Space Exploration:

Power Sources for Deep Space Probes

NSIAD-98-102: Published: May 29, 1998. Publicly Released: May 29, 1998.

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Louis J. Rodrigues
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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.

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.

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