Project Excalibur Project Excalibur was a United States government nuclear weapon s research program to develop a nuclear pumped x - ray laser as a directed energy weapon 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 soft x - ray lasers around a nuclear device . When the device detonated , it would fire soft x - ray laser beams in many directions . The goal was to aim these beams to shoot down enemy nuclear missiles near the end of , and after the missiles boost phase stage of flight . With the kill mechanism of the X - ray laser being Ablative laser propulsion shock . Limited accounts in the unclassified press indicate that the device consisted of a small nuclear device surrounded by multiple rods made of a material that served as an x - ray gain medium , releasing x - rays when " pumped " by incident photons . Each rod would function as a separate x - ray laser . The x - ray laser would be optically pumped by the extremely high density of high energy photon s that appear in the first nanoseconds of a nuclear detonation . The pumped medium would emit a pulse of coherent x - rays , in the direction of the long axis of the rod . Unlike optical lasers , in which the light is reflected by mirrors at the ends and makes multiple passes through the gain medium , in the x - ray laser the x - ray pulse is generated in a single pass through the rod . 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 gain media rods were used , each pre - aligned to point at a missile , then a large number of missiles could be destroyed in one fell swoop . The original proposal was to place many x - ray laser satellites in orbit . There needed to be at least one between the U . S . and its enemies when a massive launch of intercontinental ballistic missile s ( ICBMs ) occurred . The Soviet Union was the only foe technologically able to accomplish a massive simultaneous launch . Since satellite basing would have violated the Outer Space Treaty which prohibits nuclear weapons in space , a later proposal would have based them on " pop - up " missiles in Alaska and in an effort to be closer still to the point of launch , on SLBM s in the Sea of Okhotsk & Kara Sea . In the event of a Russian ICBM launch the laser could pop - up into space in the path of the approaching ICBMs in anticipation for interception . 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 . 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 . A number of artist ' s impressions of the device were made .