An image of the space yacht experiment. (Photo courtesy of JAXA)
Wouldn't you love to travel through outer space in a "space yacht" with the sails aloft, in much the same way as a regular yacht cleaves through the ocean with the wind in its sails? Armed with this dream, the Japan Aerospace Exploration Agency (JAXA) developed a small experimental craft and launched it in 2010. The name of the trial craft is IKAROS, taken from a character in Greek mythology (Icarus). The Ikaros of mythology lost his wings, burned by the heat of the sun. But the IKAROS that was launched into space has used the power of the sun to pass by Venus, and even now it is continuing its journey into infinite space.
No Engine or Fuel is Necessary
In May 2010, the H2A rocket blasts off, carrying IKAROS.（Photo courtesy of JAXA）
IKAROS was created with the objective of developing a "dream spacecraft" that didn't need an engine or fuel. The main body at the nucleus of the craft (just 160 cm in diameter and 80 cm thick) is surrounded by a square sail that is 14 m along its length and 20 meters across the diagonal when fully extended. The main purpose of the craft is to verify whether "solar sail" and "power sail" technologies can function in space; the former uses the sun's light to propel the craft, while the latter is a thin, power-generating, solar cell membrane stretched across the sail.
It may seem strange that the craft is propelled by the power of light, but when the sun's particles bounce on the sail, it generates a force that pushes IKAROS forward. This force is extremely weak; so much so that we would not feel it in everyday life. Even with the craft's sail fully open, the power generated could only lift an object weighing 0.2g here on earth, but in space where there is no air resistance, it is enough to move the craft's body which weights 310 kg.
In fact since IKAROS separated from its rocket, it has been verified that in the space of about 6 months, it has increased its speed by around 300 km/hour.
The Venus probe “Akatsuki” (right-hand side of the photo) and IKAROS, launched at the same time. (photo courtesy of JAXA)
Developing a Thin yet Durable Sail
The idea for a fuelless space yacht, or a craft propelled by the power of light, was around 100 years ago. The British writer Arthur C. Clarke (1917-2008), best known as the author of the book on which the movie "2001: A Space Odyssey" was based, depicted scenes of a space yacht race in his novel.
The main body of IKAROS. (Photo courtesy of JAXA)
The polyimide sail wrapped around the main body of IKAROS. (Photo courtesy of JAXA)
So far, it has been mainly Western countries that have spent decades studying the development of the space yacht. Yet it has never quite been made a reality. This has been due to the absence of the technology needed to make a stable, light yet durable sail. The extremely strong radiation and ultraviolet rays flying around in space would immediately tear ordinary vinyl or cloth to shreds.
Then, researchers at JAXA came across the new material used for the sail in this experiment; a special plastic film called "polyimide." At just 0.0075 mm thick, this film was not just light, its robustness had also been proven in outer space where it had been used in satellite insulation etc. The polyimide was redeveloped with properties that allowed it to become adhesive when heated up, allowing seams to be made without adhesive, so that they did not easily tear apart.