Solar Impulse has successfully completed its first international flight. After spending most of last week on standby waiting for favorable weather conditions, the Swiss solar powered aircraft made the run from Payerne to Brussels on Friday May 13 in a flight that lasted 12 hours 59 minutes. Hats-off to the Solar Impulse team!

Solar Impulse is an astonishing feat of engineering. It has a wingspan of over 200 feet (61 m) yet it weighs only 1600 kg (3,527 lb) and carries almost 12,000 solar cells which supply all of the energy required to keep it aloft.

The plane has actually flown for a longer duration than Friday's 12 hours 59 minute flight, setting a mark of more than 26 hours in an overnight flight last summer. The achievement of its first international flight is as much about the logistics of civil aviation as it is about performance. Solar Impulse is a slow moving aircraft – during the latest flight it flew at around 31 mph (50 km/h) – and this makes for some unique challenges when it comes to flight planning as Solar Impulse Air Traffic Control manager Niklaus Gerber explains on the Solar Impulse Blog:

"HB-SIA is an obstacle for civil and military aviation because it is not very mobile, and rather inflexible. It is slow (31 mph/50 km/h) and does not really show up on radar (you see it as a point that hardly moves). Now, alongside it, there are aircraft that are traveling at between 400 and 900 km/h. So the other aircraft are the ones that have to make adjustments to avoid it. But this scenario is theoretical because we have done everything to avoid it in planning the flight. Usually, the separation distance between aircraft is 300 meters (984 ft) vertically and 8 kilometers (5 miles) when flying at the same height. In the case of Solar Impulse, our margin of safety is much greater. And an aircraft that passes above it needs to be at least 900 meters (2,953 ft) higher, due to the turbulence it creates which descends for about 5 minutes at a rate of 150 meters (492 ft) per minute before dissipating."

Successfully negotiating these constraints in the flight from Switzerland to Belgium is therefore a big milestone in the build up towards the planned round-the-world journey.

A new future for aviation?

The project founded by Bertrand Piccard and André Borschberg (who was at the controls during the first international flight) is not geared towards producing a commercial product but instead aims to demonstrate just how much can be achieved with renewable technology. Even without the round the world trip that the team plans to undertake in 2013, it's arguable that the achievements of the past year which began with the aircraft's maiden flight in April 2010 have already gone a long way to proving the point. We could well be looking back on this period as a "Wright brothers moment" in the history of aviation.

In the flight from Payerne to Brussels, Solar Impulse covered around 390 miles (628 km) using no fuel. A rough calculation tells us that a Boeing 747 would have used around 2,000 gallons (7,570 L) of fuel to make the same trip.* Of course it's not much of a comparison when you consider that a commercial airliner can carry hundreds of people, but one can't help but think that the seeds of a new era are being sewn. Solar Impulse is powered by 4 x 10 horsepower electric engines, the Wright brothers had 12 horsepower at their disposal when they flew at Kitty Hawk in 1903. Food for thought.

Watch the majestic landing at Brussels in the Solar Impulse video below:

* A 747-400 that flies 3,500 statute miles (5,630 km) and carries 126,000 pounds (56,700 kg) of fuel will consume an average of five gallons (19 L) per mile (Boeing.com).