Unless you're an American, Russian or Chines citizen there's probably almost no chance of becoming an astronaut anyway. (Additionally, while there are more civilians than there used to be, military personnel tend to be favoured for selection).
NASA's current recruits all have a minimum of two university degrees. (One of them has five). Since those degrees are probably all science-based, they'll all be reasonably competent in mathematics but it's unlikely that many (if any) of their degree are solely in maths:
http://www1.nasa.gov/...nauts/ascans2009.html
Chris