NASA will accelerate development efforts for a new manned spacecraft that will follow the retirement of the agency's shuttle fleet, a top spaceflight official told U.S. Senate subcommittee today.

NASA's three remaining space shuttles are slated for retirement by 2010 following the completion of the International Space Station (ISS). A new spacecraft - the Crew Exploration Vehicle (CEV) - has been tapped as its replacement, but is not expected to fly its first human-carrying mission until at least 2014.

"Eliminating that gap between [shuttle retirement] and a new vehicle, and making sure it has the ability to dock with the ISS, is imperative," said William Readdy, NASA's associate administrator for human spaceflight, during a hearing before the Senate's science and space subcommittee on the state of ISS research. "We're going to accelerate the crew exploration vehicle."

Sen. Kay Hutchison (R-Texas), subcommittee chair, said that NASA must work to avoid being caught without the ability to launch its own human missions to the ISS and low-Earth orbit.

"I think that we cannot allow that kind of hiatus right now," Hutchison said to a panel of NASA program managers, astronauts and scientists. "I think of it as a national security threat to our country and I intend to pursue everything I can to look at ways to shorten that time period."

Any lengthy break between the shuttle's retirement and the first manned CEV flight will likely force the U.S. space program to look toward its international partners for human spaceflight capability, NASA officials told the subcommittee. Space agencies in both Europe and Japan are currently developing their own spacecraft to deliver cargo the ISS, they added.

"We would certainly be dependent on someone else," said Howard Ross, NASA's deputy chief scientist, during the subcommittee hearing.

NASA has already depended heavily on Russian Soyuz spacecraft to launch U.S. astronauts to the ISS, as well as Russia's unmanned Progress vehicles to resupply space station crews. In December 2004, food supplies dwindled aboard the ISS, forcing the two members of the Expedition 10 crew to modify their diet until the Dec. 24 delivery of a fresh Progress cargo ship.

That Russian dependency was spurred by the grounding of NASA's shuttle fleet following the Columbia disaster in 2003. The space agency is preparing to launch its first shuttle flight since then later this year.

"That, of course, is our dual concern," subcommittee ranking member Sen. Bill Nelson (D-Florida) told Readdy and other panel members of NASA's international reliance. "In the geopolitics of today, that's no problem, but what are the geopolitics going to be like in 2012? The two of us feel we need to accelerate the CEV."

Hutchison also pressed NASA officials and researchers to revisit the long-term scientific goals of the ISS - including the potential of designating it as a National Laboratory - to look beyond its current role to support NASA's space vision of renewed human exploration of the moon and Mars.

"I think that it is important that we not just say this is a tool for moon and Mars-related research," Hutchison said. "I think this facility is capable of doing so much more for the nation and for the world."