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How our great teamwork overcame huge obstacles to explore the unknown asteroid "Ryugu"


On February 22, 2019 (Japan Standard Time), the asteroid explorer Hayabusa2 touched down on the asteroid Ryugu, bringing its sampler horn into contact with the surface and, for the first time in history, succeeded in firing a projectile into an asteroid. If all went well, Hayabusa2’s sample container should now be carrying a precious cargo: specimens from a celestial body never visited by humankind before.

That was a remarkable feat, all the more so because Ryugu’s rocky surface was a treacherous environment for the tiny probe. The asteroid “bared its fangs,” as Yuichi Tsuda, project manager of the Japan Aerospace Exploration Agency (JAXA) Hayabusa2 mission, put it. The mission’s engineers faced a dilemma: they could only succeed at their mission by exposing the explorer to considerable danger.

How did they overcome that quandary?
We asked Dr. Takanao Saiki, who took over from Yuichi Tsuda as the JAXA project engineer overseeing the development of Hayabusa2, and Tetsuya Masuda, from the NEC team overseeing the entire technical side of the project.

Takanao Saiki (right)
Japan Aerospace Exploration Agency (JAXA) Institute of Space and Astronautical Science
(ISAS) Department of Space Flight Systems, Assistant Professor , Dr of Engineering
ISAS Hayabusa2 Project Team, Project Engineer

Tetsuya Masuda (left)
NEC Corporation
Space Systems Division

Real-time training for unexpected situations

-For Hayabusa2’s mission to the asteroid “Ryugu”, how did you build and work together as a team?

SAIKI: We refer to the activity of sending various commands to the asteroid explorer Hayabusa2 and getting it to do what the mission requires as “operations”. Discussions on proximity operations began prior to launch, but they didn’t really get going until September 2015, after Hayabusa2 had been launched and initial inspection of the explorer was completed.

NEC was involved from the start. Mr. Masuda and others responsible for the explorer’s systems took part in the discussions, as did those in charge of guidance and control, which plays a critical role during touchdown. Together we decided on the final operating procedures.

MASUDA: When our team received the schedule for arrival at the asteroid and overall training plan from JAXA (Japan Aerospace Exploration Agency) , we realized that we’d have to put together rough plans for virtually all major elements of the mission including touchdown on the asteroid in one year and a half. When we were first told the sequence of events — prepare for training and then train — I thought to myself, “This is going to be a lot of work.”

-Did everyone on the team take part in the training?

SAIKI: Yes, we had NEC take part in real-time training, where we did a dry run of the descent onto the asteroid.

MASUDA: One of the main objectives of real-time training is to drill the people involved. You actually sit in front of the computer screen in the Hayabusa2 control room and perform a simulation of the probe landing. NEC’s job was to develop operational procedures in preparation for training. But not everything goes according to procedure. All kinds of unforeseen problems and oversights come to light, which is why it’s essential to prepare by verifying everything on the simulator first and fixing any problems.

SAIKI: Doing training like that actually brings to light a lot of areas where procedures could be improved. Training personnel is the main objective, but it also has the benefit of steadily improving operational procedures for the explorer.

MASUDA: The plans had been made by human minds, so there were bound to be mistakes and oversights. We accordingly assumed that training would lead to review of plans. We prepared for the actual landing on Ryugu by first ironing out all issues that arose during training.

We might not be able to touch down

- So you were meticulous in preparing for the mission. Hayabusa2 reached Ryugu in June 2018. But then, I understand, a major hitch occurred before it made its first touchdown in February 2019.

SAIKI: In the fall of 2018, we succeeded in landing two rovers on Ryugu’s surface, MINERVA-II-1 and MASCOT. But then we had to alter our plans and postpone the first touchdown, which had been scheduled for October 2018; only the target markers were dropped to mark the landing site. That was because the surface of Ryugu was extremely rocky, rugged terrain, which was a threat to the explorer. That was a major change in plans, yet we had a problem: the precision of the touchdown maneuver still wasn’t good enough.

A sensor called a laser rangefinder (LRF) was to be used during the approach to the surface of Ryugu for touchdown. This sensor was highly susceptible to the effects of uneven terrain, so that if there were a large boulder, Hayabusa2 might assume a completely different orientation from what it was supposed to and crash into the ground.

To address this problem, instead of reacting to all the values from the LRF sensor, the explorer needed to maneuver in accordance with those provided in advance by the people back on earth based on what had been gleaned about the terrain. But the software that controls the explorer doesn’t necessarily let you do whatever you like. On the other hand, completely rewriting the software would have taken too long.

MASUDA: I kept thinking to myself, maybe we’re not going to be able to touch down…. I didn’t want to say we couldn’t, of course, but there was a huge boulder on the target landing site, and having to land on such a tiny spot seemed like a tough prospect.

SAIKI: Then someone at JAXA suggested a new way to deal with the problem, and we asked NEC whether the software could be configured that way. In the end that’s what we decided to do.

MASUDA: We didn’t actually answer until the beginning of 2019, after the New Year holidays, but the new idea immediately struck me as likely being feasible. It neatly got around the reasons no solution had been found so far.

MASUDA: Both the original Hayabusa and Hayabusa2 were space probes designed to journey to unexplored worlds where conditions were unknown. So it was not enough to be able to do just routine tasks; they had to alter their movements depending on what they encountered. We built in the flexibility to do that, and I think that worked effectively. Plus the people at JAXA have a good understanding of software flexibility, and they had a lot of suggestions — including ideas we at NEC never would have thought of on our own.

SAIKI: Usually it’s JAXA that makes the suggestions, while NEC acts as the voice of caution — like, “That can’t be done on schedule, you know.” But in this Ryugu touchdown project, both sides shared the same critical sense of emergency. It was a tough situation, but when one said “Is this possible?” the other would say “Let’s see what can be done” and explored the possibilities.

-Hayabusa2 was built to explore an unknown celestial object. What design principles and guidelines were applied in designing it?

SAIKI: For starters, we drew a great deal on the experience gained from the first Hayabusa, which was likewise a probe sent to explore an object never visited before, the asteroid Itokawa. The software was developed on that basis. We’re constantly improving and evolving the technology we’ve built up.

On the other hand, the philosophy wasn’t just to do everything as in the first Hayabusa mission. Each and every member of the Hayabusa2 team had to think and be responsible. Things wouldn’t have gone well if we’d just said to ourselves, “That’s how the original Hayabusa mission did it, so that’s how we’ll do it too.” That isn’t progress. I don’t think the mission would have been such a success if the Hayabusa2 team members hadn’t brought in fresh ideas while building on the original mission. After all, while Itokawa and Ryugu are both asteroids, they differ completely in both their gravity environment and how you land on them.

MASUDA: During the approach to Ryugu, NEC’s project manager of the original Hayabusa mission said to me, “It’s completely different from Itokawa. It’s really rugged, so you’re probably going to have a hard time.”
I was genuinely surprised at how different two asteroids could be.

SAIKI: It was certainly very different from what I’d imagined, but that’s what makes exploring unknown celestial objects so fascinating. And having the flexibility to deal with that is essential to the technology. If we stopped doing stuff like this for the next decade, the technology would quickly be lost. I think keeping it up is extremely important.

The unique teamwork of JAXA & NEC leads to success

―And so, Hayabusa2 successfully made its first dramatic touchdown on Ryugu.

SAIKI: In preparation for the touchdown on February 22, we had to develop and validate all the procedures in advance. What’s more, once we’d finished, we also had other missions to prepare for.

MASUDA: We were doing several tasks at once. It takes a month or two to develop and validate a set of procedures for a single operational plan. We had to draw up three or four sets of procedures in parallel, so to avoid confusion, we were careful to keep them separate as we worked.

SAIKI: NEC’s capabilities are truly unrivalled. They were really meticulous in their work for us. During meetings, things inevitably arise that have to be changed according to circumstances. Even so, what emerges in the end is a procedures manual that encompasses everything and misses nothing.

MASUDA: The prospect of a mission to explore an asteroid was incredibly alluring, and no one lost sight of that. I guess sharing the same common goal truly kept people motivated.

MASUDA: The people working on the Hayabusa2 project are scrupulous about roles so as to achieve as much results are possible. “What only NEC can do is this, and what only JAXA can do is that.” So when they ask us to do something, we know that only we can do it. That gives us all the more motivation to live up to their expectations.

SAIKI: We’ve been working together continuously, and we trust each other a lot. We’ve come to understand what we’re each supposed to do, and I think we managed to maintain a very effective division of duties throughout. We each knew what the other is doing, and when the going got tough, the communication between us went very smoothly. “JAXA will handle this,” we’d say, “and you at NEC, look after that, please.”
With this teamwork based on mutual trust, we will continue to work together until the return of the asteroid explorer by the end of 2020.

Interview and article by Ayano Akiyama
Published March 30, 2020

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