June 22, 2009. Copyright 2009, Graphic News. All rights reserved Solar aircraft will orbit the Earth night and day By Simon Morgan LONDON, June 22, Graphic News: ĘThe team at Swiss-based Solar Impulse has a nickname for its project to circle the globe in a sun-powered, manned aircraft which, considering its prototype has yet to take wing, could be tempting fate: ŇThe revenge of IcarusÓ. Ę Sunlight will of course be the ally and not the enemy of Bertrand Piccard, the round-the-world ballooning pioneer who is the projectŐs founder and one of the two pilots who will begin test flights with the prototype, HB-SIA, as early as this autumn. Ę HB-SIA has a limited horizon; although test flights and the first night trip are planned for this autumn and next year, its real job is to gather valuable performance data for the construction of its successor. HB-SIB, due to be built in 2011, will be tasked with the headline-grabbing missions of crossing the Atlantic and, at some point in 2012, girdling the globe in five stages. Ę Why not one continuous trip? Human weakness. There will be room for only one pilot and he will have to rest. Ę At 61 metres, the prototype aircraft has the same wingspan as an Airbus A340, but there all comparison ends. The giant wing serves two purposes; to provide the maximum area for the solar cells -- HB-SIA will take its power from 200 square metres of ultra-thin photovoltaic cells -- and to maximise uplift sufficiently to allow the aircraft to stooge along at the relatively slow and economical average speed of 70km/h. Ę This is not the first solar-powered aircraft (that was Sunrise II, 35 years ago) nor even the first manned one (Gossamer Penguin was piloted aloft in 1980). However, it is the plan to fly through the day and night that, if successful, will secure the project a place in the history books -- and has given the team its heaviest burden. Ę During daytime flight, sunlight not only has to power the propellers but must also charge the batteries that will keep the aircraft cruising through the hours of darkness. Unfortunately, weighing in at 400kg, these account for almost one third of the aircraftŐs total weight of 1,500kg, so weight-saving is the key to success. In the words of AndrŽ Borschberg, the projectŐs CEO and second pilot: ŇEverything that doesnŐt break during testing is potentially too heavyÓ. Ę ThatŐs why the aircraftŐs operational ceiling will be limited to 8,500 metres, precluding the need for a pressurised cabin and the associated weighty equipment and instrumentation, although at that height the pilot will need oxygen. Ę In a sense, the project is flying into a cul-de-sac -- the weight limitations of current photovoltaic cell technology mean there is no feasible commercial future in manned solar-powered flight. As Solar Impulse itself admits, ŇWe will probably never carry 300 passengers in a solar airplaneÓ. Ę Staying aloft for hours or even days on end is not in itself the main achievement; the remote-controlled NASA-backed Pathfinder, Centurion, and Helios unmanned flying solar wings demonstrated the potential for high-altitude, long-duration flight more than a decade ago. Ę Essentially, the project is an elaborate exercise in energy management -- the efficient generation and storage of solar power -- and, for Solar Impulse, the key goal is ŇTo show what can be achieved using renewable energies and encourage their useÓ.Ę Ę All of us, says the group, are Ňin the same situation as the Solar Impulse pilot. If he É wastes his energy, he will have to land before the rising sun enables him to continue his flight. Ę ŇAnd we, if we do not invest in the scientific means to develop new energy sources, we shall find ourselves in a major crisis, which will prevent us from handing over the planet to the next generation.Ó /ENDS