Jun 2, 2011
  By Frank Morring, Jr.

Japanese researchers are working on a solar-sail spacecraft with 10 times the surface area of the Ikaros testbed launched toward Venus last year, after achieving all of their technical objectives with the testbed.

This spacecraft will launch on a five-year mission instead of the six-month span allotted to Ikaros. Lofted as a piggyback payload with the Venus Climate Orbiter Akasuki on May 21, 2010, Ikaros passed Venus on Dec. 8.

Researchers hoped to demonstrate automatic sail deployment, power generation with thin-film solar cells on the sail surface, verification that the pressure of photons from the Sun caused the sail to accelerate, and guidance and navigation with the sail. The sail met its intended acceleration of 100 meters per second and veered off the ballistic trajectory it would have followed without the Sun’s pressure, says Yuichi Tsuda, an assistant professor in the Japan Aerospace Exploration Agency (JAXA) Space Exploration Center, in an English-language report on the experiment’s outcome.

The deployment and power generation were demonstrated early on. To control the 14 x 14-meter (46 x 46-ft.) spin-stabilized sail, the Ikaros team used a non-toxic “gas-liquid equilibrium thruster” for attitude control, and an attitude-detection system that combined a Sun sensor and Doppler measurements from the low-gain antenna.

To tilt the spin axis of the spacecraft, the team powered a liquid-crystal variable-reflectivity element mounted as a thin polyimide film around the edges of the sail off and on to throw the spinning sail off balance and tilt it as it spun. As it happened, the spacecraft required almost no fuel to keep its sail facing the Sun, even though it turned a full 180 deg. over the six months, according to Tsuda.

Drawing on experience navigating the solar-electric-powered Hayabusa asteroid sample-return mission with only one of its thrusters working, the JAXA team determined the Ikaros orbit using flight data obtained by tracking it with the 64-meter antenna at the Usuda Deep Space Center. Using that data and the control system, the team was able to fly Ikaros to the night side of the planet while the Akasuki probe flew to the opposite side, the only difference in trajectory being the sunlight pressure on the sail.

“We are still evaluating the guidance and navigation performance in detail,” Tsuda says. “Nevertheless, the Ikaros team is confident that it has obtained the solar-sailing technology.”

From Aviation Week