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updated 6/3/2013 6:49:34 PM ET 2013-06-03T22:49:34

A solar-powered airplane is poised to complete its longest flight yet — from Dallas to St. Louis — in spite of stormy weather that threatened this leg of the aircraft's historic cross-country journey.

The plane, called Solar Impulse, took off this morning (June 3) from Dallas-Fort Worth International Airport. It is scheduled to land at Lambert-St. Louis International Airport early Tuesday (June 4), at around 2:00 a.m. EDT (1:00 a.m. local time in Missouri), after roughly 21 hours in the air.

Today's flight is the third leg of Solar Impulse's unprecedented coast-to-coast expedition, which began at Moffett Airfield near San Francisco, Calif., on May 3. The plane landed in Phoenix the next day, and successfully completed its second leg, from Phoenix to Dallas, late last month. [ Images: Cross-Country Flight in a Solar-Powered Plane ]

Solar Impulse is the first aircraft capable of flying day and night without using a single drop of fuel. Instead, the plane relies solely on its solar panels and onboard batteries for power. During today's flight, the aircraft is expected to reach a cruising altitude of 27,000 feet (8,230 meters).

Each leg of Solar Impulse's flight is being streamed live online, and features commentary and information on the aircraft's position, altitude and speed. The live feed also provides camera views inside the cockpit and from Solar Impulse's mission control center in Switzerland.

En route to St. Louis

Solar Impulse founders Bertrand Piccard and André Borschberg will continue to alternate piloting the single-seater plane over the five legs of the cross-country journey, company officials said. Piccard was at the controls for today's takeoff from Dallas.

The multiple tornadoes that struck the St. Louis area Friday night (May 31), however, threatened to spoil the third leg of Solar Impulse's journey. The severe weekend storms damaged the airplane's reserved hangar at its destination in Lambert-St. Louis International Airport, company officials confirmed today.

Still, Piccard was able to take off as planned this morning, though fight controllers are paying close attention to weather conditions, and have said they will alter the plane's route if necessary.

"Postponing the flight is not an option, as the particularly difficult weather conditions in the region leave only very few flight possibilities between Dallas-Fort Worth and St. Louis, and it might be the only one this week," company officials said in a statement. "If Solar Impulse doesn't seize this opportunity, the chances of reaching [its] final destination of the Across America Mission as scheduled could be compromised."

Cross-country trip

Once Solar Impulse lands in St. Louis, an inflatable structure will be used to protect the aircraft from the elements.

"The Logistics and Mission teams are working hand-in-hand around the clock to face the challenge of bringing the airplane safely to St. Louis and ensuring its protection upon arrival," Solar Impulse officials said.

The stopover in St. Louis was chosen to honor the city's long and storied aviation history. Among the city's other contributions, St. Louis was home to Charles Lindbergh when he became the first to fly non-stop from New York to Paris in his single-seater plane, The Spirit of St. Louis.

Solar Impulse's wings span roughly the same length as a 747 jetliner, and the aircraft generates roughly the same amount of power as a small scooter, company officials have said. The coast-to-coast flight is designed to highlight the potential for "clean technologies" and the benefits of renewable energy.

Later this month, Solar Impulse will fly from St. Louis to Washington, D.C. The fifth and last leg of the trip will end in New York City in late June or early July, company officials said.

Follow Denise Chow on Twitter@denisechow. Follow LiveScience@livescience,Facebook &Google+. Original article on  LiveScience.com.

© 2012 LiveScience.com. All rights reserved.

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