Space taxis: alternatives beyond the shuttle

Astronaut Ken Bowersox should be going home next week. When he and his two crewmates stepped onto the International Space Station three months ago, the schedule seemed set. They would return to Earth on the space shuttle Atlantis, which was to launch March 1.

Instead, come Monday, Mr. Bowersox and his colleagues will whirl 240 miles overhead, much as they have for the past month, waiting for a ride that may never come.

The crew has supplies to make it until June, and it can always use a Russian "lifeboat" pod to escape. But the grounding of all shuttles during the Columbia crash investigation points out a predicament unthinkable in the earliest days of the program: NASA's near-total reliance on a fleet of aging orbiters designed in the Nixon era.

The next-generation shuttles planned since the program began - and expected to replace the original shuttles by now - are still in the realm of science fiction. Indeed, the shuttle's original mission of getting into space cheaply and frequently has proven far more difficult than ever imagined, forcing NASA to hang on-to a temperamental technology that is pushed to the brink of its capacities on every flight.

For that reason, the coming months will be crucial to America's future space fleet. The Columbia disaster has given a new urgency to plans to either replace or supplement the shuttle. Findings of the investigation could shape how these vehicles look and work.

"The cause of the problem could determine the direction that the next-generation vehicles take," says Howard McCurdy, a NASA historian at American University in Washington.

For now, the cause of the accident is still unclear. Data suggests a breach of the heat shield on the left wing, perhaps near the wheel well, but the investigation has not yet presented a convincing cause. Loose foam and space debris continue to be two of the leading culprits.

Until the investigative board reaches a conclusion, though, and the three remaining shuttles are cleared to fly again, NASA has no way to fully maintain the space station - and no Plan B.

Just two years ago, a project to build a next-generation shuttle was scrapped because of budgetary and technological constraints. Knowing this, NASA administrator Sean O'Keefe last month decided to extend the shuttles' already-extended lifetime from 2012 to 2020.

The agency, in fact, is not set to make the $50-billion decision on what the next-generation shuttle will be until 2009. It has instead focused on developing a smaller and less expensive "space plane" that would likely ride into space on top of a rocket, ferry crew to the space station, and return to Earth. Boeing is scheduled to test one proto type in 2006.

None of these projects, however, is attempting anything new. On the contrary, they are attempting to solve the same problem that the shuttle was intended to solve: How to get into space on a budget.

When the shuttle was conceived after Apollo, it was designed to be just that - a shuttle. If it could lower the cost of delivering cargo into orbit, it would open space to the orbiting ports and moon bases envisioned since the dawn of the space age. The goal was to make 25 to 50 trips a year, and save money by building a reusable vehicle. Estimates suggested that the shuttle would pay for itself with commercial payloads.

Yet the shuttle has never made more than nine flights in a year. Each mission costs nearly half a billion dollars. And businesses have turned to traditional rockets, which remain far less expensive.

What went wrong, in some senses, was the shuttle itself. Quite simply, the technology necessary to do what NASA wanted to do has still yet to be invented. Each shuttle is at once too heavy, too fragile, and too complicated to make the hoped-for six to 10 flights a year without huge budget increases.

"It's complicated because it has to be," says Tom Utsman, a former director of the shuttle program. "You were always pushing the state of the art."

For the first decade of shuttle flight, the vehicle's engines were so badly stressed on each flight, he says, that they had to be overhauled after every mission. Despite testing various materials to protect the wiring in each shuttle, cracks and damage were commonplace. The wear is such that shuttles occasionally have to be decommissioned for months to be essentially rebuilt.

The shuttle has 750 components on its "criticality 1" list, says Dr. McCurdy. "That means if any of those components fail, a catastrophic failure is imminent."

The massive maintenance regimen needed to repair and replace these systems for every mission means the shuttle is reusable in name only. And the only way to solve the problem is to build the orbiter from stronger and lighter materials that don't exist yet. The pace of progress, most say, will depend on how important the project is to NASA and Congress after Columbia's crash.

"Practically everything you touch has to be developed, from the materials to new propulsion systems," says Corin Segal of the Institute for Future Space Transport, a seven-university consortium created by NASA last year to consider ideas for second-generation shuttles. "But the focus has not been there.... We could have replaced the shuttle by now if we'd had the right level of funding."