FIGURE 1.2 A schematic showing the relative applicability of various space-based sources of electrical power. Courtesy of George Schmidt, Project Prometheus, NASA.

  • Visit multiple bodies much more easily; and

  • Significantly alter a spacecraft’s trajectory in response to information collected during a particular mission.

Nuclear reactors have the potential to overcome limitations associated with low energy and power. They do this by providing electricity and propulsion over a wide range of power levels for extended periods (years to decades), including during both transit and surface operations, without regard to the availability of either solar energy or large quantities of chemical fuel. Nuclear reactor systems, however, are expensive to develop, and their potential will be realized only if key technology issues can be overcome.


In 2002, NASA initiated the Nuclear Systems Initiative, within the Office of Space Science (now the Science Missions Directorate), to explore the use of nuclear power and propulsion systems for both human and robotic activities. According to NASA, the initiative was begun in response to identified limitations of the current paradigm for solar system exploration missions. In particular, solar power constrains power budgets and is of limited use in the outer solar system, and chemical propulsion limits spacecraft maneuverability and mission destinations.

The following year, the Nuclear Systems Initiative was renamed Project Prometheus and given three tasks:

  1. To develop a new generation of RPSs;

  2. To conduct advanced studies of nuclear power and propulsion systems; and

  3. To initiate development of the first Prometheus flight program, the Jupiter Icy Moons Orbiter (JIMO).

In February 2004, responsibility for Project Prometheus was transferred to NASA’s newly established Office of Explorations Systems (now the Explorations Systems Mission Directorate). The Office of Space Science,

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