The cockpit napping studies were done by NASA approximately 20 or 25 years ago. They showed really incontrovertible evidence that a 40-minute nap yields approximately 22 minutes of sleep and that this improves performance at top of descent.
There was an advisory circular all prepared. We were ready to launch, and then somebody raised the Jay Leno test, and I can only say that the issue was whether it would be made fun of on late-night TV, and that really killed it for the U.S. You saw similar things recently when the Secretary of Transportation said that we're not paying air traffic controllers to sleep.
Sleep is good. Sleep restores performance. Sleep sustains performance and, if you get seven or eight hours in every 24, you are going to be performing well.