Astronaut Guion Bluford about to be lowered into the training pool in the Johnson Space Center Weightless Environment Training Facility (WET-F) prior to his flight on Shuttle Mission STS-39 of 9-17 March 1991. WET-F is a 25-ft deep pool of water which allows simulation of operating in a weightless environment, especially 'spacewalks'. This allows the astronauts to practice emergency repair procedures both to the payload to be carried and to the Shuttle orbiter itself.