THERE was doubtless much celebration and more than a little relief in Washington last month when a missile fired from the USS Lake Erie destroyed a defunct spy satellite. Strange then that the technology employed in this display of American military prowess was a pale shadow of what it might have been. The exercise was the direct descendant of Ronald Reagan's grandiose Strategic Defense Initiative (SDI), which was born 25 years ago this week.

In March 1983, Reagan asked the scientists and engineers who had built the world's nuclear arsenals "to give us the means of rendering these nuclear weapons impotent and obsolete". He asked them to develop a nuclear shield that "could intercept and destroy strategic ballistic missiles before they reached our soil or that of our allies".

SDI - or the Star Wars programme, as it quickly became known - generated immense controversy because of its potential ...