Antimatter rocket
37854
159263058
2007-09-20T22:10:36Z
Arthena
123004
[[WP:AWB/T|Typo fixing]] , typos fixed: annhilation → annihilation using [[Project:AutoWikiBrowser|AWB]]
{{refimprove|date=April 2007}}
An '''antimatter rocket''' is a proposed class of [[rocket]]s that use [[antimatter]] as their power source. There are several types of design 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: those that directly use the products of antimatter annihilation for propulsion, those that heat a working fluid which is then used for propulsion, and those that heat a working fluid to generate electricity for some form of [[electric propulsion|electric spacecraft propulsion system]].
==Direct use of reaction products==
[[Antiproton]] annihilation reactions produce charged and uncharged [[meson]]s, in addition to [[gamma ray]]s. The charged mesons can be channelled by a [[magnetic nozzle]], producing thrust. This type of antimatter rocket is a '''beamed core''' configuration. It is not perfectly efficient; energy is lost as the rest mass of the charged and uncharged mesons, lost as the kinetic energy of the uncharged mesons (which can't be deflected for thrust), and lost as gamma rays.
[[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]] to derive thrust from the annihilation reaction. No viable means of reflecting gamma rays has been proposed (no solid material has this property, and [[plasma (physics)|plasma]] is not sufficiently reflective to gamma rays under practically attainable conditions).
==Antimatter heating of an exhaust fluid==
Several methods for heating an exhaust fluid using the gamma rays produced by positron annihilation have been proposed<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 | last = Smith | first = Gerald | coauthors = Metzger, John; Meyer, Kirby; Thode, Les | date 2006-03-07}}</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.
==Antimatter power generation==
The idea of using antimatter to power an [[electric 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 electric propulsion proposals (typically high specific impulse and low thrust).
==Difficulties with antimatter rockets==
The chief practical difficulties with antimatter rockets are the problems of creating antimatter and storing antimatter. 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{{Fact|date=April 2007}}. Most proposed antimatter rocket designs require a fairly small amount of antimatter (around 10 grams to reach Mars in one month)[http://science.howstuffworks.com/antimatter2.htm] 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 2007]] been performed only for small numbers of individual atoms. Storage of antimatter is typically done by trapping electrically charged frozen antihydrogen pellets in [[Penning trap|Penning]] or [[Paul trap]]s. While there is no theoretical barrier to these tasks being performed on the scale required to fuel an antimatter rocket, they are expected to be extremely (and perhaps prohibitively) expensive{{Fact|date=April 2007}}.
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.
==See also==
* [[Spacecraft propulsion]]
* [[Antimatter catalyzed nuclear pulse propulsion]]
* [[Redshift rocket]]
==References==
<references />
[[Category:Antimatter]]
[[Category:Spacecraft propulsion]]