Neil deGrasse Tyson talks about the possibility of space exploration and past human achievements in this motivation for greatness speech. Tyson discusses the idea of exploring Mars and how the cost would be astronomical. He then discusses large past accomplishments of the human race and examines what drove people to agree to pursue them.
Tyson talks about how there are really only three factors that motivate societies to pursue expensive and ambitious achievements. Those factors are worship (either of a God or royalty), fear of war and attack and economic growth. These motivations have led societies to build the great pyramids and the great wall of China, so they could lead to space discovery as well.
Tyson says that while fear of war could become a driving factor behind space exploration, it's more likely that economic growth will be behind the exploration of Mars.