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 , and flying as low as , 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 $ million in ) on 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, was run at full power (46 MW) on 14 May 1961. A larger, fully-functional ramjet engine was then developed called Tory II-C. This was run at full power (461 MW) on 20 May 1964, thereby demonstrating the feasibility of a nuclear-powered ramjet engine. Despite these and other successful tests, ICBM technology developed quicker than expected, and this reduced the need for cruise missiles. By the early 1960s, there was greater sensitivity about the dangers of radioactive emissions in the atmosphere, and devising an appropriate test plan for the necessary flight tests was difficult. On 1 July 1964, seven years and six months after it was started, Project Pluto was canceled.

Origins

During the 1950s, the United States Air Force (USAF) considered the use of nuclear powered aircraft and missiles as part of its Aircraft Nuclear Propulsion project, which was coordinated by the Aircraft Nuclear Propulsion Office. Research into missiles was coordinated by its Missile Projects Branch. The concept of using a shieldless nuclear reactor to provide a heat source for a ramjet was explored by Frank E. Rom and Eldon W. Sams at the National Advisory Committee for Aeronautics Lewis Research Center in 1954 and 1955. The principle behind the nuclear ramjet was relatively simple: motion of the vehicle pushed air in through the front of the vehicle (the ram effect). If a nuclear reactor heated the air, the hot air expanded at higher speed out through a nozzle at the back, providing thrust.

thumb|Building 2201 from above

An aggregate mine was purchased to supply the concrete for the walls of the disassembly building, Building 2201, which were thick. Building 2201 was designed to allow radioactive components to be adjusted, disassembled or replaced remotely. Operations in the main disassembly bay could be viewed through lead glass viewing windows. Hot cells adjacent to the disassembly bay were used to monitor the control rod actuators. Vaults within each cell were equipped with remote manipulators.

All controls were located in the central control room, which was air conditioned with a positive pressure so air always flowed towards the disassembly bay and the hot cells, and the used air from them was passed through filters. The main disassembly bay and the hot cells were accessible through openings that were normally covered with lead plates. There were showers and a radiation safety room for workers. Building 2201 also contained a maintenance shop, darkroom, offices, and equipment storage rooms. Scientists monitored the tests remotely via a television hook up from a tin shed located at a safe distance that had a fallout shelter stocked with two weeks' supply of food and water in the event of a major catastrophe.

Some of oil well casing was necessary to store the approximately of compressed air at used to simulate ramjet flight conditions for Pluto. Three giant compressors were borrowed from the Naval Submarine Base New London in Groton, Connecticut that could replenish the farm in five days. A five-minute, full-power test involved of air being forced over 14 million diameter steel balls that were held in four steel tanks which were heated to .

Because the test reactors were highly radioactive once they were started, they were transported to and from the test site on railroad cars.

thumb|right|Building 2201 in 2007

The other major problem with the SLAM concept was the environmental damage caused by radioactive emissions during flight, and the disposal of the reactor at the end of the mission. In addition to the ejection of radioactive gases during the flight, Merkle estimated that about 100 grams of fission products would be produced, of which he expected a few grams to be released and dispersed over a wide area. Atmospheric nuclear testing was still ongoing in the early 1960s, so the radioactive emissions were not considered to be a major problem by comparison. Although small compared to that produced by a nuclear explosion, it was a problem for testing. The noise level was estimated to be a deafening 150 decibels. There was also the possibility of the missile going out of control.

The idea of testing it over Nevada was quickly discarded. It was proposed to conduct test flights in the vicinity of Wake Island, flying a figure-eight course. The reactor would then be dumped into the Pacific Ocean where it was deep. By the early 1960s there was increasing public awareness of the undesirable environmental impacts of radioactive contamination of the atmosphere and the ocean, and the radioactive emissions from the missile were considered unacceptable wherever the tests were conducted.

The AEC requested $8 million (equivalent to $ million in ) in fiscal year 1965 for continued tests of Tory II-C and the development of Tory III, an improved version. In April 1964, the Joint Committee on Atomic Energy recommended that $1.5 million be cut from this request. This provided continued funding for Tory II-C, but not for the development of Tory III. The Department of Defense's Director of Research and Engineering, Harold Brown, favored the continuation of Project Pluto at a low level of funding to progress the technology. This was rejected by the House Appropriations Committee; the technology had been demonstrated by the successful Tory II-C tests, and if there was no longer a military requirement for it, there was no reason to continue funding. It therefore cut another $5.5 million from the funding request, leaving only $1 million for "mothballing" the project.

On 1 July 1964, seven years and six months after it was started, Project Pluto was canceled. Merkle hosted a celebratory dinner at a nearby country club for project participants where SLAM tie tacks and bottles of "Pluto" mineral water were given away as souvenirs. At its peak, Project Pluto had employed around 350 people at Livermore and 100 at Site 401, and the total amount spent had been about $260 million (equivalent to $ billion in ).

Cleanup

The Tory II-C reactor was not disassembled after the high-power test and remained at Jackass Flats until 1976, when it was disassembled at the Engine Maintenance, Assembly, and Disassembly (E-MAD) building there. In 1971 and 1972, Building 2201 was used by the Fuel Repackaging Operations Project. Fuel elements from the Tory II reactors were removed from the hot cells in Building 2201 and taken to Area 6, from whence they were shipped to the Idaho National Laboratory. Building 2201 was used in the 1970s and 1980s to house the Hydrogen Content Test Facility. Starting in 1986, the Sandia National Laboratory used it for a series of classified projects related to nuclear weapons, and in 1998 an unidentified organization used it for a classified project. Building 2201 was cleaned and decontaminated between 2007 and 2009 to make it safe for future demolition. In September 2013, it was reported that it had been demolished.

See also

  • 9M730 Burevestnik a similar Russian Project

Notes

References

Further reading

  • Directory of U.S. Military Rockets and Missiles
  • Vought SLAM pages