It sounds like something from a James Bond movie: a massive satellite, the largest ever launched, equipped with a powerful laser to take out the American anti-missile shield in advance of a Soviet first strike. It was real, though—or at least the plan was. In fact, when Soviet President Mikhail Gorbachev walked out of the October 1986 summit in Reykjavik, Iceland, because President Ronald Reagan wouldn't abandon his Strategic Defense Initiative, or SDI, the Soviets were closer to fielding a space-based weapon than the United States was. Less than a year later, as the world continued to criticize Reagan for...