On Earth the pull of gravity makes it impossible to feel the slight force exerted by light particles, or photons. But in space, where there is no gravity, photonic pressure could produce enough acceleration - one millimetre per second, per second - to travel to the Moon in 300 to 350 days, depending on the skills of the Earth-bound navigators.
Photonic pressure is very low, exerting a force of about 8gms per hectare. This means the surface area of the sails on the unmanned spacecraft must be correspondingly large. In the case of the British-designed craft, brainchild of the design and development company Cambridge Consultants, the sail is the size of 10 football pitches.
Sailing to the Moon may sound like a pastime for rich people bored by the constraints of Earth, but solar sailing could offer great advantages over conventional rockets for travelling in space.
Although the sunlight reflected off the sail exerts a tiny force, it is a continuous one, so that a solar sailing craft can pick up more velocity than can be attained by a rocket.
And unlike rockets, solar sailing craft would never need refuelling.
Nasa flirted with photon power in the 1970s, when scientists at its Jet Propulsion Laboratory in Pasadena came up with a design for such a craft, but this never got off the ground.
The American Columbus Quincentennial Consortium tried to organise a sailing race to Mars in 1992 to celebrate Columbus's voyage to America. Although this flopped, it did result in a number of solar sail designs.
By setting a less ambitious finishing post on the Moon, the hope is that the Lunar Cup will give enthusiasts a chance to prove that space sailing works.
Cambridge Consultants' sail design, originally produced for the Columbus race, is being considered with three others by Voilier Solaire Europeen in Paris, which is co-ordinating Europe's entry to the Lunar Cup. The US entry is designed by the World Space Foundation in Pasadena, California, and the Japanese entry by a group led by the Japan Space Agency.
The Cambridge Consultants sail is made from plastic two microns thick and coated in aluminium, to reflect the sunlight and harness the power of photons.
Using ingenious origami techniques, the circular sail is folded to fit into a cylinder only 4m high by 4m wide.
This makes it small enough to be launched into orbit around the Earth on Europe's Ariane rocket. Once beyond the pull of gravity, the sail will be unfurled from the cylinder and begin to pick up enough momentum to break out of Earth's orbit and be steered to the Moon.
The steering mechanism uses carbon fibre spars controlled from an Earth station to flex the sail, so that different parts receive more or less sunlight, in an exact parallel with wind-sailing on Earth.
Sailing to the Moon is slower than going by rocket, but if the technology were proved, solar sailing could open up new possibilities for longer-range space travel and exploration.
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