The panel identified four top technical challenges for TA03, all of which are related to the provision of safe, reliable, and affordable in-space power systems consistent with NASA’s current and potential mission needs. They are listed below in priority order.

1. Power Availability: Eliminate the constraint of power availability in planning and executing NASA missions.

Power is a critical limitation for space science and exploration. The availability of more power opens up new paradigms for how NASA operates and even what individual missions can accomplished. Increased power availability for human exploration missions translates into capabilities to support more astronauts at larger outposts with higher-capacity in situ resource utilization (ISRU) systems, higher data transmission rates, more capable mobility systems with shorter turnaround times, and higher capability science instruments. For robotic science missions, power availability has become critical in determining the scope of a mission that can be planned and how long it takes to reach mission destinations. This is due to the emergence of electric propulsion systems that enhance robotic mission design, so that the more power that is available, the shorter the trip time to any destination. Once at the destination, high power levels enable scientists to develop new approaches to scientific discovery and to communicate larger volumes of information more quickly back to Earth.

2. High-Power for Electric Propulsion: Provide enabling power system technologies for high-power electric propulsion for large payloads and planetary surface operations.

Advances in solar and nuclear technologies in the United States and elsewhere during the past decade offer the potential of developing power generation systems that can deliver tens to hundreds of kilowatts. For example, inverted metamorphic (IMM) solar cells are being developed to deliver 40 percent efficiency with very little mass due to removing the thick substrate used to grow the multi-layer photovoltaic semiconductor materials. New lightweight structures also greatly reduce the mass of solar arrays and enable higher power outputs. As solar arrays grow to large sizes (such as hundreds of kW for electric propulsion planetary missions), new technology will be needed for the control and pointing of the large arrays. Nuclear fission system concepts have been developed for lunar and Mars missions that provide pathways to reasonable mass reactors that can be placed and operated on a planetary surface to deliver 10 kW to 100 kW. These designs use proven fuels, power conversion technologies, and reactor materials to reduce the development and operations risk to acceptable levels. Other aspects of fission systems require technology development including heat exchangers, fluid management, scaling of power conversion devices, heat rejection components, radiation shielding, and aspects of system integration and testing.

3. Reduced Mass: Reduce the mass and stowed launch volume of space power systems.

Power systems typically comprise one third of the mass of a spacecraft at launch, and the volume available in the launch vehicle fairing can limit the size of solar arrays that can be packaged on the vehicle. New power generation, energy storage, and power delivery technologies have the potential to cut the mass and volume of these systems by a factor of two to three. Successfully developing these technologies would enable missions to include more science instruments, use smaller and less expensive launch vehicles, and/or provide higher power levels.

4. Power System Options: Provide reliable power system options to survive the wide range of environments unique to NASA missions.

NASA missions require power systems and components to survive many different types of extreme environments. This can include high radiation levels, very high or very low temperatures, very high impact forces (for planetary surface penetrators), highly corrosive environments, dusty atmospheres, and other unique extremes. In all of these challenging environments, the power system must operate predictably and reliably or the mission is

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