Cape Canaveral -- 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 the 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 the Endeavour's last mission in May, Mark Kelly? Retiring in another few months to write a memoir with his wounded congresswoman wife, Gabrielle Giffords.

Uncertain future

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 former space station resident who has flown in space three times.

These days, chief astronaut Peggy Whitson finds herself in overdrive, working hard to keep up the morale at Houston's Johnson Space Center, astronaut headquarters. 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 the 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."

Evaluating staffing

Whitson - herself a two-time space station resident - figures she needs 55 to 60 active astronauts. She has to account for absences because of injury, illness, pregnancy, even maxed-out exposure to cosmic radiation.

The National Research Council is evaluating just how many astronauts the United States really needs. 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 the 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: almost 45,000.