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Lithium-ion battery concept. |
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.
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 energy storage technology that will enable future
exploration missions to the moon and Mars. Goddard Space Flight Center,
the Jet Propulsion Laboratory, Johnson Space Center, Kennedy Space
Center, Marshall Space Flight 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 Batteries
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Li-Ion Battery Module for
Mars Rovers Spirit and Opportunity. |
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 separators) for space-rated lithium ion cells with
the following performance enhancements:
- High specific energy - amount of energy per unit mass
- High energy density - amount of energy stored per unit mass (The
higher the energy density, the less mass that is required to provide
a fixed amount of energy.)
- Wide operating temperature range: -60ºC to +60ºC
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State-of-the-art is currently -20ºC to +30ºC
- Improved reliability
- Enhanced safety
- Long cycle life - allows the cell to be charged and discharged
many times
To improve battery safety, the Energy Storage Project is developing
shut-down separators for use in lithium ion cells that would prevent
thermal run-away, even under abusive conditions. Testing is performed
under laboratory conditions to evaluate the behavior of these
cells under abusive conditions including mishandling, puncture,
overcharging, and short circuit faults. |
25 Amp-hour Battery
Module for Mars Lander (Mfg, Lithion Inc.). |
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ABSL 18650 Li-Ion Battery
Modules. |
In addition to the advanced cell and cell component development, the
project is designing a modular lithium-ion battery that is human-rated and
meets the requirements for high energy density applications. The project
team is conducting trade studies to address mass properties, safety,
thermal control, and mechanical and data interfaces to create a cost
effective battery design. They are also using analytical models and
performing hardware testing to ensure that the battery is safe and
reliable.
Once the battery is developed, the modular design can be
used to support multiple exploration missions across multiple platforms.
As a building block for future missions, the standardized batteries
may significantly reduce life cycle costs.
Fuel Cells
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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.
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Regenerative Fuel Cell
(RFC) System. |
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.
PEM Fuel Cells
Glenn is currently developing Proton Exchange Membrane (PEM) fuel
cell technology in collaboration with Johnson Space Center, Kennedy
Space Center, Goddard Space Flight Center and the 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.
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PEM fuel cell development unit. |
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.
Removing
water from fuel cells in the wide range of gravity environments in
which space operations occur (3-g during launch to 0-g while in orbit)
is currently achieved by flowing an excess of reactant gas through
the fuel cell. While some of the gas reacts to make electricity, the
velocity of the remaining (un-reacted) gas flowing through the fuel
cell channels keeps the water moving toward the outlet. With air as
the oxidizer, 80% of the gas flow through the channels does not react.
When pure oxygen is the reactant, the channels must be smaller to
maintain the velocity of the excess oxygen as it moves toward the
outlet, carrying the water along with it. The reduced channel size
(or cross sectional area) is cost effective because it results in
a smaller fuel cell. When the mixture of water and un-reacted gas
reach the outlet, it flows to a separator where the water is removed.
The water is collected in a storage tank and the remaining reactant
gas is returned to the inlet side of the fuel cell where it merges
with additional reactant gas from the fuel tank before flowing into
the fuel cell.
Separation of the water and air (as a reactant gas)
on Earth is as simple as letting the water flow to a drain and discharging
the spent air (with reduced oxygen content) into the atmosphere. In
space, water separation is done with motor driven separators and mechanical
pumps. While these devices are effective, they require an electrical
system and maintenance, which increases the overall complexity and
weight of the system. Glenn is working on separator technology that
passively (without moving parts) removes liquid water from the excess
oxygen stream prior to the gas being fed back into the fuel cell.
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 and reliability
are critical to the successful deployment of fuel cells and batteries
in NASA’s long-term exploration missions.
Contact at NASA Glenn Research Center
Chief, Advanced Capabilities
Project Office: Ann P. Over
Space Flight Systems Directorate
/ Advanced Flight Projects Office
216-433-6535
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