He makes two mistakes. 1) Nuckear thermal rockets are proven to be more than twice as efficient as chemical rockets, and he doesn't consider them as options.

He makes two mistakes. 1) Nuckear thermal rockets are proven to be more than twice as efficient as chemical rockets, and he doesn't consider them as options. 2) Asteroids are far more resource rich, provide better living habitats and are immensely cheaper to reach than Mars. Even those in the belt are at least 10 Kilometres/Sec easier to reach than Mars. Other than those quibbles, a fantastic read.