The Solar Impulse solar plane landed in St. Louis early Tuesday, completing the third leg of a planned five-flight trek from San Francisco to New York.

After taking off Monday morning from Dallas/Fort Worth International Airport, the aircraft landed in St. Louis after a flight of 21 hours and 21 minutes, its longest flight to date, CNET reported.

After the landing the Swiss-built aircraft was moved to an inflatable hangar originally designed for a planned round-the-world flight, but brought into action after a storm caused heavy damage to the airport hangar originally reserved for Solar Impulse.

"We brought the inflatable hangar to the USA for testing purposes and in fact it allowed the mission to stay on schedule," Solar Impulse co-founder Andre Borschberg said in a statement. "This exercise is now a proof of concept: rather than taking the airplane to a hangar, we have taken the hangar to the airplane."

Borschberg and Solar Impulse co-founder Bertand Piccard have been alternating pilot duties on the cross-country trek.

The first leg, beginning May 3 and piloted by Piccard, started from NASA's Moffett Field in the San Francisco Bay Area and ended in Phoenix; a Phoenix-to-Dallas flight with Borschberg at the controls began May 22.

The long flight times of each leg meant Solar Impulse had to fly through the night; 12,000 solar cells built into the wing use sunlight to charge the batteries for night flight.

A fourth flight will see the plane land in Washington, D.C., this month, while the final leg will end at JFK Airport in New York in early July.