The proposal was sharply criticized for its potential costs, doubts that it would be technologically feasible and afford complete protection against all delivery systems, concerns that it would violate the 1972 Anti-Ballistic Missile (ABM) Treaty and destabilize the nuclear balance of power.
The research was controlled by the Strategic Defense Initiative Office, an agency of the Department of Defense until 1993, when it was renamed the Ballistic Missile Defense Organization. Department of Defense cost estimates for SDI-related spending during fiscal years 1984-1994 amounted to US$32.6 billion. An independent report by the Congressional Research Service arrived at a much higher figure of US$70.7 billion .
The project was repeatedly scaled back, renamed Global Protection Against Limited Strikes (GPALS, dubbed "Son of Star Wars") in 1991, and refocused on protection from smaller attacks. GPALS was based on a ground system of rocket-launched interceptors aimed at preventing small scale launches by "rogue states" (apparently North Korea, Libya, Iraq or Iran) from impacting on the US.
President Bill Clinton almost halted the program, but it has regained momentum under President George W. Bush, whose version is called the National Missile Defense (NMD). Apparently successful tests of the interceptors have been revealed as flawed or rigged, but the system is still intended to be deployed at a cost of up to US$60 billion by 2005.
The plan is opposed by Russia and by most members of NATO. The People's Republic of China has been particularly vocal in its opposition to the system, presumably because it fears that it is really aimed at neutralising the threat of China's relatively modest missile arsenal and thus leaving the United States free to defend Taiwan if the mainland tries to conquer Taiwan. Currently, President Bush has withdrawn the United States from the ABM Treaty, in preparation for testing the still-in-development technology.
See also: ASAT weapon development