Antimatter catalyzed nuclear pulse propulsion
From Exampleproblems
Antimatter catalysed nuclear pulse propulsion is a variation of nuclear pulse propulsion based upon the injection of antimatter into a mass of nuclear fuel which normally would not be useful in propulsion. The anti-protons used to start the reaction are consumed, so it is a misnomer to refer to catalyzation.
Traditional nuclear pulse propulsion has the downside that the minimum size of the engine is defined by the minimum size of the nuclear bombs used to create thrust. With conventional technologies nuclear explosives can scale down to about 1/10 kiloton, but making them smaller seems difficult. Large nuclear explosive charges require a heavy structure for the spacecraft, and a very large (and heavy) pusher-plate assembly.
By injecting a small amount of antimatter into a subcritical mass of fuel (typically plutonium or uranium) fission of the fuel can be forced. An anti-proton has a negative electric charge just like an electron, and can be captured in a similar way by a positively charged atomic nucleus. The initial configuration, however, is not stable and radiates energy as gamma rays. As a consequence the anti-proton moves closer and closer to the nucleus until they eventually touch, at which point the anti-proton annihilates with a proton. This reaction releases a tremendous amount of energy, of which some is released as gamma rays and some is transferred as kinetic energy to the nucleus, causing it to explode. The resulting shower of neutrons can cause the surrounding fuel to undergo rapid fission or even nuclear fusion.
The lower limit of the device size is determined by anti-proton handling issues and fission reaction requirements, but the concept appear to be feasible using today's technology and infrastructure, unlike either the Orion-type system, which requires large numbers of nuclear explosive charges, or the various anti-matter drives, which require impossibly expensive amounts of antimatter.
Tuning of the performance to the mission is also possible. Rocket efficiency is strongly related to the mass of the working mass used, which in this case is the nuclear fuel. The energy released by a given mass of fusion fuel is several times larger than that released by the same mass of a fission fuel. For missions requiring short periods of high thrust, such as manned interplanetary missions, pure microfission might be preferred because it reduces the number of fuel elements needed. For missions with longer periods of lower thrust, such as outer-planet probes, a combination of microfission and fusion might be preferred because it reduces the total fuel mass.
The concept was invented at Pennsylvania State University before 1992. Since then, several groups have studied antimatter-catalyzed micro fission/fusion engines in the lab (sometimes antiproton as opposed to antimatter).
