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A wag (we forget who) once said, more or less, that you could get to space by car in an hour, if you could drive straight up. If you visit Rocketplane.com, however, you'll find a company that makes the trip sound like taking a taxi. Well, almost.

Rocket-plane Limited Inc. is developing a commercial craft for excursions to the edge of space. The company, based in Oklahoma City, is building a prototype and plans to conduct its first tests later this year.

The craft, designated Rocketplane XP, will be powered by two turbojets and one rocket engine. At first, the craft will use an RS-88 engine, on loan from NASA for three years.

According to Bob Seto, Rocketplane's vice president for engineering and analysis, the RS-88 will be used to prove vehicle systems and will be replaced by a new, lighter engine, the AR-36, which is being developed by Polaris Propulsion. The AR-36 is sized specifically for the Rocketplane XP mission, he said. Commercial flights are expected to begin in 2007.

The Rocketplane XP is the size of a four-passenger business jet, specifically a Learjet, on which the fuselage is based. The craft will take oft as a conventional plane from a runway under the power of two modified General Electric CJ610 turbojet engines.

Jets will take the Rocketplane XP from runway through the first 25,000 feet of its climb.

The company's mission profile calls for the rocket to ignite when the craft has readied an altitude of 25,000 feet. The turbojets shut down after the rocket lights, and the rocket cuts off when the craft reaches 150,000 feet.

A four-seat aircraft is designed to take passengers to space and back in less than an hour.

All that will take place in about 70 seconds, with a maximum speed of Mach 3.5.

The vehicle will continue to climb without rocket propulsion, and will exceed 330,000 feet, in the lower ionosphere, more than 60 miles off the ground. Passengers will experience three to tour minutes of weightlessness, the company says. Although the turbojets will remain available, the era 11 is designed to make a horizontal, unpowered touchdown, on the kind of landing gear used on a 30 Series Learjet. The flight will last less than an hour and cost about $200,000.

The company expects that its craft will be able to make the flight every three to five days. Reentry protection includes titanium leading edges and a ceramic paint that emits more than 93 percent of the energy it receives, the company says.

Rocketplane has signed an agreement with NASA representatives at the Johnson Space Flight Center in Houston to arrange the loan of the RS-88 rocket engine. The company will pay NASA about $30,000 to cover administrative costs and will share its test data with the agency.

According to NASA, the RS-88 was designed and built by The Boeing Co.'s former Rocketdyne Propulsion & Power unit for use on Lockheed Martin's pad-abort demonstration vehicle. In 2003, NASA tested the RS-88 in a series of 14 hot-fire tests, resulting in 55 seconds of successful engine operation.

A NASA spokesman said the padabort vehicle was an escape mechanism meant to remove astronauts from harm's way in case of an emergency on the launch pad. The engine could be fired under the crew capsule to lift personnel from danger.

Since the demonstration, the engine has been stored at the White Sands Missile Range in New Mexico.

According to NASA, the RS-88 engine is capable of 50,000 pounds of thrust. Seto said that the engine will be derated to 36,000 pounds-force. That is the rating for the AR-36. The Rocketplane has a gross takeoff weight of 19,600 lbs., with a payload of 950 lbs.

If that leaves room for a suitcase, the next step could be to get a motel to stay up there. Then you could spend the weekend.

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By Harry Hutchinson