A disembodied jet engine, attached to a hulking air vent, sits in an outdoor test facility at the Culham Science Center in Oxfordshire, England. When the engine screams to life, columns of steam billow from the vent, giving the impression of an industrial smokestack. Engineer Alan Bond sees something more futuristic. "We're looking at a revolution in transportation," he says. For Bond, the engine represents the beginning of the world's first fully reusable spaceship, a new kind of craft that promises to do what no space-faring vehicle ever has: offer reliable, affordable, and regular round-trip access to low Earth orbit.
Bond and the engineers at Reaction Engines, the aerospace company he founded with two colleagues in 1989, refer to the future craft as the Skylon. The vehicle would have a fuselage reminiscent of the Concorde and take off like a conventional airliner, accelerate to Mach 5.2, and blast out of the atmosphere like a rocket. On the return trip, Skylon would touch down on the same runway it launched from.
Bond's Synergistic Air-Breathing Rocket Engine (Sabre)—part chemical rocket, part jet engine—will make Skylon possible. Sabre has the unique ability to use oxygen in the air rather than from external liquid-oxygen tanks like those on the space shuttle. Strapped to a spacecraft, engines of this breed would eliminate the need for expendable boosters, which make launching people and things into space slow and expensive. "The Skylon could be ready to head back to space within two days of landing," says Mark Hempsell, future-programs director at Reaction Engines. By comparison, the space shuttle, which required an external fuel tank and two rocket boosters, took about two months to turn around (due to damage incurred during launch and splashdown) and cost $100 million. Citing Skylon's simplicity, Hempsell estimates a mission could cost as little as $10 million. That price would even undercut the $50 million sum that private spaceflight company SpaceX plans to charge to launch cargo on its two-stage Falcon 9 rocket.
The engine produces incredible heat as it pushes toward space, and heat is a problem. Hot air is difficult to compress, and poor compression in the combustion chamber yields a weak and inefficient engine. Sabre must be able to cool that air quickly, before it gets to the turbocompressor. In November, Reaction Engines hit a critical milestone when it successfully tested the prototype's ability to inhale blistering-hot air and then flash-chill it without generating mission-ending frost. David Willetts, British minister for universities and science, called the achievement "remarkable."
The Skylon concept has also impressed the European Space Agency (ESA), which audited Reaction Engines' designs last year and found no technical impediments to building the craft. The bigger challenge may be securing funding. While ESA and the British government have invested a combined $92 million in the project, Bond and his crew plan to turn to public and private investors for the remaining $3.6 billion necessary to complete the engine, which they say could be ready for flight tests in the next four years. Building the craft itself would require a much heftier investment: $14 billion.
The quest for a single-stage-to-orbit spaceship, or SSTO, has bedeviled aerospace engineers for decades. Bond's own exploration of the topic began in the early 1980s, when he was a young engineer working with Rolls-Royce as part of a team tasked with developing a reusable spacecraft for British Aerospace. That's when he came up with the idea of a hybrid engine. But the team struggled to figure out how to cool the engine at supersonic speeds without adding crippling amounts of weight. "By the time the plane hits Mach 2 or so, the air becomes very hot and extremely difficult to compress," Bond says. Rolls-Royce and the British government, doubtful that an easy and economical solution existed, canceled the program's funding.
NASA and Lockheed Martin, meanwhile, had their own plans for a fully reusable spacecraft, the VentureStar, intended as an affordable replacement for the partially reusable space shuttle. The VentureStar demonstrator, called X-33 (which graced the cover of this magazine in 1996), was a squat, triangular rocket that would take off vertically and glide back to Earth just as the shuttle did. Eliminating the expendable rockets needed to boost the shuttle into space could theoretically reduce the cost of launches from $10,000 per pound to $1,000 per pound. But by 2001, after sinking more than $1 billion into the project, the agency pulled the plug, citing repeated technical setbacks and ballooning costs. "We backed off because we felt it was better to focus our efforts on other, less costly ways to get payloads to orbit," says Dan Dumbacher, NASA's deputy associate administrator for exploration systems development, who spent two years working on the X-33.
With the shuttle now retired, and companies such as SpaceX under contract to resupply the International Space Station (ISS), NASA has doubled down on expendable boosters as a means of sending humans and probes well beyond Earth's orbit. NASA's new platform for deep-space exploration, the Space Launch System, will be the most powerful rocket ever built. The agency's focus on space exploration, and the need for big rockets to achieve it, means NASA no longer needs to build its own platforms just to get cargo into orbit. "From a pure technical perspective, we'd all love to go do SSTO," Dumbacher says. "But we're focused on making sure we get humans farther into space, and that's an expensive proposition."
Expendable rockets make sense for missions beyond low-Earth orbit. They can haul more cargo and more fuel than single-stage craft. Rockets also offer reliability—on average, only one out of 20 launches fail, in part because they suffer no wear and tear from repeated use. Finally, rockets come with fewer R&D costs, as much of the technology has existed since the 1960s.
But for routine missions to the ISS, or to park a small observational satellite in orbit, affordability becomes a critical consideration. SpaceX CEO Elon Musk told an audience at the National Press Club in 2011 that private spaceflights would need to follow a model closer to that of airlines. "If planes were not reusable, very few people would fly," he said. SpaceX plans to make rocket stages reusable, but there are drawbacks to that, too: While it is possible to recover rocket stages, designing bits and pieces to survive reentry in good working order adds a level of complexity and cost.
Hempsell says Skylon could potentially make 100 flights annually—which, if true, could in its first year recoup the money spent in R&D and construction, leaving only expenses like fuel, maintenance, and overhead. And Bond's engine technology, aside from keeping a launch vehicle intact from start to finish, offers another advantage: supersonic aviation. "It could enable an aircraft to fly anywhere in the world in under four hours," says Bond.
When air strikes an engine at five times the speed of sound, it can heat up to nearly 2,000 degrees Fahrenheit. Bleeding off that heat instantly, before the air reaches the turbocompressor and then the thrust chamber, was the most onerous technical challenge for Reaction Engines engineers. Bond's solution is a heat exchanger that works by running cold liquid helium through an array of tubes with paper-thin metal walls. As the scorching-hot air moves through the exchanger, the chilled tubing absorbs the energy, cooling the air to minus 238 degrees Fahrenheit in a fraction of a second. Bond says his exchanger could handle about 400 megawatts of heat (equivalent to a medium-size natural-gas plant). "If it were in a power station, it would probably be a 200-ton heat exchanger," he says. "The one we've built is about 1.4 tons."
For rocket scientists, nothing matters more than weight. "Each pound you put into orbit requires about 10 pounds or so of fuel to get it there," says NASA's Dumbacher. "The challenge with the SSTO has always been to get the craft as light as possible [and generate] as much thrust as possible." Bond estimates that Skylon would weigh about 358 tons at takeoff and hold enough hydrogen fuel to carry itself and about 16.5 tons of payload—about the same capacity as most operational rockets—into orbit.
If and when the engine passes flight tests, one of Reaction Engines' plans is to license the technology to a potential partner in the aerospace industry. Bond hopes the recent success of the heat exchanger will inspire interest. After 30 years of research, it has certainly inspired him. "It represents a fundamental breakthrough in propulsion technology," he says. "This is the proudest moment of my life."
This article originally appeared in the September 2013 issue of Popular Science.
I wish them the best of luck. I'm sure within my lifetime I will see a single stage space plane take off to space and land back on earth. I really think once there is profit in this for private industries, such as from astriod mining, or space tourism, the space industry will explode with so many companies getting into this. There are already a number of them out there.
- Just trying to keep my girlish asymptote!
Ya just got to adore a ben engine that can fly to space, develop by an engineer with the last name of Bond!
I've been following Skylon for some time now, I wish them all the succcess they hope to achieve. Truthfully, Skylon or SSTO is the only way to make space common. Imagine a fleet of these vehicles whisking payloads to LEO on a daily basis. If multiple countries operate their own fleets, there will eventually be multiple payload deliveries per day. We could finally start to build a true space presence... moon base, lunar orbital base, a lunar tether, space manufacturing, space recreation, and ultimately, deep space travel. Setting up shop on Phobos and Deimos, Mars, Titan, Europa...
Later on sky cities wafting through the Venusian atmosphere (oxygen is a lifting gas on that planet, so technically a simple Nitrogen/Oxygen atmosphere (which is what we breathe) would be sufficient to provide bouyancy in the atmosphere. An enclosed "city" will eventually happen.
It all starts with regular SSTO flights.
Very awesome breakthrough on heat exchange. This single breakthrough will ripple through a host of applications. So, basically, a Ram Air (Oxygen)induction that is super cooled used to ignite/burn rocket/hydrogen fuel. I am guessing that due to the need for Ram Air at mach 5.2 that this thing has to stop engine burn at orbit (due to lack of oxygen) and then dive back into the atmosphere to reach Ram Air induction speed again? Or am I missing something? Secondary fuel source that doesn't require oxygen? Maybe just takeoff requires Ram and not return?
"Do not try and bend the spoon. That is impossible. Only try and realize the truth - there is no spoon."
When people say that science is soulless or evil, I just point to things like this, raise one eyebrow, and smile.
This is what science, math, and engineering have to offer, and the world is more beautiful, more comfortable for human life, and more magnificent because of it.
It will carry an oxygen supply to work outside of the atmosphere. Basically, it's a rocket engine that can utilize oxygen out of the air, only while it is in air. This saves on the weight of oxygen that would otherwise be needed for the flight through the atmosphere.
Any explanation on the banana shape?
I imagine designing an engine that works with both air, with it's content of gasses other than oxygen, and a pure oxygen source, might be problematic.
The banana shape of the engines is to keep the rocket engines thrusting through the center of gravity, and the air intake pointed directly into the air flow.
Most aircraft are designed to fly with a nose up angle of attack. This way the fuselage generates lift. Since the engine inlet is extremely sensitive to the direction of airflow at high mach numbers, it is angled down 7 degrees so that air flows directly into the engine.
The nozzle is angled 7 degrees down as well, which is purely coincidence. The trust vector must go through the center of gravity, otherwise the air/spacecraft will pitch. So, the nozzle angle is purely a function of where the engines are relative to the center of gravity.
I suppose they could move the wing/engines up so that the inlet and nozzles are at the same angle, but then they wouldn't have a convenient place for the rear landing gear, and having the engines close to the ground makes them easier to service.
Bob Singer: This can't be the new shuttle because it's a UAV, unmanned and ground controlled. No one will fly astronauts/cosmonauts up to the ISS on an unmanned vehicle. Other than that, good article.
Is anyone else wondering where those 400MW of heat pulled from the intake go?
That's a considerable amount of heat that must be dissipated to the surroundings by another exchanger elsewhere in the craft. How is this being accomplished?
There are lots of unanswered questions in the article.
1. The engine is described as "hybrid." However, there is no explanation of how and why it is hybrid.
2. How does the spacecraft accelerate from zero to Mach 5 ? The Ram air stuff does not work at slow speeds.
3. The diagram shows a LOX pump. Is LOX used as the oxidiser at slow speeds ? In space ?
4. If LOX is an oxidiser for at least part of the flight, where is the tank ?
5. If LOX is used for part of the flight , its weight needs to be factored in. (Not just the weight of liquid hydrogen.)
6. The heat exchanger transfers 400 MW of heat from the air to the helium. The diagram shows a helium circulator. How is the hot helium cooled ?
7. Or does the helium start as a liquid and is dumped overboard after it heats and vaporises ? If so, the weight of helium has to be considered.
8. Helium becomes a liquid only at 4 deg K. So carrying liquid Helium has its own problems.
Heat is dissipated in vaporizing liquid helium.
did I miss something? Will the jet intake be sufficiently heat resistant to deal with reentry heat? Isn't that what killed discovery? A tile got hit on launch allowing reentry heat to go through one of the wings like a plasma torch!
you can write me at CARTYWILLIAN3@GMAIL.COM.
Wikipedia answers all of your questions.
google "SABRE (rocket engine)"
@wcarty...They have much better materials available for heat shielding now than when the shuttle was designed. Besides, there will be no external tank for debris to shed from and hit this vehicle.
I read that they had a breakthrough in developing materials for the engines to enable them to survive the intense heat which would allow prototype engines to be produced and tested. I presume this is the result of those advances. Cheers.
I must have missed a memo.
When did the shuttle program become relevant to anyone but the US Department of Espionage?
The shuttle program kept us from actual space exploration for 20 years. No lunar missions, No Mars missions, or asteroid missions except by robots. oh yea. . . . what does it matter that we have a shiny new toy primarily for the commercial interests who will be building 1 star hotels in near Earth orbit that cost $10,000 a day so you can get bruised up floating around and vomit at a spectacular view of Earth.
We dont need a new suborbital launch system for spy satellites or a taxi service to the ISS.
The Space program should be about exploration beyond Earth.
I want craft that can support bases on the Moon, flag planting ceremonies on Mars, Europa, and Titan. I want to see vehicles that can mine asteroids.
Its 2013 and we still havent even dug up that Monolith on the Moon.
@OniRaptor...NASA and SpaceX are doing what you are requesting, just a few years down the road. A cheap launch system is desperately needed for support of deep space missions and other needs. And yes, the Space Shuttle was a huge drain on resources but was unfortunately necessary for the completion of the ISS, as we were too deep into them both to cancel the programs. Science that can be only done on the ISS hopefully will pay off and make it all worth the high cost.
P.S. This will not be suborbital. SSTO-single stage to orbit.
I'm sorry, but this configuration is too absurd to even comment on. It keeps popping up on the net, for reasons that I can not understand.
The air intakes close after the air breathing stage, and presumably remains closed through reentry. To close the intake the central cone moves forward. The concentric rings you see in the intake nest to make one big cone.
The designers claim that because the Skylon is so light for its size, it will not get as hot as other re-entry vehicles like the space shuttle (1100K vs 2000K). So they think that a reinforced ceramic skin will be able to handle re-entry temperatures.
"...too absurd to comment on..."
It was so nice to see both the American and British flag, together with the Reaction Engines logo on the side of the fuselage in the picture at the beginning of the article. It seems to me that this could be the perfect example for international cooperation in space (it already is as ESA is already looking more aggressively into it). I can see a Reaction Engines/Rolls Royce partnership (I think RR was originally involved in Skylon’s predecessor, project HOTOL) providing the engines, a Boeing/Lockheed Martin/Any other building the airframe, EADS providing the avionics or any other subsystem. It is time for NASA to quit the Senate Launch System and focusing on the future of space transportation… Replace those two flags in the picture with the NASA/ESA emblems representing a true international space endeavor.
I say the engine need to be able to work in both air and vacuum,to save liquid oxygen weight.
@lreyna...NASA involvement would probably be welcome, however this craft and NASA's deep space capsule have two entirely different missions, cheers.
There was NO discussion or mention on the limit and size of carry on bags...
Another fake research program to cover for the real space program. The one that cooperates with the reptilians.
could be just a rumor .
Skylon is a very neat piece of engineering.
They get more energy out of the liquid hydrogen than you can get just burning it. How? They use the temperature difference between the ram air coming in and the liquid hydrogen to run a closed cycle helium turbine. The turbine powers a compressor takes the cooled air and compresses it to rocket chamber pressure. It takes 20 kWh/kg to liquefy hydrogen. Hydrogen only releases 50 kWh/kg from burning, so using much of the energy that went into making it a liquid is very effective.
I have seen one of the precoolers. The tubing they use is so fine it looks like fabric.
It still won't get the cost down far enough for power satellites to make economic sense. But there might be a way, though it will take considerable engineering.
This is a talk on the topic.
And this you might want to look at just for the eye candy of a second generation Skylon using laser heated hydrogen to get into orbit.
One error in this article, the helium is not liquid at any point in the cycle. You can't liquify helium with liquid hydrogen, it isn't cold enough.