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Published on MHI Graph (October 2013 Issue)

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Spirited Challengers: The Engineers Behind Space Propulsion Systems

Homegrown Technology Supports Satellites and Planetary Explorers

What does the explorer Hayabusa (MUSES-C), which retrieved the world's first asteroid sample, have in common with the satellite Hinode (SOLAR-B), which is helping to analyze how the sun works? For both spacecraft, MHI worked on the space propulsion systems that perform attitude control. Tsuyoshi Takami and Hikaru Uramachi, who develop and design space propulsion systems, shoulder the high hopes attracted by these national projects. Their skills are vital in ensuring that explorers and satellites work as planned in space.

  • Photo left: Maritime & Space Systems Department Integrated Defense & Space Systems Tsuyoshi Takami
    Photo right: Maritime & Space Systems Department Integrated Defense & Space Systems Hikaru Uramachi

Creating New Possibilities: Space Propulsion Technology

Space engineering technology is developing rapidly. Already, numerous weather, GPS and other artificial satellites are actively orbiting the earth, and together with many planetary explorers are helping to unravel the mysteries of space.
One recent example is the Hayabusa, an asteroid explorer that returned home barely intact after accomplishing many world firsts.
MHI's contribution to these cutting-edge spacecraft consists of space propulsion systems (Reaction Control System: RCS (Note1)). These systems are vital to space travel: spacecraft use RCS to turn their solar-cell modules toward the sun to generate their own electricity, adjust their directions so that their high-speed communications antennae can communicate with Earth, and maneuver during landing on or taking off from asteroids.
In his 23-year career, Takami has worked on RCS for five satellites, planetary explorers and launch vehicles as a developer and designer. According to Takami, "At JAXA (Japan Aerospace Exploration Agency), they're developing launch vehicles, satellites, and explorers. All of these are attempts at world firsts, and we handle a part of each attempt."
Uramachi, in his third year with MHI, works alongside Takami in development and design. His duties range from concept design to post-production verification tests, and even negotiating with clients.
"Our job doesn't end when the design is finished. We're involved in a number of different processes, which makes it interesting. We get to work until we verify the results of what we've done. It's a lot of work, but it feels really worthwhile," says Takami. Takami has taken pride in his wide-ranging responsibilities ever since joining MHI, and in 2000, he was assigned to the soon-to-be-famous project: Hayabusa.

  • 1RCS, which consists mainly of tanks, valves and thrusters (small rocket engine), is used to generate the reaction force for attitude control.

The Benefit of Proximity Yields a Domestic First

On Hayabusa's return in 2010, it was greeted by cheers from all over the world. In this project, MHI developed and manufactured the RCS that handles attitude control, and the propellant supply system (Note2) for the ion thruster, the main propulsion system. "For the RCS, we developed the first domestically produced low-thrust bipropellant thruster. It's tough to manufacture things from a concept, but here (at Nagasaki Shipyard & Machinery Works) we're right next door to the Nagasaki Research & Development Center, and they helped us clear all sorts of hurdles," remembers Takami.
Takami was involved with the Hayabusa's pre-launch operation for three months. "At Uchinoura Space Center, I performed launch site work, including fueling and testing pressure and functions. It was hard work, but it was fun, too. While I was working, I was so tense that my hands swelled up, and on the day after the launch, the swelling vanished, just like magic. That showed me just how much pressure I'd been feeling."
However, since Takami was in charge of the RCS, his work continued even after the launch. Once in space, there's no way to repair spacecraft if problems occur. Finding solutions for those problems is the developer's job. "During my summer vacation, I got an urgent phone call from the JAXA project manager. He said the device for fine attitude control had broken down, and he wanted to use the RCS as a substitute. We hadn't designed the RCS for fine attitude control, but we immediately ran tests with a ground test thruster and looked for the operating time that would produce the smallest possible controlling force." They subsequently checked with thrusters on the Hayabusa as it moved through space and managed to successfully land it on the asteroid Itokawa. Takami still remembers the elation of that moment.

  • 2Control valves and an ultrahigh-pressure tank that stores propellant
Photo: Checking out the in-company test drive.
Takami and Uramachi witness their designs being verified by in-company test device.

More Reliable Space Propulsion Systems Help Unlock the Secrets of Space

Takami is involved in the 2014 launch of the Hayabusa-2, not as a designer, but as development and design project manager. Now Uramachi is the one involved with development and design, under Takami's leadership. Early ambitions of manned flight led Uramachi to study aerospace engineering at a university. He was involved in the IKAROS (Note3) project as a laboratory student, and right after joining MHI, he was assigned to the Hayabusa-2. However, even Uramachi, competent as he was, found the actual work site bewildering. "I'd learned the basic techniques and knowledge involved in spacecraft systems as a student, but when actually designing an RCS, I have to consider fine details such as material compatibility and tolerance. It makes me realize just how complex on-site work can be."
Gathering samples may have been one of Hayabusa's main missions, but for Hayabusa-2, it additionally needs reliable execution of sample gathering." The craft will need consistent, high-performance quality control. According to Uramachi, "Many past satellites and explorers carried out their missions well, and many didn't. I want to figure out what caused the failures, then address the issues to make this new spacecraft more reliable."
The role of RCS isn't over until the spacecraft has completed its mission. The Hayabusa-2, scheduled to be launched in 2014, will return in 2020. It will be a long time before Takami and Uramachi can truly relax.
"Hayabusa's RCS was damaged during the landing and became inoperable, so it could not fulfill its function. We're feeling the pressure to make one that's sure to succeed this time. If the RCS is imperfect, the explorer isn't able to complete its mission," Takami says. Uramachi adds, "There are always lots of new attempts made on planetary exploration projects, and there are many things I want to try. Making the RCS more reliable is one. Manned flight is what got me interested in space, and I'd also like to work toward developing an RCS that uses green propellants that are less harmful to humans and the environment."
The asteroid Itokawa is three hundred million kilometers from Earth. A transmission takes thirty minutes to travel the distance. However, even when they'd lost Hayabusa, the project team kept calling it, and this produced miraculous results. On the Hayabusa-2, Hayabusa's successor, the apparatus into which Takami and Uramachi poured their insatiable curiosity will hopefully perform as designed.

  • 3A small solar power sail demonstrator launched on May 21, 2010
Photo: Hayabusa
Hayabusa, world's first spacecraft to retrieve asteroid sample.