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Completed TRL 4 (started at 4, targeting 6)
The Current batteries that provide energy storage on spacecraft are limited by their relatively low energy density, cycle life, and cycle duration. The Non-Flow-Through Fuel Cell (NFTFC) for High-Density Energy Storage system has a high projected energy storage density (>400 Wh/kg) and can be scaled up to accommodate long-duration discharges (e.g., to provide power throughout a 14-day lunar night). The NFTFC uses an integrated gas-liquid separation membrane to passively remove water without excess flow of reactants, which improves fuel utilization and allows for a simpler balance of plant. Flight tests aim to demonstrate system functionality – specifically that of the integrated phase separator – in a space environment.
Problem Statement
High-power, high-density energy sources are a key technology development area to enable future lunar surface operations. Incumbent lithium batteries have substantial flight heritage but relatively low energy storage densities (<300 Wh/kg at the system level). Although next-generation battery chemistries, such as lithium sulfur, have high projected energy densities, they are still in early stages of development and have lifetime issues.
The NFTFC is a high-density energy storage technology that consumes gaseous or cryogenic hydrogen and oxygen and generates usable electrical power and high-purity water as a byproduct. The NFTFC contains an integrated phase separator that removes product water from the fuel cell without wasting reactants or relying on external balance-of-plant components. NFTFC systems can achieve energy densities exceeding 400 Wh/kg, which is greater than many incumbent battery systems. Additionally, an NFTFC can be configured to run on boiloff from liquid hydrogen and oxygen propellant tanks, allowing for the efficient use of what would otherwise be a waste product.
The NFTFC is designed to solve two major problems with conventional energy storage technologies for space applications: (1) Fuel cell energy storage systems have higher energy density than battery systems, allowing for significant mass and launch cost reductions. (2) Fuel cell systems scale well for long-duration power cycles, which is relevant for missions on the lunar south pole, where solar power may not be available for extended periods. Increasing the discharge duration of fuel cells can be accomplished by increasing the size of the oxygen and hydrogen tanks with minimal modifications to the remaining balance of plant.
Technology Maturation
Flight tests on Zero Gravity Corporation’s G-FORCE ONE are expected to demonstrate system functionality – specifically the integrated phase separator – in a relevant environment. The first flight test is expected to demonstrate the performance of the system with minimal gas purging to clear water from the fuel cell. The second flight test is expected to demonstrate true non-flow-through operation. Collectively, the flight tests aim to advance this innovation’s technology readiness level (TRL) to TRL 6 and reduce the programmatic and technical barriers associated with incorporating the NFTFC into a flight system.
Integrated phase separator: Allows for a simpler system design and higher fuel utilization than conventional fuel cells High-density energy: Provides mass and launch cost reduction relative to state-of-the-art battery technology
Future Customers
Potential for NASA and commercial aerospace companies for lunar surface and in-space energy storage Applicable to the U.S. Department of Defense, including high-altitude pseudo satellites (HAPS) and satellite energy storage
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