U.S. Nuclear Rocket Programs
The Nuclear Engines for Rocket Vehicle Applications (NERVA) program officially began in 1961, when NASA issued a request for proposals and established the Space Nuclear Propulsion Office (SNPO). Various government laboratories had been studying the concept for several years, several contractors were already working on conceptual design, and space was a big topic of interest. The time seemed ripe.
A Joint Venture
SNPO was organized as a joint office with participation from the Atomic Energy Commission (AEC) and NASA. In concept it was similar to the AEC-Navy arrangement that had proven successful for the nuclear submarine and surface ship program. The AEC had expertise and monopoly authority over nuclear power reactors, while NASA was responsible for the vehicles that would use the engines.
The contract for the project was awarded to Aerojet General for the engine systems with the Astronuclear Division of Westinghouse designated as the subcontractor for the design of the nuclear reactor.
The headquarters for the reactor development was in Large, Pennsylvania. The reactors were tested in Nevada at Jackass Flats.
During the program, twelve reactors were tested, each one with modifications in fuel and control systems that provided improved power and operational flexibility.
Most of the NERVA reactors were tested in an upward pointing configuration with the nozzle exhausting hot hydrogen directly to the atmosphere. Monitoring showed that radioactive material releases were minimal and continued to be reduced as improvements were made in the reactor core designs.
Effects of Treaty Limitations
During the same time as the NERVA tests, there were several countries, including the United States, who had intensive nuclear weapons testing programs involving dozens of detonations in the air and on the ground. People living downwind of weapons test sites were concerned about being exposed to the uncontrolled doses of radioactive material that were inevitably released by the tests.
They began a well-organized protest movement that resulted in The Atmospheric Test Ban Treaty of 1963, which banned above ground nuclear weapons testing.
The Treaty was interpreted to apply to nuclear rockets, even though nuclear reactors, unlike nuclear bombs, are designed to keep radioactive fission products from escaping. This change required the development of a system to recover and scrub the gases emitted from the engine. These changes added extra time and extra costs to the rocket development without reducing any hazards to people.
The technical accomplishments of the program were impressive. The cores were able to achieve power densities 10 times as high as water cooled reactors, with levels reaching as high as 2 kw/cm3. Core coolant outlet temperatures reached 2500° C with pressures of 560 pounds per square inch absolute. (psia)
The last engine of the series, the XE’, was tested in a special test stand that allowed downward firing that simulated actual space flight conditions. It was started and stopped 28 times and operated for a total of three hours and 48 minutes, with 11 minutes at full power.
The test of the XE’ occurred in September of 1969. In 1971, the NERVA program was cancelled because NASA had no scheduled requirement for its capabilities.
NERVA was partially a casualty of the headlong rush to the moon. It was not chosen as the propulsion source for that mission because of the longer time needed for development. By the time that NERVA type rockets appeared ready to move towards flight testing, Americans had lost interest in spending huge sums of money on space travel. As a result, the early 1970s saw many project cancellations at NASA.
Beginning in the 1980s, there was a renewed interest in nuclear rocket propulsion as a result of President Reagan’s Strategic Defense Initiative (Star Wars ). The capability of the rockets to provide significant improvements in payload delivery was again recognized.
Most of the Star Wars related research remains classified, but, with the winding down of the program, the Air Force decided to declassify the fact that they were interested in nuclear rockets and to attempt to gain the interest of other agencies to continue the development.
Space Exploration Initiative
In 1992, there was a brief period of excitement in the space industry with the announcement of a presidential decision to pursue a Space Exploration Initiative (SEI) that would eventually result in a trip to Mars. Interestingly enough, one of the major justifications for selecting a nuclear rocket for the reference design was to reduce the total radiation dose received by the astronauts participating in the mission.
Natural radiation levels in space are much higher than on earth, since there is no atmospheric shielding, and the higher speed of travel made possible by the use of nuclear power reduced the time of exposure to high background radiation enough to make up for the increased exposure to the on-board source.
The idea of a trip to Mars, however, has been dropped off of the NASA priority list, and with that decision, nuclear rockets have again been declared a technology with no mission. When AEI tried to get an update on the current status of the program, AEI discovered that the man in charge of the program at the Department of Energy had decided to retire.
Funding for nuclear thermal rockets has been eliminated from the DOE budget by drastic reductions over the last three budget cycles. Unfortunately, there is no private interest in the technology, partially because of fear of regulatory agencies.