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After the ban of nuclear weapons in space by the Outer Space Treaty in 1967, nuclear power has been discussed at least since 1972 as a sensitive issue by states. [8] Space nuclear power sources may experience accidents during launch, operation, and end-of-service phases, resulting in the exposure of nuclear power sources to extreme physical conditions and the release of radioactive materials ...
The fission sail is a type of spacecraft propulsion proposed by Robert Forward that uses fission fragments to propel a large solar sail-like craft. It is similar in concept to the fission-fragment rocket in that the fission by-products are directly harnessed as working mass, and differs primarily in the way that the fragments are used for thrust.
The isotope 240 Pu has about the same thermal neutron capture cross section as 239 Pu (289.5 ± 1.4 vs. 269.3 ± 2.9 barns), [6] [7] but only a tiny thermal neutron fission cross section (0.064 barns). When the isotope 240 Pu captures a neutron, it is about 4500 times more likely to become plutonium-241 than to fission.
Energy of about 6 MeV provided by the incident neutron was necessary to overcome this barrier and cause the nucleus to fission. [4]: 10–11 [7] [8] According to John Lilley, "The energy required to overcome the barrier to fission is called the activation energy or fission barrier and is about 6 MeV for A ≈ 240. It is found that the ...
The fission-fragment rocket is a rocket engine design that directly harnesses hot nuclear fission products for thrust, as opposed to using a separate fluid as working mass. The design can, in theory, produce very high specific impulse while still being well within the abilities of current technologies.
At the saddle point, the rate of change of the Coulomb energy is equal to the rate of change of the nuclear surface energy. The formation and eventual decay of this transition state nucleus is the rate-determining step in the fission process and corresponds to the passage over an activation energy barrier to the fission reaction.
NASA artist rendering, from 1999, of the Project Orion pulsed nuclear fission spacecraft. Project Orion was a study conducted in the 1950s and 1960s by the United States Air Force, DARPA, [1] and NASA into the viability of a nuclear pulse spaceship that would be directly propelled by a series of atomic explosions behind the craft.
239 Pu has a higher probability for fission than 235 U and a larger number of neutrons produced per fission event, so it has a smaller critical mass. Pure 239 Pu also has a reasonably low rate of neutron emission due to spontaneous fission (10 fission/s·kg), making it feasible to assemble a mass that is highly supercritical before a detonation ...