Astronauts train to service Hubble in a huge, water-filled tank that simulates weightlessness. The 40-foot-deep (12 m) tank at NASA’s Johnson Space Center contains full-scale underwater mockups of Hubble, its instruments, and the carriers that hold the instruments. The astronauts wear pressurized suits similar to those they wear in orbit. They spend weeks doing this kind of training, and weeks in class. The astronauts also train using virtual reality, and in a chamber that mimics space temperatures of 200 to minus 200 degrees Fahrenheit (93 to minus 93 Celsius).