Note that he's not giving a figure for a chemical engine, but a fusion engine (sometimes termed a "torchship" due to the absurd power involved.) That would be

Note that he's not giving a figure for a chemical engine, but a fusion engine (sometimes termed a "torchship" due to the absurd power involved.) That would be strictly more efficient than VASIMR or similar. The figure would be even more ludicrous with a LOX/LH2 engine. (I did not check his math, however.)