A piloted helium-filled balloon will attempt to cross the Atlantic from Dakar in Senegal to Martinique powered only by renewable energy.

Windream One (see artist's impression above) hopes to prove that it is technologically possible to cover 5,000km (just over 3,000 miles) flying night and day using sources of energy drawn from the sea, the sun and the wind.

The craft is 28.5m long and the balloon has a capacity of 900 cubic metres. It is guided by a 'chien de mer', a curved carbon foil which will run under the water's surface.

It is linked to the balloon's nacelle by a cable whose length can be adjusted from 20-50m and which acts as a keel. This helps the crew control the flightpath by allowing the balloon to follow ocean currents.

Between February and March next year when the crossing is to take place, ocean currents running in the craft's intended direction are strong and should pull it along, aided by the wind or the craft's propeller when the wind is weaker.

Windream One has flexible solar panels which feed energy to a battery that powers a propeller to accelerate the balloon when necessary.

There are also small wind turbines aboard that help to control the craft's direction and also make electricity for the propeller.

The airship will travel at an average speed of 15 knots (just over 17 mph).

The team behind it consists of 20 private and university researchers, technical and financial partners and is sponsored by French renewable energy group Theolia.

Aeronautics expert Stéphane Rousson. creator of the project will pilot Windream One, and his co-pilot will be Peggy Bouchet, who has previously rowed solo across the Atlantic.  

Research into the Windream's aeronautical techniques will soon be completed, and the construction of the balloon, the nacelle and navigation appendages will start in June.

The first flight is scheduled to take place in Toulon in September, followed by a test journey from Nice to Corsica in October and a demonstration flight over Lake Geneva in November.

The team will then head for Dakar at the start of January 2008 to set up a new technical base. After reassembling the balloon and a new series of tests, Windream One will be on standby for a weather window, opening the way to lift off. Both air and sea conditions have to be right for the 10-day crossing.