Project Pluto' studied nuclear ramjet propulsion

Tory II-C, a nuclear ramjet engine, sits on a railroad flatcar -- its test bed. The engine was built to demonstrate the feasibility of an air-breathing jet engine powered by a nuclear reactor.
Pan Am photo.

On January 1, 1957, the U.S. Air Force and the Atomic Energy Commission selected the Lawrence Livermore National Laboratory's (LLNL) predecessor, the Lawrence Radiation Laboratory to study the feasibility of applying heat from nuclear reactors to ramjet engines.

This research became known as "Project Pluto" and was moved from Livermore, California to new facilities constructed for $1.2 million on eight square miles of Jackass Flats at the Nevada Test Site (NTS).

The complex consisted of six miles of roads, critical assembly building, control building, assembly and shop buildings, and utilities. Also required for the construction was 25 miles of oil well casing which was necessary to store the million pounds of pressurized air used to simulate ramjet flight conditions for Pluto.

The work was directed by Dr. T.C. Merkle, leader of the laboratory's R-Division.

The principle behind the ramjet was relatively simple: air was drawn in at the front of the vehicle under ram (under great force) pressure, heated to make it expand, and then exhausted out the back, providing thrust.

The notion of using a nuclear reactor to heat the air was fundamentally new. Unlike commercial reactors, which are surrounded by concrete, the Pluto reactor had to be small and compact enough to fly, but durable enough to survive a 7,000 mile trip to a potential target.

The success of this project would depend upon a series of technological advances in metallurgy and materials science. Pneumatic motors necessary to control the reactor in flight had to operate while red-hot and in the presence of intense radioactivity. The need to maintain supersonic speed at low altitude and in all kinds of weather meant the reactor, code named "Tory", had to survive temperatures of 2,500 degrees Fahrenheit, and conditions that would melt the metals used in most jet and rocket engines.

On May 14, 1961, the world's first nuclear ramjet engine, "Tory-IIA," mounted on a railroad car, roared to life for just a few seconds. Despite other successful tests the Pentagon, sponsor of the "Pluto project," had second thoughts. On July 1, 1964, seven years and six months after it was born, "Project Pluto" was canceled.