Space travel has always been about a sense of wonder.
"There's an element of exploration," says NASA astronaut James Reilly. "You are always looking over the hill [to] what's next."
But many experts wonder whether the shuttle is the best way to do it — with its ongoing technical problems, its cost — a billion dollars a mission — and its danger.
Dr. Alex Roland is a space policy expert at Duke University. He says the shuttle's problems began more than 35 years ago when it was first designed to be an inexpensive reusable space vehicle.
"There is no question in my mind that it would be best policy to say forget it," says Roland. "The economic profile for it wasn't working out at all even before it flew."
So why is the shuttle flying now?
Its goal is to finish construction of the International Space Station, where two people stay in orbit for months at a time. The station has grown in cost from $6 billion to $100 billion and it is decades behind schedule.
The space station is supposed to be for science. But many say NASA's best science is done with unmanned devices like the Hubble telescope and the Rover mission to Mars. On the space station, astronauts spend much of their time studying the effects of weightlessness on their own bodies.
"[It's] just trivial stuff," says Dr. Robert Park at the University of Maryland. "No real experiments are being done on the space station right now at all. They're just trying to stay alive!"
Indeed, last year President Bush announced the United States will replace the shuttle with a new spaceship to build a station on the moon. But NASA insists it would be wrong to stop shuttle flights now.
"Basically, it will be America stepping backwards out of space," says astronaut Reilly.
That's a step many outside NASA think might be the best policy with the aging shuttle.