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Huge sail will power JAXA mission to Trojan asteroids and back

by

Staff Writer

Japan’s space agency has its sights on unexplored asteroids as far away as Jupiter, a project that at one level draws on centuries of sail science.

The Japan Aerospace Exploration Agency this month unveiled a huge prototype solar sail designed to power a JAXA probe as it explores asteroids that circle the sun on roughly the same orbit as Jupiter. The sail measures 2,500 sq. meters and is made up of thousands of ultraslim solar panels.

“The fascination of the universe lies in its countless unknowns, and our research is a challenge to reveal the mysteries with our own hands,” said Jun Matsumoto, a JAXA researcher who designed the kite-like sail.

Analyzing the composition of the Jupiter Trojans, a group of asteroids that share Jupiter’s orbit, may help scientists understand how the solar system was formed, the space agency said.

For the probe to reach the Trojans and return, it needs to be able to generate its own power, and in space, solar energy is an abundant resource.

But since the Jupiter Trojans are far from the sun — about 778 million km, or 5.2 times the distance between the Earth and the sun — sunlight is weak. Therefore the probe needs an enormous solar sail and an energy-efficient ion engine, Matsumoto said.

JAXA has developed what looks like a square kite measuring 50 meters along each side and containing 30,000 solar panels. The film is made of 10-micrometer-thick polyimide, an electrically insulating, heat-resistant material commonly used in electronic devices. There is a hole at the center of the sail, where the space probe will be attached.

During the JAXA event at a gymnasium in Sagamihara, Kanagawa Prefecture, a full-scale model of one of the four trapezoidal components was shown to an audience of over 250 people. About 40 JAXA workers, academics and students carefully unfolded the sheet, revealing it to be about the size of two basketball courts.

The idea has been tried before. A smaller sail powered Japan’s IKAROS (Interplanetary Kite-craft Accelerated by Radiation of the Sun), which launched in 2010. That sail was also square, but each side was only 14 meters in size.

Earlier this month, the unmanned NASA spacecraft Juno, which uses three solar panels to generate electricity, successfully entered orbit around Jupiter. JAXA’s probe, which is expected to be launched in the early 2020s, will be lighter and yet will still be loaded with equipment for research, Matsumoto said.

If all goes well, the probe will return to Earth with samples taken from the asteroids in the 2050s.

As the project will last decades, the key to its success is to nurture future researchers who can keep it going.

“I am currently the youngest JAXA staffer on this project. But by the time it is completed, I might no longer be part of the team due to retirement,” said Matsumoto, 27, who dreamed of becoming an astronaut as a child. “Wherever I go, people always talk about how to train young people to become the researchers of the next generation.

“Personally, I want to show children that there are adults who aim to explore places no human has ever gone.”

Although the project still has a long way to go, Matsumoto’s personal ambition may have already been realized — judging by the reaction of young onlookers.

“I was amazed to know that we have such a huge device to venture into the universe,” said Shoma Ito, a 15-year-old junior high school student from Sagamihara. He said he was impressed by the scale of the space experiment held in his hometown.

“Someday I hope I can be a part of space research,” he said.