a fraction of tire bursts would hit the fuselage.Perhaps there is enough room to add guards that would deflect debris heading that way. If really necessary, these guards could be jettisoned after take-off."
Probabilistic risk assessment is the process of balancing likely hood of outcome against result of it happening. I'll guess they have used the Concorde data (and the Tu144 if any exists) on this and have chosen to live with the risk. Perfect safety is *never* possible. Autoland systems on aircraft are designed for 1 failure in every 1 billion uses of the specific system. Not perfect buy highly unlikely.

"Unlike a vertically launched vehicle Skylon travels very fast through a considerable amount of low-altitude air."
But quite like any military jet capable of >M1, and of course the SR71.
" I'm guessing that any bird strikes at all are a considerable hazard,"
Yet somehow these vehicles seem to survive them. You might like to look at how many Canadian geese you find flying around the equator.

And finally, with an upper stage, the Skylon might remain viable even if it's 1.0 version fails to reach orbital velocity.

"Apart from the bird-stike hazard, I think I've presented some pretty reasonable responses to these criticisms of the Skylon design."
The points you are concerned about were covered in various reports on the REL website.

" If you were attempting to pitch Skylon as equivalent to a passenger airliner,"
Which they are not. Passenger transport is considered *possible* not something any purchasers will be doing from day one. FAA rules on passenger describe them as "Spaceflight participants," rather than astronauts. I'm not sure CAA guidelines exist on this matter.

"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 tnphysics

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Re: Skylon
« Reply #335 on: 07/14/2011 09:22 PM »
Okay. What is the schedule for SKYLON? How likely is it to be built?

Offline john smith 19

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Re: Skylon
« Reply #336 on: 07/16/2011 09:56 AM »
Okay. What is the schedule for SKYLON? How likely is it to be built?

An outline of their planned schedule is here.
http://www.reactionengines.co.uk/skylon_dev.html

Most of their recent development work would probably fall under the "proof of concept" stage. As to how likely it is to be built RE have stated that a successful pre-cooler test phase (which ran through June) would result in the release of £200m in development funds.  Which is pretty serious money by alt-space standards.

As of now it's the only independently designed and funded major space project to have been a detailed audit done on it by ESA (published) and survive challenge by a 100 strong 2 day requirements review by aerospace engineers from around the world (due to be published by the UK Space Agency).

Note that UK engineering and mfg companies tend to very cautious about reporting preliminary results, especially results which are critical to their future, until they have competed detailed analysis.

As RE is a)a privately held company b) a UK mfg & engineering company and c) Running tests whose outcome are critical to its future expect some delay in releasing results as informing their investors will be a priority.

RE's approach is nearest to XCor in the US but it's approach to business is more like that of Blue Origin.

Hempsell may post more but is probably involved with part of the analysis.
"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

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Re: Skylon
« Reply #337 on: 07/16/2011 05:50 PM »
John, thanks for responding to my post. I think you've assumed I'm a Skylon "naysayer" which is very far from the truth. Discussion around advanced concepts tends to be polarized into two camps: cheerleading fans and dismissive critics. If a concept makes it to production, the reality rarely bares any resemblance to this prior hype/dismissal. A concept that looks good even when the hype has been subtracted is one everyone should pay attention to. I'm trying to have that sober discussion.

As your answers indicate, the best actual answers to my concerns are not bullet-points, but in the form of statistical projections. Bird-strike risk is a good example here. Skylon will not be indestructible. Nor will it fall out of the sky when a bird poops on it. As you say, flight history of supersonic jets (e.g. SR-71s and Concorde) should give us some confidence. Although there are differences: commercial jets are designed such that a typical bird-strike will be a maintenance issue after landing. With Skylon, any bird-strike would trigger an abort. So even if the vast majority of strikes are recoverable, it might be an operations issue that Skylon is subject to where conventional rockets are not.

I have read many of the documents at the REL site, but not yet found the documents you refer to that address this and my other points. If you have them handy, please post the links.

With burst tire risks it's the same story. If stats are on your side, then this should satisfy the naysayers. Shuttle data gives you good confidence. (But Concorde burst tire data is less rosy.)

On the subject of hype: in my post I stated that it's asking for trouble to compare Skylon with commercial (cargo or passenger) airlines, and here we agree. However, in the "commercial" promotional video at the REL web site, they depict a fleet of Skylons at what appears to be a commercial airport - there are A380s there. It's a minor criticism since we are so early in the project. Generally speaking I'm very encouraged by the realistic stance of REL. For example, stating a realistically high development cost, long test schedule, and that they are planning on the failure of a number of Nacelle Test Vehicles, all give me confidence this might actually happen.

Offline tnphysics

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Re: Skylon
« Reply #338 on: 07/16/2011 07:35 PM »
Will the engines be capable of operation on a different vehicle (with appropriate integration work)? There might be applications for this (boosting a larger vehicle comes to mind).

Offline KristianAndresen

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Re: Skylon
« Reply #339 on: 07/16/2011 09:01 PM »
Here are a couple of posts about Skylon by "Goatguy" at http://nextbigfuture.com/2011/02/skylon-spaceplane.html:

Quote
I know that amongst the British team, they're committed to the ideal of a one-body flight vessel, but the three main things I can see that would really get the payload fraction up (without compromising the use of commercial runways, rapid turn-around of flights and remarkable economy) are

1. JP-7 "traction shell" -- a la SpaceX, a conventional titanium wing and SR-71 Blackbird engines to cover the ground-to-60,000 feet at Mach 6. There are dozens mothballed, and are magnificent billion-dollar engineering marvels. Use 'em. They also cover both turbo and ram-jet operational modes. Use 'em. When the payload (the Skylon) is at altitude... fire its engines, and peel away. The traction pilot lands conventionally.

2. Solid rocket hypersonic insertion -- Next, fire up a set of SRBs. Push the bird to a steep angle of ascent, and get to Mach 12. Drop the SRBs. SRBs have winglets and return "almost" to base, parachuting the last 5000 feet into a body of water. Saves a lot of money recovering by Navy way out at sea.

3. Hydroplane landing -- While this challenges the "commercial runway" idea (which is a farce anyway), few spaceports couldn't be outfitted with a hydroplane landing strip. 6 inches of water, 100 meters wide, 2,500 meters long. The landing gear are just pontoons of a sort - without even the need to be hollow as there isn't enough water to sink into. Curved hydrodynamically to spray water laterally, there becomes no need for heavy landing gear. Skid-stop.

These answer to a lot of technical problems that the British team has engineered sub-optimal ways around. Taking off with tons of water (for cooling the brakes in an emergency take-off abort), and having landing gear that is strong (heavy) enough for the whole mission is just a big compromise. The skids shouldn't be more than 10% of the weight of landing gear. All that mass becomes payload.

Likewise, 100% of the hydrogen NOT consumed getting from zero to Mach 6 becomes payload. The traction craft has conventional "big tire" landing gear, can effect a safe abort, uses MUCH less expensive JP-7, utilizes already-engineered ramjet engines, and improves the economy markedly. Even in its special formulation, JP-7 is 1/20TH the cost of liquid hydrogen for 1 unit of energy.

Finally the use of SRBs again serves the purpose of taking the majority of the "dead weight" (unburned fuel) and gives it a big old kick in the butt without needing to burn so much of it.

The same SKYLON craft very well could make it on its fuel all the way to MEO or even Geosynchronous. Or, with all that tankage - it could just transfer all its excess hydrogen and oxygen to orbital tanks for other missions to use for satellite transfer and the like. There is ALWAYS use for "extra" hydrogen and oxygen in orbit.

The use of "conventional" runways is undermined by (a) the teams acknowledged high-loading on tiny landing wheels, and (b) by the need for special hydrogen storage, delivery, firefighting and substance control at the airport. No, the "conventional" side is just that a military-grade or aerospace port would be required, with all its attendant specializations. This is not to say that a NEW airport would need to be made, no. Just special.

[...]

The traction shell is really a formal first stage. I don't imagine there is a compelling reason to burn both the JP7 and the hydrogen (first and second stages ganged) since the winged traction shell would gain altitude using aerodynamic lift instead of raw impulse. Might just as well save the hydrogen, and use a smaller (lighter) tank.

I don't think there is a downside for having wings on the second (orbital) stage both for rarefied-atmosphere lift, and for conventional runway recovery. They do add weight, but with the traction shell is going to out-weigh the orbital stage probably by 2× to 3× It can afford to be a muscular meatball - aerodynamics is going to be the lever that converts its thrust to potential (altitude) energy.

Most "rocket scientists" propose getting as high as possible quickly - because that is the 60+ year convention of rocket science, not because the alternate lifting-body dynamics makes substantially less sense. Even in the 1950s, rocketry professionals. were considering aerodynamic body dual-mode systems such as I advocate. There were two main problems which had no technological answer: engines that were efficient enough to run in the 50,000-to-200,000 ft stratosphere at super-to-hypersonic speed, and airframe materials simultaneously light-weight, thermally stable, strong and inert enough to serve aeroframe duty under the extraordinary thermal, pressure and flexure regime of "near space".

That picture has now changed. The magnificent work alone by the Japanese through the 1980s-to-2000 (and not over by any means!) in creating outrageously durable, tough, resilient refractory ceramics is the key to the "leading edge" problem both for high-atmosphere aerodynamic loading on launch, and the very-high atmosphere compression on reëntry. These same ceramics make possible cowlings and compression cones for the hybrid ramjet/scramjet engines that in turn power the whole thing well into the mesosphere (200,000 to 500,000 ft or 60-150 km).

So I claim that it is the convergence of exemplary materials properties and a new generation of "rocket scientists" that can now explore such unconventional designs. Ultimately, we are heading toward space ports of the type only imagined by science-fiction writers of the 1950s.

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RAM/SCRAM jet engines suffer from the very riches that make them such compelling designs. The faster the inlet airstream, the higher the compression that can be achieved within the speed-of-sound cone. The problem is [ PV = nrT ] ... which implies that as pressure goes up (and volume goes down), that temperature will inevitably need to rise (in an adiabatic system). The gasses are rushing into the compression system well above the speed of sound, so the compression doesn't have any time to become non-adiabatic (i.e. to lose heat).

The current strategy - as I understand it - is to try to cool the airflow using heat exchangers, which given the speed of gas-flow, seems hopelessly optimistic. Maybe its not - after all, the Shuttle's (and virtually every rocket ever made) uses the cryogenic oxygen and/or hydrogen to cool the expansion cone and interior of the engines (along with a "film" of unburned fuel). The one way by which it could work out well for the hybrid engine would be if the amount of liquid oxygen is increased, and it is sprayed directly into the compressed inflowing air. The enrichment wouldn't hurt the hydrogen burn, and it would definitely cool the stream.

In any case, one of the most compelling reasons for going "two stage" with a traction lifter is that the kind of engine can be optimized for its operating regime. The orbital stage can have its no-spinning-parts SCRAMJET engine (which is magnificent, and highly efficient), which would be much lighter weight, and much more free from the problems of supersonic compression and heat dissipation. Indeed - I'm unable to muster a single compelling reason to try to make a single engine perform both duties.

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