Nuclear Power Applications in Space

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Nuclear Power Applications in Space
American Nuclear Society
NUCLEAR POWER ALREADY IN USE
Radioisotope Thermoelectric
Generators (RTGs) RTGs have been
used to produce power on space probes
and other missions for the past 25 years. They
use the natural decay of Plutonium-238
to create about 230 W of electricity.
Ideal for interplanetary missions, they are
compact weighing only 120 lbs, 45
inches in height, 18 inches in diameter
and operate unattended for several
decades. Plutonium Heat
Generators Small amounts of
Plutonium-238 are often placed on space
probes and vehicles. Because the natural decay
produces heat, they are optimal for
providing warmth for computers and
other systems needing room temperature operation.

• Why Nuclear For Space Exploration?
• Nuclear fuels are a million times more energy
  dense than chemical fuels
• Chemical fuels have reached their practical
  limits
• Nuclear reactors give more thrust allowing
  missions to be completed faster,
• meaning less exposure time for astronauts to
  hostile space environment
• Radioactive isotopes are able to provide heat
  and electricity for several decades
• Only nuclear reactors are a practical source of
  electricity as we move farther
• and farther away from the Sun

The Cassini Mission is powered by RTGs and the
systems kept warm by pellets of Plutonium.
Energy is Derived from Nuclear Reactions
What About Radiation From Space Reactors?

• Nuclear Fission
• Fission occurs when a free neutron strikes a
  heavy atom such as Uranium or Plutonium. This
  collision causes the atom to break apart or
  fission.
• The atom splits apart into two highly energetic
  fragments which deposit their energy making heat
• Also 2-3 additional neutrons result which can
  strike other atoms causing them to fission
  resulting in a chain reaction
• The reaction rate can be controlled in a nuclear
  reactor allowing production of electricity from
  the heat generated

Radioisotope Thermoelectric Generator (RTG)
Space is essentially an ocean of radiation. The
Sun gives off far more radiation from its fusion
than we could ever become close to matching. The
Earths magnetic field protects us from this
harmful radiation. However, astronauts are
exposed to this, and spending too much time in
space can lead to health effects. It is
important that space crafts be shielded from the
hostile radiation environment of space.
Fusion Future Propulsion

• Nuclear Fusion
• Fusion occurs when two light atoms smash into
  each other and combine
• The products are lighter than the reactants
  meaning some of the mass gets converted to energy
• Fusion is more energy dense than fission
• The most common reaction involves two hydrogen
  isotopes (Deuterium and Tritium) fusing to make
  Helium
• Nuclear fusion is the process powering the stars
• As of yet, fusion as an electricity source has
  not yet been achieved and is currently being
  researched

Although nuclear reactors give off radiation, the
crew can be protected by distance and shielding.
Note the reactor is located on the end of the
boom in the picture of the ship on the right, a
safe distance from the crew. Nuclear reactors
allow ships to reach their destination faster
actually lowering their total radiation exposure.
Since reactors are well contained, it can
withstand any reentry disasters and pose little
to no risk to the general public should such a
scenario occur.
Magnetic Confined Fusion (MCF) Propulsion This
concept is based on the Magnetic Fusion concept.
It confines Deuterium and Tritium (D-T) ions with
a magnetic field. The D-T ions are heated to a
temperature of 100 million degrees C. All matter
at this state becomes a plasma or ionized gas and
must be confined with a magnetic field. These
ions are moving so fast that they fuse when they
smash into each other. The reaction creates
highly energetic byproducts which are accelerated
out the back of the engine propelling the craft
forward. Inertial Confined Fusion (ICF)
Propulsion This engine works on the Inertial
Fusion concept. A small D-T pellet is injected
into the reactor chamber. Several lasers or
heavy ion beams fire simultaneously at the target
pellet causing the pellet to collapse and
inducing a small thermonuclear explosion similar
to a hydrogen bomb. The force of the explosion
propels the craft forward. Main technical
difficulties are in the laser driver systems
being very heavy and requiring a great deal of
power. Inertial Electrostatic Confinement (IEC)
Fusion Propulsion Electrostatic Fields are used
to accelerate fusion fuels (either D, T, or 3He)
toward the center of the grid. The grid is
mostly transparent and the particles are
accelerated toward the center at which point they
strike each other and fuse. The fusion fragments
are accelerated out of the reactor and are used
to propel the craft forward. Antiproton
Catalyzed Micro-fission/Fusion Propulsion This
propulsion scheme uses pellets mixed of Uranium
and D-T fuels. Lasers or heavy ion beams
compress the pellet. At maximum compression, a
small number of antiprotons (109) are fired at
the pellet to catalyze the Uranium fission
process. The fission heat causes a fusion burn
and the expanding plasma pushes the craft
forward. This system gets around typical
restrictions of antimatter propulsion because it
uses a relatively small amount of expensive
antimatter. This craft would be capable of
reaching Pluto in 3 years with a 100 million ton
payload.

Fission Reactors In Space

Nuclear Fission Propulsion works by having a
reactor generate heat. Liquid Hydrogen or
Ammonia propellant is pumped into a vessel by the
reactor. The propellant is heated up, vaporizes,
and is ejected out of a nozzle propelling a
spacecraft forward.
Fission Fragment Interstellar Probes The
fragments from a fission reaction are extremely
energetic and could be used for propulsion. The
fuel is located on thin disks that rotate in and
out of the reactor (see figure to left). Because
the disks are thin, many of the fragments can
escape and be accelerated by a magnetic field.
These fragments are ejected out of the probe and
the ship is propelled forward at extremely fast
velocities. It is also possible to attach a sail
to the probe allowing the fragments to push the
probe even more when far away from the Sun. The
high speeds this craft can reach make it ideal
for probing nearby stars in the future.
The first fission propulsion systems were
investigated in the 1960s and 1970s. The
capstone design from this program was called
NERVA (Nuclear Engine for Rocket Vehicle
Application). The program was cancelled in 1972
as the finishing touches of the propulsion system
were being applied. Fission propulsion is a
tested and feasible technology. Current research
is in engineering nozzles and propellant
circulation systems.
NERVA Rocket Prototype
Design and conception of the Fission Fragment
Interstellar Probe.
Designs for early Nuclear Fission Reactor
Propulsion systems in 1960s and 1970s.
Jupiter Icy Moons Orbiter
NASA has recently proposed to start work on the
Jupiter Icy Moons Orbiter (JIMO) to be completed
by around 2011. JIMO is designed to orbit three
of Jupiters moons Europa, Ganymede, and
Callisto. JIMOs mission is to find evidence of
life on the moons such as the existence of
oceans. It will collect data that will hopefully
tell us about their surfaces and perhaps some
clues as to their origins. Additionally, JIMO
will measure the radiation levels near the moons.
JIMO is to be powered by a nuclear fission
reactor projected to have a power output of
around 250,000 Watts. Compare this to Cassini
which runs on a mere 100 Watts of electricity.
JIMO will illustrate the power of nuclear fission
reactors on space probes.
Artists conception of the Jupiter Icy Moons
Orbiter approaching Europa. The fission reactor
is located at the end of the boom near the top of
the picture.
Without nuclear-powered spacecraft, we'll never
get anywhere -- Dr. Robert Zubrin
Images courtesy of NASA, JK Rawlings, and
JPL Poster by Brian C Kiedrowski