Editing Nuclear pulse propulsion (section)

===Pulsed fission-fusion propulsion===
Pulsed fission-fusion (PuFF) propulsion is reliant on principles similar to magneto-inertial fusion. It aims to solve the problem of the extreme stress induced on containment by an Orion-like motor by ejecting the plasma obtained from small fuel pellets that undergo autocatalytic fission and fusion reactions initiated by a [[Z-pinch]]. It is a theoretical propulsion system researched through the NIAC Program by the [[University of Alabama in Huntsville]].<ref>{{cite web |last=Adams |first=Robert, B. |date=2013 |title=Pulsed Fission-Fusion (PuFF) – Phase I Report |website=nasa.gov |url=https://www.nasa.gov/sites/default/files/files/Adams_2013_PhI_PuFF_inProgress.pdf |access-date=7 February 2021 |url-status=live |archive-url=https://web.archive.org/web/20220414171413/https://www.nasa.gov/sites/default/files/files/Adams_2013_PhI_PuFF_inProgress.pdf |archive-date=14 April 2022}}</ref> It is in essence a fusion rocket that uses a Z-pinch configuration, but coupled with a fission reaction to boost the fusion process.

A PuFF fuel pellet, around 1&nbsp;cm in diameter,<ref>{{cite web |last=Adams |first=Robert, B. |title=The Pulsed Fission-Fusion (PuFF) Concept for Deep Space Exploration and Terrestrial Power Generation |website=nasa.gov |url=https://www.nasa.gov/sites/default/files/atoms/files/the_pulsed_fission_-_fusion_puff_concept_for_deep_space_exploration_and_terrestrial_power.pdf |url-status=live |archive-url=https://web.archive.org/web/20220414171503/https://www.nasa.gov/sites/default/files/atoms/files/the_pulsed_fission_-_fusion_puff_concept_for_deep_space_exploration_and_terrestrial_power.pdf |archive-date=14 April 2022}}</ref> consists of two components: A deuterium-tritium (D-T) cylinder of plasma, called the ''target'', which undergoes fusion, and a surrounding [[U-235]] sheath that undergoes fission enveloped by a lithium liner. Liquid lithium, serving as a moderator, fills the space between the D-T cylinder and the uranium sheath. Current is run through the liquid lithium, a [[Lorentz force]] is generated which then compresses the D-T plasma by a factor of 10 in what is known as a Z-pinch. The compressed plasma reaches criticality and undergoes fusion reactions. However, the fusion energy gain (''Q'') of these reactions is far below breakeven (''Q'' < 1), meaning that the reaction consumes more energy than it produces.

In a PuFF design, the fast neutrons released by the initial fusion reaction induce fission in the U-235 sheath. The resultant heat causes the sheath to expand, increasing its implosion velocity onto the D-T core and compressing it further, releasing more fast neutrons. Those again amplify the fission rate in the sheath, rendering the process autocatalytic. It is hoped that this results in a complete burn up of both the fission and fusion fuels, making PuFF more efficient than other nuclear pulse concepts.<ref>{{cite journal |last=Winterberg |first=Friedwart |date=2000 |title=Autocatalytic fission–fusion microexplosions for nuclear pulse propulsion |journal=Acta Astronautica |volume=47 |issue=12 |pages=879–883 |bibcode=2000AcAau..47..879W |via=Elsevier Science Direct |doi=10.1016/S0094-5765(00)00136-3}}</ref><ref>{{cite journal |last=Adams |first=Robert, B. |date=2014 |title=Developing the Pulsed Fission-Fusion (PuFF) Engine |journal=Propulsion and Energy Forum}}</ref> Much like in a magneto-inertial fusion rocket, the performance of the engine is dependent on the degree to which the fusion gain of the D-T target is increased.

One "pulse" consist of the injection of a fuel pellet into the combustion chamber, its consumption through a series of fission-fusion reactions, and finally the ejection of the released plasma through a magnetic nozzle, thus generating thrust. A single pulse is expected to take only a fraction of a second to complete.