Photo: Credit: Jean Revillard / Solar Impulse 2 via Getty Images

The experimental aircraft that became the first solar-powered plane to fly around the world has crashed into the Gulf of Mexico during an unmanned test flight, ending a major chapter in clean-energy aviation history.

Solar Impulse 2 went down May 4 near the Mississippi coast after reportedly losing power shortly after takeoff from Stennis International Airport. The aircraft was being operated by U.S.-Spanish company Skydweller Aero, which had converted the aircraft into an autonomous platform for long-endurance flights and surveillance testing. No injuries or fatalities were reported because no crew members were onboard.

The aircraft gained worldwide attention in 2016 when Swiss aviators Bertrand Piccard and André Borschberg completed the first round-the-world flight powered entirely by solar energy. The journey took more than a year and included multiple stops across Asia, North America, Europe and the Middle East.

Solar Impulse 2 was designed mainly as a technology demonstration project rather than a commercial aircraft.

The plane had a wingspan wider than a Boeing 747 but weighed only about as much as a large SUV because of its lightweight carbon-fibre construction. More than 17,000 solar cells built into the wings powered four electric motors and charged onboard batteries for overnight flying.

Following its global flight, the aircraft was sold in 2019 to Skydweller Aero. The company adapted the plane for autonomous operations and research into aircraft capable of remaining airborne for extended periods without fuel.

Investigators with the U.S. National Transportation Safety Board are continuing to examine the cause of the crash. Preliminary reports indicate the aircraft lost power before it struck the water.