Energy Storage Technology for Future Space Science Missions

Executive Summary

The goal of the study was to assess the potential of advanced energy storage technologies to enable and/or enhance next decade (2010-2020) NASA Space Science missions, and to define a roadmap for developing advanced energy storage technologies that will enable or enhance future missions. The study was jointly sponsored by the Office of Space Science and by the Solar System Exploration Division at NASA HQ.

The specific objectives of the study were as follows:

• Assess the capabilities of current State of Practice (SOP) energy storage devices currently used in Code S missions and their potential for future improvement.
• Determine the impacts of potential advances in energy storage technology on future Code S missions.
• Review the status of the development of emerging energy storage technologies and determine the potential for developing technologies that enable or enhance Code S missions.
• Review non-NASA energy storage technology programs and assess the potential for meeting Code S needs through collaboration between NASA and other agencies.
• Formulate energy storage technology development plans to fill any gaps remaining between development programs and Code S mission needs.

The study was led by JPL and conducted by an assessment team with relevant experience in energy storage technology drawn from NASA Centers, other agencies, and universities with relevant experience in energy storage technology. Three meetings were held at which representatives of the aerospace and energy storage industry participated. The study was completed before the announcement of the President's Vision for Space Exploration in January 2004 and the formation of NASA's Exploration Office. Accordingly, none of the requirements of new exploration missions were included in the report.

Roadmap for Energy Storage Technologies

The goal of the Office of Space Science and the Solar System Exploration Division in sponsoring this study was to determine the most productive areas of investment in energy storage technology. Developing new technology and infusing it into space science missions is expensive. Accordingly, three factors must be considered in selecting the investment areas of highest priority, and in formulating the technology roadmaps for these areas:

• The potential for advanced energy storage technologies to enable and/or enhance future space science missions
• Prospects for achieving the needed technological advance with acceptable risk and affordable investment
• Potential for collaboration with other agencies with similar interests in these technologies and their willingness to share the costs.

Using these criteria, three areas of technology development programs were recommended where the primary impact will be on Mars Exploration Programs and Exploration of the Solar System missions. They are:

• Low-Temperature Primary Batteries
• Long-Life Rechargeable Batteries
• Low-Temperature Rechargeable Batteries.

Impact of Advanced Energy Storage Technologies on Future Missions

The Space Science Enterprise implements missions within five themes: Exploration of the Solar System (ESS), Mars Exploration Program (MEP), Sun-Earth Connection (SEC), Astronomical Search for Origins (ASO), and Structure and Evolution of the Universe (SEU). The impacts of advances in energy storage on missions within each theme were considered with particular focus on:

• Energy parameters (specific energy and energy density)
• Lifetime (cycle time, calendar life, self discharge rate)
• Extreme Environments (high and low temperatures and radiation)

The Space Science Enterprise implements a mix of strategic missions that are planned many years, sometimes decades, in advance and competitive missions that are selected through periodic announcements of opportunity. For strategic missions the mission designs are reasonably well defined and mission impacts are comparatively straightforward to discern. For competitive missions even the nature of these missions is uncertain and determining mission impacts of technology are less well defined.

The two themes where advances in energy storage technologies have the greatest impact are the Mars Exploration Program (MEP) and the Exploration of the Solar System (ESS). The MEP theme utilizes both strategically selected and competitively chosen missions; the ESS theme mainly utilizes competitive missions. The impact of advances in energy storage technology on missions within these themes is summarized in Table ES-1. It is clear from this table that the critical needs for new Space Science missions are high specific energy and energy density, long life, and low-temperature operation.


Mars Exploration Program

The mission categories examined included orbiters, surface missions (landers, rovers), aerial platforms (balloons, airplanes), probes, and sample return. Mars surface missions that utilize solar power must survive overnight when temperatures will fall to the -60? to -100?C range, depending on location and season.

• Mars Orbital Missions will benefit from advances in specific energy which can be applied to increase science payload or for increasing instrument power for observations on the night side of the planet for use of active sensors such as lidar, microwave, or radar
• Mars Surface Missions can benefit from improvements in rechargeable energy storage for the reasons that Li-Ion technology had such an impact on the MER missions. The benefits would be greatest for solar powered mobile missions where low-temperature performance will be particularly beneficial.
• Aerial Platform missions include short duration airplane or glider missions with lifetimes measured in minutes for gliders, hours for powered flight, and days to months for balloon missions. For airplane missions, gains in specific energy for primary storage have high impact. For balloon missions, gains in specific energy are particularly important at low night time temperatures for rechargeable batteries.
• Mars Sample Return missions are highly sensitive to mass and volume for ascent vehicles and orbital rendezvous and would be a significant beneficiary of gains in specific energy for rechargeable storage.

Exploration of the Solar System (ESS)

The ESS theme, which covers exploration of all solar system bodies except the Sun, the Earth, and Mars, is subdivided into Outer Planet Exploration, Small Body Exploration and Venus Exploration.

Outer Planet Exploration missions include orbiters in the New Frontier class, outer planet orbiters, atmospheric probes, and icy body landers such as the Titan Explorer.

• New Frontier Class Orbiter s could use radioisotope power generation systems. The missions involve long trip times and may require energy storage with long life (typically > 10 years, and in some cases up to 20 years) for load-leveling.
• Nuclear Reactor Powered Missions such as the proposed Jupiter Icy Moon Orbiter (JIMO) have a unique need for high-capacity, long storage life batteries that are needed for startup and maybe be needed for restart in the event of a reactor shut-down.
• Outer Planet Atmospheric Probes require primary energy storage technologies that can operate effectively at low and high temperatures (increasing as the probe descends into the atmosphere), are capable of withstanding high acceleration loads, and have increased mass and volume efficiency. Advances in primary storage would enable larger science payloads and increased data return.
• Icy Body Landers utilize primary energy storage in a very low-temperature environment for a limited period of time. Titan and Europa probes may encounter temperatures as low as -200?C. No battery would function at such temperatures. Therefore, it must be enclosed in a thermal protection system. However, the lower the operating temperature of the battery, the longer the power system would endure in that cold environment.

Small Body Exploration missions examined included fast flyby sample return, fast flybys with impactors and comet and asteroid rendezvous sample returns.

• Fast Fly-By Sample Return and Impactor missions would use primary batteries to power the impactor or the return capsule. In each case, extension of the operating temperature range to lower temperatures would be beneficial.
• Fast Fly-By Comet and Asteroid Sample Return : Detached probes to obtain samples from comet or asteroid surfaces will require low-temperature primary energy storage similar to that required for outer planet icy moon surface probes. Spacecraft that directly approach comets and asteroids for acquisition of samples would require substantial rechargeable energy storage as comet and asteroid rotation periods will subject the spacecraft to possibly lengthy eclipse periods. Dust mitigation may require stowage of solar arrays and use of rechargeable energy storage capacity.

Impact of Advanced Technology on Office of Space Science Missions - Summary Based on an assessment of the likely payoff from performance improvements in energy storage technology, the following technology advances were identified as having potentially high impact on space science missions:

• Primary energy storage systems with substantially improved specific energy and extended temperature range. Low temperature operation is important for missions to Mars, small bodies and the outer solar system. Primary storage systems that could operate at 460 o C are of interest in Venus exploration and potentially to SEC missions.

• Secondary (rechargeable) energy storage systems with high specific energy (200Wh/kg) that can operate for up to 15 years and sustain up to 50,000 cycles of operation. Extension of the operating range to as low as ?80?C would offer significant advantage to many mission categories.

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