There are an abundance of interstellar propulsion concepts designed to utilize nuclear energy for propulsion. Different types of nuclear energy conversion have been proposed for design, such as fission based reactors, fusion and catalyzed fission and or fusion reactors. Nuclear propulsion affords much greater energy per unit mass than chemical propulsion and as a result is a much more practical alternative for interstellar missions. Many of the technologies are currently in place to build whole concept designs into a real working spacecraft, but for practical use for interstellar voyages there remains some hurtals. The following concepts are hand-picked efforts to overcome these hurtals so as to achieve the necessary specific impulse and thrust capable propelling payloads to the stars.
Fission reactions, in which heavy elements like uranium and plutonium are broken apart, yield large amounts of energy, but harnessing this energy for propulsion has challenged star ship designers because the traditional fission propulsion concept has been designed to heat a fluid propellant like hydrogen, or water in order to produce thrust. The strength of existing materials used for engines capable of producing the necessary specific impulse to reach the stars in a timely manner however, are too weak to wistand the immense heat and pressure created within them. So how to transfer the upper theoretical limits of fission energy into thrust is detailed in these concepts . . . cont
Sustaining a fusion reaction with a net energy yield is still undemonstrated and currently the international community, primarily Europe and Japan, is spending billions of dollars to figure out how to solve the world's energy needs with this technology. The fusing of two hydrogen atoms to form one helium atom is what takes place in our sun and the energy unleashed surpasses that of fission. Theoretically fusion has the capability of producing 10^9 KJ per gram where as fission can only output approximately 10^8 KJ per gram.* Two isotopes are currently required to fuel sustained fusion reactions: deuterium and tritium. Unfortunately tritum is very radioactive with a half life of about 12 years, so with current technology considerable shielding would be required to protect crew in any such spacecraft. Many of the same problems such as heat constrain the fusion starship design. Such is the case with the magnetic confinement method (MCF), in which the reactor confines ionized fusion plasma with strong electromagnetic fields. Another method has been proposed, called inertial confinement fusion (ICF). cont
This recent design by Gerald Smith and his team at Pennsylvania State University presents an innovation, which results in a much more efficient fusion reaction as well as a smaller engine, enabling a more practical mission design based on current launch capabilities. Currently the technology is in place to store the necessary quantitiy of antiprotons for such a spacecraft. This engine is based on an inertial confinement design and is therefore theoretically capable of missions beyond the solar system. cont
Advanced Propulsion Technology Group, JPL NASA