Andre Borschberg sounds remarkably bright and alert after spending more than 60 hours straight at the controls of the Solar Impulse flight simulator. Granted, he's been able to get some sleep, sometimes napping for a whole 20 minutes at a time.

Borschberg is approaching the end of a 72-hour stint in the sim, running through a series of tests and challenges to prepare for what lies ahead when he attempts to fly around the world in a solar airplane in 2014. It's been grueling, but not so bad.

"I feel quite well, better than what I expected," Borschberg said from the cockpit mockup in Switzerland.

The point of the prolonged testing is to determine how best to manage the pilot’s needs while circumnavigating the globe in a solar plane. It also will allow the team to evaluate and refine the cockpit design. Some of the tests are simple reaction-time experiments; others are emergency drills designed to prepare Borschberg for things like losing power during a landing. Borschberg says his piloting skills haven't degraded too badly with the loss of sleep.

"The quality stays very good," he says, "but certainly it's a bit lower than somebody who has slept eight hours."

Andre Borschberg sleeping in the Solar Impulse simulator. Apparently there was no king-size option. Photo: Solar Impulse/Jean Revillard

A larger cockpit has been a big help. Compared to the first Solar Impulse that first flew in 2009, the second aircraft offers a bit more room.

"This cockpit is slightly larger than the first one," Borschberg says. "We can do some [exercise] gymnastics, it helps to stimulate the muscles and the blood circulation. And I do some meditation to smooth how I use my energy."

Borschberg has been allowed to take several "micro-naps" of about 20 minutes. It's all part of the test. When the alarm goes off, there's no hitting the snooze button. The former Swiss Air Force pilot must immediately take control of the airplane and establish straight and level flight.

"We measure the reaction time, as soon as I'm awake I go and take control of the airplane," he says. "I have to grab it and provide an action. First control [the airplane], then figure out anything else. Reaction time from alarm to when I grab the controls is 2 to 4 seconds. It is very quick."

The biggest challenges of sleep deprivation have been critical decision making and of course landing the airplane. Borschberg says he finds he needs more decision making help from the crew as the simulation progresses. This was expected though, and he says it is not a problem.

The next-generation Solar Impulse, known as HB-SIB, will have a wingspan of more than 236 feet. It will not have a true autopilot. The airplane lacks sufficient power to maintain any type of predetermined flight altitude in the event of a strong downdraft, according to Borschberg, and it is so delicate that an autopilot could cause problems in unusual circumstances. Instead, Borschberg says, the airplane will have an electronic co-pilot of sorts capable of maintaining a directional heading and alerting the pilot to any problems with the performance of the airplane.

Borschberg and Solar Impulse co-founder Bertrand Piccard hope to attempt their around-the-world solar powered flight in 2014.