The organiser's ground crew rushed out on the tarmac of the Lambert-St Louis International Airport when the aircraft, which has four electric engines and a 63 meter wingspan, landed at 1157 IST.
"I feel (like) I was coming back from another world," said pilot Bertrand Piccard upon landing. "It's almost a shock" to return to normal life.
Despite the long hours "I didn't really feel the fatigue. I felt very fortunate to be up there."
Piccard departed the Dallas-Fort Worth airport in Texas aboard the Solar Impulse at 1436 IST yesterday on the third of a five-stop journey across the United States aimed at showcasing the potential of renewable energy technologies.
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St Louis was chosen as the Midwest stopover to pay homage to aviation pioneer Charles Lindbergh and his "Spirit of St Louis," the first plane to fly from New York to Paris non-stop.
The Texas-Missouri leg was Piccard's longest flight in the single-seat cockpit to date.
Powerful storms that hit the St Louis, Missouri area late Friday rendered Solar Impulse's airport hangar unusable, so organizers deployed what they described as a "revolutionary" inflatable mobile hangar.
The hangar consists of several heavy-duty inflatable segments that attach to each other and can be sealed off like a cocoon.
The mobile hangar is designed to be used at unplanned stops, or at airports unequipped to handle the large solar airplane, said Nils Ryer, head of ground crew operations, in a video on the SolarImpulse YouTube channel.
"It's not that easy to find such a huge hangar," Ryer said. It takes around five hours to set up the hangar, which is "light, easy to use and mainly safe," he said.
The first leg of Solar Impulse's US tour took place on May 3, when Piccard flew the aircraft from the San Francisco, California area to Phoenix.