Astronaut John Young is moving fast in his bulky space suit. A glance at the checklist on his left wrist shows he is on time for starting his next task.

This is great news because every minute on the lunar surface is rare and precious and he dearly wants to make each one count. But this is not easy because the array of tasks to be accomplished is unique to each mission. When training begins, no one knows the best way to put all the tasks together so they can be achieved in the time available. The best work sequence can only be discovered by an iterative process.

The first step is to call a meeting for all interested parties (and that's a whole lot of people) and together construct the "best guess" timeline. Next, we astronauts get into our suits and, using flight-like training equipment, follow the proposed timeline. We try to make it work. It never does. But afterward everyone is much smarter, and ready with improved ideas for the next simulation. And so it goes until everyone is satisfied that the timeline is the best task mix and sequence.

I talked with John Young about this painting and his feeling about the importance of staying on the timeline. He laughed, "Neil Armstrong's first thoughts might have been 'this is one step for a man but a giant leap for mankind', but I remember vividly that after climbing down the ladder and stepping on the lunar surface mine were 'we're 20 minutes behind now and we've got to catch up'."