In 2001, one space odyssey never made it to the launch pad. The National Aeronautics and Space Administration announced in March that it was pulling the plug on X-33 and X-34, two space planes whose combined cost exceeded $1 billion.

But the market for reusable launch vehicles is still strong, and a number of private companies, with NASA's help, are looking to reach orbit within the next ten years. Many teams see a payoff in launching satellites more cheaply. Others envision space planes handling a variety of tasks from rapid package delivery to suborbital microgravity experiments.

Hard to X Plane

The X-33, a combined NASA and Lockheed Martin project, was a prototype for the full-scale VentureStar vehicle proposed by Lockheed. This piloted, fully reusable space plane was intended to replace the space shuttle, as well as function as a commercial vehicle for space tourism. (The space shuttle costs about $1,000 per pound of payload, whereas commercial space planes would need to cut the price to one-tenth of that amount.)

X-33 sparked numerous new technologies, including lightweight composite fuel tanks and a metallic thermal protection system lighter than the current silica or ceramic ones.

The X-34, developed in conjunction with Dulles, VA-based Orbital Sciences, was designed to test these and other technologies, including advanced autopiloting, intended to reduce the time, cost and personnel needed for a commercially viable space plane.

Triple X

With both programs cancelled, Lockheed Martin, Orbital and Boeing are keeping busy with several other government-funded RLV programs, bearing names like X-38, Hyper-X and Future-X.

Jack Anthony, chief of the Integrated Space Experiments Division at the Air Force Research Lab's Space Vehicles Directorate at Kirtland Air Force Base, NM, has hope for a future X-33 program, with some modifications.

"As noble as it was, it proved to be a bit farther 'out there' than we thought," he says, referring to the X-33 as a "gem of a technology."

Among the improvements Anthony hopes for is "on-demand space access," which includes short-notice launching and quick turnaround time-especially useful if, for example, a satellite fails in orbit and needs to be quickly replaced.

Anthony also expresses hope for high-performance rocket engines that use low-toxicity fuels. One of the most promising, he believes, is hydrogen peroxide, which has been used since the 1950s but needs to be refined to allow vehicles to stay in orbit for a year or longer. The Space Vehicles Directorate is exploring these possibilities.

Out to Launch

While Anthony is a big believer in commercially developed space planes, he acknowledges that the cost can be exorbitant. "My impression was they weren't getting the financial backing necessary," he said.

Enter NASA, whose Space Launch Initiative is designated to receive almost $5 billion between 2001 and 2006. By helping private companies develop reusable launchers, NASA hopes to achieve its goal of making space travel safer and cheaper for both the government and private sector by early next decade.

Earlier this year, NASA awarded a first round of R&D contracts to high fliers such as Boeing, Lockheed Martin, Orbital, Northrop/Grumman and TRW.

Also funded was Kistler Aerospace, the Kirkland, WA, developer of a two-stage-to-orbit "space truck" that is already under contract for 10 satellite launches by industry heavyweight Space Systems/Loral. Kistler has also secured the right to operate at the Nevada Test Site run by the Department of Energy.

X Marks the Prize

Beyond satellite launches, some companies are setting their sights on bringing space travel to the masses. To encourage them, the X-Prize Foundation in St. Louis, MO, is awarding a $10 million prize to the first team of researchers to launch and land a vehicle capable of transporting three people on two consecutive 100-kilometer-high flights.

Most current space plane programs try to accomplish too much in the early stages of development, said foundation chairman Peter Diamandis, speaking at the National Space Society's annual meeting in Albuquerque last May.

Rather than attempting to replace the space shuttle, the X-Prize Foundation encourages competitors to start shooting for a height of 100 kilometers. This trip, notes the foundation's Web site, is "beyond the official 50 miles that the U.S. Air Force recognizes as 'worthy of astronaut wings' but not so high that the reentry speed requires exotic heat shielding."

Up to now, launch vehicle programs have been developed for two markets: the government and communication satellite operators. But the government generally conducts about half a dozen launches per year, and commercial operators, about two dozen. "Such low launch rates, with their associated high costs, don't yield high commercial success rates," Diamandis explained.

The market for reusable launch vehicles should mature steadily. Until then, satellites will continue to climb aboard the current crop of expendable rockets-the United States' Atlas, Proton and Delta, Russia's Proton and Zenit, and Europe's Ariane.