Editing Antimatter rocket (section)

==Methods==
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 [[Electrically powered spacecraft propulsion|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.<ref name=ADA446638>[http://apps.dtic.mil/dtic/tr/fulltext/u2/a446638.pdf ''Fusion Reactions and Matter-Antimatter Annihilation for Space Propulsion''] {{Webarchive|url=https://web.archive.org/web/20231004161223/https://apps.dtic.mil/dtic/tr/fulltext/u2/a446638.pdf |date=2023-10-04 }} Claude Deutsch, 13 July 2005</ref>
Then there are hybrid solutions using antimatter to catalyze fission/fusion reactions for propulsion.

===Pure antimatter rocket: direct use of reaction products===

[[Antiproton]] annihilation reactions produce charged and uncharged [[pion]]s, in addition to neutrinos and [[gamma ray]]s. 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#Fuel|antimatter as fuel]]).<ref name=AIAA-2003-4696>[http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/38278/1/03-1942.pdf ''How to Build an Antimatter Rocket for Interstellar Missions: Systems level Considerations in Designing Advanced Propulsion Technology Vehicles''] {{webarchive|url=https://web.archive.org/web/20150502002952/http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/38278/1/03-1942.pdf |date=2015-05-02 }} Robert H. Frisbee, AIAA Paper 2003-4696, July 20–23, 2003,</ref>

[[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 reflector|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]].<ref name=AIAA-2001-3231>[http://physicsx.pr.erau.edu/ExoticPropulsion/propulsion2.pdf ''The Antimatter Photon Drive: A Relativistic Propulsion System''] Darrel Smith, Jonathan Webby, AIAA Paper 2001-3231, 2001</ref><ref name=WebbTATRSBCAR>[http://physicsx.pr.erau.edu/ExoticPropulsion/APD/APD%20Word/Thermal.pdf ''Thermal Analysis of a Tungsten Radiation Shield for Beamed Core Antimatter Rocketry''] Jonathan A. Webb</ref>

One method 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.<ref name="AA-20120821">{{cite journal |last=Winterberg |first=F. |title=Matter–antimatter gigaelectron volt gamma ray laser rocket propulsion |date=21 August 2012 |journal=[[Acta Astronautica]] |volume=81 |issue=1 |pages=34–39 |bibcode = 2012AcAau..81...34W |doi = 10.1016/j.actaastro.2012.07.001 }}</ref>

A new annihilation process has purportedly been developed by researchers from the University of Gothenburg, Sweden. Several annihilation reactors have been constructed in the past years{{when|date=November 2024|reason=which past years?}} which attempted to convert [[hydrogen]] or [[deuterium]] into relativistic particles through laser annihilation. The technology was explored by research groups led by Prof. Leif Holmlid and Sindre Zeiner-Gundersen, and a third relativistic particle reactor is currently being built at the University of Iceland. In theory, emitted particles from hydrogen annihilation processes could reach 0.94c and can be used in space propulsion.<ref>{{cite journal |last1=Holmlid |first1=Leif |last2=Zeiner-Gundersen |first2=Sindre |title=Future interstellar rockets may use laser-induced annihilation reactions for relativistic drive |journal=Acta Astronautica |url=https://iopscience.iop.org/article/10.1088/1402-4896/ab1276/pdf  |date=1 October 2020 |volume=175 |pages=32–36 |doi=10.1016/j.actaastro.2020.05.034 |bibcode=2020AcAau.175...32H |doi-access=free |hdl=20.500.11815/2191 |hdl-access=free }}</ref> However the veracity of Holmlid's research is under dispute and no successful implementations have been peer reviewed or replicated.<ref>{{cite conference | title=Comment on 'Ultradense protium p(0) and deuterium D(0) and their relation to ordinary Rydberg matter: a review' 2019 Physica Scripta 94, 075005 | author=Klavs Hansen | year=2022| arxiv=2207.08133 }}</ref>

===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, [[Atomic number|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]] (<math>I_{\text{sp}}</math> ~ 10<sup>3</sup> sec) due to temperature limitations of the solid. However, the antimatter energy conversion and heating efficiencies are typically high due to the short [[Mean free path|mean path]] between collisions with core atoms ([[efficiency]] <math>\eta_e</math> ~ 85%).<ref name=ADA446638/>
Several methods for the '''liquid-propellant thermal antimatter engine''' using the gamma rays produced by antiproton or positron annihilation have been proposed.<ref name=Vulpetti1987>{{cite journal |last1=Vulpetti |first1=G. |title=A further analysis about the liquid-propellant thermal antimatter engine design concept |journal=Acta Astronautica |date=August 1987 |volume=15 |issue=8 |pages=551–555 |doi=10.1016/0094-5765(87)90155-X |bibcode=1987AcAau..15..551V }}</ref><ref>{{cite web |title= Positron Propelled and Powered Space Transport Vehicle for Planetary Missions |url= http://www.niac.usra.edu/files/library/meetings/fellows/mar06/1147Smith.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.niac.usra.edu/files/library/meetings/fellows/mar06/1147Smith.pdf |archive-date=2022-10-09 |url-status=live |last= Smith |first= Gerald |author2= Metzger, John|author3= Meyer, Kirby|author4= Thode, Les |date=2006-03-07 |access-date=2010-04-21}}</ref> These methods resemble those proposed for [[nuclear thermal rocket]]s. 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 [[nozzle|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.<ref name=Vulpetti1989>{{cite journal |last1=Vulpetti |first1=Giovanni |last2=Pecchioli |first2=Mauro |title=Considerations about the specific impulse of an antimatter-based thermal engine |journal=Journal of Propulsion and Power |date=September 1989 |volume=5 |issue=5 |pages=591–595 |doi=10.2514/3.23194 }}</ref>

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 (<math>I_{\text{sp}}</math> ~ 2 × 10<sup>3</sup> sec). However, the longer mean free path for thermalization and absorption results in much lower energy conversion efficiencies (<math>\eta_e</math> ~ 35%).<ref name=ADA446638/>

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 (<math>I_{\text{sp}}</math> ~ 10<sup>4</sup>-10<sup>5</sup> sec), the long mean free path results in very low energy utilization (<math>\eta_e</math> ~ 10%)<ref name=ADA446638/>

===Antimatter power generation===

The idea of using antimatter to power an [[Electrically powered spacecraft propulsion|electric space drive]] has also been proposed. These proposed designs are typically similar to those suggested for [[nuclear electric rocket]]s. Antimatter annihilations are used to directly or indirectly heat a working fluid, as in a [[nuclear thermal rocket]], but the fluid is used to generate electricity, which is then used to power some form of electric space propulsion system. The resulting system shares many of the characteristics of other charged particle/electric propulsion proposals, that typically being high specific impulse and low thrust (see also [http://large.stanford.edu/courses/2017/ph240/payzer1/ antimatter power generation]).<ref name=Seitzman>[http://soliton.ae.gatech.edu/people/jseitzma/classes/ae4451/electricpropulsion2.pdf ''Electric Rocket Propulsion: A Background''] {{Webarchive|url=https://web.archive.org/web/20130805125119/http://soliton.ae.gatech.edu/people/jseitzma/classes/ae4451/electricpropulsion2.pdf |date=2013-08-05 }} Jerry M. Seitzman, 2003-2004</ref><ref name=US20140026535A1>[https://patents.google.com/patent/US20140026535 ''High Specific Impulse Superfluid and Nanotube Propulsion Device, System and Propulsion Method''] Michael Wallace, Joseph D. Nix, Christopher W. Smith, 2014</ref>

===Catalyzed fission/fusion or spiked fusion===

This is a hybrid approach in which antiprotons are used to [[Antimatter-catalyzed nuclear pulse propulsion|catalyze a fission/fusion reaction]] or to "spike" the propulsion of a [[fusion rocket]] or any similar applications.

The antiproton-driven [[Inertial confinement fusion]] (ICF) Rocket concept uses pellets for the [[Fusion power|D-T reaction]].  The pellet consists of a hemisphere of fissionable material such as [[Uranium|U<sup>235</sup>]] with a hole through which a pulse of antiprotons and positrons is injected. It is surrounded by a hemisphere of fusion fuel, for example deuterium-tritium, or lithium deuteride. Antiproton annihilation occurs at the surface of the hemisphere, which ionizes the fuel. These ions heat the core of the pellet to fusion temperatures.<ref name=NIAC98-02FR>{{cite report |first1=Terry |last1=Kammash |year=1998 |title=Antiproton Driven Magnetically Insulated Inertial Confinement Fusion (Micf) Propulsion System |url=http://www.niac.usra.edu/files/studies/final_report/361Kammash.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.niac.usra.edu/files/studies/final_report/361Kammash.pdf |archive-date=2022-10-09 |url-status=live |citeseerx=10.1.1.498.1830 }}</ref>

The antiproton-driven Magnetically Insulated Inertial Confinement Fusion Propulsion (MICF) concept relies on self-generated magnetic field which insulates the plasma from the metallic shell that contains it during the burn. The lifetime of the plasma was estimated to be two orders of magnitude greater than implosion inertial fusion, which corresponds to a longer burn time, and hence, greater gain.<ref name=NIAC98-02FR/>

The antimatter-driven [[aneutronic fusion|P-B<sup>11</sup>]] concept uses antiprotons to ignite the P-B<sup>11</sup> reactions in an MICF scheme. Excessive radiation losses are a major obstacle to ignition and require modifying the particle density, and plasma temperature to increase the gain. It was concluded that it is entirely feasible that this system could achieve I<sub>sp</sub>~10<sup>5</sup>s.<ref name=NASA7347634540>{{cite journal |last1=Kammash |first1=Terry |last2=Martin |first2=James |last3=Godfroy |first3=Thomas |title=Antimatter Driven P-B11 Fusion Propulsion System |journal=AIP Conference Proceedings |date=17 January 2003 |volume=654 |issue=1 |pages=497–501 |doi=10.1063/1.1541331 |bibcode=2003AIPC..654..497K |hdl=2027.42/87345 |hdl-access=free }}</ref>

A different approach was envisioned for [[AIMStar]] in which small fusion fuel droplets would be injected into a cloud of antiprotons confined in a very small volume within a reaction [[Penning trap]]. Annihilation takes place on the surface of the antiproton cloud, peeling back 0.5% of the cloud. The power density released is roughly comparable to a 1 kJ, 1 ns laser depositing its energy over a 200&nbsp;μm ICF target.<ref name=AIAA-99-2700>{{cite journal |last1=Lewis |first1=Raymond |last2=Meyer |first2=Kirby |last3=Smith |first3=Gerald |last4=Howe |first4=Steven |title=AIMStar - Antimatter Initiated Microfusion for pre-cursor interstellar missions |journal=35th Joint Propulsion Conference and Exhibit |year=1999 |doi=10.2514/6.1999-2700 |citeseerx=10.1.1.577.1826 }}</ref>

The [[ICAN-II]] project employs the antiproton catalyzed microfission (ACMF) concept which uses pellets with a molar ratio of 9:1 of D-T:U<sup>235</sup> for [[nuclear pulse propulsion]].<ref name=AIAA-1998-3589>[https://www.engr.psu.edu/antimatter/Papers/ICAN.pdf  "Antiproton-Catalyzed Microfission/Fusion Propulsion Systems for Exploration of the Outer Solar System and Beyond"] {{webarchive |url=https://web.archive.org/web/20140805152150/https://www.engr.psu.edu/antimatter/Papers/ICAN.pdf |date=August 5, 2014 }} G. Gaidos, R.A. Lewis, G.A. Smith, B. Dundore and S. Chakrabarti, AIAA Paper 1998-3589, July 1998</ref>