Last year, two Swiss pilots became the first to fly across the United States in a featherweight plane using the power of the sun.

Now they are back with a more ambitious plan, to be announced today, to fly an even more advanced solar airplane around the world early next year, beginning and ending in oil-rich Abu Dhabi, United Arab Emirates.

The journey, like its cross-country predecessor, will not be continuous, more to meet the needs of the pilots than those of the plane, which, with an elaborate combination of solar cells and lithium batteries, can fly day and night.

In the earlier trip, the men flew roughly 24 hours before stopping. But this time the pilots — who will trade off the roughly dozen legs of the trip — must fly for up to five days and nights at a time because of the ocean crossings.

“We trained in the simulator for longer times, for three or four days, but, of course, we never flew — that’s going to be the first time,” said André Borschberg, one of the pilots. “You need an airplane which is reliable — you cannot do the maintenance in the flight.”

The men’s mission has drawn support from dozens of entrepreneurs and companies, including Mountain High Equipment & Supply of Redmond, which designed an oxygen system for the cross-U.S. flight last year, according to previous reports in The Bulletin.

It has also become an unlikely incubator for a variety of technologies, including a thin insulation that can allow refrigerators to have more internal space and a product developed with NASA that makes urine drinkable. The pilots are also developing a way to produce oxygen with solar energy, but that will not be available until later flights, Borschberg said.

But, the men said, one of the biggest commercial applications for the plane itself could be as a kind of satellite replacement, making it into a sustainable high-altitude, unmanned platform with cameras or communications equipment.

Designing the plane — a carbon-fiber frame, with more than 17,000 solar cells and a sheer wrapping — has been a relentless drive to reduce weight, Bertrand Piccard, the other pilot, said. The cockpit fits only one, so both men have developed techniques using yoga, meditation and self-hypnosis to rest or remain alert as necessary — including sleeping for no more than 20 minutes at a time 10 or so times a day. The method worked so well that Borschberg even tried it on vacation, he said.

Still, the new model plane has more legroom and a reclining seat to make the journey more comfortable. The men anticipate about 25 days of flying over a period of four to five months, stopping in Asia, the United States and Southern Europe or North Africa before returning to the United Arab Emirates.

The tour was the brainchild of Piccard, a psychiatrist who grew up in an exploration-oriented family and was part of the team that was first to circumnavigate the globe nonstop in a balloon. He became enamored of the idea of flying without fuel when a propane shortage nearly ended the balloon ride in 1999. He met Borschberg, an engineer and entrepreneur who had been a jet fighter pilot in the Swiss air force, after Piccard presented his idea to the Swiss Institute of Technology, which put Borschberg in charge of studying the project.

Sultan Ahmed al-Jaber, minister of state of the United Arab Emirates and the chief executive of renewable energy company Masdar, said the collaboration between the mission and his country was natural, given its investments in renewable energy and clean technologies.

“It’s a country that fits with the message we have,” Piccard said. “It’s an oil-producing country that invests a lot for renewable energy knowing that oil will not be forever. We don’t fight against oil — we just show that we can diversify and be more energy-efficient.”

Borschberg added that oil should be left to producing new materials, saying, “It’s a fabulous molecule.”