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[[Imatge:Lunar base concept drawing s78 23252.jpg|thumb|300px|Concepció artística d'una catapulta electromagnètica a la [[Lluna]].]]

Una '''catapulta electromagnètica''' és un mètode proposat de [[Llançament espacial sense coet|llançament espacial sense coets]] que utilitzaria un [[motor lineal]] per [[Acceleració|accelerar]] i catapultar [[Càrrega útil|càrregues útils]] a altes velocitats. Les catapultes electromagnètiques existents i contemplades empren bobines de filferro energitzades per electricitat per fer [[Electroimant|electroimants]], tot i que també s'ha proposat una catapulta electromagnètica rotativa.<ref>{{ref-web |cognom=Pearson |nom=J. |url=http://www.star-tech-inc.com/papers/asteroids/asteroids.pdf |títol=''Asteroid retrieval by rotary rocket'' |llengua=anglès |obra=AIAA |data=16 de gener de 1980 |consulta=3 de març de 2022}}</ref> L'encesa seqüencial d'una fila d'electroimants accelera la càrrega útil al llarg d'un camí. Després de deixar el camí, la càrrega útil continua movent-se a causa de la [[quantitat de moviment]].

Tot i que qualsevol dispositiu utilitzat per impulsar una càrrega útil [[balística]] és tècnicament una catapulta electromagnètica, en aquest context una catapulta electromagnètica és essencialment un [[canó de Gauss]] que accelera magnèticament un paquet que consisteix en un suport magnetizable que conté una càrrega útil. Una vegada que la càrrega útil s'ha accelerat, les dues se separen i el suport s'alenteix i es recicla per a una altra càrrega útil.

Les catapultes electromagnètiques es poden utilitzar per impulsar naus espacials de tres maneres diferents: Es podria utilitzar una gran catapulta electromagnètica a terra per llançar naus espacials lluny de la Terra, la [[Lluna]] o un altre cos. Una petita catapulta electromagnètica podria estar a bord d'una nau espacial, llançant peces de material a l'espai per impulsar-se. Una altra variació tindria una instal·lació massiva en una lluna o un asteroide per enviar projectils per ajudar a una nau llunyana.

Les catapultes electromagnètiques miniaturitzats també es poden [[Canó de Gauss#Aplicació potencial|emprar com a armes]] d'una manera similar a les armes de foc clàssiques o els canons que utilitzen combustió química. També són possibles els híbrids entre els [[canó de Gauss|canons de Gauss]] com els [[Canó de rail helicoïdal|canons de rail helicoïdals]].<ref>{{ref-publicació |cognom=Kolm |nom=H. |display-authors=etal |url=http://www.coilgun.info/theorymath/electroguns.htm |article=''Electromagnetic Guns, Launchers, and Reaction Engines'' |llengua=anglès |publicació=MIT |any=1980}}</ref>

== Catapultes electromagnètiques fixes ==
{{see also|Space gun}}
Mass drivers need no physical contact between moving parts because they guide their projectiles by dynamic magnetic levitation, allowing extreme reusability in the case of solid-state power switching, and a functional life of - theoretically - up to millions of launches. While marginal costs tend to be accordingly low, initial development and construction costs are highly dependent on performance, especially the intended mass, acceleration, and velocity of projectiles. For instance, while [[Gerard K. O'Neill|Gerard O'Neill]] built his first mass driver in 1976–1977 with a $2000 budget, a short [[Mass Driver 1|test model]] firing a projectile at 40&nbsp;m/s and 33 [[g-force|g]],<ref>Compare:
{{cite journal
|last1 = Henson
|first1 = Keith
|author-link1 = Keith Henson
|last2 = Henson
|first2 = Carolyn
|author-link2 = Carolyn Meinel
|title = 1977 Space Manufacturing Facilities Conference
|url = http://www.nss.org/settlement/L5news/L5news/L5news7706.pdf
|journal = L5 News
|publisher = L-5 Society
|date = June 1977
|volume = 2
|issue = 6
|page = 4
|access-date = 2017-11-27
|quote = The stars of this conference [...] were Professor Henry Kolm of Massachusetts Institute of Technology and the group of student volunteers who built the first mass driver [...] In its best test, the mass driver prototype produced an acceleration of thirty-three gravities. This is more than Dr. O'Neill [...] had considered necessary for a lunar surface mass driver. [...] The mass driver was demonstrated several times during breaks between conference sessions, each time with a round of applause for the team who built it in less than four months on a budget of $2,000.
|archive-url = https://web.archive.org/web/20170505100448/http://www.nss.org/settlement/L5news/L5news/L5news7706.pdf
|archive-date = 2017-05-05
|url-status = dead
}}</ref>
his next model had an order-of-magnitude greater acceleration<ref>Compare:
{{cite journal
|last1 = Snow
|first1 = William R.
|last2 = Dunbar
|first2 = R. Scott
|author-link2 = R. Scott Dunbar
|last3 = Kubby
|first3 = Joel A.
|last4 = O'Nell
|first4 = Gerard K.
|author-link4 = Gerard K. O'Neill
|title = Mass Driver Two: A Status Report
|url = https://classes.soe.ucsc.edu/ee070/Fall07/UNSECURE/Pictures%20of%20the%20Mass%20Driver%20discussed%20in%20class/Mass%20Driver%20Two%20-%20A%20Status%20Report.pdf
|journal = IEEE Transactions on Magnetics
|date = January 1982
|volume = Mag-18
|issue = 1
|page = 127
|access-date = 2017-11-26
|quote = Mass Driver Two combines for the first time all the essential features of an operational mass driver, with the exception of bucket recirculation and payload handling. Its nominal design acceleration is 5000 m/s2, for a final velocity of 112 m/s.
|doi = 10.1109/tmag.1982.1061777
|bibcode = 1982ITM....18..127S
|archive-url = https://web.archive.org/web/20120722020519/http://classes.soe.ucsc.edu/ee070/Fall07/UNSECURE/Pictures%20of%20the%20Mass%20Driver%20discussed%20in%20class/Mass%20Driver%20Two%20-%20A%20Status%20Report.pdf
|archive-date = 2012-07-22
|url-status = dead
}}</ref>
after a comparable increase in funding, and, a few years later, researchers at the University of Texas estimated that a mass driver firing a 10 kilogram projectile at 6000&nbsp;m/s would cost $47 million.<ref name = massdriver2>[http://www.soe.ucsc.edu/classes/ee070/Fall07/UNSECURE/Pictures%20of%20the%20Mass%20Driver%20discussed%20in%20class/Mass%20Driver%20Two%20-%20A%20Status%20Report.pdf IEEE Transactions on Magnetics, Vol Mag-18, No. 1]{{Dead link|date=March 2020 |bot=InternetArchiveBot |fix-attempted=yes }}, January 1982. Retrieved May 10, 2011.</ref>{{qn|date=November 2017}}<ref>[http://www.utexas.edu/research/cem/IEEE/PR%2083%20Gully%20Publications.pdf Electromagnetic Launchers for Space Applications]. Retrieved May 10, 2011.</ref>{{failed verification|date=November 2017}}

For a given amount of energy involved, heavier objects go proportionally slower. Light{{clarify|date=June 2020}} objects may be projected at 20&nbsp;km/s or more. The limits are generally the expense of energy storage able to be discharged quickly enough and the cost of power switching, which may be by semiconductors or by gas-phase switches (which still often have a niche in extreme pulse power applications).<ref>{{cite web |url= http://www05.abb.com/global/scot/scot256.nsf/veritydisplay/8a528b3efd5df655c12578470029b1f6/$file/eml08aw_high%20current%20high%20voltage%20switches%20for%20electromagnetic%20launch%20%28eml2008%29.pdf |title= High Current, High Voltage Solid State Discharge Switches for Electromagnetic Launch Applications}}</ref><ref>{{cite web|url= http://www.electricstuff.co.uk/pulse.html|title= Pulse Power Switching Devices - An Overview}}</ref><ref>{{cite web|url= http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA428435|title= Scanning the Technology: Modern Pulsed Power|access-date= April 27, 2011|archive-date= December 1, 2012|archive-url= https://web.archive.org/web/20121201183324/http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA428435|url-status= dead}}</ref> However, energy can be stored inductively in superconducting coils. A 1&nbsp;km long mass driver made of superconducting coils can accelerate a 20&nbsp;kg vehicle to 10.5&nbsp;km/s at a conversion efficiency of 80%, and average acceleration of 5,600 g.<ref name=L5news>{{Cite web |url=http://www.nss.org/settlement/L5news/1980-massdriver.htm |title=L5 news, Sept 1980: Mass Driver Update |access-date=2009-07-28 |archive-url=https://web.archive.org/web/20171201042921/http://www.nss.org/settlement/L5news/1980-massdriver.htm |archive-date=2017-12-01 |url-status=dead }}</ref>

Earth-based mass drivers for propelling vehicles to orbit, such as the [[StarTram]] concept, would require considerable capital investment.<ref name = startram>{{cite web|url= http://www.startram.com/resources|title= StarTram2010: Maglev Launch: Ultra Low Cost Ultra High Volume Access to Space for Cargo and Humans|access-date= 2011-04-28|archive-url= https://web.archive.org/web/20170727013646/http://www.startram.com/resources|archive-date= 2017-07-27|url-status= dead}}</ref> The Earth's relatively strong gravity and relatively thick atmosphere make the implementation of a practical solution difficult. Also, most if not all plausible launch sites would propel spacecraft through heavily-traversed air routes. Due to the massive [[turbulence]] such launches would cause, significant [[air traffic control]] measures would be needed to ensure the safety of other aircraft operating in the area.

With the proliferation of reusable rockets to launch from Earth (especially first stages) whatever potential might have once existed for any economic advantage in using mass drivers as an alternative to chemical rockets to launch from Earth is becoming increasingly doubtful. For these reasons many proposals feature installing mass drivers on the [[Moon]] where the lower [[gravity]] and [[Atmosphere of the Moon|lack of atmosphere]] greatly reduce the required velocity to reach lunar orbit, also, lunar launches from a fixed position are much less likely to generate issues with respect to matters such as traffic control.

Most serious mass-driver designs use superconducting coils to achieve reasonable energetic efficiency (often 50% to 90+%, depending on design).<ref>{{cite journal|bibcode= 1980ITM....16..719K|title= Electromagnetic Launchers|doi= 10.1109/TMAG.1980.1060806|journal=IEEE Transactions on Magnetics|volume=16|issue=5|date=September 1980|last1= Kolm|first1= H.|last2= Mongeau|first2= P.|last3= Williams|first3= F.|pages= 719–721}}</ref> Equipment may include a superconducting bucket or aluminum coil as the payload. The coils of a mass driver can induce [[eddy current]]s in a payload's aluminum coil, and then act on the resulting [[magnetic field]]. There are two sections of a mass driver. The maximum [[acceleration]] part spaces the coils at constant distances, and synchronizes the coil currents to the bucket. In this section, the acceleration increases as the velocity increases, up to the maximum that the bucket can take. After that, the constant acceleration region begins. This region spaces the coils at increasing distances to give a fixed amount of velocity increase per unit of time.

Based on this mode, a major proposal for the use of mass drivers involved transporting lunar-surface material to space habitats for processing using [[solar energy]].<ref>[http://settlement.arc.nasa.gov/75SummerStudy/Table_of_Contents1.html NASA, 1975: Space Settlements: A Design Study] {{Webarchive|url=https://web.archive.org/web/20170625000423/https://settlement.arc.nasa.gov/75SummerStudy/Table_of_Contents1.html |date=2017-06-25 }}. Retrieved 2011-05-09.</ref> The Space Studies Institute showed that this application was reasonably practical.

In some designs, the payload would be held in a bucket and then released, so that the bucket can be decelerated and reused. A disposable bucket, on the other hand, would avail acceleration along the whole track. Alternatively, if a track were constructed along the entire circumference of the Moon (or any other celestial body without a significant atmosphere) then a reusable bucket's acceleration would not be limited by the length of the track - however, such a system would need to be engineered to withstand substantial [[centrifugal force]]s if it were intended to accelerate passengers and/or cargo to very high velocities.

=== A la Terra ===
In contrast to cargo-only chemical [[space gun|space-gun]] concepts, a mass driver could be any length, affordable, and with relatively smooth acceleration throughout, optionally even lengthy enough to reach target velocity without excessive [[g-force|g forces]] for passengers. It can be constructed as a very long and mainly horizontally aligned [[launch track]] for spacelaunch, targeted upwards at the end, partly by bending of the track upwards and partly by [[Earth's curvature]] in the other direction.

Natural elevations, such as mountains, may facilitate the construction of the distant, upwardly targeted part. The higher up the track terminates, the less resistance from the atmosphere the launched object will encounter.<ref>{{cite web |url=http://spacemonitor.blogspot.com/2007/03/magnetic-launch-system.html |work=The Space Monitor |title=Magnetic Launch System}}</ref>

The 40 [[megajoule]]s per kilogram or less [[kinetic energy]] of projectiles launched at up to 9000&nbsp;m/s velocity (if including extra for drag losses) towards [[low Earth orbit]] is a few [[kilowatt-hours]] per kilogram if efficiencies are relatively high, which accordingly has been hypothesized to be under $1 of electrical energy cost per kilogram shipped to [[Low Earth Orbit|LEO]], though total costs would be far more than electricity alone.<ref name = startram/> By being mainly located slightly above, on or beneath the ground, a mass driver may be easier to maintain compared with many other structures of [[non-rocket spacelaunch]]. Whether or not underground, it needs to be housed in a pipe that is [[vacuum pump]]ed in order to prevent internal air [[Drag (physics)|drag]], such as with a mechanical shutter kept closed most of the time but a [[plasma window]] used during the moments of firing to prevent loss of vacuum.<ref>{{cite web |url=http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA426465&Location=U2&doc=GetTRDoc.pdf |title=Advanced Propulsion Study |access-date=2011-05-03 |archive-date=2012-12-01 |archive-url=https://web.archive.org/web/20121201194510/http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA426465&Location=U2&doc=GetTRDoc.pdf |url-status=dead }}</ref>

A mass driver on Earth would usually be a compromise system. A mass driver would accelerate a payload up to some high speed which would not be enough for orbit. It would then release the payload, which would complete the launch with rockets. This would drastically reduce the amount of velocity needed to be provided by rockets to reach orbit. Well under a tenth of orbital velocity from a small rocket thruster is enough to raise [[perigee]] if a design prioritizes minimizing such, but hybrid proposals optionally reduce requirements for the mass driver itself by having a greater portion of [[delta-v]] by a rocket burn (or orbital [[momentum exchange tether]]).<ref name = startram/> On Earth, a mass-driver design could possibly use well-tested [[Maglev train|maglev]] components.

To launch a space vehicle with humans on board, a mass driver's track would need to be almost 1000 kilometres long if providing almost all the velocity to [[Low Earth Orbit]], though a lesser length could provide major launch assist. Required length, if accelerating mainly at near a constant maximum acceptable [[g-force]] for passengers, is proportional to velocity squared.<ref name = physics>{{cite web |url=http://hyperphysics.phy-astr.gsu.edu/hbase/mot.html#mot1 |title=Constant Acceleration}}</ref> For instance, half of the velocity goal could correspond to a tunnel a quarter as long needing to be constructed, for the same acceleration.<ref name = physics/> For rugged objects, much higher accelerations may suffice, allowing a far shorter track, potentially circular or [[Helix|helical]] (spiral).<ref>{{cite web |url=http://techfreep.com/magnets-not-rockets-could-fling-satellites-into-space.htm |title=Magnets, Not Rockets, Could Fling Satellites Into Space |access-date=2008-05-04 |archive-date=2017-12-01 |archive-url=https://web.archive.org/web/20171201041611/http://techfreep.com/magnets-not-rockets-could-fling-satellites-into-space.htm |url-status=dead }}</ref> Another concept involves a large ring design whereby a space vehicle would circle the ring numerous times, gradually gaining speed, before being released into a launch corridor leading skyward.

Mass drivers have been proposed for the disposal of nuclear waste in space: a projectile launched at much above Earth's [[escape velocity]] would escape the Solar System, with atmospheric passage at such speed calculated as survivable through an elongated projectile and a very substantial heatshield.<ref name=L5news/><ref>
{{cite book
|editor-last=Horton |editor-first=T. E.
|title=Thermophysics of Atmospheric Entry
|publisher=[[American Institute of Aeronautics and Astronautics]]
|date=1982
|isbn=978-0-915928-66-8
|first1=Chul |last1=Park
|first2=Stuart W. |last2=Boden
|chapter=Ablation and deceleration of mass-driver launched projectiles for space disposal of nuclear wastes
|pages=201–225
|doi=10.2514/5.9781600865565.0201.0225
}}
</ref>{{Verify source|date=October 2019}}

== Catapultes electromagnètiques basades en naus espacials ==
A [[spacecraft]] could carry a mass driver as its primary engine. With a suitable source of electrical power (probably a [[nuclear reactor]]) the spaceship could then use the mass driver to accelerate pieces of matter of almost any sort, boosting itself in the opposite direction. At the smallest scale of reaction mass, this type of drive is called an [[ion drive]].{{Citation needed|date=March 2021}}

No absolute theoretical limit is known for the size, acceleration or muzzle energy of linear motors. However, practical engineering constraints apply for such as the power-to-mass ratio, [[waste heat]] dissipation, and the energy intake able to be supplied and handled. Exhaust velocity is best neither too low nor too high.<ref name = neofuel>{{cite web|url=http://www.neofuel.com/optimum/|title=Physics of Rocket Systems with Separated Energy and Propellant}}</ref>

There is a mission-dependent limited optimal exhaust velocity and [[Specific Impulse#Rockets|specific impulse]] for any thruster constrained by a limited amount of onboard spacecraft power. Thrust and momentum from exhaust, per unit mass expelled, scales up linearly with its velocity ([[momentum]] = mv), yet kinetic energy and energy input requirements scale up faster with velocity squared ([[kinetic energy]] = {{frac||1|2}} mv<sup>2</sup>). Too low an exhaust velocity would excessively increase propellant mass needed under the [[rocket equation]], with too high a fraction of energy going into accelerating propellant not used yet. Higher exhaust velocity has both benefit and tradeoff, increasing propellant usage efficiency (more momentum per unit mass of propellant expelled) but decreasing thrust and the current rate of spacecraft acceleration if available input power is constant (less momentum per unit of energy given to propellant).<ref name = neofuel/>

[[Electrically powered spacecraft propulsion|Electric propulsion]] methods like mass drivers are systems where energy does not come from the propellant itself. (Such contrasts to [[chemical rocket]]s where [[propulsive efficiency]] varies with the ratio of exhaust velocity to vehicle velocity at the time, but near maximum obtainable specific impulse tends to be a design goal when corresponding to the most energy released from reacting propellants). Although the specific impulse of an electric thruster itself optionally could range up to where mass drivers merge into [[particle accelerator]]s with fractional-lightspeed exhaust velocity for tiny particles, trying to use extreme exhaust velocity to accelerate a far slower spacecraft could be suboptimally low thrust when the energy available from a spacecraft's reactor or power source is limited (a lesser analogue of feeding onboard power to a row of spotlights, photons being an example of an extremely low momentum to energy ratio).<ref name = neofuel/>

For instance, if limited onboard power fed to its engine was the dominant limitation on how much payload a hypothetical spacecraft could shuttle (such as if intrinsic propellant economic cost was minor from usage of extraterrestrial soil or ice), ideal exhaust velocity would rather be around 62.75% of total mission [[delta-v|delta v]] if operating at constant specific impulse, except greater optimization could come from [[Specific Impulse#Rockets|varying exhaust velocity]] during the mission profile (as possible with some thruster types, including mass drivers and [[VASIMR|variable specific impulse magnetoplasma rockets]]).<ref name = neofuel/>

Since a mass driver could use any type of mass for reaction mass to move the spacecraft, a mass driver or some variation seems ideal for deep-space vehicles that scavenge reaction mass from found resources.

One possible drawback of the mass driver is that it has the potential to send solid reaction mass travelling at dangerously high relative speeds into useful orbits and traffic lanes. To overcome this problem, most schemes plan to throw finely-divided [[dust]]. Alternatively, liquid oxygen could be used as reaction mass, which upon release would boil down to its molecular state. Propelling the reaction mass to solar [[escape velocity]] is another way to ensure that it will not remain a hazard.

== Catapultes electromagnètiques híbrides ==

A mass driver on a [[spacecraft]] could be used to "reflect" masses from a stationary mass driver. Each deceleration and acceleration of the mass contributes to the [[momentum]] of the spacecraft. The lightweight, fast spacecraft need not carry [[reaction mass]], and does not need much electricity beyond the amount needed to replace losses in the electronics, while the immobile support facility can run off power plants able to be much larger than the spacecraft if needed. This could be considered a form of [[beam-powered propulsion]] (a macroscopic-scale analogue of a [[particle beam]] propelled magsail). A similar system could also deliver pellets of fuel to a spacecraft to power another propulsion system.<ref name="Singer1979">{{cite journal|last1=Singer|first1=C.E.|year=1979|doi=10.2172/5770056 |title=Interstellar Propulsion Using a Pellet Stream for Mass Transfer |url=http://www.osti.gov/bridge/servlets/purl/5770056-4HSXxH/5770056.pdf |access-date=May 9, 2011}}</ref><ref>{{cite web |url=http://www.centauri-dreams.org/?p=458 |title=Interstellar Flight Using Near-Term Technologies |access-date=May 9, 2011 |work=Centauri Dreams |first=Paul |last=Gilster |date=April 20, 2005}}</ref><ref name = momentumtransfer>[http://www.freepatentsonline.com/5305974.pdf U.S. Patent #5305974, Spacecraft Propulsion by Momentum Transfer]. Retrieved May 9, 2011.</ref><ref>{{cite book |chapter-url=https://books.google.com/books?id=tIfJM8Nu8iYC&pg=PA120 |title=Deep Space Probes: To The Outer Solar System and Beyond |page=120 |chapter=8.5: A Torodial Ramscoop |first=Gregory L. |last=Matloff |publisher=Springer |year=2005 |isbn=9783540247722 |access-date=May 9, 2011}}</ref>

Another theoretical use for this concept of propulsion can be found in [[space fountain]]s, a system in which a continuous stream of pellets in a circular track holds up a tall structure.

== Catapultes electromagnètiques com a armes ==

Small to moderate size high-acceleration electromagnetic projectile launchers are currently undergoing active research by the US Navy<ref>{{cite web|url=http://www.onr.navy.mil/Media-Center/Fact-Sheets/Electromagnetic-Railgun.aspx|title=U.S. Navy|access-date=2013-06-11|archive-date=2017-11-08|archive-url=https://web.archive.org/web/20171108033843/https://www.onr.navy.mil/Media-Center/Fact-Sheets/Electromagnetic-Railgun.aspx|url-status=dead}}</ref> for use as ground-based or ship-based weapons (most often [[railgun]]s but [[coilgun]]s in some cases). On larger scale than weapons currently near deployment but sometimes suggested in long-range future projections, a sufficiently high velocity [[linear motor]], a mass driver, could in theory be used as intercontinental artillery (or, if built on the [[Moon]] or in orbit, used to [[Space weapon#Orbital bombardment|attack a location on Earth's surface]]).<ref>[http://cat.inist.fr/?aModele=afficheN&cpsidt=15669700 Applications of coilgun electromagnetic propulsion technology]. Retrieved May 9, 2011.</ref><ref>[http://www.princeton.edu/~ota/disk2/1990/9003/900307.PDF Affordable Spacecraft: Design and Launch Alternatives, Chapter 5, Page 36]. Retrieved May 9, 2011.</ref><ref>[http://www.dresmara.ro/resources/carti/sdcasqdr.pdf QDR 2001: Strategy-Driven Choices for America's Security, Chapter 11, Global Reach/Global Power School] {{webarchive|url=https://web.archive.org/web/20120323185409/http://www.dresmara.ro/resources/carti/sdcasqdr.pdf |date=2012-03-23 }}. Retrieved May 9, 2011.</ref> As the mass driver would be located further up the gravity well than the theoretical targets, it would enjoy a significant energy imbalance in terms of counter-attack.

== Intents pràctics ==
<!-- Deleted image removed: [[File:Northrup Electric Gun.png|thumb|140px|Edwin Northrup's 1937 Electric Gun Mass Driver]] -->

One of the first engineering descriptions of an "Electric Gun" appears in the technical supplement of the 1937 science fiction novel "Zero to Eighty" by "Akkad Pseudoman",<ref>{{cite book|last=Pseudoman|first=Akkad|title=Zero to Eighty|date=1937|publisher=Princeton University Press|location=Princeton, New Jersey}}</ref> a pen name for the Princeton physicist and electrical entrepreneur [[Edwin Fitch Northrup]]. Dr. Northrup built prototype coil guns powered by kHz-frequency three-phase electrical generators, and the book contains photographs of some of these prototypes. The book describes a fictional circumnavigation of the moon by a two-person vehicle launched by a Northrup electric gun.

Later prototype mass drivers have been built since 1976 ([[Mass Driver 1]]), some constructed by the U.S. [[Space Studies Institute]] in order to prove their properties and practicality. [[Coilgun#Potential uses|Military R&D on coilguns]] is related, as are [[maglev|maglev trains]].

[[SpinLaunch]], a company founded in 2014, conducted the initial test of their test accelerator in October 2021.<ref>{{Cite web|last=Sheetz|first=Michael|date=2021-11-09|title=Alternative rocket builder SpinLaunch completes first test flight|url=https://www.cnbc.com/2021/11/09/spinlaunch-completes-first-test-flight-of-alternative-rocket.html|access-date=2021-11-11|website=CNBC|language=en}}</ref>

== Vegeu també ==
{{Portal|Spaceflight|Science}}
* [[Electromagnetic Aircraft Launch System]]
* [[Railgun]]
* [[Plasma railgun]]
* [[Helical railgun]]
* [[Coilgun]]
* [[Ram accelerator]]
* [[Light-gas gun]]
* [[Linear motor]]
* [[StarTram]]
* [[Launch loop]]
* [[Space fountain]]
* [[Spacecraft propulsion]]

===People===
* [[Eric Laithwaite]] and the Maglifter project
* [[Gerard K. O'Neill]]
* [[Henry Kolm]]

==References==
{{Referències|30em}}

== Enllaços externs ==
* [http://www.coilgun.info/theory/electroguns.htm Electromagnetic Guns] {{Webarchive |url=https://web.archive.org/web/20080516063621/http://www.coilgun.info/theory/electroguns.htm |date=2008-05-16 }}—una pàgina que descriu la recerca sobre motors lineals al MIT
* [https://web.archive.org/web/20060923071521/http://www.belmont.k12.ca.us/ralston/programs/itech/SpaceSettlement/spaceresvol2/electromag.html Llançament electromagnètic de material lunar]
* {{ref-web |nom=David |cognom=Shiga |url=https://www.newscientist.com/article/dn10180-huge-launch-ring-to-fling-satellites-into-orbit.html |títol=''Huge 'launch ring' to fling satellites into orbit'' |llengua=anglès |obra=New Scientist |data=3 d'octubre de 2006}}<!-- article sobre la recerca d'un conductor de massa circular -->

{{Non-rocket spacelaunch}}
{{Spacecraft propulsion}}
{{emerging technologies|topics=yes|space=yes}}

{{DEFAULTSORT:Mass Driver}}
[[Category:Magnetic devices]]
[[Category:Magnetic propulsion devices]]
[[Category:Space colonization]]
[[Category:Spacecraft propulsion]]
[[Category:Non-rocket spacelaunch]]
[[Category:Emerging technologies]]

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[[Fitxer:Lunar base concept drawing s78 23252.jpg|miniatura|Dibuix d'una catapulta electromagnètica]]
[[Fitxer:Lunar base concept drawing s78 23252.jpg|miniatura|Dibuix d'una catapulta electromagnètica]]
Una '''catapulta electromagnètica''' és una obra hipotètica d'[[enginyeria]], igual que l'[[ascensor espacial]], que permetria abaratir el cost dels llançaments a [[òrbita]].
Una '''catapulta electromagnètica''' és una obra hipotètica d'[[enginyeria]], igual que l'[[ascensor espacial]], que permetria abaratir el cost dels llançaments a [[òrbita]].

Revisió del 22:37, 3 març 2022

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One of the first engineering descriptions of an "Electric Gun" appears in the technical supplement of the 1937 science fiction novel "Zero to Eighty" by "Akkad Pseudoman",[1] a pen name for the Princeton physicist and electrical entrepreneur Edwin Fitch Northrup. Dr. Northrup built prototype coil guns powered by kHz-frequency three-phase electrical generators, and the book contains photographs of some of these prototypes. The book describes a fictional circumnavigation of the moon by a two-person vehicle launched by a Northrup electric gun.

Later prototype mass drivers have been built since 1976 (Mass Driver 1), some constructed by the U.S. Space Studies Institute in order to prove their properties and practicality. Military R&D on coilguns is related, as are maglev trains.

SpinLaunch, a company founded in 2014, conducted the initial test of their test accelerator in October 2021.[2]

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References

  1. ↑ Pseudoman, Akkad. Zero to Eighty. Princeton, New Jersey: Princeton University Press, 1937. 
  2. ↑ Sheetz, Michael. «Alternative rocket builder SpinLaunch completes first test flight» (en anglès). CNBC, 09-11-2021. [Consulta: 11 novembre 2021].

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Plantilla:Non-rocket spacelaunch Plantilla:Spacecraft propulsion Plantilla:Emerging technologies

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Dibuix d'una catapulta electromagnètica

Una catapulta electromagnètica és una obra hipotètica d'enginyeria, igual que l'ascensor espacial, que permetria abaratir el cost dels llançaments a òrbita.

El concepte és molt simple: es tracta d'una rampa de gran longitud en la qual, mitjançant camps magnètics, s'accelera l'objecte que es desitja posar en òrbita. Les tècniques propostes poden ser ben la del canó de Gauss o bé la del canó electromagnètic. La seva realització en la pràctica, no obstant això, no és tan senzilla.

El primer inconvenient és la construcció de la catapulta. Es tracta d'una obra de diversos quilòmetres de longitud al llarg de la qual s'ha de mantenir una inclinació constant i s'han de disposar els elements que permetin generar el camp magnètic. És doncs, una obra d'enginyeria de gran envergadura i, per tant, notablement cara.

El segon problema és l'acceleració necessària per posar el cos en òrbita. En una catapulta espacial es prescindeix de l'ús de coets impulsors, per la qual cosa el cos ha de sortir amb la velocitat necessària per aconseguir l'òrbita. Aconseguir una velocitat tan alta en uns pocs quilòmetres exigeix acceleracions que poden arribar a ser de l'ordre de milers de g, la qual cosa les fa inviables per llançar éssers humans (fins i tot elements mecànics sensibles poden resultar danyats). Les acceleracions poden reduir-se augmentant la longitud de la catapulta, però això augmentaria la dificultat de la seva construcció.

Un tercer problema és l'atmosfera. Velocitats de sortida tan altes impliquen fregaments molt elevats, semblants als quals sofreix un vehicle que realitza el seu reentrada en l'atmosfera, amb els problemes que això implica quant a les temperatures. Es podria minimitzar aquest problema situant la catapulta en llocs alts, on l'atmosfera és menys densa, però per facilitat d'ús seria convenient que el dispositiu es trobés en zones properes a l'equador, la qual cosa limita el nombre possible d'emplaçaments idonis. Un d'aquests llocs seria l'altiplà andí a Sud-amèrica.

A causa dels inconvenients derivats de l'atmosfera i de les altes acceleracions (que impedeixen el llançament d'éssers vius i, per extensió, d'astronautes) la catapulta sembla un mitjà poc adequat per sortir de la Terra.

Malgrat aquestes dificultats, les utilitats d'una possible catapulta electromagnètica en la Terra són molt variades, per exemple, per posar satèl·lits en òrbita, llançar sondes no tripulades a l'espai exterior, llançar les peces o materials per construir estacions espacials o edificis lunars, llançar material radioactiu d'alta activitat dirigit a planetes inhabitables que segur mai trepitjarem com Júpiter, com a arma per poder llançar projectils dirigits cap a algun asteroide que posi en perill l'existència a la terra.

Una utilització i emplaçament més lògics para la catapulta seria la posada en òrbita de minerals en brut o de metalls des de la Lluna. Els avantatges són varis: d'una banda la gravetat lunar és molt menor que la terrestre, la qual cosa facilita la posada en òrbita de materials mitjançant aquest mètode; d'altra banda, la Lluna manca d'atmosfera, evitant els problemes de fregament i escalfament. De fet, la Lluna ha estat considerada ja des dels primers treballs de Tsiolkovsky com un port intermedi en els viatges interplanetaris dins del sistema solar i els optimistes plans de la NASA en els anys 1960 ja incloïen bases mineres i catapultes en la seva superfície. Encara que és molt probable que per llançar el material necessari per construir això en la lluna d'una manera rendible faci mancada primer tenir una catapulta electromagnètica a la terra.

Catapultes espacials en la ciència-ficció

El primer esment conegut és la novel·la A trip to Venus de John Munro, publicada en 1897, una descripció minuciosa d'un accelerador lineal magnètic.

En la pel·lícula Quan els mons xoquen (Rudolph Maté, 1951), podem observar una rampa, encara que no electromagnètica, que s'aprofita de l'energia potencial gravitatòria per conferir impuls a la nau.

En 1965 Arthur C. Clarke reprenia el concepte en el seu relat Maelstrom II.

En 1966, Robert A. Heinlein en La Lluna és una cruel amant, mostra una catapulta empleada per enviar materials a la Terra. I quan els colons lunars es rebel·len, és emprada per llançar roques sobre la superfície terrestre.

Després de l'èxit dels Transbordadors nord-americans, la idea de la catapulta electromagnètica es va abandonar també en la ficció; però en els últims anys, quan s'ha posat en dubte la idoneïtat del sistema de les naus llançadora per arribar a l'espai, la ciència-ficció s'ha tornat a fer ressò d'aquest disseny.

En una de les seqüències de Interstella 5555 (Kazuhisa Takenôchi, 2003) es pot apreciar clarament una estructura en forma de tobogan que serveix per rellançar la nau.

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