Editing Interplanetary spaceflight (section)

====Fusion rockets====
[[Fusion rocket]]s,  powered by [[nuclear fusion]] reactions, would "burn" such light element fuels as deuterium, tritium, or <sup>3</sup>He.  Because fusion yields about 1% of the mass of the nuclear fuel as released energy, it is energetically more favorable than fission, which releases only about 0.1% of the fuel's mass-energy. However, either fission or fusion technologies can in principle achieve velocities far higher than needed for Solar System exploration, and fusion energy still awaits practical demonstration on Earth.

One proposal using a fusion rocket was [[Project Daedalus]].  Another fairly detailed vehicle system, designed and optimized for crewed Solar System exploration, "Discovery II",<ref>[https://web.archive.org/web/20110610051632/http://gltrs.grc.nasa.gov/reports/2005/TM-2005-213559.pdf PDF] C. R. Williams et al., 'Realizing "2001: A Space Odyssey": Piloted Spherical Torus Nuclear Fusion Propulsion', 2001, 52 pages, NASA Glenn Research Center</ref> based on the D<sup>3</sup>He reaction but using hydrogen as reaction mass, has been described by a team from NASA's [[Glenn Research Center]].  It achieves characteristic velocities of >300&nbsp;km/s with an acceleration of ~1.7•10<sup>−3</sup> ''g'', with a ship initial mass of ~1700 metric tons, and payload fraction above 10%.

Fusion rockets are considered to be a likely source of interplanetary transport for a [[planetary civilization]].<ref>{{Cite web|title=The Physics of Interstellar Travel : Official Website of Dr. Michio Kaku|url=https://mkaku.org/home/articles/the-physics-of-interstellar-travel/|access-date=2021-09-27|archive-date=2019-07-08|archive-url=https://web.archive.org/web/20190708003829/http://mkaku.org/home/?page_id=250|url-status=live}}</ref>