Editing Fusion rocket

{{short description|Rocket driven by nuclear fusion power}}
[[File:Schematic of the Fusion Driven Rocket including major subsystems.png|thumb|A schematic of a fusion-driven rocket by [[NASA]]]]
A '''fusion rocket''' is a theoretical design for a [[rocket]] driven by [[nuclear fusion|fusion]] propulsion that could provide efficient and sustained [[Spacecraft propulsion|acceleration in space]] without the need to carry a large fuel supply. The design requires fusion power technology beyond current capabilities, and much larger and more complex rockets.

Fusion [[nuclear pulse propulsion]] is one approach to using nuclear fusion energy to provide propulsion.

Fusion's main advantage is its very high [[specific impulse]], while its main disadvantage is the (likely) large mass of the reactor. A fusion rocket may produce less radiation than a [[nuclear fission|fission]] rocket, reducing the shielding mass needed. The simplest way of building a fusion rocket is to use [[hydrogen bomb]]s as proposed in [[Project Orion (nuclear propulsion)|Project Orion]], but such a spacecraft would be massive and the [[Partial Nuclear Test Ban Treaty]] prohibits the use of such bombs. For that reason bomb-based rockets would likely be limited to operating only in space. An alternate approach uses electrical (e.g. [[ion thruster|ion]]) propulsion with electric power generated by fusion instead of direct thrust.

== Electricity generation vs. direct thrust ==

Spacecraft propulsion methods such as [[ion thruster]]s require electric power to run, but are highly efficient. In some cases their thrust is limited by the amount of power that can be generated (for example, a [[mass driver]]). An electric generator running on fusion power could drive such a ship. One disadvantage is that conventional electricity production requires a low-temperature energy sink, which is difficult (i.e. heavy) in a spacecraft. Direct conversion of the kinetic energy of fusion products into electricity mitigates this problem.<ref name="futurism 20201007">{{cite web |last1=Robitzski |first1=Dan |title=This Scientist Says He's Built a Jet Engine That Turns Electricity Directly Into Thrust |url=https://futurism.com/scientist-jet-engine-electricity-thrust |website=Futurism |access-date=19 August 2023 |archive-url=https://web.archive.org/web/20230831121152/https://futurism.com/scientist-jet-engine-electricity-thrust |archive-date=31 August 2023 |date=7 October 2020 |url-status=live}}</ref>

One attractive possibility is to direct the fusion exhaust out the back of the rocket to provide thrust without the intermediate production of electricity. This would be easier with some confinement schemes (e.g. [[magnetic mirror]]s) than with others (e.g. [[tokamak]]s). It is also more attractive for "advanced fuels" (see [[aneutronic fusion]]). [[Helium-3]] propulsion would use the fusion of [[helium-3]] atoms as a power source. Helium-3, an [[isotope]] of helium with two [[proton]]s and one [[neutron]], could be fused with [[deuterium]] in a reactor. The resulting energy release could expel propellant out the back of the spacecraft. Helium-3 is proposed as a power source for spacecraft mainly because of its lunar abundance. Scientists estimate that 1 million tons of accessible helium-3 are present on the moon.<ref name="helium3">{{cite web |last1=Wakefield |first1=Julie |date=30 June 2000 |title=Moon's Helium-3 Could Power Earth |url=https://fti.neep.wisc.edu/fti.neep.wisc.edu/gallery/pdf/space_com063000.pdf |archive-url=https://web.archive.org/web/20230131211416/https://fti.neep.wisc.edu/fti.neep.wisc.edu/gallery/pdf/space_com063000.pdf |archive-date=31 January 2023 |url-status=live |access-date=3 October 2010 }}</ref> Only 20% of the power produced by the D-T reaction could be used this way; while the other 80% is released as neutrons which, because they cannot be directed by magnetic fields or solid walls, would be difficult to direct towards thrust, and [[Neutron radiation#Health hazards and protection|may in turn require shielding]]. Helium-3 is produced via [[beta decay]] of [[tritium]], which can be produced from deuterium, lithium, or boron.

Even if a self-sustaining fusion reaction cannot be produced, it might be possible to use fusion to boost the efficiency of another propulsion system, such as a [[Variable specific impulse magnetoplasma rocket|VASIMR]] engine.{{Citation needed|date=October 2023|reason=Not stated in the Wikipedia page for VASIMIR.}}

== Confinement alternatives ==

=== Magnetic ===
To sustain a fusion reaction, the plasma must be confined. The most widely studied configuration for terrestrial fusion is the [[tokamak]], a form of [[magnetic confinement fusion]]. Currently tokamaks weigh a great deal, so the thrust to weight ratio would seem unacceptable.<ref name=":0">"The large mass and the need for a high power removal of a terrestrial fusion reactor make the MCF [Magnetic Confinement Fusion] and the ICF [Inertial Confinement Fusion] hardly implementable for space propulsion applications. Rocket mass is indeed a hard constraint in space propulsion, and power exhaust is a critical issue in space due to the absence of an efficient thermal sink." {{Cite journal |last1=Meschini |first1=Samuele |last2=Laviano |first2=Francesco |last3=Ledda |first3=Federico |last4=Pettinari |first4=Davide |last5=Testoni |first5=Raffella |last6=Torsello |first6=Daniele |last7=Panella |first7=Bruno |date=2023-06-07 |title=Review of commercial nuclear fusion projects |journal=Frontiers in Energy Research |volume=11 |doi=10.3389/fenrg.2023.1157394 |doi-access=free |issn=2296-598X }}</ref> [[NASA]]'s [[Glenn Research Center]] proposed in 2001 a small aspect ratio spherical torus reactor for its "Discovery II" conceptual vehicle design. "Discovery II" could deliver a crewed 172 metric tons payload to [[Jupiter]] in 118 days (or 212 days to [[Saturn]]) using 861 metric tons of [[hydrogen]] propellant, plus 11 metric tons of [[Helium-3]]-[[Deuterium]] (D-He3) fusion fuel.<ref name="realizing2001">{{cite conference |title=Realizing "2001: A Space Odyssey": Piloted Spherical Torus Nuclear Fusion Propulsion |id=NASA/TM—2005-213559 |conference=37th Joint Propulsion Conference and Exhibit |publication-date=March 2005 |date=July 2001 |publisher=[[Glenn Research Center]] |url=https://ntrs.nasa.gov/api/citations/20050160960/downloads/20050160960.pdf |archive-url=https://web.archive.org/web/20230704080840/https://ntrs.nasa.gov/api/citations/20050160960/downloads/20050160960.pdf |archive-date=4 July 2023 |url-status=live |last1=Williams |first1=Craig H. |last2=Dudzinski |first2=Leonard A. |last3=Borowski |first3=Stanley K. |last4=Juhasz |first4=Albert J. }}</ref> The hydrogen is heated by the fusion plasma debris to increase thrust, at a cost of reduced [[exhaust velocity]] (348–463&nbsp;km/s)  and hence increased propellant mass.

=== Inertial ===
The main alternative to magnetic confinement is [[inertial confinement fusion]] (ICF), such as that proposed by [[Project Daedalus]]. A small pellet of fusion fuel (with a diameter of a couple of millimeters) would be ignited by an [[electron beam]] or a [[laser]]. To produce direct thrust, a [[magnetic field]] forms the pusher plate. In principle, the Helium-3-Deuterium reaction or an [[aneutronic fusion]] reaction could be used to maximize the energy in charged particles and to minimize radiation, but it is highly questionable whether using these reactions is technically feasible. Both the detailed design studies in the 1970s, the [[Orion drive]] and Project Daedalus, used inertial confinement. In the 1980s, [[Lawrence Livermore National Laboratory]] and NASA studied an ICF-powered "Vehicle for Interplanetary Transport Applications" (VISTA). The conical VISTA spacecraft could deliver a 100-tonne payload to [[Mars]] orbit and return to Earth in 130 days, or to Jupiter orbit and back in 403 days. 41 tonnes of deuterium/[[tritium]] (D-T) fusion fuel would be required, plus 4,124 tonnes of hydrogen expellant.<ref name="interplanetary">{{cite conference |title=Interplanetary Space Transport Using Inertial Fusion Propulsion |last1=Orth |first1=C. D. |conference=9th International Conference on Emerging Nuclear Energy Systems |location=Tel Aviv |date=20 April 1998 |publication-date=July 1998 |id=UCRL-JC-129237 |publisher=[[Lawrence Livermore National Laboratory]] |url=http://www.boomslanger.com/images/istuifp.pdf |archive-url=https://web.archive.org/web/20111215124046/http://www.boomslanger.com/images/istuifp.pdf |archive-date=15 December 2011 |url-status=dead |access-date=4 September 2011 }}</ref> The exhaust velocity would be 157&nbsp;km/s.

The very large necessary mass and the challenge of managing the heat produced in space may make an ICF reactor unworkable in space travel.<ref name=":0" />

=== Magnetized target ===
[[Magnetized target fusion]] (MTF) is a relatively new approach that combines the best features of the more widely studied magnetic confinement fusion (i.e. good energy confinement) and inertial confinement fusion (i.e. efficient compression heating and wall free containment of the fusing plasma) approaches. Like the magnetic approach, the fusion fuel is confined at low density by magnetic fields while it is heated into a [[Plasma (physics)|plasma]], but like the inertial confinement approach, fusion is initiated by rapidly squeezing the target to dramatically increase fuel density, and thus temperature. MTF uses "plasma guns" (i.e. electromagnetic acceleration techniques) instead of powerful lasers, leading to low cost and low weight compact reactors.<ref name="magnetizedfusion">{{cite tech report |title=Magnetized Target Fusion in Advanced Propulsion Researc |last1=Cylar |first1=Rashad |publisher=[[Marshall Space Flight Center]]/[[University of Alabama]] |year=2002 |url=https://ntrs.nasa.gov/api/citations/20030093609/downloads/20030093609.pdf |archive-url=https://web.archive.org/web/20230519175557/https://ntrs.nasa.gov/api/citations/20030093609/downloads/20030093609.pdf |archive-date=19 May 2023 |url-status=live }}</ref> The NASA/[[Marshall Space Flight Center|MSFC]] Human Outer Planets Exploration (HOPE) group has investigated a crewed MTF propulsion spacecraft capable of delivering a 164-tonne payload to Jupiter's moon [[Callisto (moon)|Callisto]] using 106-165 metric tons of propellant (hydrogen plus either D-T or D-He3 fusion fuel) in 249–330 days.<ref name="inspaceconcept">{{cite tech report |title=Conceptual Design of In-Space Vehicles for Human Exploration of the Outer Planets |last1=Adams |first1=R. B. |last2=Alexander |first2=R. A. |last3=Chapman |first3=J. M. |last4=Fincher |first4=S. S. |last5=Hopkins |first5=R. C. |last6=Philips |first6=A. D. |last7=Polsgrove |first7=T. T. |last8=Litchford |first8=R. J. |last9=Patton |first9=B. W. |last10=Statham |first10=G. |last11=White |first11=P. S. |last12=Thio |first12=Y. C. F. |publisher=[[Marshall Space Flight Center]], ERC Inc., [[United States Department of Energy]] |url=https://ntrs.nasa.gov/api/citations/20040010797/downloads/20040010797.pdf |archive-url=https://web.archive.org/web/20230831124233/https://ntrs.nasa.gov/api/citations/20040010797/downloads/20040010797.pdf |archive-date=31 August 2023 |url-status=live |date=November 2003 |id=NASA/TP—2003–212691 }}</ref> This design would thus be considerably smaller and more fuel efficient due to its higher exhaust velocity (700&nbsp;km/s) than the previously mentioned "Discovery II", "VISTA" concepts.

=== Inertial electrostatic ===
Another popular confinement concept for fusion rockets is [[inertial electrostatic confinement]] (IEC), such as in the [[Farnsworth-Hirsch Fusor]] or the [[Polywell]] variation under development by Energy-Matter Conversion Corporation (EMC2). The [[University of Illinois]] has defined a 500-tonne "Fusion Ship II" concept capable of delivering a 100,000&nbsp;kg crewed payload to Jupiter's moon Europa in 210 days. Fusion Ship II utilizes [[ion rocket]] thrusters (343&nbsp;km/s exhaust velocity) powered by ten D-He3 IEC fusion reactors. The concept would need 300 tonnes of [[argon]] propellant for a 1-year round trip to the Jupiter system.<ref name="fusionship2">{{cite web |title=Fusion Ship II - A Fast Manned Interplanetary Space Vehicle Using Inertial Electrostatic Fusion |last1=Webber |first1=J. |last2=Burton |first2=R. L. |last3=Momota |first3=H. |last4=Richardson |first4=N. |last5=Shaban |first5=Y. |last6=Miley |first6=G. H. |url=http://fti.neep.wisc.edu/iecworkshop/PDF/TECHNICAL_TALKS/webber.pdf |archive-url=https://web.archive.org/web/20120617045338/http://fti.neep.wisc.edu/iecworkshop/PDF/TECHNICAL_TALKS/webber.pdf |archive-date=17 June 2012 |url-status=dead |year=2003 |publisher=[[University of Illinois]], U-C, Department of Nuclear, Plasma and Radiological Engineering }}</ref> [[Robert Bussard]] published a series of technical articles discussing its application to spaceflight throughout the 1990s. His work was popularised by an article in the [[Analog Science Fiction and Fact]] publication, where Tom Ligon described how the fusor would make for a highly effective fusion rocket.<ref name="analog-12-1998">{{cite magazine |url=http://torsatron.tripod.com/fusor/fusor.html |title=The World's Simplest Fusion Reactor: And How to Make It Work |magazine=Analog Science Fiction & Fact |last=Ligon |first=Tom |date=December 1998 |volume=118 |issue=12 |location=New York |url-status=dead |archive-url=https://web.archive.org/web/20060615044323/http://torsatron.tripod.com/fusor/fusor.html |archive-date=2006-06-15 }}</ref>

=== Antimatter ===
A still more speculative concept is [[antimatter-catalyzed nuclear pulse propulsion]], which would use [[antimatter]] to catalyze a fission and fusion reaction, allowing much smaller fusion explosions to be created. During the 1990s an abortive design effort was conducted at Penn State University under the name [[AIMStar]].<ref name="antimatterpennn">{{cite journal |journal=[[Acta Astronautica]] |volume=44 |issue=2–4 |doi=10.1016/S0094-5765(99)00046-6 |title=AIMStar: Antimatter Initiated Microfusion For Pre-cursor Interstellar Missions |url=http://www.engr.psu.edu/antimatter/Papers/AIMStar_99.pdf |last1=Lewis |first1=Raymond A. |last2=Meyer |first2=Kirby |last3=Smith |first3=Gerald A. |last4=Howe |first4=Steven D. |archive-url=https://web.archive.org/web/20140616201812/http://www.engr.psu.edu/antimatter/Papers/AIMStar_99.pdf |archive-date=June 16, 2014 |year=1999 |pages=183–186 |url-status=dead |publisher=[[Pennsylvania State University]] |bibcode=1999AcAau..44..183G }}</ref> The project would require more antimatter than can currently be produced. In addition, some technical hurdles need to be surpassed before it would be feasible.<ref name="antimatternasa">{{cite tech report |url=http://www.engr.psu.edu/antimatter/papers/nasa_anti.pdf |title=Antimatter Production for Near-term Propulsion Applications |year=1999 |access-date=2013-05-24 |url-status=dead |archive-url=https://web.archive.org/web/20070306065325/http://www.engr.psu.edu/antimatter/Papers/NASA_anti.pdf |archive-date=2007-03-06 |last1=Schmidt |first1=G. R. |last2=Gerrish |first2=H. P. |last3=Martin |first3=J. J. |last4=Smith |first4=G. A. |last5=Meyer |first5=K. J. |publisher=[[NASA]] & [[Pennsylvania State University]] }}</ref>

==Development projects==
*{{annotated link|Direct Fusion Drive}}
*[[Nuclear pulse propulsion#MSNW Magneto-Inertial Fusion Driven Rocket|MSNW Magneto-Inertial Fusion Driven Rocket]]

==See also==
*[[Helium-3]]
*[[Nuclear propulsion]]
*[[Rocket propulsion technologies (disambiguation)]]

==References==
{{Reflist|30em}}

==External links==
* {{cite news |last1=Graham-Rowe |first1=Duncan |title=Nuclear fusion could power NASA spacecraft |date=23 January 2003 |magazine=[[New Scientist]] |url=https://www.newscientist.com/article/dn3294-nuclear-fusion-could-power-nasa-spacecraft/ |archive-url=https://web.archive.org/web/20230831135331/https://www.newscientist.com/article/dn3294-nuclear-fusion-could-power-nasa-spacecraft/ |archive-date=31 August 2023 |url-status=live |access-date=15 August 2021 }}
* {{cite tech report |title=The Case and Development Path for Fusion Propulsion |year=2012 |archive-url=https://web.archive.org/web/20121114180625/https://thespaceshow.files.wordpress.com/2012/10/cassibry-et-al-case-for-fusion-0728121.pdf |archive-date=14 November 2012 |url-status=dead  |url=https://thespaceshow.files.wordpress.com/2012/10/cassibry-et-al-case-for-fusion-0728121.pdf |last1=Cassibry |first1=Jason |last2=Cortez |first2=Ross |last3=Stanic |first3=Milos |last4=Seidler |first4=William |last5=Adams |first5=Rob |last6=Statham |first6=Geoff |last7=Fabisinski |first7=Leo |publisher=[[University of Alabama]], [[Boeing]], [[Marshall Space Flight Center]], ERC Inc., ISS Inc. }}
* {{cite web |title=The Fusion Driven Rocket: Nuclear Propulsion through Direct Conversion of Fusion Energy |date=25 March 2019 |access-date=15 August 2021 |publisher=[[NASA]] |last1=Slough |first1=John |editor-last1=Hall |editor-first1=Loura |url=https://www.nasa.gov/directorates/spacetech/niac/2012_Phase_II_fusion_driven_rocket/ |archive-url=https://web.archive.org/web/20230601185850/https://www.nasa.gov/directorates/spacetech/niac/2012_Phase_II_fusion_driven_rocket/ |archive-date=1 June 2023 |url-status=live }}
{{spacecraft propulsion}}
{{Nuclear propulsion}}
{{emerging technologies|topics=yes|space=yes}}

{{DEFAULTSORT:Fusion Rocket}}
[[Category:Rocket propulsion]]
[[Category:Nuclear spacecraft propulsion]]
[[Category:Fusion power|Rocket]]
[[Category:Hypothetical technology]]