SDI

Strategic Defense Initiative (SDI), United States military research programme to develop a defence system to destroy incoming enemy missiles.

"Star Wars"

The Strategic Defense Initiative was first proposed on March 28, 1983, when President Ronald Reagan, in regretting that peoples' security rested upon "the threat of instant US retaliation to deter a Soviet attack", appealed to America's scientific community, "who gave us nuclear weapons … to give us the means of rendering these nuclear weapons impotent and obsolete". Reagan's vision was the deployment of such effective ballistic missile defences that the whole populations of the United States, America's Western European allies, Canada, and Japan would be protected from an all-out nuclear attack.

Such a ballistic missile defence was to involve many weapon systems in space, including a network of satellites and space battle stations, equipped with such exotic weapons as high-energy lasers, particle beams, electromagnetic rail guns, X-ray lasers, and computer-guided mini-missiles, all controlled by a space battle management system using supercomputers. President Reagan's SDI was therefore dubbed "Star Wars"-evoking space battle scenes from the famous film.

SDI was the most expensive military project in history; the estimates of the total cost range up to a trillion (million million) dollars. Despite warnings from many eminent scientists and technologists that an effective SDI was technologically impossible, about $40 billion was spent on research and development.

Background to SDI

Proposals for defending the mainland of the United States against a long-range ballistic missile attack, particularly by Soviet intercontinental ballistic missiles (ICBMs), date back at least 40 years. Soviet interest in ballistic missile defence is as long-standing. By the end of the 1950s both superpowers were replacing long-range bombers with ballistic missiles as the main element in their strategic nuclear forces. Attention therefore switched from anti-aircraft defences to ballistic missile defences.

Ballistic Missile Defence

Early proposals involved a two-layered ballistic missile defence in which enemy warheads would first be intercepted outside the Earth's atmosphere by missiles with a range of about 700 km (434 mi). Enemy warheads that survived the first layer of defence would be attacked with high-acceleration missiles within the Earth's atmosphere at ranges of up to 40 km (25 mi).