Back in June, the Solar Impulse became the first solar-powered aircraft to achieve intercontinental flight, when it flew from Madrid to Morroco. That flight was part of a larger 6,000-kilometer (3,728-mile) journey which started on May 24th, and ends this Tuesday when the aircraft returns to its starting point of Payerne, Switzerland.

Known as the 2012 Crossing Frontiers mission, the solar-powered odyssey has been broken into eight legs consisting of about 800 kilometers (497 miles) each. The plane visited four countries, and is currently in Toulouse, France. For the entire trip, its four 10-hp motors have been powered only by energy gathered through its 12,000 wing-top photovoltaic panels, and stored in its 400 kg (882 lb) of lithium batteries

The plane is scheduled to take off from the Toulouse-Francazal airport at 5:00am UTC (Coordinated Universal Time) on Tuesday, piloted by Bertrand Piccard. It will proceed south over the Massif Central mountains, ending up at the Franco-Swiss border at about 3:00pm. It will subsequently cross the Jura mountains in the Alps, then go into a holding pattern until the thermal updrafts have calmed down enough to allow for a safe landing at Payerne airfield. That landing is expected to occur sometime after 6:00pm.

The entire flight will be streamed live on the Solar Impulse website. Observers along the route should be able to get a fairly good look at the aircraft, as it will be flying at an altitude of only 3,600 meters (11,811 feet).

Although Solar Impulse has already broken the world record for the farthest distance covered by a solar-powered aircraft, bigger things are planned – Crossing Frontiers is apparently a “dress rehearsal” for a planned flight around the world.