Did you see
the movie The Martian? The hero, Mark Watney, an astronaut given up for
dead by NASA, uses a radioisotope thermoelectric generator (RTG), a sort-of
"space battery," to keep warm during his trek across Mars.
The movie is
science fiction but these devices are real- NASA has been using RTGs to power
satellites for nearly forty years, and they've been used on
major trips to the moon and other planets. But NASA recently announced plans to
use nuclear power in a different way- one that hasn't been fully attempted in
fifty years.
The RTGs like
Mark Watney’s harness the heat from passive radioactive decay and produce a few
hundred watts of electricity, which on Earth would be enough to run a handful
of household appliances. But a mission to Mars would require far more power.
Now, NASA is working on a reactor that splits atoms, as reactors on Earth do,
to make 100 times more electricity than an RTG. The initial plan calls for 40
kilowatts, which on Earth would meet the needs of a small apartment building.
For three
years, NASA has been working on the project, which it calls Kilopower (Kilo is
the Latin prefix for thousand.) According to the development team, which is
based at Los Alamos National Laboratory, "The Kilopower technology
demonstration is the practical and affordable first step to getting a reactor
power system in space. We're seizing the opportunity to demonstrate
system-level technology readiness of space fission power."
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| Artist's conception of the Kilopower reactor. |
Surface
exploration requires readily available power, but electricity-generating
reactors make up only a small slice of nuclear's role in space. So far, RTGs
have been much more common than reactors, beginning in the 1950s.
On December 8,
1953, President Eisenhower delivered his "Atoms-for-Peace" address in
which he described the promise and potential of nuclear energy for humanity.
Six years later, the first radioisotope thermoelectric generator, SNAP 3-A (for
Space Nuclear Auxiliary Program), sat on his desk in the Oval Office. This new
technology created by the Atomic Energy Commission (AEC) inspired wonder and
awe not only from the President, but from the public as well. This new
technology made it possible for nuclear energy to power the instruments aboard
a satellite.
RTGs convert
heat into electric power. They sometimes also function as simple heat
generators to keep satellite components from freezing in the deep cold of
space. The heat comes from the natural decay of a radioactive isotope,
typically plutonium 238.
As the country
entered the space race and the tremendous pressure to advance technologically,
NASA realized the usefulness of RTGs. They were lightweight, compact, had no
moving parts, and only depended on readily available plutonium, rather than the
sometimes-unavailable sun. Plutonium 238, a different type of plutonium than
used in weapons or power reactors, also seemed to be the most fitting fuel for
the job. It has a half-life of 88 years, meaning it puts out high heat and can
power the spacecraft for decades.
The first U.S.
spacecraft powered by an RTG was the Navy's Transit 4A navigation satellite,
which was launched in 1961. That day, the front-page headline of the New York
Journal American read: "U.S. ORBITS ATOMIC BATTERY." The government
and the public enthusiastically embraced nuclear energy as a means to lead the
world in space exploration and technology.
RTGs
progressed in the sixties. Like the 3A, the 1964 SNAP-9A used plutonium 238 and
was expected to operate for five to ten years. It generated 25 watts of
electrical power. RTGs went on to power many more missions throughout the
seventies and eighties, including the Cassini space probe, which is completing its
mission exploring Saturn in the next few months. Pioneer and Voyager missions
used RTGs, as does the Curiosity robotic rover currently exploring Mars.
However,
project Kilopower marks the first time in fifty years that NASA is looking to
use nuclear energy in a different form. Back in the 1960s, the agency began
working on a way to put a nuclear reactor into space. While RTGs generate heat
through the simple decay of a radioactive isotope like plutonium, reactors
generate far greater quantities of heat by the splitting of uranium atoms in a
controlled nuclear reaction. In 1965, the SNAP-10A launched from Vandenberg Air
Force Base with the goal of producing 500 Watts of electricity for at least one
year. With such technology, NASA could start the nuclear reaction remotely when
the satellite entered orbit.
The project
ultimately succeeded, as the reactor produced more than 600 watts of power.
After forty-three days, however, an unrelated failure in the Agena spacecraft
caused the reactor to shut off. While Russia has launched over thirty reactors
into space, the United States has only launched one: SNAP-10A. Now, NASA plans
to start testing a new reactor for space at the end of this year.
The new
reactor is about 6.5 feet tall and produces 1 kilowatt of electric power, about
as much as is consumed by a window air conditioner. The project managers
envision 40 kilowatts and multiple small reactors on Mars in the future.
Nuclear energy remains the best option for power, as Mars receives less
sunlight than earth, making solar power an unrealistic option.
Kilopower begs
the question- if reactors here on Earth require refueling and maintenance, how
will reactors on space comply with this requirement? Dr. Bhavya Lal of the
Science and Technology Policy Institute in Washington, D.C. says that ideally,
the reactor would be designed so it would need to be minimally refueled. The
Kilopower design uses high-enriched uranium, which allows a greater operational
lifetime. Many of these logistical questions can be explored after the testing
that begins at the end of this year.
Both the space
community and the nuclear energy industry eagerly wait to see how the Kilopower
reactor will perform. The potential of electricity on Mars means further
exploration and discovery, and nuclear energy is the key to operating there.
Although fifty years has passed since the last reactor left Earth, AEC Chairman
Glenn Seaborg said in the 1960s what still holds true today:
"The
presence of the ‘atomic battery’ in the satellite is a symbol of a ‘marriage’
that was bound to occur—between Space and the Atom. We have known for some time
that the two were made for each other."
Before we can
even think about making Mars habitable, we must figure out a way to support
astronauts exploring the surface. Sunlight is only one-third as strong on Mars
as on Earth, and as happens here, the sun is only up for half the day. So solar
energy can't provide the immense amount of electricity needed to power a Mars
base. NASA explains that it will need nuclear power in many places, including
craters in shadow, and has several research efforts now under way.
Nuclear
reactors don't just have applications on the actual surface of a planet,
either: they can also be a key to getting there. NASA just awarded BWXT Nuclear Energy a contract to design a
nuclear thermal propulsion reactor. On a manned trip to Mars, this reactor
would create an electric current that shoots ions out of the back of a rocket,
propelling the spaceship forward.
A lot has
changed since Eisenhower first marveled at the SNAP 3-A in the Oval Office. But
as new projects like Kilopower and thermal propulsion reactors take shape,
nuclear energy's many applications echo what Seaborg said fifty years ago.
There is an eternal, unmatched link between nuclear energy and space.
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