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The prolonged grounding of NASA’s space shuttle fleet after its first flight in two and half years has some wondering whether the United States should retire the vehicle even earlier than 2010.

NASA announced Aug. 18 that it is not planning to launch the shuttle again before March to allow more time to solve the foam-shedding problems that marred Discovery’s July 26 return to flight.

NASA Administrator Mike Griffin expressed confidence that the space agency will fix the shuttle’s foam problem, get the vehicle flying again early next year and substantially finish on-orbit construction of the international space station before retiring the space shuttle in 2010.

“We are giving ourselves what we hope is plenty of time to evaluate where we are,” Griffin said during a press conference here announcing the slip to March. “We don’t see the tasks remaining before us being as difficult as the path behind us.”

The space exploration plan outlined by U.S. President George W. Bush in 2004 called for NASA to return the shuttle to flight, complete assembly of the space station by 2010 then retire the shuttle and build new vehicles for taking astronauts to the Moon.

NASA has spent more than $10 billion on the space shuttle program since the February 2003 Space Shuttle Columbia accident and is asking Congress to approve $4.5 billion for the program for 2006. The latest uncertainty about the shuttle comes as NASA and the White House are in the midst of preparing a 2007 budget request expected to include substantial funding for building a Crew Exploration Vehicle and its launcher.

Some space advocates and U.S. government officials said the shuttle fleet’s latest stand down raises fresh doubts about NASA’s ability to finish the space station before 2010 and begs the question whether it would be wiser for the agency to retire the shuttle now and plow the savings into the new hardware.

Others, however, said that hasty retirement of the shuttle — and the resulting impact on jobs — would create a political backlash that could put NASA’s broader space exploration plans in jeopardy.

Marc Schlather, president of ProSpace, a grass-roots space lobbying group based here, said NASA’s unexpected stand down just one mission into a manifest that at one time called for 28 flights by the end of 2010 is a reminder of just how fickle the shuttle can be.

“Our concern all along is that the shuttle may retire itself before anybody at NASA makes that decision final,” Schlather said, explaining that safety considerations could prevent NASA from accomplishing the four or five flights a year seen as the minimum for constructing by the end of 2010 a space station that includes Europe’s and Japan’s research facilities.

“That leaves NASA and the president with one of two possible decisions — either accept that [the space station] will not be completed or fly shuttle indefinitely until it is completed,” Schlather said. “Obviously that second option makes less sense with every stand down.”

A Bush Administration official who deals with NASA said consideration has been given more than once since the Columbia accident to expediting the shuttle’s retirement but was rejected each time out of concern for the political impact.

“There are people here at very high levels that have been asking, why not just shut the darn thing down?’” the official said. “The reason why we’ve continued it is because we felt it was in the best political interest.”

The official said that shuttle’s latest grounding gives fresh ammunition to advocates in the administration who would like to speed up the timetable for ending the shuttle program.

Griffin acknowledged Aug. 18 that NASA’s thinking on shuttle has changed. “We are not trying to get a specific number of flights out of the shuttle system. We are working toward an expeditious but orderly retirement of the shuttle,” he said, adding that at the same time, NASA thinks “that absent major problems, we can essentially complete the space station in the time we have available.”

NASA’s announcement came one day after the release of a final report from the Stafford-Covey Return to Flight Task Group, an independent panel that watched over NASA’s effort to resume shuttle flights after the 2003 Columbia disaster. The 220-page report, while mostly positive, included a minority report signed by seven of the task group’s 26 members blasting NASA’s return-to-flight effort, citing “a cycle of smugness substituting for knowledge” and faulting NASA for, among other things, setting unrealistically early launch dates.

Griffin said the group’s criticism was included at his insistence.

While Griffin said NASA should take time to read the full report, including the scathing minority comments, he does not think NASA is suffering “a crisis in confidence.”

“We’ve worked hard at NASA over the last two and a half years to improve that situation that led to the loss of Columbia,” he said. “But we don’t suppose that we’re done, and one of the reasons why I was very receptive to the minority report was because we can’t get done unless we’re willing to listen to all of the hard truths. So we’re going to be looking at our engineering processes.”

Bill Gerstenmaier, NASA’s foam investigation lead and newly appointed associate administrator for space operations, said the decision to push toward a March 2006 launch date is not final and is pending another two weeks of trouble-shooting efforts by tank engineers. But he said it appears likely that tanks will have to be sent back to their manufacturer in Louisiana for modifications, making launching again this year all but impossible.

Gerstenmaier said pushing the next flight out to March would allow NASA to use Discovery for the next mission instead of Atlantis, which otherwise would have to have flown two missions back to back because the lighter orbiter is needed to carry heavy solar arrays up on the next space station assembly mission. “[T]hat’s a much better overall flight sequence,” he said.

The new target launch window opens March 4 and closes March 19, according to NASA. If NASA does not make March it would have to wait for a window that runs from May 3 to May 22. After that, NASA would have an opportunity to launch between June 30 and July 19.

John Logsdon, director of the Space Policy Institute at George Washington University here and a member of the Columbia Accident Investigation Board, said pushing the next flight off until March was a “prudent decision.”

“The March date seems to me to both provide the breathing room needed to understand if the foam-shedding problem can be fixed in a reasonable time frame or to have a full discussion of alternatives with all interested parties if it cannot,” Logsdon said.

Arnold Aldrich, a former NASA associate administrator for space systems development, said NASA has made much progress in the past two and a half years in its understanding of the external tank. “I see the additional improvements necessary for this system, based upon the results of the Discovery flight, as well within our reach, and NASA appears to be zeroing in on a reasonable date for the next launch based upon the work that must be accomplished,” he said.

Tariq Malik contributed to this article from New York. Comments: