This week has already seen full-power tests of the engines
The prototype of a solar-powered plane destined for a record round-the-world journey has made its first trip across a runway.
On Thursday, the plane covered at least 2km at speeds of up to five knots on the landing strip in Switzerland.
This week saw the Solar Impulse plane outside its hangar for the first time, with tests of its motors and computer.
As wide as a jumbo jet but weighing just 1,500 kg, it will be piloted by Swiss adventurer Bertrand Piccard.
The plane's maiden flight is scheduled for February, and a final version will attempt to cross the Atlantic in 2012.
Thursday's "taxiing" test was carried out with a security trolley device under the cockpit to protect the craft in case the landing gears broke.
But Friday's test will be carried out without this device. The team will also try to double the speed to 10 knots.
A spokesperson for Solar Impulse said the first runway test went just as planned.
"It was just fantastic today. We are very excited about it," she told BBC News.
Today's activities are designed to give the test pilot a feel for how the plane moves on the ground.
If the tests are successful, the next step will be a short flight, or "flea hop" in about two weeks' time.
Solar Impulse chief executive Andre Borschberg told BBC News: "We'll take off at the beginning of the runway, fly a few metres above it - a little bit like the Wright brothers did in 1903 - and then land again, to see how it behaves at the beginning of the flight.
"If this is satisfactory, we will dismantle it and transport it [to Payerne air force base in western Switzerland] where we will do the real first flight of about two hours, in February."
But each step will be a careful one, Mr Borschberg stressed.
"This is truly a new design - an airplane the size of an Airbus and the weight of a mid-sized car - so we're not taking risks by not understanding something."