Another interesting fact, although it isn’t required, many astronauts have been either boy scouts or girl scouts.

Astronaut training involves scuba and deep sea diving. If you are a swimmer, you might want to learn diving as well.

See the NASA site for high school students. Click on the Career Information link for details on how to become an astronaut.

http://www.nasa.gov/audience/forstudents/9-12/features/index.html

It is not too early to begin getting involved with NASA, there are contests, jobs, internships and other opportunities for high school students.

You could also spend a summer at NASA as an intern

http://www.nasaexplores.com/show2_912a.php?id=03-064&gl=912

Facts about astronauts

http://www.nasaexplores.com/show2_k_4a.php?id=02-062&gl=k4

With rare exception, the principle requirement is a heavy background in science (including medicine). As far as I know, there have been no English Literature junkies or artists up there unless it is their second or third forte. Language skills may come in useful with international efforts, but its probably lesser to other more science based skills.

Like any other discipline, you build on your previous experience. Good grades now help you do more appropriate things later which in turn look good for the application, etc.

To date, NASA has hired people who are at the leading edge of their disciplines, which does not, alas, prevent them from having other problems just like the rest of the general population (drinking, the desire to kill off competitors for your lover’s affection, etc). It may be that they soon start adding a ton of psychological profiling on top of what they currently have (to see how you’ll handle stress, vertigo, etc).

In addition, NASA looks for people who can “sell the process.” That is, people who can educate others about what we are doing in space and why. This is perhaps the biggest reason for the “Teacher in space” program – to get the word out about what space means to the average person.

And of course health is still pretty important. There are a number of non-obvious medical constraints (e.g. if you’ve had LASEK surgery, you are automatically excluded – I sure hope that one changes.) in addition to the obvious ones (blood pressure in a certain range, height and weight in a certain range, etc).

20/20 eyesight is required for shuttle pilots and presumably pilots of future spacecraft though I would think that would be less and less important as more stuff is done with avionics and computers than “by eye”.

Good luck!