Editing Interstellar travel (section)

==== Nuclear fission powered ====

===== Fission-electric =====
Nuclear-electric or plasma engines, operating for long periods at low thrust and powered by fission reactors, have the potential to reach speeds much greater than chemically powered vehicles or nuclear-thermal rockets. Such vehicles probably have the potential to power solar system exploration with reasonable trip times within the current century. Because of their low-thrust propulsion, they would be limited to off-planet, deep-space operation. [[Electrically powered spacecraft propulsion]] powered by a portable power-source, say a [[nuclear reactor]], producing only small accelerations, would take centuries to reach for example 15% of the [[velocity of light]], thus unsuitable for interstellar flight during a single human lifetime.<ref>{{citation|url=http://daedalus-zvezdolet.narod.ru/doceng/07eng.doc |title=Project Daedalus: The Propulsion System Part 1; Theoretical considerations and calculations. 2. REVIEW OF ADVANCED PROPULSION SYSTEMS |url-status=dead |archive-url=https://web.archive.org/web/20130628001133/http://daedalus-zvezdolet.narod.ru/doceng/07eng.doc |archive-date=2013-06-28 }}</ref>

===== Fission-fragment =====
[[Fission-fragment rocket]]s use [[nuclear fission]] to create high-speed jets of fission fragments, which are ejected at speeds of up to {{convert|12,000|km/s|mi/s|abbr=on}}. With fission, the energy output is approximately 0.1% of the total mass-energy of the reactor fuel and limits the effective exhaust velocity to about 5% of the velocity of light. For maximum velocity, the reaction mass should optimally consist of fission products, the "ash" of the primary energy source, so no extra reaction mass need be bookkept in the mass ratio.

===== Nuclear pulse =====
{{Main|Nuclear pulse propulsion}}
[[File:Modern Pulsed Fission Propulsion Concept.jpg|thumb|Modern Pulsed Fission Propulsion Concept]]Based on work in the late 1950s to the early 1960s, it has been technically possible to build spaceships with [[nuclear pulse propulsion]] engines, i.e. driven by a series of nuclear explosions. This propulsion system contains the prospect of very high [[specific impulse]] and high [[Power-to-weight ratio|specific power]].<ref>{{cite web
 | url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19760065935_1976065935.pdf
 | title=Nuclear Pulse Vehicle Study Condensed Summary Report (General Dynamics Corp.)
 | date=January 1964
 | author=[[General Dynamics]] Corp.
 | publisher=U.S. Department of Commerce National Technical Information Service
 | access-date=7 July 2017
 | archive-date=11 May 2010
 | archive-url=https://web.archive.org/web/20100511090218/https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19760065935_1976065935.pdf
 | url-status=live
 }}</ref>

[[Project Orion (nuclear propulsion)|Project Orion]] team member [[Freeman Dyson]] proposed in 1968 an interstellar spacecraft using nuclear pulse propulsion that used pure [[deuterium fusion]] detonations with a very high fuel-[[burnup]] fraction. He computed an exhaust velocity of 15,000&nbsp;km/s and a 100,000-tonne space vehicle able to achieve a 20,000&nbsp;km/s [[delta-v]] allowing a flight-time to [[Alpha Centauri]] of 130 years.<ref>{{cite journal
 |author=Freeman J. Dyson
 |date=October 1968
 |title=Interstellar Transport
 |journal=[[Physics Today]]
 |volume=21 |issue=10 |page=41
 |doi=10.1063/1.3034534
|bibcode=1968PhT....21j..41D}}</ref> Later studies indicate that the top cruise velocity that can theoretically be achieved by a Teller-Ulam thermonuclear unit powered Orion starship, assuming no fuel is saved for slowing back down, is about 8% to 10% of the speed of light (0.08-0.1c).<ref>Cosmos by Carl Sagan</ref> An atomic (fission) Orion can achieve perhaps 3%-5% of the speed of light. A nuclear pulse drive starship powered by fusion-antimatter catalyzed nuclear pulse propulsion units would be similarly in the 10% range and pure matter-antimatter annihilation rockets would be theoretically capable of obtaining a velocity between 50% and 80% of the speed of light. In each case saving fuel for slowing down halves the maximum speed. The concept of using a [[magnetic sail]] to decelerate the spacecraft as it approaches its destination has been discussed as an alternative to using propellant, this would allow the ship to travel near the maximum theoretical velocity.<ref>{{cite journal | title= Use of Mini-Mag Orion and superconducting coils for near-term interstellar transportation | author1= Lenard, Roger X. | author2= Andrews, Dana G. | journal= Acta Astronautica | date= June 2007 | volume= 61 | issue= 1–6 | url= http://www.space-nation.org/images/a/a1/Mini-Mag_Orion_and_superconducting_coils_for_near-term_interstellar_transportation_LenardAndrews.pdf | doi= 10.1016/j.actaastro.2007.01.052 | pages= 450–458 | bibcode= 2007AcAau..61..450L | access-date= 2013-11-24 | archive-date= 2014-06-17 | archive-url= https://web.archive.org/web/20140617053903/http://www.space-nation.org/images/a/a1/Mini-Mag_Orion_and_superconducting_coils_for_near-term_interstellar_transportation_LenardAndrews.pdf | url-status= dead }}</ref> Alternative designs utilizing similar principles include [[Project Longshot]], [[Project Daedalus]], and [[Mini-Mag Orion]]. The principle of external nuclear pulse propulsion to maximize survivable power has remained common among serious concepts for interstellar flight without external power beaming and for very high-performance interplanetary flight.

In the 1970s the Nuclear Pulse Propulsion concept further was refined by [[Project Daedalus]] by use of externally triggered [[inertial confinement fusion]], in this case producing fusion explosions via compressing fusion fuel pellets with high-powered electron beams. Since then, [[laser]]s, [[ion beam]]s, [[neutral particle beam]]s and hyper-kinetic projectiles have been suggested to produce nuclear pulses for propulsion purposes.<ref>{{cite book |author=Winterberg |first=Friedwardt |title=The Release of Thermonuclear Energy by Inertial Confinement |date=2010 |publisher=World Scientific |isbn=978-981-4295-91-8}}</ref>

A current impediment to the development of ''any'' nuclear-explosion-powered spacecraft is the [[Partial Test Ban Treaty|1963 Partial Test Ban Treaty]], which includes a prohibition on the detonation of any nuclear devices (even non-weapon based) in outer space. This treaty would, therefore, need to be renegotiated, although a project on the scale of an interstellar mission using currently foreseeable technology would probably require international cooperation on at least the scale of the [[International Space Station]].

Another issue to be considered, would be the [[g-force]]s imparted to a rapidly accelerated spacecraft, cargo, and passengers inside (see [[Inertia negation]]).