Flying a Reusable Space Plane Directly to Orbit

When Luke Skywalker jumps into an X-wing fighter and flies off into space in the Star Wars movies, he's performing a feat that is impossible today. Current orbital launchers are large, multistage affairs that combine the thrust of a series of throwaway rocket stages to escape Earth's gravitational clutches and send a small payload into the void above.

How much simpler and cheaper it would be if one vehicle could accomplish the same task and return intact, again and again. Such a reusable single-stage-to-orbit (SSTO) craft might finally enable regular, truly affordable access to space. But a practical SSTO vehicle is no easy objective. For decades it has been the holy grail for the many rocket scientists and engineers who have tried—and failed—to develop one.

The main difficulty lies in designing and building a vehicle light enough and powerful enough to reach orbit with a viable payload, explains Alan Bond, one of the more persistent of the latter-day grail questers. "Existing technology can't hack it," Bond asserts, "but it's not off by much."

Almost two decades ago, Bond and two veteran research colleagues formed a small R&D firm in Oxfordshire, England. Their company, Reaction Engines, Ltd., set out to develop an SSTO space plane called Skylon. The ambitious design is based on a novel hybrid jet–rocket engine concept that just may provide the necessary boost. Today, a dozen Reaction researchers are working to perfect the engine's key technologies.

Although many aerospace observers consider the effort altogether quixotic given the daunting technical and economic barriers involved, others are cautiously hopeful. "The hybrid engine concept goes back almost a half century, and no one could make it work efficiently," says David Whalen, chair of the space studies department at the University of North Dakota (U.N.D.). "But make it work and you have a new era in access to low Earth orbit space."

Most conventional launch boosters employ weighty cryogenic propellants—liquid hydrogen and liquid oxygen—but Bond realized back in the 1980s that atmospheric oxygen might feed a jet engine for the lower-altitude part of the journey.

The fundamental problem, he says, is that conventional jets become impractical at velocities exceeding about Mach 2.7 (2.7 times the speed of sound); the inflowing air slows rapidly on entering the engine and generates more heat than most available materials can withstand.

In addition, at speeds above Mach 2.7 the incoming air is so hot that "you can't do any useful work on it," Bond says. A standard jet engine employs spinning compressor fans to pressurize inflowing air so that it releases large amounts of energy when mixed with fuel and burned. "Hot air won't do the job," he continues, "so you must precool the air before it enters the compressor, a concept that had been lurking around since the 1960s." Bond conceived the idea of using the ultracold liquid hydrogen fuel as a heat sink to take the excess heat out of the incoming air and use some of the hot air to support fuel combustion. At the fringes of space, the dual-mode power plant would switch to a conventional rocket engine, drawing on the liquid hydrogen and a small supply of liquid oxygen to propel the winged craft into orbit at a final speed of Mach 25.

The hybrid propulsion concept was attractive enough that in the mid-1980s Britain's BAE Systems and Rolls-Royce seized on it for an SSTO space plane project called HOTOL (horizontal takeoff and landing). But after HOTOL was canceled in the late 1980s, Bond, Richard Varvill and John Scott-Scott established Reaction Engines to carry on. Bond serves as the firm's managing director, Varvill is technical director and chief designer, and Scott-Scott is engineering director.

Soon the team will begin a series of milestone ground tests using a scaled-down precooler unit and a Viper turbojet engine. If the trials are successful, they could open the way for full-scale development of the air-breathing rocket engine.

As currently envisioned, Skylon would cost an estimated $10 billion to develop, but Bond claims its operational cost per kilogram of orbital payload would be one fiftieth that of current vehicles. So far, the project has consumed about $7 million in private and public funds, and this week the European Space Agency kicked in another $1.25 million. "We hope to complete demonstrating the critical technologies in three years," Varvill states. After that, Reaction Engines will seek to establish a public–private partnership to build the prototype.

Pablo de Leon, Whalen's colleague at U.N.D., shares his co-worker's views: "The concept might work. If it does, Reaction Engines will reach an SSTO vehicle before anybody else." And, he says, the engine's development seems to have advanced of late. But financing high-altitude tests will be extremely difficult, de Leon notes: "Funding to reach that level of maturity will be a challenge as difficult as the technical ones, or even greater."

A green Escape

Cam and Lisa Clayton are, like many of the rest of us, middle-class parents trying to balance work and family. Somewhere in that mix, you'll also find concern for the environment that needs to find a balance with real-world transportation needs and a real-world budget.

And so buying a new 2008 Ford Escape Hybrid was not easy.

"It was nearly $40,000, which is a lot," says Cam Clayton, a geotechnical engineer whose profession has taken him face-to-face with environmental issues. "But we decided that we could afford it and it was the right thing to go."

Yes, but $40,000 is $40,000, and in a marketplace where comparable, non-hybrid crossover utility vehicles sell for $10,000 less, $40,000 took a big bite out of the Clayton family budget. Raising two teenagers is expensive and demands on the family finances will only become greater when university arrives for their two sons.

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Batteries are recharged as the Escape is driven; you won’t need to plug in your Escape every night. (FORD)

"But as I said," Cam repeats for emphasis, "it was worth it. We think we should do our part."

The Claytons are somewhat early adopters of hybrid technology. I say "somewhat" because Ford introduced the first-generation Escape Hybrid as a 2005 model and Toyota and Honda have been selling hybrids for a decade now.

Nonetheless, gasoline-electric hybrids are hardly mainstream yet, accounting for less than 2 per cent of all new vehicle sales in Canada.

A bigger hybrid push is coming, though, and that should mean prices will come down. In that vein, Honda is strongly suggesting its 2010 Insight hybrid subcompact will sell in the $20,000-range.

But even at that, there is no denying the hybrid premium. The Honda Fit, which shares some of its mechanical underpinnings with the Insight and is about the same size, starts at less than $15,000; the 2009 Prius lists for $27,710, while a Toyota Matrix with more total passenger volume than a Prius starts at less than $16,000.

The Clayton's Escape Hybrid, a four-wheel-drive compact CUV equipped like my recent tester, starts at $36,799, compared to $27,499 for the least-expensive gasoline-only Escape with four-wheel drive. The base Escape Hybrid, front-drive only, goes for $34,399, versus $23,999 for the starter version of the gasoline Escape.

In fairness, all the hybrids listed here are better equipped than the comparable gasoline model models listed here. Nonetheless, going hybrid typically adds $4,000-$6,000 to the price of a new vehicle.

At least hybrids also qualify for government rebates worth up to $3,000 in parts of Canada. That takes some of the sting out of the sticker.

Here's the rub. My tester, with the $2,700 navigation system package, $100 federal excise tax and the $1,300 destination and delivery charge, ended up at $39,399 plus taxes. That's a big financial commitment for significantly lower emissions and a modest fuel economy gain.

Look at the numbers. The Escape Hybrid AWD is rated at 7.0 litres/100 km city and 7.4 on the highway, versus 10.9 city/7.9 highway for the four-cylinder, gas-only Escape AWD.

According to Natural Resources Canada's calculations, you can expect to save about $500 a year on fuel with the hybrid. You'll also reduce the amount of CO2 you blow into the environment by 1,152 kg each year.

It's hard to put a price on CO2 just now, but unless fuel prices jump dramatically, the Claytons will need to drive their Escape Hybrid for seven to 10 years before they have recovered the hybrid premium in reduced fuel costs.

They have put real money behind their environmental commitment, but not everyone can afford to do so.

For those who can, the five-passenger Escape Hybrid is a nice little rig. The hybrid basics include a 2.3-litre, 155-horsepower, four-cylinder engine assisted or temporarily replaced by an electric motor. Together, they are rated at 177 hp.

The electric motor is, indeed, powerful enough to move the hybrid on its own. Batteries are recharged as the Escape is driven; the Claytons will not need to plug in their Escape every night.

The transmission is a continuously variable automatic, which means there are no steps in the gears, but rather a belt-and-pulley system finds optimal engine speeds at all times — which itself delivers a 2- to 5-per-cent fuel economy gain.

Ford updated the whole Escape lineup for 2008, installing more fuel efficient powertrains, retuning the suspension, updating the exterior and completely redoing the interior.

Ah, the interior. Ford has gone Earth-friendly here. The standard seat upholstery is made of recycled materials. Ford recently won a CAA Pyramid award for delivering the first North American application of seating surfaces made entirely of recycled materials.

Ford estimates these recycled seats save about 600,000 gallons of water, 1.8 million pounds of CO2 equivalents and more than seven million kilowatt hours of electricity. (Full disclosure: I was one of the judges who voted to give Ford this award.)

The seats feel comfortable enough, and while the cabin looks nice and all the controls and instruments make sense, there still is a lot of hard plastic in there.

Nice touches include a 110-volt, 150-watt console power outlet for a computer; readings on top of the dashboard for time, date, temperature and direction; cellphone/iPod holders in the centre console; cargo-hold access through the rear window or lift-open tailgate; and rear seats that fold flat, providing you remove headrests. There's a cap-less fuel-filler nozzle, too.

The real story, though, is the hybrid powertrain. The lower emissions and improved fuel economy come from using a small engine boosted by an electric motor when more power is needed. When the rig inches along in traffic, the Escape can also run in electric-mode only.

The interaction between the gas and electric drive systems is pretty close to seamless. Most drivers will need to pay attention or the electric motor's comings and goings will go entirely unnoticed.

Still, this hybrid weighs 1,721 kg and most of the giddy-up comes from the 153-hp, four-cylinder engine. It works pretty hard at times; when pushed for passing or to go up a hill, the four-banger climbs beyond 4,000 rpm and stays there despite the electric boost that makes for combined horsepower of 177.

Green as it is, the Escape Hybrid is also safe, earning full five-star U.S. Government crash test scores for both frontal and side impacts. In addition to the full array of airbags, the hybrid comes standard with electronic stability control to help keep drivers out of trouble in the first place.

The list of standard equipment is long — power windows, stereo, automatic climate control and the like — while the optional navigation system in my tester was easy to use. It takes directions via Ford's Sync system. Sync allows you to literally ask the system for directions, search for hotels or restaurants and so on. Sync is not difficult to use, either.

The Claytons didn't say, but I will suggest that the powertrain could use a bit more off-the-line vitality and the Escape gets noisy at higher speeds. I also found that on cold mornings, the gas engine had to get everything going; the batteries snoozed until warmed up.

But in the long run — and you'll need to keep it for the long run to recover the hybrid premium — the Escape Hybrid delivers on its promise of lower emissions and better fuel economy in a practical package.

UPDATED: Swiss develop cheaper, alternate Hybrid-like technology

Zurich (Switzerland) - Swiss engineers believe they've developed an alternative, competitive technology to electric hybrids such as the popular Toyota Prius which could someday make hybrids more globally affordable. They are referring to something called a pneumatic hybrid.

Pneumatic hybrid technology is being developed by professor Lino Guzzella and his team through the Swiss Federal Institute of Technology Zurich (ETH). Guzzella describes the pneumatic concept as being similar to that of electric, but with the engine having a compressed air tank connected instead of a battery unit. "When required, e.g. when starting from rest or after changing gear, compressed air flows into the engine through an electronically controlled valve. If fuel is also injected, the engine responds quickly," he said.

The research engine utilizes air power to supplement the gasoline engine's power. While this makes it a hybrid engine, there is no battery or electric motor and the number of gasoline engine pistons is reduced from four to two.


The ETH reports this compressed air supply allows for engine downsizing, halving the number of cylinders from four to two. This is said to reduce frictional losses by half as well as increase average overall efficiency. Power loss is compensated for by an installed turbocharger, which "exploits the exhaust gas enthalpy as an energy source."

Initial tests in the European Test Cycle reportedly show the engine's average efficiency increases from 18 to 24 percent, resulting in a fuel savings of one-third. It is said that, although the fuel savings achieved by the pneumatic hybrid are not as large as that of an electric hybrid, it offers a better price-performance ratio - since it does not require expensive batteries which decrease in efficiency over time.

ETH reports that their new engine concept has aroused the interest of several major motor companies and automotive suppliers, who have obtained information from on-site visits.

UPDATED: Swiss develop cheaper, alternate Hybrid-like technology

Zurich (Switzerland) - Swiss engineers believe they've developed an alternative, competitive technology to electric hybrids such as the popular Toyota Prius which could someday make hybrids more globally affordable. They are referring to something called a pneumatic hybrid.

Pneumatic hybrid technology is being developed by professor Lino Guzzella and his team through the Swiss Federal Institute of Technology Zurich (ETH). Guzzella describes the pneumatic concept as being similar to that of electric, but with the engine having a compressed air tank connected instead of a battery unit. "When required, e.g. when starting from rest or after changing gear, compressed air flows into the engine through an electronically controlled valve. If fuel is also injected, the engine responds quickly," he said.

The research engine utilizes air power to supplement the gasoline engine's power. While this makes it a hybrid engine, there is no battery or electric motor and the number of gasoline engine pistons is reduced from four to two.


The ETH reports this compressed air supply allows for engine downsizing, halving the number of cylinders from four to two. This is said to reduce frictional losses by half as well as increase average overall efficiency. Power loss is compensated for by an installed turbocharger, which "exploits the exhaust gas enthalpy as an energy source."

Initial tests in the European Test Cycle reportedly show the engine's average efficiency increases from 18 to 24 percent, resulting in a fuel savings of one-third. It is said that, although the fuel savings achieved by the pneumatic hybrid are not as large as that of an electric hybrid, it offers a better price-performance ratio - since it does not require expensive batteries which decrease in efficiency over time.

ETH reports that their new engine concept has aroused the interest of several major motor companies and automotive suppliers, who have obtained information from on-site visits.