A is for Astronaut—but also what your report card needs to be filled with all the way through grad school. The path to NASA is cutthroat, and you'll need genius-level grades—especially in math and science—to put you in the running. This means a bachelor's degree in Earth or space sciences or engineering (at least), and a graduate degree if you're really serious about this (source).
If you want to pilot the space vehicles of the future, a military academy may be your ticket. You'll earn your wings and get lots of flight time and technical training. Of course, if war breaks out, you might have to go through that first, but considering what's on the line when you're flying a craft that's trying to fight the forces of gravity and win, a little warzone leadership may actually come in handy.
Besides the experience, there are the qualifications that go along with being a human being in outer space. You have to be in tip-top physical shape, and it's more than being able to squeeze out a few pushups. For all you pilot wannabes, you have to have good vision and 1,000 hours of flight time in a jet.
You've also got to fit NASA's anthropomorphic qualifications, a.k.a. you've got to be small enough to fit inside the teeny tiny space station, but large enough that you won't go slipping out of your seat on launch. This means no basketball players or jockeys need apply.
In a complete reverse from the origins of the space program, we now work fairly closely with Russia. This means you'll even be expected to learn Russian (source). Not only will many of your fellow crew members be cosmonauts, most of the people who put you into space and bring you back will be Russian as well. You're going to need more than just da and nyet if you want to get by.