The demise of the space shuttle Columbia has sparked a new debate over the usefulness of the shuttle program. Space agency officials and members of Congress have said the shuttle program will continue. But shuttle critics are getting a new hearing in the wake of the Columbia disaster.

Much like the 1986 explosion of the space shuttle Challenger, the unexplained disintegration of Columbia has shaken the space agency NASA to its core.

Key members of Congress have been quick to rally in support of the space program. New York Republican Congressman Sherwood Boehlert, who chairs the House Science Committee that oversees the U.S. space program, told NBC television that a congressional inquiry into the Columbia disaster will ask some tough questions about the future of the space shuttle.

"I think we should continue the space shuttle and the space station, and just about every government leader has said the same thing," said Congressman Boehlert. "But we have to reassess the cost, we have to look at the possible sacrifices. There are a lot of decisions we have to make in the future."

The general success of the space shuttle has made it easy to forget that the program has had its share of critics over the years. Among them is former NASA engineer Don Nelson. He was so concerned about the age and safety of the shuttle fleet that he wrote a letter to President George W. Bush last year urging a moratorium on shuttle flights.

"What I wanted the president to do was to limit the number of crew on the [shuttle] vehicle so that if we did have a problem, they would be people who had absolutely had to be there to fly the mission," he told NBC's Today show.

Another shuttle critic is former NASA historian Alex Roland, now a professor at Duke University in North Carolina. He argues that the shuttle program has been more expensive, more dangerous and less productive than was promised when it began more than 20 years ago. He told NBC television that space agency officials also ignored some of the warnings about shuttle safety contained in a report on the Challenger explosion.

"After the [1986] Challenger accident, the Rodgers Commission and all the other bodies that investigated the shuttle program told NASA two things: do not rely primarily on the space shuttle - it is too fragile, too complicated, too risky a technology - and move immediately to begin to design and develop a replacement vehicle," said Professor Roland. "Here we are, 17 years later, [and] NASA is still massively dependent upon the shuttle, and now our civilian program will shut down until they can fix it, and there is no new launch vehicle in sight."

But even as shuttle critics take their moment in the spotlight, shuttle defenders are busy making the case that the shuttle program needs to be fixed, not cancelled.

"I think the space shuttle is the greatest flying machine ever built by mankind," said former astronaut Jerry Linenger, a veteran of shuttle flights and a lengthy stay aboard the now defunct Russian Mir space station. He said the aging shuttle fleet is constantly being upgraded "It is an incredible vehicle. It is not a 1980 vehicle. Columbia was not a 1981 vehicle. It has been modified, improved."

Another shuttle defender is James Oberg, a former NASA engineer and a leading expert on space disasters. He told VOA's Focus that the shuttle will remain the backbone of NASA's human space flight program for the foreseeable future

"As technology improves in propulsion and in power and in metallurgy, the time may come when more efficient systems with the shuttle's capabilities can be built," said Mr. Oberg. "We still don't see how to do that. We're still using the shuttle because it remains the best engineering answer to the kinds of tasks it has been assigned to do."

NASA would like to retire the shuttle fleet by 2012 and is already working with several U.S. aerospace companies to develop a successor spacecraft.