Overall Finding

NASA and its partners in other federal agencies such as the Department of Energy have taken some important first steps in what will be a long-term program to harness nuclear power and propulsion technologies for the benefit of space exploration activities. Nevertheless, while these technologies hold promise, their positive and negative aspects must be clearly understood. If nuclear propulsion systems are developed and demonstrated, they will give researchers access to previously inaccessible objects and destinations, enabling them to conduct comprehensive studies of a type, and with a flexibility, not previously contemplated in the history of space exploration (see text boxes in Chapters 4 and 6). However, spacecraft nuclear propulsion is in its infancy and will require a great deal of technological development. As shown in Chapter 2, the performance figures from NASA’s studies of the Jupiter Icy Moons Orbiter (JIMO) and its parametric studies of candidate post-JIMO missions reveal a significant performance gap (in terms of, for example, transit time and launch mass) between what appears to be currently feasible and what is desirable from a scientific perspective.

The material presented in Chapter 2 also suggests that NASA’s current nuclear propulsion activities may be too narrowly focused on a single technology—nuclear-electric propulsion—and might benefit from a broader assessment of other technological approaches. Unfortunately, the study committee’s ability to examine technical factors related to these concerns was somewhat limited because circumstances beyond its control indefinitely postponed the second phase of the study, which would have provided detailed inputs from a panel of space nuclear power experts.

By today’s standards, the spacecraft using nuclear propulsion systems, regardless of the exact technologies employed, will be very large, very heavy, very complex, and, almost certainly, very expensive. To what extent will the development and deployment of such technologies interfere with the diversity of space science missions? Such diversity gives scientific breadth and depth to these pursuits and is essential for the long-term health and vitality of all space science activities.

On the other hand, it is difficult to imagine that the space science goals of the period beyond 2015 will still be addressed with the power and propulsion technologies of the Mariners, Pioneers, and Voyagers. But it is equally difficult to imagine how it will be possible to transition smoothly from an era of Cassini, Mars Exploration Rovers, New Horizons, Discovery, and Explorers to one whose mix of activities is as diverse but now also includes super-flagship-class NEP missions.

Finding: Nuclear power and propulsion technologies appear, in general, to have great promise and may in some senses be essential for addressing important space science goals in future decades. This is particularly true for the fields of solar and space physics and solar system exploration, and especially so with respect to near- to mid-term applications of radioisotope power systems. Nevertheless, the committee has significant reservations about the scientific utility of some of NASA’s current nuclear research and development activities, about NASA’s current technological approach to the implementation of nuclear propulsion, and about the agency’s ability to integrate a new class of large and potentially very expensive nuclear missions into its diverse and healthy mix of current missions.

The committee elaborates on this finding below and makes specific related recommendations.

Additional Major Findings

Radioisotope Power Systems

Finding: Radioisotope power system technologies will enable varied and rich space science activities.

NASA is investing in both RPSs and fission reactors as power sources for future missions. RPSs, which have a long history of enabling science investigations, could provide power for a broad range of missions, from landers at Mars or Venus to orbiters at the planets of the outer solar system. To do so they must be able to operate in a number of modes (e.g., on orbiters, landers, and rovers) and environments (e.g., extremes of hot and cold, the vacuum of deep space, or planetary atmospheres). RPSs might also be useful for different classes

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