The last U.S. spacecraft mission to Venus was in 1989 with the launch of Magellan. Even though Magellan spent the next five years radar mapping the surface and gathering high resolution gravity data, much remains a mystery about our so-called sister planet. Did Venus experience a run-a-way greenhouse effect at some point in its history? Why is the surface pressure 90 times greater on Venus then on Earth? Why is the planet so hot? These are only a few of the question that must be answered if we are to learn more about Venus's past and possibly Earth's future.