We all think about space exploration, but we also need to think about dodging 50 years of debris from space exploration - aluminum, steel, nylon, even liquid sodium from Russian satellites. Sierra Club hasn't started fundraising over this issue yet but they might after reading this article.
According to NASA, there are more than 21,000 pieces of 'space junk' roughly the size of a baseball in orbit, and about 500,000 pieces that are golf ball-sized. Sure, space is big, but when a piece of space junk strikes a spacecraft, the collision occurs at a velocity of 5 to 15 kilometers per second, roughly ten times faster than a speeding bullet.