Project Pluto


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
United States Department of Energy Nevada Test Site (NTS) in 1961 and 1964.

Below, you
will find the declassified documents available thus far. More requests are
open, and when documents are received, they will be added here.

Declassified Documents

Impact of the High Development Cost of Advanced Flight Propulsion Systems on
Development Policy
, October 1965 [75 Pages, 3.7MB] – A discussion of
techniques for handling R and D funds to reduce the investment risk in
implementing programs for new propulsion systems, particularly systems which
are novel and advanced. To guide the funding management, relevant R and D
activities are described in detail, followed by a discussion of criteria to be
met before an engine qualifies for consideration.

Ramjet Propulsion System Applied Research and Advanced Technology (Project
Pluto). Volume V. Propulsion System Test Planning and Ground Test Facility
, 15 February 1963 [92 Pages, 24.8MB] – Test planning
studies in this report present the concept of test programs, their scope, test
objectives, probable testing schedule, estimated number of test weeks and test
runs, existing facilities which can be utilized, and test conditions. The
schedule and test plans presented are based upon the program outlined in the
Air Force Development/Plan for Pluto. Flight engine ground test facility
criteria are updated to reflect the latest facility studies and test planning.
The site selection core drilling program and underground air storage experiment
are described.

Ramjet Propulsion System Applies Research and Advanced Technology (Project
Pluto). Volume VI. Structural Materials Investigations
, 15 February 1963
[163 Pages, 5.8MB] – This is the “best copy available.”  Although hard to
read, I would recommend downloading it, and zooming in on the document with
Adobe Acrobat, to get a bit of an easier reading experience.

Ramjet Propulsion System Applied Research and Advanced Technology (Project
Pluto). Volume VII. Propulsion System Design and Structural Analysis
, 15
February 1963 [163 Pages, 39MB] – This volume contains the results of
design, structures, and materials studies and structures component testing of a
nuclear propulsion system in support of the Pluto reactor program. These
studies include design concepts, structural analysis of steady state and
dynamic loads, material evaluation, and recommended dynamic and structural test
programs. The methods of analysis used have been outlined in each case for

Ramjet Propulsion System Project Pluto
, 30 January 1962 [382 Pages,
37.9MB] – Contents: Propulsion System Design and Analysis — Tory IIC
design data, Performance analysis, Engine performance summary, Heat transfer
and thermal stress analysis, Mechanical and structural design, Neutronics,
Radiation analysis and shielding, Aerodynamic experiments, Structural
experiments, and Materials investigations; Propulsion System Controls — General
status, Control system analysis, Control system components, and Radiation
effects Testing; Flight Engine Facility and Test Planning — Facility design
studies, and Underground air storage experiment.

Nuclear Propulsion Systems. Project Pluto
, 15 November 1959 [165
Pages, 123MB] – To provide accurate and reliable control of a nuclear
ramjet, it is necessary to provide materials and components for the
control system which will operate in an environment dictated by the nuclear
characteristics of the system. A similar problem is encountered in providing
nuclear propulsion for manned aircraft. Much work has been done on
establishing reliable components for this purpose; however, the environment to
be encountered in missile applications is more severe. Thus, it was
necessary to accumulate as much available data as possible on radiation
effects and then extend the data experimentally to cover the particular
problems encountered with PLUTO.

Additional Information

January 1, 1957, the U.S. Air Force and the U.S. 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
“. The work was directed by Dr. Ted Merkle, leader of the laboratory’s

carried out at Livermore, California, the work was moved to new facilities
constructed for $1.2 million on 8 square miles (21 km2) of
Jackass Flats at the NTS, known as Site 401. The complex consisted of 6 miles
(10 km) of roads, critical assembly building, control building, assembly
and shop buildings, and utilities. Also required for the construction was 25
miles (40 km) of oil well casing which was necessary to store the
approximately 1,000,000 pounds (450,000 kg) of pressurized air used to simulate
ramjet flight conditions for Pluto.

principle behind the nuclear ramjet was relatively simple: motion of the
vehicle pushed air in through the front of the vehicle (ram effect), a nuclear
reactor heated the air, and then the hot air expanded at high speed out through
a nozzle at 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
(11,000 km) trip to a potential target. The nuclear engine could, in
principle, operate for months, so a Pluto cruise missile could be left airborne
for a prolonged time before being directed to carry out its attack.

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
radiation. The need to maintain supersonic speed at low altitude and in all
kinds of weather meant the reactor, code named “Tory”, had to survive high
temperatures and conditions that would melt the metals used in most jet and
rocket engines. Ceramic fuel elements would have to be used; the contract to
manufacture the 500,000 pencil-sized elements was given to the Coors Porcelain

The proposed
use for nuclear-powered ramjets would be to power a cruise missile, called
SLAM, for Supersonic Low Altitude Missile. In order to reach ramjet speed, it
would be launched from the ground by a cluster of conventional rocket boosters.
Once it reached cruising altitude and was far away from populated areas, the
nuclear reactor would be made critical. Since nuclear power gave it almost
unlimited range, the missile could cruise in circles over the ocean until
ordered “down to the deck” for its supersonic dash to targets in the Soviet
Union. The SLAM as proposed would carry a payload of many nuclear weapons to be
dropped on multiple targets, making the cruise missile into an unmanned bomber.
After delivering all its warheads, the missile could then spend weeks flying
over populated areas at low altitudes, causing tremendous ground damage with
its shock wave. When it finally lost enough power to fly, and crash-landed, the
engine would have a good chance of spewing deadly radiation for months to come.

On May 14,
1961, the world’s first nuclear ramjet engine, “Tory-IIA”, mounted on a
railroad car, roared to life for a few seconds. Three years later, “Tory-IIC”
was run for five minutes at full power. Despite these and other successful
tests the Pentagon, sponsor of the “Pluto project”, had second thoughts. The
weapon was considered “too provocative”, and it was believed that it would
compel the Soviets to construct a similar device, against which there was no
known defense. Intercontinental ballistic missile technology had proven to be
more easily developed than previously thought, reducing the need for such
highly capable cruise missiles. On July 1, 1964, seven years and six months
after it was started, “Project Pluto” was canceled.

The above was provided by Wikipedia.