I think they are referring to this passage in wikipedia? Kinda a stretch... https://en.wikipedia.org/wiki/Nuclear_photonic_rocket#Power_sources https://en.wiki

I think they are referring to this passage in wikipedia? Kinda a stretch... https://en.wikipedia.org/wiki/Nuclear_photonic_rocket#Power_sources https://en.wikipedia.org/wiki/Nuclear_photonic_rocket#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."