With a renewed spirit of discovery in space exploration, NASA plans to replace the aging space shuttle fleet with the new Crew Exploration Vehicle to travel beyond low Earth orbit (LEO) and return astronauts to the Moon. One of the critical components in a space-flight system is electrical energy storage. This year, researchers and engineers developed and tested the first high-energy lithium-ion (Li-ion) engineering model (EM) battery for human space flight for LEO and lunar missions.
Li-ion EM battery (front) and battery charge-control system (back).
The Li-ion EM (see the photograph) is a twin battery with eight 50-A-hr Li-ion cells connected in series on each side. It weighs about 100 lb. Although the EM was designed as a twin battery for an efficient power system packaging concept, a single battery could easily be built from the basic twin-battery design. The single battery could be used in a distributed power system in a space-flight vehicle where volume was limited. The battery is sized for both LEO and low lunar orbit (LLO) cycle regimes and with an N+2 battery level redundancy scheme to provide 5 to 7 kW of power during a 35-min Earth shadow and a 46.5-min lunar shadow. The N+2 redundancy scheme provides a fault-tolerant system while maintaining full performance capability and reducing battery system mass. An example of an N+2 redundancy scheme follows: A five-battery system with each battery sized for one-third performance capability can maintain full performance capability after two battery failures. The five-battery system mass is lower than the mass of three batteries with full performance capability.
The Li-ion EM has successfully passed protoflight vibration levels and thermal cycles, and it has demonstrated the required LEO and LLO charge-discharge cycle capability. The mission requirements include 240 LEO cycles, a 2.5- to 6-day cruise period, 2200 LLO cycles, and a 2.5- to 6-day return period with 8 LEO cycles. Demonstrations of the battery included LEO cycles at 45-percent depth-of-discharge (DOD) and LLO cycles at 60-percent DOD at 20 °C. Short-circuit and overcharge safety tests that were performed on battery cells of the same design provided valuable engineering data for the battery design. Furthermore, limited LEO/LLO cycle tests were performed with a separate eight-cell stack (same cell design). Another eight-cell stack was built for the life-cycle test. In addition, a battery charge-control system (BCCS) was built and demonstrated with the Li-ion EM battery. The BCCS features a nondissipative charge-control method that provides charging and individual cell balancing for the battery. The Li-ion EM battery system has been delivered to the NASA Glenn Research Center, and the battery with the BCCS will continue to undergo additional LLO cycle testing to evaluate performance.
The Li-ion EM and BCCS development effort has significantly advanced the technology readiness level, and the EM battery design is now a strong candidate for human space flight in LEO and lunar missions that require a battery for energy storage. The development effort is led by Glenn, with a Lockheed Martin Space Systems Company contract for hardware development, integration, and testing.
Find out more about ExplorationSystems research at Glenn: http://exploration.grc.nasa.gov
Nang Pham, 216-433-6165, Nang.T.Pham@nasa.gov
Tom Miller, 216-433-6300, Thomas.B.Miller@nasa.gov
Scott Graham, 216-977-7123, Scott.R.Graham@nasa.gov
Authors: Nang T. Pham and Thomas B. Miller
Headquarters program office: Exploration Systems Mission Directorate
Programs/projects: Exploration Systems Research and Technology
Last updated: December 14, 2007
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