Editing Interplanetary spaceflight (section)

====Electric propulsion====
[[File:Ion Engine Test Firing - GPN-2000-000482.jpg|thumb|A xenon ion engine being tested at [[NASA|NASA's]] [[Jet Propulsion Laboratory]], 1999]]
[[Spacecraft electric propulsion|Electric propulsion]] systems use an external source such as a [[nuclear reactor]] or [[solar cell]]s to generate [[electricity]], which is then used to accelerate a chemically inert propellant to speeds far higher than achieved in a chemical rocket. Such drives produce feeble thrust, and are therefore unsuitable for quick maneuvers or for launching from the surface of a planet. But they are so economical in their use of
[[working mass]] that they can keep firing continuously for days or weeks, while chemical rockets use up reaction mass so quickly that they can only fire for seconds or minutes. Even a trip to the Moon is long enough for an electric propulsion system to outrun a chemical rocket – the [[Apollo program|Apollo]] missions took 3 days in each direction.

NASA's [[Deep Space 1|Deep Space One]] was a very successful test of a prototype [[ion drive]], which fired for a total of 678 days and enabled the probe to run down Comet Borrelly, a feat which would have been impossible for a chemical rocket. ''[[Dawn (spacecraft)|Dawn]]'', the first NASA operational (i.e., non-technology demonstration) mission to use an ion drive for its primary propulsion, successfully orbited the large [[main-belt asteroid]]s [[1 Ceres]] and [[4 Vesta]].  A more ambitious, nuclear-powered version was intended for a Jupiter mission without human crew, the [[Jupiter Icy Moons Orbiter]] (JIMO), originally planned for launch sometime in the next decade. Due to a shift in priorities at NASA that favored human crewed space missions, the project lost funding in 2005.  A similar mission is currently under discussion as the US component of a joint NASA/ESA program for the exploration of [[Europa (moon)|Europa]] and [[Ganymede (moon)|Ganymede]].

A NASA multi-center Technology Applications Assessment Team led from the [[Johnson Spaceflight Center]], has as of January 2011 described "Nautilus-X", a concept study for a multi-mission space exploration vehicle useful for missions beyond [[low Earth orbit]] (LEO), of up to 24 months duration for a crew of up to six.<ref>[https://archive.today/20120918055537/http://www.spaceref.com/news/viewsr.html?pid=36068 Nautilus-X] – NASA's Multi-mission Space Exploration Vehicle Concept</ref><ref>{{cite web|url=https://nss.org/wp-content/uploads/NautilusX-Multi-Mission-Space-Exploration-Vehicle.pdf |title=NAUTILUS-X: NASA/JSC Multi-Mission Space Exploration Vehicle|date=January 26, 2011|website=National Space Society|access-date=15 March 2025}}</ref> Although [[Nautilus-X]] is adaptable to a variety of mission-specific propulsion units of various low-thrust, high [[specific impulse]] (I<sub>sp</sub>) designs, nuclear ion-electric drive is shown for illustrative purposes.  It is intended for integration and checkout at the [[International Space Station]] (ISS), and would be suitable for deep-space missions from the ISS to and beyond the Moon, including [[Lagrangian point|Earth/Moon L1]], [[Lagrangian point|Sun/Earth L2]], [[Near-Earth object|near-Earth asteroidal]], and Mars orbital destinations.  It incorporates a reduced-g centrifuge providing artificial gravity for crew health to ameliorate the effects of long-term 0g exposure, and the capability to mitigate the space radiation environment.<ref>[http://moonandback.com/2011/02/21/nasa-team-produces-nautilus-x-a-fascinating-spacecraft/  "NASA Team Produces NAUTILUS-X, A Fascinating Spacecraft"] {{Webarchive|url=https://web.archive.org/web/20130526114516/http://moonandback.com/2011/02/21/nasa-team-produces-nautilus-x-a-fascinating-spacecraft/ |date=2013-05-26 }} February 21, 2011</ref>