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The Strategic Defense Initiative (SDI) was a national ballistic missile defense program for the United States launched by a speech by President Ronald Reagan on 23 March 1983. Reagan said, "I call upon the scientific community who gave us nuclear weapons to turn their great talents to the cause of mankind and world peace: to give us the means of rendering these nuclear weapons impotent and obsolete." This has been referred to as the "Star Wars" speech, as it was initially detracted as science fiction and a waste of money. The Strategic Defense Initiative eventually came to be known colloquially as the Star Wars.
The SDI was shut down in 1993 by President Bill Clinton, and replaced by the Ballistic Missile Defense Organization (BMDO), putting a greater emphasis on regional rather than national missile defense. Over 10 years, the Strategic Defense Initiative spent $25 billion US Dollars on research and testing, but never achieved its objective of producing a reliable anti-missile system. Whether the SDI should ever have been launched was an extremely controversial and politicized topic at the time, and continues to be today.
The initial impetus for the SDI was when Reagan heard that a scientist at Lawrence Livermore National Laboratory, Peter L. Hagelstein, had designed a nuclear explosion-powered x-ray laser. National strategists imagined a curtain of such lasers, initially mounted on missiles, then on satellites, as an impenetrable wall to stop any incoming ballistic missiles. However, when this design was actually tested, just three days after the Star Wars speech, it was a total failure.
But the SDI was not only about the x-ray laser design, and numerous other approaches were considered and researched over the next decade. The chemical laser MIRACL (Mid-Infrared Advanced Chemical Laser) was built in 1985 and used to successfully shoot down a Titan booster during a test. Investigations into hypervelocity rail guns led to improvements in the technology, but nothing that could have feasibly prevented a swarm of incoming Soviet missiles. A system of space-based, watermelon-sized mini-missiles called Brilliant Pebbles was called "the crowning achievement of the Strategic Defense Initiative," although it was never deployed, and the project was canceled in 1994.
The modern opinion of the success of the SDI is mixed. Advocates say the program resulted in many important technological spin-offs, such as battle lasers and cameras for satellites. Some even go so far to say that the collapse of the Soviet Union can be attributed to fear over the Strategic Defense Initiative. Detractors say the whole program was unfeasible from the start, and the money would have been better spent on individually targeted projects outside the auspices of a missile defense program. United States national missile defense research continues today, and tests have shown some limited success. At best, such systems would likely shoot down no more than a few dozen missiles, while in a true nuclear war, hundreds if not thousands of nuclear missiles would be launched. Perhaps research will eventually produce a highly capable anti-missile system, but that day is not yet here.