Project Pluto

Project Pluto was a United States government program to develop nuclear-powered ramjet engines for use in cruise missiles. Two experimental engines were tested at the Nevada Test Site (NTS) in 1961 and 1964 respectively. On 1 January 1957, the U.S. Air Force and the U.S. Atomic Energy Commission selected the Lawrence Radiation Laboratory to study the feasibility of applying heat from a nuclear reactor to power a ramjet engine for a Supersonic Low Altitude Missile. This would have many advantages over other contemporary nuclear weapons delivery systems: operating at Mach 3, or around 3,700 kilometers per hour (2,300 mph), and flying as low as 150 meters (500 ft), it would be invulnerable to interception by contemporary air defenses, carry more nuclear warheads with greater nuclear weapon yield, deliver them with greater accuracy than was possible with intercontinental ballistic missiles (ICBMs) at the time, and, unlike them, could be recalled. This research became known as Project Pluto, and was directed by Theodore Charles (Ted) Merkle, leader of the laboratory's Radiation Division. Originally carried out at Livermore, California, testing was moved to new facilities constructed for $1.2 million (equivalent to $10 million in 2024) on 21 square kilometers (8 sq mi) at NTS Site 401, also known as Jackass Flats. The test reactors were moved about on a railroad car that could be controlled remotely. The need to maintain supersonic speed at low altitude and in all kinds of weather meant that the reactor had to survive high temperatures and intense radiation. Ceramic nuclear fuel elements contained highly enriched uranium oxide fuel and beryllium oxide was used both as neutron moderator and as neutron reflector. After a series of preliminary tests to verify the integrity of the components under conditions of strain and vibration, Tory II-A, the world's first nuclear ramjet engine,...