NASA
They go underwater in a giant pool of water, it is the closest to 0 gravity on earth. Occasionally, they go into a plane called 'Vomit Comet'. The plane goes high up in the atmosphere and descends...
"An astronaut" is the correct form, not "a astronaut." "an" is used instead of "a" whenever the word it modifies begins with a vowel.
They use centrifical force machines to duplicate high G-forces. They train underwater to simulate weightlessness.
yes of course otherwise how will they know about space and astronauts