Undergraduate / Voltaire or Neil Armstrong? Who's the better influence for my essay? [4]

I think writing about Voltaire is good. If that's what you're passionate about, it should make for a better essay. Also, I'm sure the Aerospace Engineering department will get plenty of essays about Neil.

It is ok to go over 500 as long as you don't exceed the written limit on the application. Do try to keep it a concise as possible because the people reading your essay will be reading hundreds just like yours. I think a page to a page and a half is fine.