From virtually the beginning of the twentieth century, those interested in the human exploration of space have viewed as central to that endeavor the building of an Earth-orbital space station that would serve as the jumping-off point to the Moon and the planets, Always, space exploration supporters believed, a permanently occupied space station was necessary outpost in the new frontier of space. The more technically minded recognized that once humans had achieved Earth orbit about 250 miles above the surface-the presumed location of any space station- the vast majority of the atmosphere and the gravity well would have been conquered, and then human being were about halfway to anywhere they might want to go.