Interest in rockets that use fission reactors as the heat source has centered on manned flights to Mars. The demands of such missions require rockets that are several times more powerful than the chemical rockets in use today.Rocket engines operate according to the basic principles expressed in Newton's third law of motion: for every action there is an equal and opposite reaction. In a chemical rocket, hot gases are created by chemical combustion; in a nuclear rocket heating of the propellant in a nuclear reactor creates hot gas. In either case, the hot gases flow through the throat of the rocket nozzle where they expand and develop thrust.Extensive development effort has been expended on nuclear rockets. The nuclear Rover/ NERVA rocket programs provide a very high confidence level that the technology for a flight nuclear rocket exists. These programs demonstrated power levels between 507 MWt and 4,100 MWt and thrust levels of up to 930 kN (200,000 Ibf). Specific impulse, a measure of rocket performance, was more than twice that of chemical rockets. Ground testing and technology development has been done on several concepts described in this book. However, though there appear to be no technical barriers to the development of a successful nuclear rocket, no nuclear rockets have been flown in space.This book describes the fundamentals of nuclear rockets, the safety and other mission requirements, developmental history of various concepts both in the U.S. and Russia, and it summarizes key developmental issues.

For operating in severe environments, long life and reliability, radioisotope power systems have proven to be the most successful of all space power sources. Two Voyager missions launched in 1977 to study Jupiter, Saturn, Uranus, Neptune, and their satellites, rings and magnetic fields and continuing to the heliosphere region are still functioning over thirty years later. Radioisotope power systems have been used on the Moon, exploring the planets, and exiting our solar system. There success is a tribute to the outstanding engineering, quality control and attention to details that went into the design and production of radioisotope power generation units. Space nuclear radioisotope systems take the form of using the thermal energy from the decay of radioisotopes and converting this energy to electric power. Reliability and safety are of prime importance. Mission success depends on the ability of being able to safely launch the systems and on having sufficient electrical power over the life of the mission. Graceful power degradation over the life of a mission is acceptable as long as it is within predictable limits. Electrical power conversion systems with inherent redundancy, such as thermoelectric conversion systems, have been favored to date. Also, radioactive decay heat has been used to maintain temperatures in spacecraft at acceptable conditions for other components. This book describes how radioisotope systems work, the requirements and safety design considerations, the various systems that have been developed, and their operational history.

The advantages of space nuclear fission power systems can be summarized as: compact size; low to moderate mass; long operating lifetimes; the ability to operate in extremely hostile environments; operation independent of the distance from the Sun or of the orientation to the Sun; and high system reliability and autonomy. In fact, as power requirements approach the tens of kilowatts and megawatts, fission nuclear energy appears to be the only realistic power option. The building blocks for space nuclear fission electric power systems include the reactor as the heat source, power generation equipment to convert the thermal energy to electrical power, waste heat rejection radiators and shielding to protect the spacecraft payload. The power generation equipment can take the form of either static electrical conversion elements that have no moving parts (e.g., thermoelectric or thermionic) or dynamic conversion components (e.g., the Rankine, Brayton or Stirling cycle). The U.S. has only demonstrated in space, or even in full systems in a simulated ground environment, uranium-zirconium-hydride reactor power plants. These power plants were designed for a limited lifetime of one year and the mass of scaled up power plants would probably be unacceptable to meet future mission needs. Extensive development was performed on the liquid-metal cooled SP-100 power systems and components were well on their way to being tested in a relevant environment. A generic flight system design was completed for a seven year operating lifetime power plant, but not built or tested. The former USSR made extensive use of space reactors as a power source for radar ocean reconnaissance satellites. They launched some 31 missions using reactors with thermoelectric power conversion systems and two with thermionic converters. Current activities are centered on Fission Surface Power for lunar applications. Activities are concentrating on demonstrating component readiness. This book will discuss the components that make up a nuclear fission power system, the principal requirements and safety issues, various development programs, status of developments, and development issues.