Fifty-eight years ago, almost to the day, President Kennedy declared what was, at the time, a bold national goal: To send a man to the moon within a decade, and “return him safely to Earth.” The greatest challenge of Apollo was not the former, but the latter.

There are too many problems with Michael Griffin and Scott Pace’s op-ed on propellant depots [“Propellant Depots Instead of Heavy Lift?” Oct. 31, page 17] to address them all in a single letter to the editor.