The photon drive was first dreamed up in 1935 by German space pioneer Eugen Saenger, and has been seen in various science fiction stories since.
The photon drive as currently envisioned uses an advanced, concave gamma ray mirror that reflects the intense and highly energetic gamma rays created by 1:1 matter-antimatter annihilation. This gamma ray mirror would have to reflect nearly 100% on the incoming energy, and do so without significant degradation in the reflective surface. The matter-antimatter reaction would take place directly on the focal point of the concave mirror on the aft end of the spacecraft, which would act like a pusher plate similar to the ORION nuclear pulse drive scheme. Because the reaction takes place at the mirror’s focal point, all the light hitting it from the annihilation reaction is reflected in the same direction.
Exact statistics on a photon drive’s thrust capabilities or specific impulse are unavailable, probably because no one has ever done a serious theoretical analysis of the idea. However, it is reasonable to assume its capabilities would be similar to that of interstellar lightsails, except that the photon drive ship in essence carries its own light source with it, making it far more compact, efficient, and maneuverable. Also, as gamma rays are significantly more energetic than visible light, the photon drive would probably be capable of greater thrust than a lightsail, maybe capable of sustaining significant fractions of standard gravity (.1g or so) as opposed to a lightsail’s projected 0.0007 g. Also like an interstellar lightsail, it would be capable of eventually achieving significant fractions of lightspeed, perhaps 50% C or more.
Matter/antimatter annihilations produce a large percentage of gamma rays as a byproduct. In conventional antimatter rockets, these gamma rays are ignored, treated primarily as a hazardous waste product of the reaction. Adding a gamma ray mirror to the drive would increase the amount of usable energy from the reaction by as much as 40%, greatly improving its performance and power.
http://spaceboy.nasda.go.jp/note/rocket/e/roc15b_e.htmlhttp://www.orionsarm.com/eg/p/Ph.html http://www.chrissdomain.com/ChrissCrazyIdeas/Ideas/PhotonRocket/photon_rocket.htm http://www.geocities.com/womplex_oo1/WasteHeatPropulsion.pdf
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