According to NASA and JPL officials, most deep space missions beyond Mars, including the Cassini mission, must use RTGs to generate electrical power. To obtain the necessary presidential approval to launch space missions carrying large amounts of radioactive material, such as Cassini, NASA is also required to convene an interagency review of the nuclear safety risks posed by the mission. Safety, Environmental Impact, and Launch Approval Processes for the Cassini Mission

The processes used by NASA to assess the safety and environmental risks associated with the Cassini mission reflected the extensive analysis and evaluation requirements established in federal laws, regulations, and executive branch policies. After completion of the interagency review process, NASA requested and was given nuclear launch safety approval by the Office of Science and Technology Policy, within the Office of the President, to launch the Cassini spacecraft. Cassini Launch Approval Process

Agencies planning to transport nuclear materials into space are required by a presidential directive to obtain approval from the Executive Office of the President before launch. To prepare for and support the approval decision, the directive requires that an ad hoc Interagency Nuclear Safety Review Panel review the lead agencies’ nuclear safety assessments. NASA’s Consideration of a Non-Nuclear Power Source for Its Cassini Mission

NASA regulations require that, as part of the environmental analysis, alternative power sources be considered for missions planning to use nuclear power systems. The studies also noted that, even if the large arrays could have been launched to Saturn on the Cassini spacecraft, they would have made the spacecraft very difficult to maneuver and increased the mission’s risk of failure due to the array’s uncertain reliability over the length of the 12-year mission. Investments in Advanced Power Generation Systems

Since 1968, NASA, DOE, and DOD have together invested more than $180 million in solar array technology, according to a JPL estimate. For example, in fiscal year 1998, NASA and DOD will invest $10 million for research and development of advanced solar array systems, and NASA will invest $10 million for research and development of advanced nuclear-fueled systems. Two improvements to solar array systems that are currently being developed could extend the range of some solar array-powered spacecraft and science operations beyond the orbit of Mars. Future Nuclear-Powered Space Missions

NASA is currently studying eight future space missions between 2000 and 2015 that will likely use nuclear-fueled electrical generators. NASA and JPL officials also pointed out that planned future missions may not need to use Earth swingby trajectories. Scope and Methodology

To obtain information about the processes used by NASA to assess the safety and environmental risks of the Cassini mission, NASA’s efforts and costs to develop non-nuclear power sources for deep space missions, and future space missions for which nuclear-fueled power sources will be used, we interviewed officials at NASA Headquarters in Washington, D.C.; JPL in Pasadena, California; and DOE’s Office of Nuclear Energy, Science, and Technology in Germantown, Maryland. According to National Aeronautics and Space Administration (NASA) and Department of Energy (DOE) officials, no radioactive fuel was released from the fuel cells, and the fuel was recycled and used on a subsequent space mission.
Why GAO Did This Study

Pursuant to a congressional request, GAO reviewed the use of nuclear power systems for the Cassini spacecraft and other space missions, focusing on: (1) the processes the National Aeronautics and Space Administration (NASA) used to assess the safety and environmental risks associated with the Cassini mission; (2) NASA's efforts to consider the use of a non-nuclear power source for the Cassini mission; (3) the federal investment associated with the development of non-nuclear power sources for deep space missions; and (4) NASA's planned future nuclear-powered space missions.

What GAO Found

GAO noted that: (1) federal laws and regulations require analysis and evaluation of the safety risks and potential environmental impacts associated with launching nuclear materials into space; (2) as the primary sponsor of the Cassini mission, NASA conducted the required analyses with assistance from the Department of Energy (DOE) and the Department of Defense (DOD); (3) in addition, a presidential directive required that an ad hoc interagency panel review the Cassini mission safety analyses; (4) the directive also required that NASA obtain presidential approval to launch the spacecraft; (5) NASA convened the required interagency review panel and obtained launch approval from the Office of Science and Technology Policy, within the Office of the President; (6) while the evaluation and review processes can minimize the risks of launching radioactive materials into space, the risks themselves cannot be eliminated, according to NASA and Jet Propulsion Laboratory (JPL) officials; (7) as required by NASA regulations, JPL considered using solar arrays as an alternative power source for the Cassini mission; (8) engineering studies conducted by JPL concluded that the solar arrays were not feasible for the Cassini mission primarily because they would have been too large and heavy and had uncertain reliability; (9) during the past 30 years, NASA, DOE, and DOD have invested over $180 million in solar array technology, the primary non-nuclear power source; (10) in FY 1998, NASA and DOD will invest $10 million to improve solar array systems, and NASA will invest $10 million to improve nuclear-fueled systems; (11) according to NASA and JPL officials, advances in solar array technology may expand its use for some missions; however, there are no currently practical alternatives to using nuclear-fueled power generation systems for most missions beyond the orbit of Mars; (12) NASA is planning eight future deep space missions between 2000 and 2015 that will likely require nuclear-fueled power systems to generate electricity for the spacecraft; (13) none of these missions have been approved or funded, but typically about one-half of such planned missions are eventually funded and launched; (14) advances in nuclear-fueled systems and the use of smaller, more efficient spacecraft are expected to substantially reduce the amount of nuclear fuel carried on future deep space missions; and (15) thus, NASA and JPL officials believe these future missions may pose less of a health risk than current and prior missions that have launched radio isotope thermoelectric generators into space.