Japanese Spacecraft Deploys Solar Sail
A camera captures the second stage of solar sail deployment on the Japanese Ikaros mission. Four thin tethers that mechanically connect the solar sail membrane with the main body can be seen extending downward on both left and right sides of the image, while a harness that provides the electrical connection extends from the center to the lower left.
Credit: JAXA

Japan's new solar sail spacecraft has fully deployed its sail and begun generating power through its embedded solar cells, according to Japanese officials.

The solar sail, named Ikaros (Interplanetary Kite-craft Accelerated by Radiation Of the Sun), aims to become the first successful space mission propelled solely by sunlight. But first the Japan Aerospace Exploration Agency (JAXA) must begin testing the navigational systems that will guide Ikaros toward Venus and beyond.

"We will measure and observe the power generation status of the thin film solar cells, accelerate the satellite by photon pressure, and verify the orbit control through that acceleration," JAXA officials said in a statement Friday.

Ikaros reached orbit last month by piggybacking on the launch of a larger JAXA mission, the Venus climate orbiter called Akatsuki ("Dawn" in Japanese). Both spacecraft launched along with four small satellites on May 20 (early morning local Japan time on May 21), from the Tanegashima Space Center on Tanegashima island in Japan.

Deployment of the solar sail began on June 3, as the circular disc-like package spun up to about 25 revolutions per minute and allowed four weighted tips to begin dragging the folded solar sail outward to form the shape of a cross. Once that first stage had completed, the solar sail membrane was released to fill out its kite shape.

The 700-pound (315 kg) Ikaros is designed to use only the pressure of sunlight as propulsion during its journey. But it also has thin film solar cells built within its kite-like frame that can generate electricity.

JAXA hopes that the demonstration could eventually lead to future spacecraft which combine solar sailing with electricity for ion-propulsion engines — not unlike a sailing boat that also uses a solar-powered engine.

The mission also has the goal of demonstrating navigational guidance and control for solar sails. An earlier Japanese solar sail mission merely deployed from a sounding rocket in 2004, but did not attempt controlled flight.

Past U.S. solar sail attempts faltered before ever reaching orbit because of a Russian rocket malfunction and the third failed flight of SpaceX's Falcon 1 rocket. A British space mission the size of a shoebox could also demonstrate solar sail propulsion sometime next year. That mission, called CubeSail, will aim to use sails as brakes to take down failing satellites.

Ikaros will take the same starting trajectory as the Akatsuki Venus climate orbiter, but it won't make a pit stop at the shrouded planet. Instead, the Japanese solar sail is scheduled to pass through the orbit of Venus and continue on a long, three-year journey to the other side of the sun.