The first Solar Impulse airplane, HB-SIA, has demonstrated repeatedly that it can stay up all day and all night. The idea of perpetual flight has enticed designers for years, but the idea of a perpetual pilot has not – until the space age. Charles Lindbergh had a restless night before his May 20, 1927 takeoff for Europe and spent much of the 33-1/2 hour flight battling his nearly overwhelming need for sleep. A solar-powered flight will be considerably slower, and thus longer in duration, than Lindbergh’s epic voyage, however. With planned flights for HB-SIB, the second Solar Impulse craft, anticipated to span continents and oceans, the need for maintaining pilot health and alertness becomes imperative. As the team explains, “Over the several years Solar Impulse has proved that is its possible to fly with unlimited endurance. But as we know, Solar Impulse is more than a technical challenge. It is also about pushing human limits to new levels. “The Transatlantic …