It Powers, it Speeds, Now it Steers

Japan's small solar power sail demonstrator, Ikaros, has shown it can steer itself using liquid-crystal devices along its edge that can either reflect or diffuse sunlight. The spacecraft has already proved it's accelerating under light pressure and generating power from solar cells covering its surface - so it's three for three so far.Photo: JAXAThe Japan Aerospace Exploration Agency (JAXA) says two things are important for a spinning solar sail like Ikaros: to generate a small attitude control torque constantly without causing the flexible membrane to oscillate; and to control the large angular momentum of a spinning membrane without using propellant.By turning the power to the liquid-crystal devices on and off as the sail spins, to control their reflectivity, Ikaros is able to generate a tiny amount of torque to change its attitude. When reflectivity is reduced, the sunlight pressure on that edge of the sail is reduced, creating a difference in thrust between one side and the other and generating the torque.JAXA confirmed the devices could provide attitude control by measuring the angle between the sail's spin axis and a line connecting Ikaros and the Sun. Before the devices were activated, this Sun angle was gradually increasing. When they were ...