CAPE CANAVERAL, Fla. (AP) -- NASA's new boss made an impassioned case Thursday for speeding up development of a new spacecraft so that the United States will not lose access to space when the shuttle is retired, but warned something else will have to be sacrificed.

Administrator Michael Griffin told a Senate subcommittee in Washington that to cover the cost of the shuttle replacement's accelerated debut, he may be forced to delay some space station and exploration research.

"We can't do everything on our plate, and we have to have priorities and first things first,'' he said.

Griffin wants to fly the proposed new spacecraft as soon as possible once the space shuttle fleet is retired in 2010 - avoiding a four-year gap in which the United States would have no way to launch astronauts.

The current plan, which he inherited when he took over NASA last month, calls for the new vehicle to carry a crew into orbit by 2014 and be capable of traveling to the moon and Mars, with modifications, in the years beyond.

Griffin said he finds that four-year launch gap unacceptable and hopes to have a plan for closing it by mid-July. The new crew exploration vehicle, or CEV, is a key part of President Bush's plan for returning astronauts to the moon by 2020.

"CEV needs to be safe, it needs to be simple, it needs to be soon,'' Griffin told reporters later in the afternoon.

The six-year gap between the 1975 Apollo-Soyuz mission and the 1981 debut of the shuttle damaged both the U.S. space program and the nation, Griffin said. "I don't want to do it again.''

"The United States of America should always have its own access to space,'' said Sen. Barbara Mikulski, D-Md.

Griffin told the Senate subcommittee on commerce, justice and science that he does not know how much it will cost to accelerate development of the crew exploration vehicle, still in the early design phase. But he said by choosing a single contractor in 2006, rather than having two contractors competing in flight in 2008 as envisioned by the former NASA administrator, $1 billion or more could be saved for use in the near term.

Additional money could be saved by putting off research at the international space station - such as experiments geared toward long-term moon stays or Mars habitation _ and possibly eliminating the handful of shuttle flights needed to fly that equipment, Griffin said. Eighteen shuttle missions are currently on the books to finish building the space station, along with 10 supply runs for a grand total of 28.

Right now, NASA's three remaining shuttles are grounded as the agency struggles to remedy all the safety concerns arising from the 2003 Columbia tragedy. Managers hope to launch Discovery on the first mission since the disaster in mid-July; repair work is going slow, though, and the schedule is tight.

Griffin assured the senators he would use a scalpel rather than a meat ax in cutting the research budget for the space station and other exploration systems, and would look at delaying projects not yet begun.

"Now the research ... is very valuable and it must be done,'' he said. "But if it is delayed a very few years in order to allow us to complete and affect a suitable transition between systems, then I believe that that delay would be worth it. And that would be where I would look for the money.''

Griffin pledged that NASA will complete the space station, currently just half built. But if the station still isn't finished when the shuttles are retired, the space agency may turn to unmanned rockets to haul up the remaining gear.

As for the Hubble Space Telescope, Griffin has ordered work to begin on one last shuttle servicing mission, with $291 million set aside in next year's budget. Whether that mission takes place will depend on the success of the next two shuttle missions.

Griffin's predecessor, Sean O'Keefe, ruled out Hubble visits by astronauts because of post-Columbia safety concerns.

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