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Hayabusa 2's ion engines a huge improvement on predecessor's

JAXA associate professor Kazutaka Nishiyama, who developed the Hayabusa 2 probe's ion engine, poses for a photo behind a device testing ion engine neutralizers at the JAXA Sagamihara campus in Sagamihara, Kanagawa Prefecture, on June 19, 2018. (Mainichi)

The successful arrival on June 27 of the Hayabusa 2 explorer at the asteroid Ryugu after a 3.5-year journey spanning 280 million kilometers has proved the reliability and durability of the probe's ion engines -- a stark contrast to its predecessor's thrusters that were dogged by repeated serious trouble.

The scientist responsible for the ion engines' development and operation, associate professor Kazutaka Nishiyama of the Japan Aerospace Exploration Agency (JAXA), is proud of his brainchild's success. "The device is hard to break down," 47-year-old Nishiyama said.

The Hayabusa 2 ion engine uses ionized xenon gas to obtain propulsion power. As a thruster on Earth, it's very weak and only has enough power to move a one-yen coin, but its continuous use in space eventually accelerated the probe to a very high speed.

When using ionized xenon for propulsion, it has to be electrically neutralized, but on the first-generation Hayabusa three out of four neutralizers broke down or were degraded, pushing the project to the verge of a failure with the probe feared unable to return to Earth.

Nishimura was responsible for the original Hayabusa's troubled engine's operation, nursing the thruster back to a functional state on multiple occasions during his seven-year, 1,600-hour support of the spacecraft -- the longest period among project members. While working with the probe, Nishiyama developed a larger ion engine. Models of the neutralizers used on the Hayabusa 2 were continuously tested in a laboratory, stacking up 49,000 hours of operational time, more than double the original goal of 20,000 hours.

The Hayabusa 2 ion engine has proved stable in space, with the number of unscheduled shutdowns around one-fourth of the first-generation engine. Its operation for the outbound trip was suspended on June 3 as planned.

Nishiyama said of the thruster's successful performance, "The longer you move your own hands and operate the thing, the more you become confident. I believed that we would complete the outbound trip successfully. It all came down to putting the device together on Earth. I did everything I needed to do."

Nishiyama's ion engine will play a key role in bringing Hayabusa 2 back to Earth in 2020. "A device remains a toy if it cannot function in space," said Nishiyama, who is eager to prove the technology he developed in space. "The laboratory walls are not the limit of my work."

(Japanese original by Tomohiro Ikeda, Science & Environment News Department)

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