Solar Driven Aircraft

One might think also of a solar-driven aircraft The availability of photoactive organic polymers may give rise to photovoltaic "sails" for the collection of solar energy in flight. 

The US military has a need for extreme long-duration unmanned air vehicles (UAV), and a hydrogen-powered, fuel cell-driven electric aircraft is a leading candidate. Without an internal combustion (1C) or jet engine, a fuel-cell UAV would be very quiet. Furthermore, there is the potential to electrolyze effluent water (or airborne water vapor) using solar power, giving the UAV an almost unlimited flight duration. 

The field of propulsion deals with the means by which aircraft, missiles, and spacecraft are propelled toward their destinations. Subjects of development include propellers and rotors driven by internal combustion engines or jet engines, rockets powered by solid- or liquid-fueled engines, spacecraft powered by ion engines, solar sails or nuclear reactors, and matter-antimatter engines. Propulsion system metrics include thrust, power, cycle efficiency, propulsion efficiency, specific impulse, and thrust-specific fuel consumption. Advances in this field have enabled hiunanity to travel across the world in a few hours, visit space and the Moon, and send probes to distant planets. 

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