The Solar Impulse 2 plane took off Monday from Nagoya, ending a frustrating four-week hiatus during its unprecedented bid to circle the world without fuel.

Flight engineers spotted a possible cloudless stretch over the Pacific and in a pre-dawn scramble got the solar-powered plane airborne from Nagoya Airport, where it has been grounded since June 1.

"We are very, very happy," project spokeswoman Elke Neumann said by phone from the airport. "We have now packed the hangar up. We are just doing the last logistical operations."