Nuclear Science and Technology and How It Influences Your Life http://www.aboutnuclear.org/ return to interactive version
	Space : History A Brief History of Space Nuclear Power and Aerospace Nuclear Science and Technology Many ideas for harnessing the power of the atom have been put forth since the early 1900's.  Some of the most intriguing have dealt with the use of nuclear energy to power aircraft and later spacecraft. The Atomic Airplane While the use of nuclear energy to power airplanes had been discussed in magazines such as Popular Mechanics, the idea was treated as little more than science fiction until 1946, when the Army Air Force formed the Nuclear Energy for the Propulsion of Aircraft project, known as NEPA, by issuing a contract to Fairchild Engine and Airplane Corporation.  NEPA produced many reports and some studies, but overall, little progress was made towards building a nuclear-powered plane.  (View an example of a report issued from NEPA.) The first realistic assessment of using nuclear power for aero applications came with the Lexington Project - a study sponsored by the Atomic Energy Commission and prepared by MIT in 1948.  The goal was to see whether the United States could build a nuclear-powered airplane.  The study concluded that it was technically achievable, though it might take well over a decade to build a flying aircraft.  Some military planners desired an airplane that could fly across the globe without landing or refueling and funding for research and development of a nuclear powered airplane began. Nuclear Airplane Prototype, Spring 1952 In 1949 the Aircraft Nuclear Propulsion (ANP) project was established at Oak Ridge National Laboratory. Between 1949 and 1963 (when the ANP project was canceled) a tremendous amount of work was done in the areas of radiation shielding, compact reactor design and materials research (for instance, the first large-scale non-destructive testing of materials was done at Oak Ridge as part of ANP).  Though the project was canceled before a working prototype was flown, the experience and knowledge gained in the effort would pay dividends in the coming decades. Nuclear Rockets Taking a step beyond atomic airplanes, the U.S. government began funding programs to build a nuclear-powered rocket.  The concept was known by the acronym NTR, for Nuclear Thermal Rocket, as the idea was to run a cool gas through a very hot reactor powered by atomic energy and shoot the super-heated gas out of a nozzle, resulting in propulsion far greater than that from chemically-powered rockets. The ROVER program, which began at Los Alamos National Laboratory in 1953, studied and built several reactors that would be used in a nuclear-powered rocket.  This research was begun as a backup to the chemically-powered rockets being developed for the Intercontinental Ballistic Missile program (ICBM), since at the time researchers were not sure they could build a chemically-powered rocket that would make it to the other side of the globe. The reactor designs were developed under the names KIWI (to develop the basic technology of nuclear thermal rockets), Phoebus (to test designs for interplanetary voyages), Peewee-1 (to test smaller, more compact reactor designs) and the Nuclear Furnace-1 (to test advanced fuels and designs for reducing emissions of radioactive material into the atmosphere). President Kennedy leaving the Rocket Development Station at the Nevada Test Site after viewing a full-scale mock-up of a NERVA engine on December 8, 1962.  (Courtesy of DOE.) In 1961 the Nuclear Engines for Rocket Vehicle Applications (NERVA) program took the research done by the ROVER program and began building working rockets from it.  NASA issued a request for proposals and established the Space Nuclear Propulsion Office (SNPO) to drive NERVA.  The rocket was envisioned for use in a human mission to Mars and, eventually, the outer solar system. NERVA was organized as a joint effort between the Atomic Energy Commission (AEC) and NASA, with much inspiration and technology taken from the Aircraft Nuclear Propulsion program.  The idea was to re-create the success story of the AEC-Navy arrangement that had developed and built small power plants for the nuclear submarine and surface ship program.  The AEC had the expertise and the sole authority in the U.S. to oversee nuclear reactors for civilian use, and NASA would develop the rockets or ships that would use the engines. The reactors were developed in Large, Pennsylvania, and tested in Nevada.  During the program, twelve reactors were tested, each one with modifications in fuel and control systems that provided improved power and operational flexibility. Basic Layout of a NERVA engine.  (Courtesy of NASA.) Most of the NERVA reactors were tested with the nozzle firing hot hydrogen directly into the atmosphere.  Radioactive material releases were minimal and were reduced as improvements were made in the reactor designs. The program was a success.  The United States built and tested nuclear rockets that were twice as powerful as the largest and most powerful chemical rockets ever built at a fraction of the size. After years of research, development and successful testing, the NERVA program was cut from NASA's budget in 1973.  The nuclear rocket program shut down.  The U.S. ended human missions to the moon and canceled plans to send astronauts to Mars. View The Science Behind It All for more information on these incredible rockets. The RTG, Nuclear Workhorse in Space While nuclear airplanes and rockets were being designed and then eventually shelved, the most successful application of nuclear energy in space was born - a safe, effective and reliable power source known as the Radioisotope Thermoelectric Generator (RTG) has powered satellites to the far reaches of the solar system and beyond. In the early years of space research scientists knew they needed a long-lived power source that would also be compact and able to endure a rocket ride into space.  Chemical batteries, fuel cells and solar panels were all tried.  Batteries and fuel cells were limited by their fuel, and solar panels took up large amounts of space and would not be effective for missions far from the sun. A new concept was investigated – a power generator that worked from the heat given off by a decaying radioactive source. An RTG consists of two pieces: a radioactive element used as a heat source (such as Plutonium-238, which becomes physically hot as it decays) and a way to convert heat into electricity.  The heat is converted to electricity by a thermoelectric converter which takes advantage of the Seebeck Effect. The Seebeck Effect is a principle of thermoelectricity discovered in 1822, where a voltage is produced when electrons move across the junction of two different types of material, usually metals or semiconductors, when the materials are at different temperatures.  View The Science Behind It All for more details on how an RTG takes advantage of this well-known principle. A Radioisotope Thermoelectric Generator.  (Courtesy of NASA.) On June 29, 1961, the United States Navy launched the first satellite powered by an RTG that generated 3 watts of electricity.  Since that time the U.S. has launched a total of 26 spacecraft using RTGs (with these satellites or spacecraft often using more than one RTG to generate the needed electricity).  RTGs provided power on the moon’s surface during the Apollo missions, kept the Pioneer and Voyager satellites going on their long trips through the solar system and most recently have powered the Galileo mission to Jupiter, the Ulysses mission to the Sun and the Cassini mission to Saturn. There have been accidents involving RTG-powered satellites.  These were all caused by rocket failure or by a satellite dropping back to earth.  The RTG power supplies were never a cause of the accident as there are no parts that would explode, rupture or otherwise affect a spacecraft. More Information: RTG Safety