The huge, sun-powered plane, which smashed the longest solo record last summer from Japan to Hawaii, took off from Oahu's Kalaeloa Airport on Friday for an approximately 90-minute maintenance flight, according to the mission's blog
At an altitude of about 8,000 feet over the Pacific, test pilot Markus Scherdel performed maintenance checks and verified the plane's newly installed technology — including a new battery cooling system.
The new systems "performed superbly," according to the blog.
Pilot Andre Borschberg monitored the aircraft from Hawaii, the blog said, while fellow pilot Bertrand Piccard followed it from "the other side of the world."
Piccard "confessed It was a true relief" to see Si2 back in the sky, the blog said, "after the past months of uncertainty."
Last year, global excitement grew as the plane completed each segment of its journey from west to east starting last March in Abu Dhabi and continuing to Oman, India, to Myanmar, China, Japan and then to Hawaii.
Si2 is expected to take off from Hawaii on a flight path toward Phoenix, Arizona, resuming what organizers hope will be the first round-the-world journey by a solar-powered airplane.
The plane's wingspan is greater than a Boeing 747's, but it flies only about as fast as a car and weighs only about as much as a large SUV.