Photon engine

Photon engine has replaced the normal spaceship engines in human spaceships by the end of 20th and the beginning of 21st century. It utilizes energy of thermonuclear fusion of hydrogen-tritium plasma (the design also allows to use elementary matter-antimatter reactions) combined with s.c. absolute reflector, a material reflecting any (!) electromagnetic waves without loss, to create a propelling force capable of accelerating a spaceship up to relativistic sub-light speeds. See The Land of Crimson Clouds for more info.

Subspace jump has replaced the photon engine in the 21st century.