The Skylon Space Plane - One step closer

[Zac Naloen]

Link: http://news.nationalpost.com/2012/11/28 ... ny-claims/

As a Brit I have no small amount of pride that a British company is behind this technology, I just hope they can reach the next mile stone and actually build the engine and then have some successful test flights. An actual space plane is still a long way off. But each milestone successfully reached gets the excitement levels up just that little bit more.

LONDON — A small British company with a dream of building a re-usable space plane has won an important endorsement from the European Space Agency (ESA) after completing key tests on its novel engine technology.

Reaction Engines Ltd believes its Sabre engine, which would operate like a jet engine in the atmosphere and a rocket in space, could displace rockets for space access and transform air travel by bringing any destination on Earth to no more than four hours away.

That ambition was given a boost on Wednesday by ESA, which has acted as an independent auditor on the Sabre test program.

“ESA are satisfied that the tests demonstrate the technology required for the Sabre engine development,” the agency’s head of propulsion engineering Mark Ford told a news conference.

“One of the major obstacles to a re-usable vehicle has been removed,” he said. “The gateway is now open to move beyond the jet age.”

The space plane, dubbed Skylon, only exists on paper. What the company has right now is a remarkable heat exchanger that is able to cool air sucked into the engine at high speed from 1,000 degrees Celsius to minus 150 degrees in one hundredth of a second.

This core piece of technology solves one of the constraints that limit jet engines to a top speed of about 2.5 times the speed of sound, which Reaction Engines believes it could double.


SHROUDED IN SECRECY

With the Sabre engine in jet mode, the air has to be compressed before being injected into the engine’s combustion chambers. Without pre-cooling, the heat generated by compression would make the air hot enough to melt the engine.

The challenge for the engineers was to find a way to cool the air quickly without frost forming on the heat exchanger, which would clog it up and stop it working.

Using a nest of fine pipes that resemble a large wire coil, the engineers have managed to get round this fatal problem that would normally follow from such rapid cooling of the moisture in atmospheric air.

They are tight-lipped on exactly how they managed to do it.

“We are not going to tell you how this works,” said the company’s chief designer Richard Varvill, who started his career at the military engine division of Rolls-Royce. “It is our most closely guarded secret.”

The company has deliberately avoided filing patents on its heat exchanger technology to avoid details of how it works – particularly the method for preventing the build-up of frost – becoming public.

The Sabre engine could take a plane to five times the speed of sound and an altitude of 25 km, about 20% of the speed and altitude needed to reach orbit. For space access, the engines would then switch to rocket mode to do the remaining 80%.


WikimediaCG rendering of the proposed Skylon vehicle climbing through the atmosphere.G rendering of the proposed Skylon vehicle climbing through the atmosphere.

IT COULD EVEN MAKE THE TEA

Reaction Engines believes Sabre is the only engine of its kind in development and the company now needs to raise about 250 million pounds ($400-million) to fund the next three-year development phase in which it plans to build a small-scale version of the complete engine.

Chief executive Tim Hayter believes the company could have an operational engine ready for sale within 10 years if it can raise the development funding.

The company reckons the engine technology could win a healthy chunk of four key markets together worth $112-billion a year, including space access, hypersonic air travel, and modified jet engines that use the heat exchanger to save fuel.

The fourth market is unrelated to aerospace. Reaction Engines believes the technology could also be used to raise the efficiency of so-called multistage flash desalination plants by 15%. These plants, largely in the Middle East, use heat exchangers to distil water by flash heating sea water into steam in multiple stages.

The firm has so far received 90% of its funding from private sources, mainly rich individuals including chairman Nigel McNair Scott, the former mining industry executive who also chairs property developer Helical Bar.

Chief executive Tim Hayter told Reuters he would welcome government investment in the company, mainly because of the credibility that would add to the project.

But the focus will be on raising the majority of the 250-million pounds it needs now from a mix of institutional investors, high net worth individuals and possibly potential partners in the aerospace industry.


STANDING START

Sabre produces thrust by burning hydrogen and oxygen, but inside the atmosphere it would take that oxygen from the air, reducing the amount it would have to carry in fuel tanks for rocket mode, cutting weight and allowing Skylon to go into orbit in one stage.

Scramjets on test vehicles like the U.S. Air Force Waverider also use atmospheric air to create thrust but they have to be accelerated to their operating speed by normal jet engines or rockets before they kick in. The Sabre engine can operate from a standing start.

If the developers are successful, Sabre would be the first engine in history to send a vehicle into space without using disposable, multi-stage rockets.

Skylon is years away, but in the meantime the technology is attracting interest from the global aerospace industry and governments because it effectively doubles the technical limits of current jet engines and could cut the cost of space access.

The heat exchanger technology could also be incorporated into a new jet engine design that could cut 5 to 10 percent — or $10-20 billion — off airline fuel bills.

That would be significant in an industry where incremental efficiency gains of 1% or so, from improvements in wing design for instance, are big news.

[Sea Skimmer]

This engine concept goes back to 1950s US work, it was completely absurd then, still pretty absurd now. On the other hand anything that may involve hydrogen slush is fucking awesome. I forget if SABRE is going to try to spill the CO2 and nitrogen overboard, this is the optimal way to make LACE work so you only have to liquefy the oxygen. Its also the most complicated approach, but that might be needed since no scramjet is involved to bridge the turbofan-rocket gap. Either way, good luck too them, they'll need it.

[Zac Naloen]

They aren't liquefying the air in this engine while pre-cooling. The engineering of how that will work is over my head though.

[Zac Naloen]

Also, it doesn't look they are dumping CO2 and Nitrogen. It's not really a LACE engine at all.

[Crayz9000]

The design, from what I understand, will not rely on nitrogen for its cooling stage in the actual engine. They only used a nitrogen boiler because it was more practical here on the ground.

The cooling loops are two-stage: The in-engine stage will be a closed loop exchanger operating with liquid helium. That loop will then exchange its heat with the hydrogen fuel, which is then promptly burned in the engine.

[Sky Captain]

If wikipedia is correct this type of engine don't liquefy air it only cools it so the heat generated by compression don't melt the turbine.
Hope they succeed because this technology could put the Europe in forefront in space launch business.

[Sea Skimmer]

Well if it isn't LACE with net mass increase in flight, then I now understand why people call the project unworkable bullshit then, because it probably is even if the engine itself ever works.

[Crayz9000]

Here's a simplified coolant loop diagram:



Basically the main differences between SABRE and LACE are the closed-loop helium heat exchange system, and the lower pressure of the cryogenic hydrogen fuel. SABRE isn't trying to liquefy the incoming air, only compress it slightly above the liquefaction point. Expansion of the liquid hydrogen provides all the cooling needed.

[The Duchess of Zeon]

Yeah, SABRE is a serious, viable concept, the work was originally started by the British government in the 1960s for a spaceplane proposal, Skimmer, and the engineers who were working on it have been running a low-order research company trying to finish making it work ever since the project got cancelled, so it wasn't just some random person's idea, it was actually a government project which was historically cancelled, but more or less actually switched to the civilian market. The project then evolved into the BAe-Rolls Royce collaborative effort for a spaceplane to meet the shuttle requirements (the original ones the shuttle never met), but as single-stage-to-orbit. It was cancelled in 1988 by the Conservative government as a cost-cutting measure and since then it's been done as a private venture anyway.

Essentially, SABRE is doing LACE-without-mass-increase on the cheap by running air at very high pressure into the reaction chamber with the liquid hydrogen, instead of liquifying it entirely. It's actually more plausible to build because it minimizes the amount of the incredibly bulky and complex LH2 piping. There's just the pump and heat exchanger for it, that's it. Then expansion drives it through the He circulator pump and toward the reaction chamber.

You might call it a poor-man's LACE: It doesn't work nearly as well in absolute efficiency terms, but the maths for it going to orbit add up and it's much easier of a problem in terms of metallurgy. LACE to some extent was an attempt to make a DC-3 in 1912; the Space Shuttle was a Wright Flyer. SABRE is more or less deciding that a Vickers Vimy is good enough for now.

[Sky Captain]

If they can make the engine work at required performance levels then a lot will depend on how good are their current weight estimates for Skylon. If it turns out they need to strengthen the structure here and there , thermal protection turns out to be heavier than expected it is easy to come to a situation where the cargo capacity is eaten up leaving little room for useful payload.

[Crayz9000]

No question about that. My understanding is that they've designed and modeled the ship's spaceframe based on modern materials properties, even going so far as as to choose a specific variant of resin-impregnated carbon fiber that fit their needs. However, even with an accurate computer simulation, problems crop up that nobody really expected...

[Sea Skimmer]

Every major aircraft designed by computer model has ended up needing major weight increases for strength and other features, and none of them had as radical of requirements as a space plane or so much unbuilt and undesigned technology. It only takes a 4% mass increase before it can't even reach orbit at all, let alone with payload. Meanwhile they claim this shall all be done for less money then its taking to screw up the A400M, sure. At least with a proper LACE you have a lot more design flexibility in the aircraft side of things. Complicated sure, but weight is not nearly so critical as an attempt to just single stage to orbit.

[Starglider]

Every major aircraft designed by computer model has ended up needing major weight increases for strength and other features

That said the HOTOL design is nearly 30 years old and the Skylon design is over 10 years old, surely improvements in materials and structures have improved the margin over that time.

[Sea Skimmer]

People claimed working designs on paper for spaceplanes in the 1960s. Now meanwhile A400M, 787, F-35 come to mind as all being about ten years old in detail design, heavily designed on computers, and all have come out substantially heavier then expected while being far less radical then any space plane could be. No major advances in materials have taken place since Skylon was 'designed' in a generalized way, a huge difference exists between the design they have and one production ready. Something to the tune of about ten billion dollars of detail engineering even by the designers own optimistic cost estimate. Carbon nanotube composites are now production reality, but they are not rated for aircraft structural applications and most likely won't be for at least twenty years.

30 year old paper designs mean about nothing. Do you realize the staggering number of assumptions that have to go into such pure paper airplanes? Its bad enough when everything required is well understood, never mind radically new and not even demonstrated full scale in the lab. HOTOL had massive problems while it was still in the paper phase anyway, which were never resolved at the time all funding was suspended. The US put billions into the Rockwell X-30 in the 1980s, that was never going to work either even had the required scramjets been invented, which I might add are all and all much more proven technology since at least they've actually flown, then we have the awesome X-33 SSTO, which totally worked on paper, except for the minor problem of the required fuel tank being impossible to actually build. Pity such details exist in life.

I'd love it if Skylon worked, but the history behind every similar project is not an endorsement. Like I was saying, LACE and its ultimate 'Alchemist' evolution which dumps the nitrogen and Co2, is the one golden nugget behind all this because it just lets the entire concept of single stage to orbit be redefined and the tight weight margins go away. If a LACE engine can work, it isn't in doubt that a useful spaceplane could be built. With anything else is really open to question.

[Sea Skimmer]

Wow you know I thought HOTOL had more work put into then it did, I thought it was ~100 million pound project before the plugged was pulled. Turns out single digit millions of pounds were enough to figure out the massive stability problems essentially made it unworkable, before you even considered the raw engineering issues that were always expected. It never entered full scale development at all. They did not even define what development would really require. Flawed from the onset. The configuration of Skylon is entirely different because of this, but the end result is also a less weight efficient approach. So HOTOL is proof that people can come up with really bad paper designs, and not much else. It doesn't have the excuse X-30 did either, of being a communist defeating scare tactic alongside two thirds of the Star Wars ABM stuff.

[The Duchess of Zeon]

Even if the spaceplane part is unfeasible the functional precooler means that reliable Mach 5.5 range manned high altitude flight is probably feasible within the next two decades.

[Sea Skimmer]

I'd take the successful ignition and acceleration of US scramjets in open flight as a much better sign of manned hypersonic flight becoming real then subscale component lab work myself. Said scramjets also happen to work with something remotely like conventional aircraft fuel, JP-7, rather then LOX and liquid hydrogen that constantly want to leak and explode. This engine will have a future for space travel if it works, its not going to have much of one for manned aircraft flight simply because of those fuel handling issues.

[Zac Naloen]

The article is about a successful test of a full size pre-cooler.

You could attach that pre-cooler to any engine, or even anything that needs pre-cooling, it doesn't have to be Sabre. Their proof of concept for a super-sonic aircraft doesn't use Sabre for example.

[Sky Captain]

The article is about a successful test of a full size pre-cooler.

You could attach that pre-cooler to any engine, or even anything that needs pre-cooling, it doesn't have to be Sabre. Their proof of concept for a super-sonic aircraft doesn't use Sabre for example.

According to the picture posted above showing engine operation they need LH2 for precooler to work because LH2 is used as heat absorber.

[Crayz9000]

The article is about a successful test of a full size pre-cooler.

You could attach that pre-cooler to any engine, or even anything that needs pre-cooling, it doesn't have to be Sabre. Their proof of concept for a super-sonic aircraft doesn't use Sabre for example.

According to the picture posted above showing engine operation they need LH2 for precooler to work because LH2 is used as heat absorber.

LH2 is the second stage of the precooler loop. Liquid helium is used for the precooler itself to avoid hydrogen embrittlement. The liquid helium loop then exchanges its heat with the hydrogen in a separate heat exchanger. For this test, to simplify things they used liquid nitrogen for the second stage heat exchanger, since it's much easier to work with.

[Sky Captain]

The article is about a successful test of a full size pre-cooler.

You could attach that pre-cooler to any engine, or even anything that needs pre-cooling, it doesn't have to be Sabre. Their proof of concept for a super-sonic aircraft doesn't use Sabre for example.

According to the picture posted above showing engine operation they need LH2 for precooler to work because LH2 is used as heat absorber.

LH2 is the second stage of the precooler loop. Liquid helium is used for the precooler itself to avoid hydrogen embrittlement. The liquid helium loop then exchanges its heat with the hydrogen in a separate heat exchanger. For this test, to simplify things they used liquid nitrogen for the second stage heat exchanger, since it's much easier to work with.

In the end it is still LH2 that takes the heat away so they need cryogenic fuel to act as heat sink. Maybe if they can use some other easier to manage fuel that still is cryogenic the engine could be made to work. A supersonic passenger jet that uses cryogenic fuel will be very expensive to operate because it will need entirely new infrastructure at every airport.

[Crayz9000]

Some work has apparently been done on cryogenic methane-powered aircraft:

http://spinoff.nasa.gov/spinoff/spinite ... d+Airplane

[Sea Skimmer]

The Soviets got further with liquid methane powered designs then NASA did, they flew a Tu-154 airliner on the stuff, as Tu-155, which was first tested with liquid hydrogen. Problem is the bulk of the required fuel tanks means lots of drag as they also need to be circular or spheres to be an acceptable weight, and the plumbing is much more expensive to maintain, so no incentive exists to use it on commercial aircraft until and unless liquid fuels become much more expensive. The airport side of things is actually easier to deal with. Tupolev came up with methane powered variants of all its major airliners and they all had enormous full length blisters on the roof to hold the tanks. The Tu-155 just put the high bulk fuel tanks inside the fuselage in place of passenger and cargo space.

Sort of like this, though I'm not sure who's aircraft this actually is.