The Role of Nuclear Energy in the Future of Human Spaceflight

Sean Copeland
March 22, 2012

Submitted as coursework for PH241, Stanford University, Winter 2012

Fig. 1: Required solar array size under ideal conditions at Earth and Mars orbital distances. Efficiency values are from reference [5].


Since the conclusion of the Apollo program in 1972, human spaceflight has been limited to a region of space called Low Earth Orbit (LEO). In that time, crews have demonstrated the ability to launch, recover, and repair satellites, have studied the effects of long exposure to microgravity, and ushered in a new era of international collaboration in space activities with the construction of the International Space Station (ISS).

Within the last decade, there has been a resurgence of U.S. political interest in a return to human spaceflight beyond LEO. Since 2004, space policy has been driven by the Vision for Space Exploration, and the Review of Human Spaceflight Plans Committee, directing the development of the next generation of NASA spacecraft and exploration technology. [1,2] The long-term goals, stated by NASA, focus on technology development to support a manned landing on the surface of Mars. To accomplish this, one of three technology development paths can be taken. These paths are described below:

The selection of the path forward has great significance on the mission architecture and the necessary hardware. This report will discuss the implications of that choice on the power subsystem and the role that nuclear-based energy sources may play in the future of manned spaceflight.

Common Spacecraft Power Technologies

Space systems require power to maintain orientation, communicate, operate scientific instruments, and to run life-support systems. In the last half-century, four technologies have primarily been used for spacecraft and satellites: batteries, fuel cells, photovoltaic cells, and nuclear systems. A brief description of each of these technologies follows.

Powering the Future of Human Spaceflight

Each of the missions previously highlighted impose specific requirements and challenges on the power subsystem that must be matched with the advantages and disadvantages inherent in the power generating technologies currently available. In particular, three items are of primary interest: mission duration, space environmental conditions, and desired electrical power. Fig. 1 relates solar array size to desired power under ideal conditions at Earth and Mars. This figure represents a "best case" scenario and forms a foundation upon which we can evaluate the suitability for solar-based power generation for missions of interest. [6]