Antimatter rocket

An antimatter rocket is a proposed class of rockets that use antimatter as their power source. There are several designs that attempt to accomplish this goal. The advantage to this class of rocket is that a large fraction of the rest mass of a matter/antimatter mixture may be converted to energy, allowing antimatter rockets to have a far higher energy density and specific impulse than any other proposed class of rocket. M 0 M 1 = ( 1 + Δ v c 1 − Δ v c ) c 2 I sp {displaystyle {frac {M_{0}}{M_{1}}}=left({frac {1+{frac {Delta v}{c}}}{1-{frac {Delta v}{c}}}} ight)^{frac {c}{2I_{ ext{sp}}}}}     (I) d M ship M ship = − d v ( 1 − I sp v c 2 ) ( 1 − v 2 c 2 ) ( − I sp c 2 v 2 + ( 1 + a ) v + a I sp ) {displaystyle {frac {dM_{ ext{ship}}}{M_{ ext{ship}}}}={frac {-dv(1-I_{ ext{sp}}{frac {v}{c^{2}}})}{(1-{frac {v^{2}}{c^{2}}})(-{frac {I_{ ext{sp}}}{c^{2}v2}}+(1+a)v+aI_{ ext{sp}})}}}     (II) d M ship M ship = − d v ( − I sp c 2 v 2 + ( 1 − a ) v + a I sp ) {displaystyle {frac {dM_{ ext{ship}}}{M_{ ext{ship}}}}={frac {-dv}{(-{frac {I_{ ext{sp}}}{c^{2}v^{2}}}+(1-a)v+aI_{ ext{sp}})}}}     (III) M 0 M 1 = ( ( − 2 I sp Δ v / c 2 + 1 − a − ( 1 − a ) 2 + 4 a I sp 2 / c 2 ) ( 1 − a + ( 1 − a ) 2 + 4 a I sp 2 / c 2 ) ( − 2 I sp Δ v / c 2 + 1 − a + ( 1 − a ) 2 + 4 a I sp 2 / c 2 ) ( 1 − a − ( 1 − a ) 2 + 4 a I sp 2 / c 2 ) ) 1 ( 1 − a ) 2 + 4 a I sp 2 / c 2 {displaystyle {frac {M_{0}}{M_{1}}}=left({frac {(-2I_{ ext{sp}}Delta v/c^{2}+1-a-{sqrt {(1-a)^{2}+4aI_{ ext{sp}}^{2}/c^{2}}})(1-a+{sqrt {(1-a)^{2}+4aI_{ ext{sp}}^{2}/c^{2}}})}{(-2I_{ ext{sp}}Delta v/c^{2}+1-a+{sqrt {(1-a)^{2}+4aI_{ ext{sp}}^{2}/c^{2}}})(1-a-{sqrt {(1-a)^{2}+4aI_{ ext{sp}}^{2}/c^{2}}})}} ight)^{frac {1}{sqrt {(1-a)^{2}+4aI_{ ext{sp}}^{2}/c^{2}}}}}     (IV) An antimatter rocket is a proposed class of rockets that use antimatter as their power source. There are several designs that attempt to accomplish this goal. The advantage to this class of rocket is that a large fraction of the rest mass of a matter/antimatter mixture may be converted to energy, allowing antimatter rockets to have a far higher energy density and specific impulse than any other proposed class of rocket. Antimatter rockets can be divided into three types of application: those that directly use the products of antimatter annihilation for propulsion, those that heat a working fluid or an intermediate material which is then used for propulsion, and those that heat a working fluid or an intermediate material to generate electricity for some form of electric spacecraft propulsion system.The propulsion concepts that employ these mechanisms generally fall into four categories: solid core, gaseous core, plasma core, and beamed core configurations. The alternatives to direct antimatter annihilation propulsion offer the possibility of feasible vehicles with, in some cases, vastly smaller amounts of antimatter but require a lot more matter propellant.Then there are hybrid solutions using antimatter to catalyze fission/fusion reactions for propulsion. Antiproton annihilation reactions produce charged and uncharged pions, in addition to neutrinos and gamma rays. The charged pions can be channelled by a magnetic nozzle, producing thrust. This type of antimatter rocket is a pion rocket or beamed core configuration. It is not perfectly efficient; energy is lost as the rest mass of the charged (22.3%) and uncharged pions (14.38%), lost as the kinetic energy of the uncharged pions (which can't be deflected for thrust), and lost as neutrinos and gamma rays (see antimatter as fuel). Positron annihilation has also been proposed for rocketry. Annihilation of positrons produces only gamma rays. Early proposals for this type of rocket, such as those developed by Eugen Sänger, assumed the use of some material that could reflect gamma rays, used as a light sail or parabolic shield to derive thrust from the annihilation reaction, but no known form of matter (consisting of atoms or ions) interacts with gamma rays in a manner that would enable specular reflection. The momentum of gamma rays can, however, be partially transferred to matter by Compton scattering. A recent approach is to utilize an ultra-intense laser capable of generating positrons when striking a high atomic number target, such as gold. The only concept known to reach relativistic velocities uses a matter-antimatter GeV gamma ray laser photon rocket made possible by a relativistic proton-antiproton pinch discharge, where the recoil from the laser beam is transmitted by the Mössbauer effect to the spacecraft. 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 ( I sp {displaystyle I_{ ext{sp}}} ~ 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 η e {displaystyle eta _{e}} ~ 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 materials considerations, typically being in the range of 1000–2000 seconds. The gaseous core system substitutes the low-melting point solid with a high temperature gas (i.e. tungsten gas/plasma), thus permitting higher operational temperatures and performance ( I sp {displaystyle I_{ ext{sp}}} ~ 2 × 103 sec). However, the longer mean free path for thermalization and absorption results in much lower energy conversion efficiencies ( η e {displaystyle eta _{e}} ~ 35%). The plasma core allows the gas to ionize and operate at even higher effective temperatures. Heat loss is suppressed by magnetic confinement in the reaction chamber and nozzle. Although performance is extremely high ( I sp {displaystyle I_{ ext{sp}}} ~ 104-105 sec), the long mean free path results in very low energy utilization ( η e {displaystyle eta _{e}} ~ 10%)