NASA has received 6,300 applications from people wanting to be astronauts, the second-highest number in the space agency's history.
"This is a great time to join the NASA family," NASA administrator Charles Bolden said. "Our newest astronauts could launch aboard the first commercial rockets to the space station the next generation of scientists and engineers who will help us reach higher and create an American economy that is built to last."
NASA typically receives between 2,500 to 3,500 applications. The highest response was in 1978 with 8,000 applicants.
The rigorous and lengthy selection process begins with a review of applicants by a team of mostly active astronauts who prepare a short-list of candidates.
Those who make the cut will be brought to the Johnson Space Center for further interviews, medical examinations and psychological testing.
"We will be looking for people who really stand out," said Peggy Whitson, chief of the astronaut office at NASA's Johnson Space Center and chair of the astronaut selection board.
"Our team not only will be looking at their academic background and professional accomplishments but also at other elements of their personality and character traits — what types of hobbies they have or unique life experiences. We want and need a mix of individuals and skills for this next phase of human exploration."
Nine to 15 applicants will be chosen to be part of NASA's 21st astronaut class, which will be announced in the spring of 2013.
They will undergo two years of initial training, including space station systems, Russian language and spacewalking skills. Those who complete the training will be assigned technical duties at Johnson and, ultimately, missions.
Astronauts need to learn Russian because the only way to ferry people and cargo to the International Space Station is on the Russian Soyuz rocket, after NASA retired its aging fleet of shuttles.
So far, Chris Hadfield is the only Canadian astronaut who has been assigned a space mission. He is scheduled to take off in November aboard a Soyuz rocket and spend six months aboard the space station.
Two other astronauts with the Canadian Space Agency, David Saint-Jacques and Maj. Jeremy Hansen, are based in Houston and haven't so far been assigned a mission in orbit.
More rigorous screening
NASA reviewed its medical and psychological screening and followup health-care procedures for astronauts in 2007 "to ensure [they]
have the level of psychological and medical care and attention they need" following a bizarre love triangle involving two of its astronauts.
Lisa Nowak, 46, a navy captain and married mother of three, was a member of NASA's astronaut class of 1996 and had flown on one mission, STS-121 in 2006. She became upset that Colleen Shipman was dating her former love interest, NASA shuttle pilot Bill Oefelein.
Nowak confronted Shipman in the parking lot of Orlando International Airport in February 2007 after driving 1,600 kilometres from Houston. She had worn diapers so she could drive straight through without stopping.
Her lawyer told court she suffered from major depression, obsessive-compulsive disorder, insomnia and a "brief psychotic disorder with marked stressors."
She pleaded guilty to felony burglary and misdemeanour battery and was sentenced to a year on probation in 2009. Both Nowak and Oefelein were dismissed from NASA.