Project Excalibur was a United States government nuclear weapons research program to develop a nuclear pumped x-ray laser for ballistic missile defence. It became part of the Strategic Defense Initiative (SDI). Conceived by nuclear scientist Edward Teller, the concept involved packing large numbers of expendable x-ray lasers into a nuclear bomb. When it detonated, the bomb would fire laser beams in many directions. The intention was to shoot down enemy nuclear missiles.
The plan was to place the whole apparatus on a satellite in orbit. It would have actually required many satellites in orbit, since there needed to be at least one between the U.S. and its enemies when a massive launch of intercontinental ballistic missiles (ICBMs) occurred. The Soviet Union was the only foe technologically able to accomplish a massive simultaneous launch.
The x-ray laser gain medium would be pumped by the extremely high density of high energy photons that appear in the first nanoseconds of a nuclear detonation. During these nanoseconds, the photon density is nearly as high as in regular matter. The pumped medium would emit a pulse of coherent x-rays, in the direction of the long axis of the medium. The calculations showed that the extremely high gain and high energy pulse from the lasers would occur before the detonation destroyed the lasers and the rest of the satellite. If large numbers of pieces of gain media were used, each pre-aligned to point at a missile, then a large number of the missiles could be destroyed in one fell swoop.
The project was proposed as a solution to the problems of using optical lasers in satellites to shoot down missiles: if a large nearly simultaneous launch of ICBMs occurred, the Space Based Laser could not destroy them all, since it was designed to fire upon one at a time. It was felt that the large optics of the SBL could not be re-positioned to point from one missile to the next quickly enough. A considerable amount of research went into rapidly re-targeting the Space Based Laser so that many missiles could be destroyed in time to deal with the massive attack. However, it remained out of reach, giving rise to the Excalibur approach, which was viewed as something of a desperate approach even by those who worked on the project.
Ten known tests of nuclear-pumped x-ray lasers were conducted between 1978 and 1988.[1] The project was determined to be out of reach of current technology and was formally abandoned in 1992. Since then, its main influence has been its appearances in science fiction. Research was redirected to laser satellites and kinetic weapons under the Strategic Defense Initiative.