Nuclear Power Applications in Space - American Nuclear Society by dffhrtcv3


									                                                                                                                          Nuclear Power Applications in Space
                                                                                                                                                                                   American Nuclear Society
                                                   Why Nuclear For Space Exploration?                                                                                                                                                                                                                     NUCLEAR POWER ALREADY IN USE
• Nuclear fuels are a million times more energy dense than chemical fuels                                                                                                                                                                                                                                Radioisotope Thermoelectric Generators (RTGs)
• Chemical fuels have reached their practical limits
• Nuclear reactors give more thrust allowing missions to be completed faster,                                                                                                                                                                                                                                                        RTGs have been used to produce power on space probes
meaning less exposure time for astronauts to hostile space environment                                                                                                                                                                                                                                                               and other missions for the past 25 years. They use the natural
• Radioactive isotopes are able to provide heat and electricity for several decades                                                                                                                                                                                     The Cassini Mission is powered
                                                                                                                                                                                                                                                                                                                                     decay of Plutonium-238 to create about 230 W of electricity.
• Only nuclear reactors are a practical source of electricity as we move farther                                                                                                                                                                                        by RTGs and the systems kept                                 Ideal for interplanetary missions, they are compact weighing
and farther away from the Sun                                                                                                                                                                                                                                           warm by pellets of Plutonium.                                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
 Energy is Derived from Nuclear Reactions                                                                                                                     What About Radiation From Space Reactors?                                                                                                                              probes and vehicles. Because the natural decay produces heat,
                                                                                                                                                                                                                                                                                                                                     they are optimal for providing warmth for computers and
                                                                                                                                                                                                                                                                                                                                     other systems needing room temperature operation.
                                                                      Nuclear Fission                                                                                                                                                                                   Radioisotope Thermoelectric
                                                                                                                                                                                                             Space is essentially an ocean of radiation. The Sun        Generator (RTG)
                                                                      • Fission occurs when a free neutron strikes a heavy atom such as                                                                      gives off far more radiation from its fusion than we
                                                                      Uranium or Plutonium. This collision causes the atom to break apart
                                                                      or fission.                                                                                                                            could ever become close to matching. The Earth’s
                                                                      • The atom splits apart into two highly energetic fragments which                                                                      magnetic field protects us from this harmful radiation.
                                                                      deposit their energy making heat
                                                                      • Also 2-3 additional neutrons result which can strike other atoms                                                                     However, astronauts are exposed to this, and spending
                                                                      causing them to fission resulting in a chain reaction                                                                                  too much time in space can lead to health effects. It is
                                                                      • The reaction rate can be controlled in a nuclear reactor allowing
                                                                      production of electricity from the heat generated                                                                                      important that space crafts be shielded from the
                                                                                                                                                                                                             hostile radiation environment of space.

                                                                       Nuclear Fusion
                                                                                                                                                                                                                                                                                                      Fusion & Future Propulsion
                                                                                                                                                                Although nuclear reactors give off radiation, the
                                                                       • Fusion occurs when two light atoms smash into each other and
                                                                                                                                                                crew can be protected by distance and shielding.
                                                                       • The products are lighter than the reactants meaning some of the                        Note the reactor is located on the end of the boom in                                                                                                   Magnetic Confined Fusion (MCF) Propulsion
                                                                       mass gets converted to energy
                                                                       • Fusion is more energy dense than fission
                                                                                                                                                                the picture of the ship on the right, a safe distance
                                                                       • The most common reaction involves two hydrogen isotopes                                from the crew. Nuclear reactors allow ships to reach                                                                                                    This concept is based on the Magnetic Fusion concept. It confines
                                                                       (Deuterium and Tritium) fusing to make Helium                                                                                                                                                                                                    Deuterium and Tritium (D-T) ions with a magnetic field. The D-T ions
                                                                       • Nuclear fusion is the process powering the stars
                                                                                                                                                                their destination faster actually lowering their total
                                                                       • As of yet, fusion as an electricity source has not yet been achieved                   radiation exposure. Since reactors are well                                                                                                             are heated to a temperature of 100 million degrees C. All matter at this
                                                                       and is currently being researched                                                                                                                                                                                                                state becomes a plasma or ionized gas and must be confined with a
                                                                                                                                                                contained, it can withstand any reentry disasters
                                                                                                                                                                and pose little to no risk to the general public should                                                                                                 magnetic field. These ions are moving so fast that they fuse when they
                                                                                                                                                                such a scenario occur.                                                                                                                                  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
                                                                                                         Fission Reactors In Space                                                                                                                                                                                      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
                                                            Nuclear Fission Propulsion works by having a reactor generate                                                                                                                                                                                               fire simultaneously at the target pellet causing the pellet to collapse
                                                                                                                                                                                       Fission Fragment Interstellar Probes
                                                            heat. Liquid Hydrogen or Ammonia propellant is pumped into a                                                                                                                                                                                                and inducing a small thermonuclear explosion similar to a hydrogen
                                                            vessel by the reactor. The propellant is heated up, vaporizes, and                                                                                                                                                                                          bomb. The force of the explosion propels the craft forward. Main
                                                                                                                                                                                       The fragments from a fission reaction are extremely energetic and                                                                technical difficulties are in the laser driver systems being very heavy
                                                            is ejected out of a nozzle propelling a spacecraft forward.
                                                                                                                                                                                       could be used for propulsion. The fuel is located on thin disks that                                                             and requiring a great deal of power.
                                                                                      The first fission propulsion systems were                                                        rotate in and out of the reactor (see figure to left). Because the disks
                                                                                      investigated in the 1960s and 1970s. The                                                         are thin, many of the fragments can escape and be accelerated by a
                                                                                      capstone design from this program was called                                                     magnetic field. These fragments are ejected out of the probe and the
                                                                                      NERVA (Nuclear Engine for Rocket Vehicle                                                         ship is propelled forward at extremely fast velocities. It is also possible                                                      Inertial Electrostatic Confinement (IEC) Fusion Propulsion
                                                                                      Application). The program was cancelled in                                                       to attach a sail to the probe allowing the fragments to push the probe
                                                                                      1972 as the finishing touches of the propulsion                                                  even more when far away from the Sun. The high speeds this craft can                                                             Electrostatic Fields are used to accelerate fusion fuels (either D, T, or
                                                                                      system were being applied. Fission propulsion                                                    reach make it ideal for probing nearby stars in the future.                                                                      3He) toward the center of the grid. The grid is mostly transparent and
                                                                                      is a tested and feasible technology. Current                                                                                                                                                                                      the particles are accelerated toward the center at which point they
                                                                                      research is in engineering nozzles and                                                                                                                                                                                            strike each other and fuse. The fusion fragments are accelerated out of
                                                            NERVA Rocket Prototype    propellant circulation systems.                           Design and conception of the Fission
                                                                                                                                                                                                                                                                                                                        the reactor and are used to propel the craft forward.
                                                                                                                                                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
                                                                                                                                                                                                                                                                                                                        Antiproton Catalyzed Micro-fission/Fusion Propulsion
                                                            Orbiter (JIMO) to be completed by around 2011. JIMO is designed
                                                            to orbit three of Jupiter’s moons: Europa, Ganymede, and Callisto.                                                                                                                                                                                          This propulsion scheme uses pellets mixed of Uranium and D-T fuels.
                                                            JIMO’s mission is to find evidence of life on the moons such as the                                                                                                                                                                                         Lasers or heavy ion beams compress the pellet. At maximum
                                                            existence of oceans. It will collect data that will hopefully tell us                                                                                                                                                                                       compression, a small number of antiprotons (10^9) are fired at the
                                                            about their surfaces and perhaps some clues as to their origins.                                                                                                                                                                                            pellet to catalyze the Uranium fission process. The fission heat causes
                                                            Additionally, JIMO will measure the radiation levels near the                                                                                                                                                                                               a fusion burn and the expanding plasma pushes the craft forward.
                                                            moons. JIMO is to be powered by a nuclear fission reactor                                                                                                                                                                                                   This system gets around typical restrictions of antimatter propulsion
                                                            projected to have a power output of around 250,000 Watts.                                                                                                                                                                                                   because it uses a relatively small amount of expensive antimatter. This
        Artist’s conception of the Jupiter Icy Moons        Compare this to Cassini which runs on a mere 100 Watts of                                                                                                                                                                                                   craft would be capable of reaching Pluto in 3 years with a 100 million
        Orbiter approaching Europa. The fission reactor
                                                            electricity. JIMO will illustrate the power of nuclear fission reactors                                                                                                                                                                                     ton payload.
        is located at the end of the boom near the top of
        the picture.                                        on space probes.

                  “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

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