Space exploration requires electrical power and an efficient means
of storing energy. This energy must be stored safely, under a wide
range of environmental conditions, and for extended periods of time.
Portable utility pallet houses regenerative fuel
cells to provide power during eclipse periods on planetary surfaces.
Stored energy is especially important during night time when solar
energy is not available or during eclipse or periods of shadow when
solar energy is blocked from reaching the solar arrays.
Energy is necessary to power rovers, tugs, habitats, experiments, beacons,
astronaut tools, and in-situ resource utilization equipment, which
is used to obtain material resources from lunar regolith (soil). Energy
is needed to run equipment inside the space suits including liquid
cooling and ventilation systems, communications equipment, bio-instrumentation
and other life support systems.
NASA’s Glenn Research Center is leading the Energy Storage Project
to develop technology that will enable future exploration missions
to the moon and Mars. The Jet Propulsion Laboratory, Johnson Space
Center, Kennedy Space Center, universities, and industry partners are
collaborating with Glenn on this project. As an ongoing effort, the
project team identifies new materials and manufacturing methods that
will enhance the capability and safety of fuel cells and batteries.
The Energy Storage Project team examines the requirements of NASA’s
Constellation Program. Trade studies are conducted to determine where
the team should focus their technology development efforts to address
gaps between the Program requirements and performance characteristics
of the current technology.
Lithium-Ion Battery used in Extravechicular
These technologies provide the opportunity to demonstrate dual-use
technologies for clean and renewable energy for terrestrial applications
as advances envisioned for space use are also expected to provide
benefits for homes, cars and other Earth-based applications.
Lithium Ion Batteries
Advanced batteries with high specific energy and long cycle life
can extend the range of planetary robots and mobility systems and
reduce the mass of landing systems (increasing available payload
mass) while adding functionality by providing more power. For
crew excursions, compact spacesuit batteries with even greater specific
energy are critical for extending mission durations and therefore
Batteries used in automobiles and trucks contain a number of individual
cells. Many batteries, such as those found in flashlights (D-cells)
and TV remotes (AA-cells), are comprised of just one electrochemical
cell. This project is developing advanced cell components (electrode
materials, electrolytes and safety devices) for space-rated lithium
ion cells with the following enhancements:
- High specific energy - amount of energy per unit mass
- High energy density - amount of energy stored per unit volume
- Cell-level safety – tolerance to electrical and thermal abuse
|Fabricating advanced electrodes
at Glenn Research Center. The electrodes are then assembled
into cells for further testing.
Cathodes (positive plates), anodes (negative
plates) and separators are stacked to form a prismatic cell. Electrolyte
fills the voids and safety components include electrode coatings
and electrolyte additives.
To reach our performance goals, we are developing:
- Silicon-composite anodes to significantly improve capacity by
developing elastomeric binders and nanostructures to extend cycle
- Novel layered-oxide cathodes with lithium-excess compositions
to improve capacity; and
- Electrolytes that are stable at high voltages.
To reach our safety goals we are developing:
- Nano-particle circuit breakers to reversibly shut-down the cell
in a hazardous situation;
- Flame-retardant electrolytes to prevent fire and flame without
degrading battery performance; and
- Cathode coatings to increase the thermal stability of the cell.
These components are being developed individually at a variety of
companies and universities, and screened for performance and compatibility
at Glenn. Manufacturability advice is given by an industrial
partner, who also scales up the material and builds cells from the
||Testing lithium-ion cells to
determine the performance of advanced components in a representative
Shuttle Flight Unit
Fuel cells are enabling technologies for many aspects of lunar surface
operations. In applications where electrical power is needed for
an extended period of time, fuel cells are a viable option. The total
amount of energy available from a fuel cell is dependent on the size
of the hydrogen and oxygen reactant tanks. The reactants feed into
a fuel cell to produce electricity with drinkable water as a by-product.
Regenerative Fuel Cell
There are two types of fuel cells. Primary fuel cells convert oxygen
and hydrogen into electrical energy and water, but stop producing
electricity once the reactant supply is depleted. Regenerative fuel
cells produce electrical energy in the same way as primary fuel cells.
However, they are also capable of recovering the reactants by using
electricity to split the product water molecules into hydrogen and
oxygen in a process called electrolysis. For this process, electricity
could be provided by solar arrays or a fission power system.
Glenn is currently developing Proton Exchange Membrane (PEM) fuel
cell technology in collaboration with the Johnson Space Center, Kennedy
Space Center, and Jet Propulsion Laboratory. This fuel cell chemistry
is smaller and more efficient than previous types such as the alkaline
fuel cells used on the Space Shuttle. Its compact size helps reduce
the overall mass and volume of the spacecraft’s power system.
“Non-Flow-Through” Proton Exchange
Membrane Fuel Cell System Model
Commercial fuel cells use air as the oxidizer reactant, which has
an oxygen content of only 21%. The PEM fuel cells that NASA is developing
operate with an oxidizer reactant that is 100% oxygen. This means
that the reactant tank only stores pure oxygen, so all of
its contents can produce electrical energy (rather than only 21%).
Without nitrogen in the tank, the tank can be smaller and more lightweight.
To reduce system mass, volume and parasitic power, and increase system
lifetimes even further for both primary and regenerative PEM fuel
cells, we are developing “non-flow-through” technology,
in which product water generated at the electrode surface wicks across
the adjacent gas cavity by capillary action across a screen and through
a hydrophilic membrane into a water coolant cavity within each cell
of the stack. There are no recirculating reactants, and hence
no requirement for providing either recirculation or external product
water separation from two-phase reactant streams. Therefore,
there is no need for the major components that provide these functions,
and no resulting weight, volume, parasitic power, reliability, life,
or cost penalties. These major flow-through PEM fuel cell components
can comprise 25-35% of total system mass, so their elimination offers
a major advantage for non-flow-through systems.
“Flow-through” PEM fuel cell technology is the more
conventional approach as it is widely used in terrestrial applications. This
is because terrestrial air supplies must be purged of everything
except oxygen, and this purge system can therefore carry away the
product water. Because the reliability of regenerative fuel
cells is such a high risk for lunar surface systems, we have
elected to pursue non-flow-through technology based on data indicating
that non-flow-through technology should both reduce mass by ~40%
and eliminate the life-limiting balance-of-plant components.
Testing hydrogen/oxygen fuel cell system at
Glenn Research Center.
Although non-flow-through technology will eliminate ancillary components
associated with reactant flow management, the thermal management
system for the primary fuel cell and electrolyzer also requires ancillary
components. To increase their lifetimes, we have developed passive
thermal management technologies to replace current active pumped
liquid coolant loops. These technologies include pyrolytic
graphite plates and flat-plate heat pipes for direct insertion into
fuel cell and electrolysis stacks, replacing individual cell coolant
The materials from which fuel cells are made must be very durable
since pure oxygen is more corrosive than air. The proton exchange
membrane, fuel cell channels and other materials wetted by the reactant
oxygen must all be corrosion resistant to achieve a fuel cell with
long operational life. Catalyst formulations, a critical material
in fuel cells, take part in the oxygen-hydrogen reaction to make
electricity, but are not consumed during the process. The catalysts
must also be resistant to corrosion by the flow of oxygen through
the fuel cell.
Through lithium ion battery and fuel cell technology development
efforts, Glenn is addressing critical energy storage requirements
for spaceflight applications. Reducing weight and improving overall
performance, reliability and safety are critical to the successful
deployment of fuel cells and batteries in NASA’s long-term
Advanced rechargeable lithium-ion batteries
add operational capability for a lunar lander ascent stage.
Advanced fuel cell technology provides power to the descent
stage and initial power on the lunar surface.
Contact at NASA Glenn Research Center
Acting Chief, Advanced
Capabilities Project Office: John
Space Flight Systems Directorate
/ Advanced Flight Projects Office