Yesterday, the team that produced the first solar-powered aircraft that could fly around the clock unveiled its successor, Solar impulse 2, a craft that it hopes will be able to fly around the world. The airplane is a large collection of impressive feats of engineering: it's large enough to have a wingspan similar to a 747's, yet it weighs just a bit more than the average automobile (2,300 kg or 5,000 lb).

The Solar Impulse team is headed by Bertrand Piccard, the first man to take a balloon around the globe, and André Borschberg, an engineer and entrepreneur. The two were both on hand to introduce the new plane and discuss what's involved with their round-the-world flight, scheduled for next year. Large portions of the flight will be over land, which means that the aircraft can potentially land whenever it's convenient, allowing the two pilots to exchange roles and restock the cabin.

But the plane will also have to cross the Atlantic and Pacific, which will take an estimated five days, given that Solar Impulse 2's maximum speed is only 140 km/hour (about 85 mph), and it will spend a considerable amount of time flying more slowly.

The flight will require a carefully choreographed flight pattern. While under full power during the day, the plane will charge run its four 17.5 horsepower engines at full speed and gain altitude, charging batteries all the way. (It can store 165 kilowatt-hours in batteries that are tucked in behind the engines.) At night, the engines will run off batteries at a much slower speed, and Solar Impulse 2 will gradually glide down closer to sea level before restarting a climb the next day.

The nighttime power conservation is strict enough that the craft's average output will be just 15 horsepower over a 24-hour period. Fortunately, that power will be put into motors that are 97 percent efficient, so little of it will be wasted.

Having a pilot along for this yo-yo ride across the ocean means that the cramped cabin of the original Solar Impulse needed a major redesign. Borschberg joked that "We went from a bad economy class on the first plane to a good business class seat." The new seat will be able to be reconfigured so that it also serves as a toilet and folds flat into a bed. Computer monitors will keep track of the pilot's health at all times and wake them if there's any sign of trouble with the aircraft. Both Piccard and Borschberg are training in meditation and self-hypnosis techniques that will let them stay focused despite the potential monotony.

Because it needs to climb to over 7 km (almost 23,000 feet) by nightfall, an oxygen supply will be stashed in the cabin area. And just in case, the cabin will also include a parachute and a raft. "We didn't want to take swimming lessons," Borschberg said.

The new aircraft's front is much larger than its predecessor's to fit all the additional hardware. The body of the plane is also broader in order to accommodate additional solar panels on top. Beyond that, however, the overall shape is quite similar. But there have been significant internal changes as well. The carbon fiber coating of the wing, for example, is now made of sheets that weigh less than an equivalent area of printer paper.

The changes mean that Solar Impulse 2 will be more fragile on the ground and tougher to handle in turbulent conditions. The net result is that the most risky part of the round-the-world effort probably won't be the flying, but the landing.

Test flights of the new machine should start in a few weeks, with the global flight planned for next March.