When NASA is considering astronauts for the Astronaut Candidate Program, they look for people who have varying backgrounds. Mission Specialists are typically people who have training as engineers, physicists, mathematicians, or other areas of science.
The commander and pilot of the Shuttle Missions, each of which is given an STS number (STS stands for Space Transport System,) are typically Air Force officers with a significant amount of training in flight. All of the astronauts learn how to fly, and most will fly themselves to Florida a week or more before a launch to do some final rehearsing.
Mission Specialists are the scientists who do experiments on the shuttle. Depending on the shuttle mission, it may be necessary for an astronaut to do intricate work outside the vehicle. This is the case when it comes to repairing the Hubble Telescope. One mission involved replacing gyroscopes, while another involved replacing the battery power pack that made it possible for the telescope to transmit information back to earth.
Astronaut training begins with a program entitled the Astronaut Candidate Training Program. This program is a two year ordeal involving both classroom training and rigorous basic mission training. The candidates must first pass extensive physical examinations. During the first week of Astronaut Candidate Training, the astronauts will have to take three swimming tests.
The first will require that they swim three lengths of a short course or 25 meter swimming pool. They must swim the three lengths without stopping. The second test requires that they swim those three lengths once again, only this time, they must so while wearing a flight suit and sneakers. For the third test, they must tread water continuously for ten minutes. The astronaut candidates will also be required to take the military water survival course.
The classroom work involves all sorts of scientific training, some of which may be taught by more experienced astronauts, but NASA also brings other instructors and engineers in to lecture the candidates. The basic classroom instruction takes about a year. Once they have successfully completed this phase, they can go on to the Basic Mission Training.
As part of the Basic Mission Training, astronauts will be required to take scuba instruction. They will also have to pass whatever tests are necessary to allow them to become fully accredited SCUBA divers. The reason the SCUBA instruction is so important is that astronauts who go on space walks train in one of NASA's two giant tanks.
Additionally, the astronauts will learn everything from basic repairs on a space craft to the routine upkeep, and even food preparation. They will also spend time in the simulators where they can experience weightlessness. They will also be required to take flying instruction.
There is no guarantee that astronaut candidates become full fledged astronauts just by going through the training. It is incredibly rigorous and demanding, and the candidates must complete every aspect of the program successfully. In addition to the successful completion of the program, the evaluations that were taking place throughout the course of the program will be reviewed, and the decision will ultimately be based on both of these things. Not all of the astronaut candidates are able to complete the training program successfully, in which case, they will not be hired as astronauts.
Astronauts who successfully pass the Astronaut Training Program and evaluation period then go on to get assigned to some post training job. The post training job will vary according to the astronaut's expertise. Once they are assigned to a crew, they then begin the Advanced Mission Training. That training requires that they learn all of the practical aspects of mission work. They will learn how to live in weightlessness, repair and maintain the spacecraft, learn to fix their food, learn how to deal with personal hygiene and bathroom issues while in weightlessness, and they will learn how to workout in weightlessness.
They will have pseudo dress rehearsals to practice every aspect of the mission. Astronauts who are required to go on space walks will train in one of NASA's specially designed tanks. They will train in a suit that is modified to accomodate the underwater conditions.
NASA has replicas of the shuttle so that astronauts can practice working in a life size model of the real shuttle. Different missions have different purposes. There have been many missions in which the Shuttle docks with the International Space Station. In the past, astronauts have spent time on Mir. Astronauts who are going to spend time working with other Russian astronauts or cosmonauts will train by actually going to Russia. They will learn the language in addition to all of the other things they must do.
For missions in which space walks are involved, NASA has an 11 million gallon pool at the Johnson Space Center in Houston. The pool is designed to recreate the atmosphere of space to the greatest degree possible, even to the point of containing replicas of the Hubble Telescope and the International Space Station. An astronaut who is going to do a space walk, especially one that requires the astronaut to do detailed and intricate work to repair things, will practice everything that will be done for many months before the mission, right in the pool.
Regardless of what phase of training an astronaut is going through, the entire training program is incredibly rigorous and demanding. Even the astronauts who successfully complete the training programs and go on missions may not stay with the space program for more than a few years.
For Mission Specialists, astronaut training really begins with their college education when they start the coursework that will pave the way for their future acceptance as astronauts. Pilot Astronauts begin their training the moment they join the military.