http://apcnasa3ozl2j74htizuzba5b6nhugbg2qze2nrz43siunkct555fpid.onion
Near-term nuclear electric power systems promise a two order of magnitude increase. Matter-antimatter annihilation may be the ultimate source with a theoretical energy density 10 10 times that of conventional chemical propellants. Note, however, that there are significant technological challenges to achieving these theoretical or "ideal" energy density limits.