(AP) -- NASA's mighty astronaut corps has become a shadow of what it once was. And it's only going to get smaller.
It's down to 60 from an all-time high of 149 just a decade ago, with more departures coming once Atlantis returns this week from the very last space shuttle voyage.
With no replacement on the horizon for the shuttle, astronauts are bailing fast, even though the International Space Station will need crews for at least another decade.
The commander of Discovery's last flight back in March, Steven Lindsey? Gone to a company whose proposed commercial spacecraft resembles a mini-shuttle; his last day at NASA was Friday.
The skipper of Endeavour's last mission in May, Mark Kelly? Retiring in another few months to write a memoir with his wounded congresswoman wife, Gabrielle Giffords.
The captain of Atlantis, Christopher Ferguson, assured The Associated Press from orbit late last week that he'll be sticking around after this final shuttle journey of them all. At least one of his crew, though, isn't so sure.
After spending her childhood wanting to be an astronaut - and achieving that goal in 1996 - Atlantis astronaut Sandra Magnus now has to figure out what the next chapter holds.
"Now that I'm an astronaut, the whole idea of what I want to do when I grow up comes back full circle," said Magnus, a scientist and former space station resident who's flown in space three times.
What a difference a decade makes.
NASA's fabled astronaut corps numbered 149 in 2000-2001, the biggest group ever. Then shuttles were zooming back and forth building the space station, and a crew was being groomed to fly aboard Columbia to the Hubble Space Telescope. Now the space station is finished, Columbia is gone and the 30-year shuttle program is ending.
These days, chief astronaut Peggy Whitson finds herself on overdrive, working hard to keep up the morale at Houston's Johnson Space Center, astronaut headquarters, while trying to convince outsiders that America still needs a robust astronaut corps in the shuttle-less era.
After all, she's got a space station to staff.
Two Americans usually are among the six people living on the orbiting lab at any given time, hitching rides up and down on Russian Soyuz capsules. Private U.S. companies hope to take over this taxi job in three to five years, freeing NASA up to explore true outer space. First the goal was the moon, now it's an asteroid and Mars.
"It's a very dynamic time, and a lot of folks aren't real comfortable with all the uncertainties," Whitson said. "None of us are."
Ferguson observed from space Friday that former military pilots make up about one-third of the astronaut corps, so he's not surprised so many commander types are departing.
"Pilots like to do what pilots like to do, and that's fly airplanes," the retired Navy captain told the AP.
Whitson - herself a two-time space station resident - figures she needs 55 to 60 active astronauts "at a bare minimum and for pretty much the duration." She said she has to account for absences due to injury, illness, pregnancy, even maxed-out exposure to cosmic radiation.
The National Research Council is evaluating just how many astronauts America really needs. A report by a committee of retired NASA leaders, ex-astronauts and others is expected next month.
Depending on the findings, NASA may start taking applications soon for a new, albeit small, astronaut class. No matter the size, there will be plenty of applicants, all eager to join this exclusive club. Only 330 Americans have been chosen by NASA to become astronauts, beginning with the seven original Mercury astronauts in 1959. The number of applicants over the decades: nearly 45,000.
More than 3,500 applied for the nine slots in the 2009 astronaut class, the most recent, even though the shuttle's fate was clear. Those selected were in their 30s and 40s.
The same thing happened after the Challenger and Columbia disasters in 1986 and 2003, said Duane Ross, NASA's manager of astronaut candidate selection. He theorizes that the more NASA is in the news, the more the attention and, consequently, applicants.
Ross said he told the 2009 hopefuls up front: "You guys are not going to be flying shuttle period, you guys are space station astronauts."
Translation: as much as five years of training, Russian language immersion, half-year space stays. No more sprinting back and forth to orbit for a week or two. Plenty of desk duty, too, in between flights, assisting from Houston with future exploration projects and other matters.
NASA's first shuttle pilot, Robert Crippen, waited out the lengthy gap between Apollo and the space shuttle. Nearly 12 years passed from the time he became an astronaut in 1969 until his first spaceflight on Columbia in 1981 alongside moonwalker John Young.
"I figured, well, it's the best thing in town as far as I'm concerned, so I went in knowing it was going to be at least a decade before I had an opportunity to fly," said Crippen, now 73. "I believe there will be people who still would want to stick around and do that."
Army Lt. Col. Mark Vande Hei, Class of 2009, is one of them. While he anticipates flying to the space station in the middle of this decade, he'd jump at the chance to fly to an asteroid in 2025. That's the favored destination of the Obama administration, to be followed up with a trip to Mars in the 2030s.
"It's an adventurous, challenging, interesting job," Vande Hei said last week, "and even if you're not flying in space, you're participating in a space program where somebody else is getting up into space."
But what if you've already flown in space? Then what?
Andrew Feustel, Class of 2000 and a member of Endeavour's last crew in May, said that's the topic of conversation at home and in the hallways of the astronaut office at Johnson Space Center.
"When I started with the program, I never realized there would need to be a third career," said Feustel, a geophysicist who worked in mines once upon a time.
"That's the trick, is to figure out how do you top that," he said. "I don't think you can."
Explore further: How bad can solar storms get?