Recent studies by R. W. Bussard have shown that charged nuclei of certain light element isotopes can be electrostatically compressed to sufficient density for nuclear fusions to occur. And the resulting fusion reactions involved such nuclei amid no neutrons and induced no radioactivity at all. Such "clean" fusion reactions can develop 4 to 8 times more engine thrust per fuel flow rate than chemical reactions with attractive engine thrust-to-weight ratios -- ratios in the 3 to 6 g range. This paper shows that such propulsion could enable a 2-to 5-fold improvement in the payload delivery efficiency of earth-to-orbit aerospace planes and the accomplishment of environmentally favorable hypersonic flight.