How do you survive in a remote, mountainous region that
has no water or wind and sometimes goes without sunlight for
weeks?
This
is not the premise for a survivalist reality show; it's a
question NASA must answer before sending humans to live and
work on the moon.
Within the next twenty years, people again will explore the
vast lunar terrain. This time, we're going to build a
permanent outpost where we will conduct scientific research,
learn to live off the land, and test new technologies for
future missions to Mars and beyond.
During the day, solar arrays will generate electricity for
habitats, life support systems, rovers, communications
systems and other equipment. But lunar nights last up to 334
hours in some places. Even at the moon's south pole, the sun
never rises high. Mountains and hills block sunlight from
reaching the surface, and night bathes the moon in total
darkness for more than 100 hours.
NASA's Glenn Research Center in Cleveland is leading an
effort to develop systems that could store energy for use
during the long, frigid lunar nights. The solution may be a
fuel cell system that originally was designed for a
high-altitude solar-electric airplane.
In 2005, Electrical Engineer David Bents and his team at
Glenn demonstrated the first and only fully closed-loop,
regenerative fuel cell ever operated. Though the technology
never was implemented on the airplane, Glenn engineers are
gleaning valuable information from the project as they
design a next-generation regenerative fuel cell for the
moon.
How It Works:
A
typical hydrogen fuel cell combines hydrogen from a tank and
oxygen from the air to produce electricity, leaving water
and heat as its only byproducts. A regenerative fuel cell
also works in reverse, using electricity to divide the water
into hydrogen and oxygen, which are fed back into the fuel
cell to produce more electricity.
"What makes our regenerative fuel cell unique is that it's
closed loop and completely sealed," Bents said. "Nothing
goes in and nothing comes out, other than electrical power
and waste heat. The hydrogen, oxygen and product water
inside are simply recycled over and over again."
In other words, instead of using oxygen from the air like
other regenerative fuel cells, the closed-loop system
re-uses the oxygen extracted from the water. That makes it
ideal for use on the moon, where there is no oxygen.
"On the moon, you would start with a tank of water. You'd
use the solar arrays to make hydrogen and oxygen during the
day, then use the hydrogen and oxygen to make electricity
during the night when there's no sun," said Bents. "Ideally,
if nothing broke and nothing wore out, it could run forever
without being refueled."
The system is very similar to a rechargeable battery, but it
can store four to six times more energy than a battery of
the same weight.
An Energy Storage Milestone
In the summer of 2005, Glenn demonstrated the first fully
closed-loop regenerative fuel cell ever operated. It
completed five continuous day and night cycles. That's
nowhere near forever, but at the end of the demonstration,
it had not leaked and was capable of running at least one
more cycle.
Those
five days of operation were the result of several years of
hard work. The team's diligence paid off by proving a
regenerative fuel cell's potential as an energy storage
device for aerospace solar power systems.
Since the demonstration in 2005, the team has modified and
upgraded much of the software, circuitry and hardware to
make the system run more reliably.
The lessons they learned and information they gathered in
the process will be invaluable to Glenn's Energy Storage
Project Office when it develops a prototype system to work
in the harsh lunar environment.
"Even though it was originally designed for an airplane, the
system has given us a leg up," said Ann Over, chief of
Glenn's Advanced Capabilities Project Office. "The knowledge
we gained will feed directly into our lunar regenerative
fuel cell technology program."
Glenn plans to begin work in 2008 on a prototype
regenerative fuel cell system for the lunar outpost.
