payload, such a reactor could drive a photon rocket at nearly 10−5 m/s² (10−6g; see g-force). This could perhaps provide interplanetary spaceflight capability from Earth orbit. Nuclear fusion reactors could also be used, perhaps providing somewhat higher power. A design proposed in the 1950s by Eugen Sänger used positron-electron annihilation to produce gamma rays. Sänger was unable to solve the problem of how to reflect, and collimate the gamma rays created by positron-electron annihilation; however, by shielding the reactions (or other annihilations) and absorbing their energy, a similar blackbody propulsion system could be created. An antimatter-matter powered photon rocket would (disregarding the shielding) obtain the maximum c specific impulse; for this reason, an antimatter-matter annihilation powered photon rocket could potentially be used for interstellar spaceflight. Theoretically, other designs such as spacecraft using a Kugelblitz micro black hole could also be used for interstellar travel given the efficiency of black holes in converting matter into energy. See also Photon rocket Spacecraft propulsion Radioisotope rocket External links Application of nuclear photon engines for deep-space exploration by Andrey V. Gulevich, Eugeny A. Ivanov, Oleg F. Kukharchuk, Victor Ya. Poupko, and Anatoly V. Zrodnikov. AIP Conference Proceedings "Interstellar rendezvous missions employing fission propulsion systems," Lenard, R.X., and Lipiniski, R.J., in Proceedings of the Space Technology Applications Int'l Forum, 2000 On the conversion of infrared radiation from fission reactor-based photon engine into parallel beam, Gulevich, A. V.; Levchenko, V. E.; Loginov, N. I.; Kukharchuk, O. F.; Evtodiev, D. A.; Zrodnikov, A. V., in Proceedings of the Space Technology Applications Int'l Forum, 2002 Long-life space reactor for photon propulsion, Sawada, T.; Endo, H.; Netchaev, A., in Proceedings of the Space Technology Applications Int'l Forum, 2002 Nuclear spacecraft propulsion