Cohete de antimateria

Rockets using antimatter as their power source

Un cohete de antimateria propuesto

Un cohete de antimateria es una clase propuesta de cohetes que utilizan antimateria como fuente de energía. Hay varios diseños que intentan lograr este objetivo. La ventaja de esta clase de cohete es que una gran fracción de la masa en reposo de una mezcla de materia y antimateria se puede convertir en energía, lo que permite que los cohetes de antimateria tengan una densidad de energía y un impulso específico mucho mayores que cualquier otra clase de cohete propuesta. ^[1]

Métodos

Los cohetes de antimateria se pueden dividir en tres tipos de aplicaciones: los que utilizan directamente los productos de la aniquilación de antimateria para la propulsión, los que calientan un fluido de trabajo o un material intermedio que luego se utiliza para la propulsión, y los que calientan un fluido de trabajo o un material intermedio que luego se utiliza para la propulsión, y los que calientan un fluido de trabajo o un material intermedio. Material para generar electricidad para algún tipo de sistema de propulsión eléctrica de naves espaciales . Los conceptos de propulsión que emplean estos mecanismos generalmente se dividen en cuatro categorías: configuraciones de núcleo sólido, núcleo gaseoso, núcleo de plasma y núcleo irradiado. Las alternativas a la propulsión de aniquilación directa de antimateria ofrecen la posibilidad de vehículos viables con, en algunos casos, cantidades mucho más pequeñas de antimateria, pero que requieren mucha más materia propulsora. ^[2] Luego están las soluciones híbridas que utilizan antimateria para catalizar reacciones de fisión/fusión para la propulsión.

Cohete de antimateria pura: uso directo de productos de reacción

Las reacciones de aniquilación de antiprotones producen piones cargados y descargados , además de neutrinos y rayos gamma . Los piones cargados pueden ser canalizados por una boquilla magnética , produciendo empuje. Este tipo de cohete de antimateria es un cohete de piones o una configuración de núcleo irradiado . No es perfectamente eficiente; la energía se pierde como masa en reposo de los piones cargados (22,3%) y sin carga (14,38%), perdida como energía cinética de los piones sin carga (que no pueden desviarse para impulsarse); y se perdieron como neutrinos y rayos gamma (ver antimateria como combustible ). ^[3]

También se ha propuesto la aniquilación de positrones para los cohetes. La aniquilación de positrones produce únicamente rayos gamma. Las primeras propuestas para este tipo de cohetes, como las desarrolladas por Eugen Sänger , suponían el uso de algún material que pudiera reflejar los rayos gamma, utilizado como vela ligera o escudo parabólico para derivar el empuje de la reacción de aniquilación, pero no se conoce ninguna forma de materia. (que consta de átomos o iones) interactúa con los rayos gamma de una manera que permitiría la reflexión especular. Sin embargo, el impulso de los rayos gamma puede transferirse parcialmente a la materia mediante la dispersión Compton . ^{[4] [5]}

Un método para alcanzar velocidades relativistas utiliza un cohete de fotones láser de rayos gamma GeV materia-antimateria, posible gracias a una descarga relativista de pellizco de protón-antiprotón, donde el retroceso del rayo láser se transmite a la nave espacial mediante el efecto Mössbauer . ^[6]

Investigadores de la Universidad de Gotemburgo supuestamente han desarrollado un nuevo proceso de aniquilación. En los últimos años se han construido varios reactores de aniquilación que intentaron convertir hidrógeno o deuterio en partículas relativistas mediante aniquilación por láser. La tecnología fue explorada por grupos de investigación dirigidos por el profesor Leif Holmlid y Sindre Zeiner-Gundersen, y actualmente se está construyendo un tercer reactor de partículas relativista en la Universidad de Islandia. En teoría, las partículas emitidas durante los procesos de aniquilación del hidrógeno podrían alcanzar los 0,94 cy podrían utilizarse en la propulsión espacial. ^[7] Sin embargo, la veracidad de la investigación de Holmlid está en duda y no se han revisado ni replicado implementaciones exitosas. ^[8]

Cohete térmico de antimateria: calentamiento de un propulsor

Este tipo de cohete de antimateria se denomina cohete térmico de antimateria, ya que la energía o el calor de la aniquilación se aprovecha para crear un escape a partir de material o propulsor no exótico.

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 ( ${\displaystyle I_{\text{sp}}}$ ~ 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 ${\displaystyle \eta _{e}}$ ~ 85%).^[2]Several methods for the liquid-propellant thermal antimatter engine using the gamma rays produced by antiproton or positron annihilation have been proposed.^[9][10] 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.^[11]

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 ( ${\displaystyle I_{\text{sp}}}$ ~ 2 × 10³ sec). However, the longer mean free path for thermalization and absorption results in much lower energy conversion efficiencies ( ${\displaystyle \eta _{e}}$ ~ 35%).^[2]

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 ( ${\displaystyle I_{\text{sp}}}$ ~ 10⁴-10⁵ sec), the long mean free path results in very low energy utilization ( ${\displaystyle \eta _{e}}$ ~ 10%)^[2]

Antimatter power generation

The idea of using antimatter to power an electric space drive has also been proposed. These proposed designs are typically similar to those suggested for nuclear electric rockets. 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 (An associated article further detailing antimatter power generation).^[12][13]

Catalyzed fission/fusion or spiked fusion

This is a hybrid approach in which antiprotons are used to 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 D-T reaction. The pellet consists of a hemisphere of fissionable material such as U235 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.^[14]

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.^[14]

The antimatter-driven P-B¹¹ concept uses antiprotons to ignite the P-B¹¹ 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_sp~10⁵s.^[15]

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 μm ICF target.^[16]

The ICAN-II project employs the antiproton catalyzed microfission (ACMF) concept which uses pellets with a molar ratio of 9:1 of D-T:U²³⁵ for Nuclear pulse propulsion.^[17]

Difficulties with antimatter rockets

The chief practical difficulties with antimatter rockets are the problems of creating antimatter and storing it. Creating antimatter requires input of vast amounts of energy, at least equivalent to the rest energy of the created particle/antiparticle pairs, and typically (for antiproton production) tens of thousands to millions of times more.^[18][19] Most storage schemes proposed for interstellar craft require the production of frozen pellets of antihydrogen. This requires cooling of antiprotons, binding to positrons, and capture of the resulting antihydrogen atoms - tasks which have, as of 2010^[update], been performed only for small numbers of individual atoms. Storage of antimatter is typically done by trapping electrically charged frozen antihydrogen pellets in Penning or Paul traps. There is no theoretical barrier to these tasks being performed on the scale required to fuel an antimatter rocket. However, they are expected to be extremely (and perhaps prohibitively) expensive due to current production abilities being only able to produce small numbers of atoms, a scale approximately 10²³ times smaller than needed for a 10-gram trip to Mars.

Generally, the energy from antiproton annihilation is deposited over such a large region that it cannot efficiently drive nuclear capsules. Antiproton-induced fission and self-generated magnetic fields may greatly enhance energy localization and efficient use of annihilation energy.^[20][21]

A secondary problem is the extraction of useful energy or momentum from the products of antimatter annihilation, which are primarily in the form of extremely energetic ionizing radiation. The antimatter mechanisms proposed to date have for the most part provided plausible mechanisms for harnessing energy from these annihilation products. The classic rocket equation with its "wet" mass ( ${\displaystyle M_{0}}$)(with propellant mass fraction) to "dry" mass ( ${\displaystyle M_{1}}$)(with payload) fraction ( ${\displaystyle {\frac {M_{0}}{M_{1}}}}$), the velocity change ( ${\displaystyle \Delta v}$) and specific impulse ( ${\displaystyle I_{\text{sp}}}$) no longer holds due to the mass losses occurring in antimatter annihilation.^[3]

Another general problem with high powered propulsion is excess heat or waste heat, and as with antimatter-matter annihilation also includes extreme radiation. A proton-antiproton annihilation propulsion system transforms 39% of the propellant mass into an intense high-energy flux of gamma radiation. The gamma rays and the high-energy charged pions will cause heating and radiation damage if they are not shielded against. Unlike neutrons, they will not cause the exposed material to become radioactive by transmutation of the nuclei. The components needing shielding are the crew, the electronics, the cryogenic tankage, and the magnetic coils for magnetically assisted rockets. Two types of shielding are needed: radiation protection and thermal protection (different from Heat shield or thermal insulation).^[3][22]

Finally, relativistic considerations have to be taken into account. As the by products of annihilation move at relativistic velocities the rest mass changes according to relativistic mass–energy. For example, the total mass–energy content of the neutral pion is converted into gammas, not just its rest mass. It is necessary to use a relativistic rocket equation that takes into account the relativistic effects of both the vehicle and propellant exhaust (charged pions) moving near the speed of light. These two modifications to the two rocket equations result in a mass ratio ( ${\displaystyle {\frac {M_{0}}{M_{1}}}}$) for a given ( ${\displaystyle \Delta v}$) and ( ${\displaystyle I_{\text{sp}}}$) that is much higher for a relativistic antimatter rocket than for either a classical or relativistic "conventional" rocket.^[3]

Modified relativistic rocket equation

The loss of mass specific to antimatter annihilation requires a modification of the relativistic rocket equation given as^[23]

where ${\displaystyle c}$ is the speed of light, and ${\displaystyle I_{\text{sp}}}$ is the specific impulse (i.e. ${\displaystyle I_{\text{sp}}}$=0.69 ${\displaystyle c}$).

The derivative form of the equation is^[3]

where ${\displaystyle M_{\text{ship}}}$ is the non-relativistic (rest) mass of the rocket ship, and ${\displaystyle a}$ is the fraction of the original (on board) propellant mass (non-relativistic) remaining after annihilation (i.e., ${\displaystyle a}$=0.22 for the charged pions).

Eq.II is difficult to integrate analytically. If it is assumed that ${\displaystyle v\sim I_{\text{sp}}}$, such that ${\displaystyle (1-{\frac {I_{\text{sp}}v}{c^{2}}})\sim (1-{\frac {v^{2}}{c^{2}}})}$ then the resulting equation is

Eq.III can be integrated and the integral evaluated for ${\displaystyle M_{0}}$ and ${\displaystyle M_{1}}$, and initial and final velocities ( ${\displaystyle v_{i}=0}$ and ${\displaystyle v_{f}=\Delta v}$). The resulting relativistic rocket equation with loss of propellant is^[3][23]

Other general issues

The cosmic background hard radiation will ionize the rocket's hull over time and poses a health threat. Also, gas plasma interactions may cause space charge. The major interaction of concern is differential charging of various parts of a spacecraft, leading to high electric fields and arcing between spacecraft components. This can be resolved with well placed plasma contactor. However, there is no solution yet for when plasma contactors are turned off to allow maintenance work on the hull. Long term space flight at interstellar velocities causes erosion of the rocket's hull due to collision with particles, gas, dust and micrometeorites. At 0.2 ${\displaystyle c}$ for a 6 light year distance, erosion is estimated to be in the order of about 30 kg/m² or about 1 cm of aluminum shielding.^[24][25]

See also

• Nuclear photonic rocket

References

1. Schmidt, George (2012). "Nuclear Systems for Space Power and Production". 62nd International Astronautical Congress 2011 : (IAC 2011) : Cape Town, South Africa, 3-7 October 2011. International Astronautical Federation. Paris: International Astronautical Federation. pp. 6792–6812. ISBN 978-1-61839-805-5. OCLC 795367347.
2. Fusion Reactions and Matter-Antimatter Annihilation for Space Propulsion Claude Deutsch, 13 July 2005
3. How to Build an Antimatter Rocket for Interstellar Missions: Systems level Considerations in Designing Advanced Propulsion Technology Vehicles Archived 2015-05-02 at the Wayback Machine Robert H. Frisbee, AIAA Paper 2003-4696, July 20–23, 2003,
4. The Antimatter Photon Drive: A Relativistic Propulsion System Darrel Smith, Jonathan Webby, AIAA Paper 2001-3231, 2001
5. Thermal Analysis of a Tungsten Radiation Shield for Beamed Core Antimatter Rocketry Jonathan A. Webb
6. Winterberg, F. (21 August 2012). "Matter–antimatter gigaelectron volt gamma ray laser rocket propulsion". Acta Astronautica. 81 (1): 34–39. Bibcode:2012AcAau..81...34W. doi:10.1016/j.actaastro.2012.07.001.
7. Holmlid, Leif; Zeiner-Gundersen, Sindre (1 October 2020). "Future interstellar rockets may use laser-induced annihilation reactions for relativistic drive". Acta Astronautica. 175: 32–36. Bibcode:2020AcAau.175...32H. doi:10.1016/j.actaastro.2020.05.034. hdl:20.500.11815/2191.
8. Klavs Hansen (2022). Comment on 'Ultradense protium p(0) and deuterium D(0) and their relation to ordinary Rydberg matter: a review' 2019 Physica Scripta 94, 075005. arXiv:2207.08133.
9. Vulpetti, G. (August 1987). "A further analysis about the liquid-propellant thermal antimatter engine design concept". Acta Astronautica. 15 (8): 551–555. Bibcode:1987AcAau..15..551V. doi:10.1016/0094-5765(87)90155-X.
10. Smith, Gerald; Metzger, John; Meyer, Kirby; Thode, Les (2006-03-07). "Positron Propelled and Powered Space Transport Vehicle for Planetary Missions" (PDF). Archived (PDF) from the original on 2022-10-09. Retrieved 2010-04-21.
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12. Electric Rocket Propulsion: A Background Archived 2013-08-05 at the Wayback Machine Jerry M. Seitzman, 2003-2004
13. High Specific Impulse Superfluid and Nanotube Propulsion Device, System and Propulsion Method Michael Wallace, Joseph D. Nix, Christopher W. Smith, 2014
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15. Kammash, Terry; Martin, James; Godfroy, Thomas (17 January 2003). "Antimatter Driven P-B11 Fusion Propulsion System". AIP Conference Proceedings. 654 (1): 497–501. Bibcode:2003AIPC..654..497K. doi:10.1063/1.1541331. hdl:2027.42/87345.
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