Editing Laser propulsion (section)

==History==
The basic concepts underlying a photon-propelled "sail" propulsion system were developed by [[Eugene Sanger]] and the Hungarian physicist György Marx.  Propulsion concepts using laser-energized rockets were developed in the 1970s by [[Arthur Kantrowitz]]<ref>{{Cite journal |last=Kantrowitz |first=Arthur |date=May 1972 |title=Propulsion to Orbit by Ground Based Lasers |journal=Astronautics and Aeronautics}}</ref> and Wolfgang Moekel,<ref>{{Cite web|url=http://researchspace.csir.co.za/dspace/bitstream/10204/1014/1/Michaelis1_2006.pdf|title=Michaelis, MM and Forbes, A. 2006. Laser propulsion: a review. ''South African Journal of Science'', '''102'''(7/8), 289-295}}</ref> with a variant using laser ablation pioneered by Leik Myrabo.<ref name="Myrabo 1976">Myrabo, L.N. 1976."[http://ayuba.fr/pdf/myrabo1976.pdf MHD propulsion by absorption of laser radiation]," ''Journal of Spacecraft and Rockets", Vol. 13, 8, pp. 466–472. doi 10.2514/3.27919</ref> An exposition of Kantrowitz's laser propulsion ideas was published in 1988.<ref>A. Kantrowitz, in  [[International Conference of Laser Applications|''Proceedings of the International Conference on Lasers '87'']], [[F. J. Duarte]], Ed. (STS Press, Mc Lean, VA, 1988).</ref><ref>{{Cite journal |last=Kantrowitz |first=Arthur |date=1989-07-01 |title=Laser propulsion to earth orbit. Has its time come? |url=https://ntrs.nasa.gov/citations/19900000827 |journal=NASA. Langley Research Center, Second Beamed Space-Power Workshop |language=en}}</ref>

Laser propulsion systems may transfer [[momentum]] to a spacecraft in two different ways. The first way uses [[photon]] [[radiation pressure]] to drive momentum transfer and is the principle behind [[solar sail]]s and laser sails. The second method uses the laser to help expel mass from the spacecraft as in a conventional rocket. Thus, the first uses the laser for both energy and reaction mass, while the second uses the laser for energy, but carries reaction mass.  Thus, the second is fundamentally limited in final spacecraft velocities by the [[rocket equation]].