Solar-power plane heads into first night flight

PAYERNE, Switzerland, July 7 (Reuters) - A solar-powered aircraft designed to fly round the clock without traditional aviation fuel or polluting emissions headed on Wednesday into its crucial first night flight.

The plane, named Solar Impulse, took off for its first 24-hour test flight just after dawn from an air base near this central Swiss town and began climbing above nearby lakes and mountains toward a peak altitude of 8,500 meters (27,900 feet).

"It is going well. This is an incredible moment," said Bertrand Piccard, one of the two initiators of the project who himself carried out the first non-stop round-the-world flight in a hot-air balloon just 11 years ago.

At the controls of the wide-winged aircraft is engineer and former Swiss airforce pilot Andre Borschberg, co-founder of the Solar Impulse project with Piccard, who comes from a family of explorers and adventurers.

Borschberg will bring the carbon-fiber plane back down again to 1,500 meters (4,500 feet) before nightfall to glide on the stored power and land at Payerne in the morning. He told reporters by radio link that it was behaving perfectly.

The Solar Impulse, which has 12,000 solar cells built into its 64.3 meter (193-foot) wings is a prototype for an aircraft that its creators hope will carry out its first circumnavigation of the globe in 2012.

With a wingspan the same size as an Airbus A340 and, at 1,600 kg (3,500 lb), weighing only as much as a medium-sized car, the plane is powered by four electric motors and is designed to save energy from its solar cells in high-performance batteries.

A total of six years under development, it has already carried out two short but successful test flights, the last above Payerne in April when it spent 87 minutes in the air and reached a height of 1,200 meters (3,600 feet).

"The intention of this mission is to demonstrate the potential of renewable energy and clean technologies," says Piccard, whose father Jacques was a pioneer of under-water exploration in a bathyscaphe.

Claude Nicollier, a four-times astronaut and head of the craft's test flight program, said the revolutionary project excited him as much as the space flights in which he had taken part.

Solar Impulse is ultimately expected to attain an average flying speed of 70 km (44 miles) an hour and reach a maximum altitude of 8,500 meters (27,900 feet).

The project's budget is 100 million Swiss francs ($94 million), 80 million francs of which has been secured from sponsors, according to spokeswoman Rachel de Bros.

Belgian chemicals company Solvay, Swiss watchmaker Omega, part of the Swatch group, and German banking giant Deutsche Bank, are the three main sponsors.

Ecole Polytechnique Federale de Lausanne, a leading Swiss research university, is acting as scientific and technological adviser for the project.

(Reporting by Vincent Fribault; Writing by Robert Evans and Stephanie Nebehay; Editing by Jonathan Lynn and Paul Casciato)