This story was updated at 11:16 a.m. EDT.
NASA will likely have to continue flying its aging space shuttle fleet beyond its planned 2010 retirement date in order to complete construction of the International Space Station, a presidential panel said Tuesday.
Former astronaut Sally Ride, a member of the Review of U.S. Human Space Flight Plans Committee, said that it was unlikely NASA could meet the current deadline of retiring the space shuttle by next year, as is currently planned. The first operational flights of the agency?s replacement for the shuttle, the Orion spacecraft, may also be delayed a year or so beyond its 2015 target, she added.
The review panel was appointed by the White House Office of Science and Technology Policy to reevaluate NASA's current direction, including the goal of returning humans to the moon by 2020. It is expected to issue a report in August.
Ride and the other members of the panel's subgroup examining plans for the International Space Station and space shuttle predicted that the currently scheduled shuttle flights will take until about March 2011 to complete.
"There's little margin remaining in the current manifest," Ride said. "NASA is considering safety first" when deciding when to launch shuttle missions, but "the closer you get to a hard and fast deadline, the more difficult that becomes."
NASA plans to launch seven more shuttle missions after the current flight of Endeavour, which undocked from the station Tuesday, to complete construction of the orbiting lab.
"The manifest as currently stated through 2010 is exceptionally ambitious and requires a flight rate that is approximately twice what the post Columbia flight rate has been," said review panel member Charles Kennel, chair of the National Academies Space Studies Board.
The panel also proposed that the International Space Station's working lifetime be extended through at least 2020, beyond the planned decommissioning in 2015, which is only five years after it is fully assembled.
"We think all of the options going forward should include an extension of ISS in some form," Ride said.
The panel felt that it would be a poor return on investment to utilize the station for only a short time after spending about 25 years to build it. In addition, the other international partner countries working on the station have all strongly pushed for an extension to the laboratory's lifetime.
Extending the launch plans to mid-2011 would add about $1.5 billion in unbudgeted costs for NASA, though.
Additionally, the review panel estimated that NASA's next generation human space exploration program, Constellation, is likely to be delayed past its planned 2015 launch date. The Constellation spaceship, called Orion, will probably first launch humans at least a year or two late because of budget cuts and technical difficulties.
"It is likely that the initial operation capability for the next human rated launch vehicle will come no earlier than 2017, and there is a significant probability that it will be several years," Kennel said.
Ride blamed the Constellation delay on a gap between the goals laid out for the program by former President George W. Bush, and the budget allocated to NASA by Congress to achieve them.
"NASA has not been given the resources to support this vision," she said. "You can't expect the agency to achieve grand and glorious goals" and then not provide the necessary funding, she said.
- Video - NASA's Constellation Journey Begins: Part 1, Part 2
- End in Sight: Final Space Shuttle Missions Slated
- Image Gallery - The First 100 Space Shuttle Flights
Editor's note: This article was updated to correct the cost of extending shuttle flights through March 2011.