NASA's Associate Administrator of Space Operations Bill Gerstenmaier at a news conference Thursday, "From an overall standpoint, we think March 4th is the time frame we are looking at."
The announcement came a day after an independent panel tasked with monitoring NASA's compliance with numerous safety recommendations released a report saying the space agency is still plagued by a flawed leadership style and engineering practices that led to the 2003 Columbia disaster.
The shuttle Columbia burned up as it was re-entering the Earth's atmosphere on Feb. 1, 2003, killing all seven astronauts aboard. A piece of foam from the external fuel tank punched a hole in the heat shield on the orbiter's wing during liftoff, allowing superheated gases generated during re-entry to melt the metal structure under the wing, causing the shuttle to destabilize and break apart.
NASA grounded the remaining shuttle fleet and spent the next two-and-a-half years integrating safety devices and procedures into the shuttle program.
The space shuttle Discovery then successfully launched July 26 on a 12-day mission to test the safety procedures and dock with the International Space Station.
During Discovery's launch, however, cameras captured the image of a large piece of insulating foam falling off the fuel tank and barely missing the orbiter.
Numerous safety checks and an unprecedented spacewalk confirmed the shuttle had sustained no damage that would put it in danger during re-entry.
Nonetheless, even as Discovery was in orbit, NASA announced it was grounding all future shuttle flights until the persistent problem of foam loss could be fixed.
Atlantis was scheduled to be the next vehicle to take supplies to the space station but was now going to have to do back-to-back missions to carry a heavy truss to the station, said Gerstenmaier, Reuters reported.
NASA Administrator Michael Griffin said the space agency's whole thinking on the shuttle was changing.
"We are not trying to get a specific number of flights out of the shuttle system," he said. "We are working toward an expeditious but orderly retirement of the shuttle system over the next five years. We are going to use the shuttle system between now and then to assemble the space station."
The space station has enough food, water and other critical supplies to last through the end of the year, Gerstenmaier said.
Russia will continue to fly cargo and crew to the station, although only the shuttle can carry the large pieces needed to finish it.
The "Return to Flight" task group, co-chaired Tom Stafford and Richard Covey, issued a final report Wednesday that found NASA had made significant strides to correct the conditions that led to the deaths of the Columbia crew. But seven of the group's 26 members issued a separate assessment saying problems lingered in every aspect of the shuttle's return to flight, reported the Los Angeles Times.
NASA continues to put schedule ahead of safety, follows lax engineering practices and exhibits an unwillingness to learn from its mistakes, the seven members wrote.
Stafford and Covey said they thought the shuttle was safer than it was in 2003 and NASA's efforts to reshape the agency after the loss of the Columbia were commendable, if imperfect, according to the LA Times.
The task group was set up by former NASA Administrator Sean O'Keefe in 2003 to observe and report on the agency's efforts to implement new safety protocols.