The Mercury and Gemini space programs put the first American in space, the first American in orbit, and the first American Space Walk. The Apollo program began with disaster. The crew, pictured above, were killed in a capsule fire during practice on the launch pad. The accident resulted from the pure oxygen environment in the capsule. Pure oxygen can be highly flammable. From left to right, the men were Gus Grissom, Ed White, and Roger Chaffee.