Editing Fusion rocket (section)

== 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.}}