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{{More citations needed|date=November 2020}} |
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In a traditional '''nuclear photonic rocket''', an onboard [[nuclear reactor]] would generate such high temperatures that the [[blackbody radiation]] from the reactor would provide significant thrust. The disadvantage is that it takes much [[Power (physics)|power]] to generate a small amount of [[thrust]] this way, so [[acceleration]] is very low. The [[photon]] radiators would most likely be constructed using [[graphite]] or [[tungsten]]. Photonic rockets are technologically feasible, but rather impractical with current technology based on an onboard nuclear power source. |
In a traditional '''nuclear photonic rocket''', an onboard [[nuclear reactor]] would generate such high temperatures that the [[blackbody radiation]] from the reactor would provide significant thrust. The disadvantage is that it takes much [[Power (physics)|power]] to generate a small amount of [[thrust]] this way, so [[acceleration]] is very low. The [[photon]] radiators would most likely be constructed using [[graphite]] or [[tungsten]]. Photonic rockets are technologically feasible, but rather impractical with current technology based on an onboard nuclear power source. However, the recent development of Photonic Laser Thruster (PLT), the Beamed [[Laser propulsion|Laser Propulsion]] (BLP) with photon recycling, promises to overcome these issues by separating the nuclear power source and the spacecraft and by increasing the thrust to nuclear power ratio (specific thrust) by orders of magnitude.<ref>{{Cite journal|last=Bae|first=Young K.|date=2012|title=Prospective of Photon Propulsion for Interstellar Flight|journal=Physics Procedia|volume=38|pages=253–279|doi=10.1016/j.phpro.2012.08.026|issn=1875-3892|doi-access=free}}</ref> |
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==Energy requirements and comparisons== |
==Energy requirements and comparisons== |
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A laser could be used as a photon rocket engine, and would solve the reflection/collimation problem, but lasers are absolutely less efficient at converting energy into light than blackbody radiation is—though one should also note the benefits of lasers vs blackbody source, including unidirectional controllable beam and the mass and durability of the radiation source. The limitations posed by the [[Tsiolkovsky rocket equation|rocket equation]] can be overcome, as long as the reaction mass is not carried by the spacecraft. In the Beamed [[Laser Propulsion]] (BLP) concept, the photons are beamed from the photon source to the spacecraft as coherent light. [[Robert L. Forward]] pioneered interstellar propulsion concepts including photon propulsion and [[antimatter rocket]] propulsion. However, BLP is limited because of the extremely low thrust generation efficiency of photon reflection. One of the best ways to overcome the inherent inefficiency in producing thrust of the photon thruster by amplifying the momentum transfer of photons by recycling photons between two high reflectance mirrors. |
A laser could be used as a photon rocket engine, and would solve the reflection/collimation problem, but lasers are absolutely less efficient at converting energy into light than blackbody radiation is—though one should also note the benefits of lasers vs blackbody source, including unidirectional controllable beam and the mass and durability of the radiation source. The limitations posed by the [[Tsiolkovsky rocket equation|rocket equation]] can be overcome, as long as the reaction mass is not carried by the spacecraft. In the Beamed [[Laser Propulsion]] (BLP) concept, the photons are beamed from the photon source to the spacecraft as coherent light. [[Robert L. Forward]] pioneered interstellar propulsion concepts including photon propulsion and [[antimatter rocket]] propulsion. However, BLP is limited because of the extremely low thrust generation efficiency of photon reflection. One of the best ways to overcome the inherent inefficiency in producing thrust of the photon thruster by amplifying the momentum transfer of photons by recycling photons between two high reflectance mirrors. |
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Photon recycling multiple times over distances in a passive optical cavity, which consists of two high-reflectance mirrors only, expands laser beam diameter, thus forms a [[Fabry–Pérot interferometer|Fabry-Perrot optical resonance cavity]] in which any small movement of mirrors would destroy the resonance condition and null photonic thrust. Bae, however, discovered<ref>{{Cite journal|last=Bae|first=Young K.|date=2008|title=Photonic Laser Propulsion: Proof-of-Concept Demonstration|journal=Journal of Spacecraft and Rockets|language=en-US|volume=45|issue=1|pages=153–155|doi=10.2514/1.32284|issn=0022-4650}}</ref> that in an active optical cavity formed by two high-reflectance mirrors and a laser gain medium in between, similar to the typical laser cavity, photon recycling becomes insensitive to the movement of mirrors. Bae named<ref>{{Cite journal|last=Bae|first=Young|date=2007-09-18|title=Photonic Laser Propulsion (PLP): Photon Propulsion Using an Active Resonant Optical Cavity|journal=AIAA SPACE 2007 Conference & Exposition|language=en-US|location=Reston, Virginia|publisher=American Institute of Aeronautics and Astronautics|doi=10.2514/6.2007-6131|isbn=9781624100161}}</ref> the laser thruster based on the photon recycling in an active optical cavity Photonic Laser Thruster (PLT). In 2015 his team demonstrated the number of photon recycling up to 1,540 over a distance of a few meters and photonic thrusts up to 3.5 mN with the use of a 500 W laser system.<ref>{{Cite web|url=https://www.researchgate.net/publication/323390665|title=Demonstration of a mN-Class Photonic Laser Thruster|last=Bae|first=Young|date=2016|website=ResearchGate|publisher=AIAA SPACE 2007 Conference & Exposition. Reston, Virginia: American Institute of Aeronautics and Astronautics|language=en|access-date=2018-11-22}}</ref> In [https://www.youtube.com/watch?v=TzLEK8Zq7Pk the laboratory demonstration], a Cubesat (0.75 kg in weight) was propelled with PLT. PLT powered by a [[nuclear reactor]] or solar power can in principle overcome “the tyranny of the rocket equation,” which implies that the required onboard fuel mass exponentially increases as a function of the destination velocity for conventional thrusters, thus, if successfully developed, can expand human space endeavors beyond earth orbits.<ref>{{Cite web|url=https://www.researchgate.net/publication/298090729|title=The photonic railway|last=Bae|first=Young|date=2016|website=ResearchGate|publisher=Book Chapter 4 of New Frontiers in Space Propulsion, Nova Science Publisher|language=en|access-date=2018-11-22}}</ref> |
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==Power sources== |
==Power sources== |
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* [[Spacecraft propulsion]] |
* [[Spacecraft propulsion]] |
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* [[Radioisotope rocket]] |
* [[Radioisotope rocket]] |
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==References== |
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{{Reflist}} |
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==External links== |
==External links== |
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