NASA and a team of aerospace contractors reached a milestone in defining a second-generation reusable space transportation system with the release today of a status report on the first year of the effort. At present, some 15 different concepts are being hotly studied.

The plan to develop a replacement for the Space Shuttle -- a first generation system -- is being carried out under NASA's Space Launch Initiative (SLI). The announcement took place at NASA Headquarters in Washington, D.C.

A number of concepts have already been evaluated. The second-generation vehicle will have a two-stage-to-orbit propulsion system based on engines fueled by all kerosene, all hydrogen or a combination of kerosene and hydrogen, Smith said.

"When first stage separates from the launch vehicle it would actually turn around and fly back to the launch site. It would be pretty neat to see a launch and a landing within a few minutes of each other," Smith said.

"So this is the first year of a decade-long activity," Smith said. A major goal of the SLI program is to field a launch system that is far safer, more reliable, and more affordable than today's space shuttle, he said.

One tough-to-do assignment for the SLI-derived launch system, Smith said, is attaining a 1 in 10,000 probability of losing a crew. Today, the probability for crew loss onboard a shuttle is between 1 and 250 and 1 in 500, he said.

Furthermore, a second-generation reusable launch system is being sought that lowers the cost-per-pound to orbit from $10,000 to just $1,000 a pound. The second-generation launcher would be capable of lofting crew and cargo separately.

Joining Smith in the briefing were representatives of three SLI contract teams. Each group is delving into various configurations of second-generation launchers and their uses.

"We're on our way to whittling that down to three by end of the year (from 15). Then we'll go into a competition next year and come out with the two leading concepts," Smith said.

Those teams joining NASA in the SLI studies are: The Boeing Company of Seal Beach, California; Lockheed Martin Corp. of Denver, Colorado; and a team including Orbital Sciences Corp. of Dulles, Virginia, and Northrop Grumman of El Segundo, California.

"We're looking at both an Earth-to-orbit two stage and then a crew transfer vehicle architecture," said Michael Coats, former astronaut, and now vice president of reusable space transportation systems at Lockheed Martin Space Systems.

One of the main goals of the SLI is a much safer and more reliable crew transport vehicle of some type, Coats said. While the shuttle program has worked hard to make human space travel safe, it's 25-year-old technology, he said.

"We think we can do a whole lot better than that. So we're looking at an order of magnitude improvement in crew survivability," Coats said. "To get closer to the 1 in 10,000 goal we need a crew escape system," he said.

Boeing's Kevin Neifert, director of next generation launch systems, said his firm, along with SLI duties, is hard at work on the X-37 program. That vehicle will fly from space, enabling NASA to flight test key technologies for use in a full-scale reusable system, he said.

Antonio Elias, general manager of advanced programs for Orbital Sciences Corporation, is looking into a space plane as part of their SLI work, in cooperation with Northrop Grumman. The space plane, about the size of a mid-size jet, could be fitted atop different launchers. This permits alternate human access to space in the event the space shuttle, or the craft's main reusable launch booster, was grounded with a technical problem, he said.

Northrop's Doug Young, director of space systems, said his company is drawing upon a proven track record of integrating several high-tech aerospace projects. Several SLI horizontal concepts being eyed by Northrop, in fact, draw upon a huge winged shaped vehicle, akin to the company's B-2 bomber design.

As for horizontal versus vertical launch systems, Young said runway takeoff offers certain bonuses. Deployment and launch is not locked into weather conditions or launch windows as rigorously as a given fixed site, he said.

"We're still looking at the two [vertical and horizontal launch] and not resolved on which one is going to best yet. They both have their set of advantages," Young said.