The Strategic Defense Initiative (SDI) is a U.S. research and development program designed to create an effective defense against nuclear-missile attack, initiated by President Reagan in 1983. As envisioned, the system uses a "layered" defense in which enemy missiles would come under continuous attack from the time they are launched to just before they reach their targets, a total of about 30 minutes. See; Ballistic Missile Defense.

A U.S. research and development program begun during the administration of President Ronald Reagan to develop space-based defensive measures against ballistic missile attack.

A defense system nicknamed "Star Wars" that combined computerized radar monitoring of incoming missiles and shooting them down with automated interceptor missiles. Controversial from the start, the program is being dismantled in the 1990s.

Popularly known as "Star Wars," President Reagan's strategic defense initiative (SDI) proposed the construction of an elaborate computer-controlled defense system capable of destroying enemy missiles in outer space where they would do no harm.

The Strategic Defense Initiative (SDI), commonly called Star Wars after one of the popular science fiction movies of the time, was proposed by U.S. President Ronald Reagan on March 23, 1983Federation of American Scientists. http://www.fas.org/spp/starwars/program/milestone.htm Missile Defense Milestones. Accessed March 10, 2006. to use ground-based and space-based systems to protect the United States from attack by strategic nuclear ballistic missiles.