Despite its potential to support NASA's manned spaceflight ambitions, the International Space Station (ISS) will fall short unless it sees larger crews, more science and a comprehensive plan to bolster future exploration efforts, according to a report released this week.

The report, performed by a National Research Council (NRC) panel of scientists, found the space station a key resource for the development of technologies required for future exploration, but lacking in manpower and direction.

"[Our] charges included a review of...whether the station was really important for space exploration, and we think it is," said panel chair Mary Jane Osborn, a professor with the University of Connecticut Health Center in Farmington, Connecticut.

But crew limitations and the absence of an integrated plan to use the station to work toward NASA's goal of a new manned lunar mission by 2018 caused some concern to NRC panel members.

"It's very vital indeed since otherwise, you don't really know what you're doing," Osborn said of an integrated ISS plan, adding that increasing station crew size will be a boon for scientific research. "It would allow a significant improvement."

ISS crews have been limited to two astronauts - down from three members - since the 2003 Columbia accident. They are slated to return to a three-person level with the arrival of European astronaut Thomas Reiter aboard NASA's STS-121 shuttle flight set to launch no earlier than May 2006, when the 13th ISS crew will be aboard.

Panel members urged NASA to push for a full, six-astronaut ISS crew by 2008, the earliest the agency believes the station could be ready to sustain such a crew size.

NASA officials said the agency has received the panel's report.

"We're essentially still reviewing it," said NASA spokesperson Allard Beutel said of the report. "We do believe that our 2007 budget will address the overall plans for completing the space station, including our objectives and obligations to our international partners."

NASA plans to launch up to 19 more shuttle flights, 18 of them to the ISS, before the three-orbiter fleet is retired in 2010. The space agency's shuttles are the only vehicles currently capable of delivering the station's most massive components, and NASA officials are working with their international partners to determine the final order of those flights.

But panel members found that at NASA should develop a backup plan to deliver vital ISS components should the agency's aging shuttle fleet be unable to complete the station by its retirement date, according to the report.