SPACE CENTER, Houston (AP) -- George Zamka has been an astronaut for almost seven years and he still hasn't made it to space. But he's far from alone. Grounded for two years, a third of the nation's nearly 150 astronauts have never flown in space, and some wonder when they will.
"Part of being at NASA is very few people get to fly in space,'' Zamka said. "Everyone else gets their enjoyment by contributing to the space mission.''
The last class of astronauts has already been warned that it's unclear whether any of them will fly during the shuttle era -- which ends in five years. All face an uncertain future and development of the next-generation space vehicle could take until 2015.
"They knew very well that they arrived at the sunset of the shuttle and the dawn of the new vehicle and they may be exposed to the gap in between the two,'' Zamka said of the newest class of astronauts. "For the last classes, there has been an effort made to make sure they are informed as to what the wait may be like. And they come anyway.''
Forty-six of the nation's 142 astronauts have not flown in space; some of them are rookies, others have waited for years.
Zamka didn't think his wait would be so long. He expects to be assigned to a flight in another two years and hopes to fly within the next four.
By that time, he'll have waited a decade.
"The nature of the business is it is a risky business, and certainly, part of that risk is delays and unforeseen events,'' Zamka said. "A lot of these things are just out of my control.''
Astronaut Mark Polansky, who has flown one space mission and is set to command a mission next year, said some of his colleagues have expressed concern about where they are in line and when the opportunity to fly will come their way.
Zamka tries not to focus on it and says it only crosses his mind when he's idle.
"We are not stewing over here because we are not flying,'' he said. "We are all busy trying to get back to flying. We all turn ourselves to the task at hand and that is how we deal with it.''
They get inspiration from former astronauts, such as Story Musgrave, who waited 16 years to fly. He was selected as an astronaut in 1967 and didn't make it to space until 1983.
"I never had the attitude: 'I finally made it,''' Musgrave said from his Florida home. "That wasn't the way I was thinking.''
Instead Musgrave said he concentrated on the tasks before him and working to be the best in the business.
"Space is my calling,'' Musgrave said. "It was not a stepping stone to something greener. It was a calling, so I just took it as far as I could.''
Musgrave ultimately flew on six shuttle missions before leaving NASA in 1997. Since his departure, Musgrave has written numerous scientific papers and worked as a consultant.
Shuttle missions have been halted since the Columbia accident two years ago that killed all seven crew members. May is the target for the next shuttle flight, but even that is a tentative date.
There was a similar grounding of shuttles after the Challenger explosion in January 1986 while repairs were made. But back then, only two or three astronauts worked full-time to correct the solid rocket booster problem that caused that disaster, said astronaut Pam Melroy.
This time it's different.
Virtually all astronauts are intimately involved in the shuttle improvements, which include the ability to make repairs in space.
"The focus is very heavily on the astronauts and the crew, because they are going to have to actually go out and do this,'' Melroy said of the in-orbit repairs.
Almost everyone in the astronaut office is involved with return-to-flight in some way. The training, studying and additional work have been relentless, the astronauts say.
Those who aren't in a shuttle crew are assigned a variety of return-to-flight tasks and research on the development of a new space vehicle and President Bush's moon-to-Mars plan outlined last year.
Astronaut Andy Thomas, one of the crew members tentatively set to fly in May, has been concentrating on the three spacewalks for the next mission, which will test a variety of inspection and repair techniques.
"Even though we are not flying, it is a very busy time, it really is,'' Thomas said as he made sure two of his colleagues were properly strapped in and lowered into the neutral buoyancy lab pool. "It is an ambitious undertaking.''
NASA would like to get a few more flights out of its three aged shuttles -- built on 30-year-old technology -- before they are phased out in 2010.
Once the shuttles are retired, it could take until 2015 for NASA to have a new vehicle ready to go.
"People are not shirking that opportunity just because there is a wait in front of them,'' Zamka said. "This is a wonderful opportunity to be in the line or the window to fly in space at some time.''