Skip says that they can get to the Moon without escape velocity, which is impossible. If they don't go fast enough, they end up in orbit.
When Skip and Harry discuss the projected plan to the rest of the crew, the question of fuel type is raised. Harry states that "According to Mel we can do it with less than a thousand gallons". One of his staff says "A thousand gallons? It took NASA over a hundred thousand gallons". In actuality, between all 3 stages of the Apollo 11 Saturn V, the rocket consumed over 966,650 gallons of fuel to launch.