Solar Impulse, the first aeroplane designed to fly day and night without requiring fuel and without producing carbon emissions, is to make its first international flight, from Payerne in Switzerland to Brussels.

The prototype has been ready for take-off since May 2nd and will depart as soon as the weather permits. Confirmation of the impending flight will be communicated 24 hours in advance via www.solarimpulse.com and the flight can be followed live online. Having to be in Brussels by May 23rd at the latest represents an additional source of pressure for flight director Raymond Clerc, who will have to find a favourable weather window at a time of year that often has unpredictable conditions. A mission as challenging as this requires contributions from a whole team of specialists, including meteorological experts, notably route-planner Luc Trullemans, air traffic controllers, engineers and IT specialists.

The aircraft will be displayed in Brussels from May 23rd to 29th and will then attempt to fly on to Paris Le Bourget, to appear at the Paris Air Show from June 20th.

Quite apart from its symbolic significance, the first international flight is also a big technical challenge for the Solar Impulse team. To operate in environments as complex as the international air traffic network and the taxiways of Brussels, the 14th biggest European airport, means anticipating and studying every possible eventuality, so as to be able to react quickly if unexpected circumstances arise.

Because of the aircraft's categorisation as experimental, special authorisations requiring lengthy procedures, had to be obtained from the civil aviation authorities in each of the countries overflown.

"Flying Solar Impulse through European airspace to land at an international airport is an incredible challenge, and success depends on the support we receive from all the authorities concerned," stressed ceo André Borschberg.