a relativistic proton-antiproton pinch discharge, where the recoil from the laser beam is transmitted by the Mössbauer effect to the spacecraft. A new annihilation process has allegedly been developed by researchers from Gothenborg University. Several annihilation reactors have been constructed in the past years where Hydrogen or Deuterium is converted into relativistic particles by laser annihilation. The technology has been demonstrated by research groups led by Prof. Leif Holmlid and Sindre Zeiner-Gundersen at research facilities in both Sweden and Oslo. A third relativistic particle reactor is currently being built at the University of Iceland. The emitted particles from Hydrogen annihilation processes may reach 0.94c and can be used in space propulsion. Note, however, that the veracity Leif Holmlid's research is under dispute. Thermal antimatter rocket: heating of a propellant This type of antimatter rocket is termed a thermal antimatter rocket as the energy or heat from the annihilation is harnessed to create an exhaust from non-exotic material or propellant. The solid core concept uses antiprotons to heat a solid, high-atomic weight (Z), refractory metal core. Propellant is pumped into the hot core and expanded through a nozzle to generate thrust. The performance of this concept is roughly equivalent to that of the nuclear thermal rocket ( ~ 103 sec) due to temperature limitations of the solid. However, the antimatter energy conversion and heating efficiencies are typically high due to the short mean path between collisions with core atoms (efficiency ~ 85%). Several methods for the liquid-propellant thermal antimatter engine using the gamma rays produced by antiproton or positron annihilation have been proposed. These methods resemble those proposed for nuclear thermal rockets. One proposed method is to use positron annihilation gamma rays to heat a solid engine core. Hydrogen gas is ducted through this core, heated, and expelled from a rocket nozzle. A second proposed engine type uses positron annihilation within a solid lead pellet or within compressed xenon gas to produce a cloud of hot gas, which heats a surrounding layer of gaseous hydrogen. Direct heating of the hydrogen by gamma rays was considered impractical, due to the difficulty of compressing enough of it within an engine of reasonable size to absorb the gamma rays. A third proposed engine type uses annihilation gamma rays to heat an ablative sail, with the ablated material providing thrust. As with nuclear thermal rockets, the specific impulse achievable by these methods is limited by