For a long time we have run an advertisement in North Sails entitled: “Sails built in Space.” The uniqueness of this moulding technology justifies the advertisement. The photo of the suspended sail maker over a 3DL/ 3DI mould, though an everyday occurrence in the ‘North World’, creates a real image of space travel and weightlessness. The idea of sailing in space has a lot of logic to it and is not just fiction.
The principle is that propulsion can be generated by mirrored surfaces reflecting the radiation present in space, generated by stars and massive objects.
The force created is small but even deflects spacecraft from their planned route, much like crossing a weak tide. The adjustments made in trajectory in today’s space missions come from this unpredictable bombardment. Kepler observed in a letter to Galileo in 1610 that heavenly breezes stretched the tails of comets away from the sun. This force can accelerate an object and if the sail is large, smooth and reflective this can be a real means of propulsion.
James Clark Maxwell, in 1861, in his pioneering works on electro-magnetism, concluded that light has momentum and can thus exert a pressure. As ideas developed through the works of Plank, Einstein, Bohr and others, we started to see a very different world where subatomic particles behaved both as waves and particles. Any radiation has momentum. However we may understand this, we can sail not only with the terrestrial wind but can use the movements and inner world of the heavens to sail through space.
The radiation does not create a dynamic force like the wind, so the sail has to be supported. Many sails are built from polyimide film coated with evaporated aluminium. Some steer by electronically controlled liquid crystal panels which diffuse light thus reducing momentum when on and enabling when off. Like a rudder on a boat this pushes one side or the other of the craft.
The deployment of sails appear to follow two main techniques, the simple use of unfolding arms and spin systems. With talk of sails up to a kilometre square in the not so distant future, many ideas are there to be explored, but the use of mass increased sail corners and spin seems the most reliable as a means of deployment. All solutions require light, high tensile strength materials to meet the dynamic loads, which in space are greater than imagined. Weaker sails have a tendency to ripple, which distorts the reflective surface, oscillates, and increases structural failure.
Earlier aluminium coated Mylar films have been challenged by carbon fibre light sails. Current talk is of nano mesh weaving to produce an extremely smooth surface where the spaces are smaller than half the wavelength of the light. The weight with this technique drops from 12g/m2 to 3g/m2.
In the early days of maritime exploration the very medium in which sailors functioned was that which killed them. If we master the challenges of propulsion systems for manned space travel, the very elements will once more threaten the sailor. Besides the notion of distance and time, while trapped in a spacecraft, radiation levels and comparative weightlessness will certainly take its toll. On earth maritime safety has greatly progressed.
The extreme challenges of space will in time surely be met and man may not be marooned on earth forever.
I see a host of parallels between these two worlds. The current 3Di sails are a long way from a primitive deployed skin; sailing the Nile using Egyptian cotton; or the Vikings crossing the seas with woven wool or even the simple laminates used on many boats today. The 3Di development programme creates an ever stronger, more stable, smoother, lighter membrane. The leap into space is not just a photo of a sail maker in a suspended bag. For years, when people have asked me about the future of sail making, I have joked that it’s a ‘dinosaur’, but if we are able to embrace new technologies as an extension of the craft of sail making then maybe we are not yet extinct.
Editor’s note: For more information on this fascinating subject, visit: http://sail.planetary.org
