Popular Mechanics (USA)
A Brief History of NTP Programs
In 1961, NASA and the Atomic Energy Commission investigated the use of NTP with the Nuclear Engine for Rocket Vehicle Application (NERVA) program. Like DRACO, NERVA would generate thrust by using a nuclear reactor to heat and expel hydrogen. NASA envisioned using an NTP engine as the third and final stage of an otherwise chemical rocket. But
NASA ultimately scrapped the promising program in 1973 due to lack of funding.
In the early 1960s, Project Orion aimed to put a spacecraft into orbit and beyond by detonating a string of nuclear bombs underneath it—an idea made possible by shielding the spacecraft (and spacefarers) with a large graphite plate. The craft would ride the shockwave into the atmosphere on a pillar of successive nuclear explosions. However, the Partial Nuclear-Test Ban Treaty of 1963 outlawed nuclear explosions above ground and in space, putting an end to Orion.
PROJECT TIMBER WIND
In the 1980s, the Pentagon established the Strategic Defense Initiative to build an air-, land-, and spacebased defense system to stop a nuclear attack. This required lifting large payloads into space. Enter Timber Wind, which studied using NTP to intercept intercontinental ballistic missiles. Timber Wind eventually died along with the Cold War, as the Soviet Union ceased to be a major threat and the rationale for a space-based defense system evaporated.