NASA selects astronauts from a diverse pool of applicants with a wide variety of backgrounds.
Only a few are chosen from thousands of applications.
There are no age restrictions.
Flying experience is not a requirement.
Astronauts earn $64,724 to $141,715 per year.
Since the start of the manned space program in the late 1950s, only 330 astronauts have been selected.
Faster than a speeding bullet, 8.5 minutes, 3,000 mph and 3.5 G's -- it was the ride of a lifetime.
"By the time you get into orbit, it feels like an elephant standing on your chest," said Dr. Robert Satcher Jr. "It was a spectacular ride, especially the first few minutes."
Satcher, a surgical oncologist at M.D. Anderson Cancer Center in Houston, is a former astronaut who traveled to the International Space Station in 2009. On Monday, he spoke to doctors and residents at Erlanger Health System, describing the experience and ongoing research on medical issues in space.
Satcher, 46, said becoming an astronaut was a natural extension of his interest in science. With a doctorate in chemical engineering from Massachusetts Institute of Technology and medical degree from Harvard Medical School, he worked as an orthopedic surgeon before being selected to become an astronaut in 2004.
In November 2009, Satcher flew on the shuttle Atlantis to the International Space Station, where he spent nearly 10 days in space and did two space walks. He even operated on the space shuttle's robotic arms.
Dr. Paul Apyan, an orthopedic surgeon and associate professor at the University of Tennessee College of Medicine, heard Satcher speak at a conference last year and immediately knew he wanted to bring him to Erlanger.
"We need to get young people interested, to expose them to different experiences," Apyan said. "We can have an astronaut from Chattanooga."
Although nine out of NASA's 60 astronauts are doctors, Satcher was the only orthopedic surgeon. Because back pain and musculoskeletal injuries are some of the most common problems in zero gravity, his background was valuable, Satcher said.
Bodies change in zero gravity -- people get taller and lose weight, Satcher said. Joint pain also goes away because people no longer put weight on their joints.
But medicine in space has many unknowns -- doctors have never treated a broken bone or done surgery in space, he said.
With budget cuts across all spectrums of federal government, NASA has cut way back on its manned space programs, something Satcher said he's sorry to see happen.
"We need to get back to deep-space exploration," Satcher said. "The whole effort of exploration cuts to the heart of what we do as scientists."
Satcher retired from NASA in November. NASA has retired its shuttles, and astronauts now must use Russian rockets to reach the space station. At 6 foot 3, Satcher said he is too tall to fly in Russia's spacecraft. Rather than waiting to see if the U.S. will restart its shuttle program or what may change in NASA, he said he decided to return to medicine full time.
Training and working as an astronaut changed his approach to medicine, teaching him the value of working as a team, he said.
"I think it gives you a different perspective," he said.