The solar-powered aeroplane, Solar Impulse, has completed a three-day flight over the Pacific Ocean

The solar-powered aeroplane, Solar Impulse, has completed a three-day flight over the Pacific Ocean

It flew over San Francisco’s Golden Gate Bridge on Saturday evening as it prepared to land in California

The plane took off from Hawaii on Thursday, where it underwent repairs for the past eight months after its batteries were damaged during the flight from Japan

"I crossed the bridge. I am officially in America," said pilot Bertrand Piccard as he flew above San Francisco Bay

Solar Impulse started the journey last March in Abu Dhabi. The trip has involved two different pilots flying separate legs

Piccard will land the plane later on Saturday evening at Moffett Airfield, located in Mountain View in Silicon Valley

Solar Impulse gets all its energy from the sun - through the 17,000 photovoltaic cells that cover the top surfaces of the craft

These power propellers during the day, but also charge batteries that the vehicle’s motors can then call on during the night

Starting in Abu Dhabi, UAE, in March, Solar Impulse crossed Oman, India, Myanmar, and China

That five-day, five-night crossing set a record for the longest ever non-stop solo aeroplane journey

But the vehicle’s batteries overheated during the trip, forcing the project to stop on the Pacific archipelago while repairs were conducted

A further 20m euros (16m pounds; 23m dollars) had to be raised from supporters during the winter to keep the project going for another year

Piccard shares flying duties with his business partner, Andre Borschberg

It was Borschberg who flew into Kalaeloa last July, and he will next take the controls on the next leg across the US mainland

The pair’s intention is to reach New York by the start of June, to begin preparations for an Atlantic crossing

Assuming this is completed successfully, it should then be a relatively straightforward run back to the "finish line" in Abu Dhabi

They first trialled a smaller plane, taking it on a trans-America crossing in 2013

The version of the vehicle they currently fly is considerably bigger

Because the prop-driven craft moves so slowly, mission legs can take several days and nights of continuous flight

This means Piccard and Borschberg - whoever is at the controls - have to stay alert for nearly all of the time they are airborne

They are permitted only catnaps of up to 20 minutes - in the same way a single-handed, round-the-world yachtsman would catch small periods of sleep

They also have to endure the physical discomfort of being confined in a cockpit that measures just 3.8 cubic metres in volume - not a lot bigger than a public telephone box

"Each flight you do brings new learning that you can use to improve the quality, reliability and performance of the aeroplane."