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Astonished by Itokawa's Unexpected Appearance

Q. What aspect of the HAYABUSA mission made the biggest impression on you?

Asteroid Itokawa
Asteroid Itokawa
Asteroid Itokawa
Asteroid Itokawa

What I remember most is receiving images of the asteroid Itokawa from HAYABUSA after arrival. Itokawa looked completely different from what we had imagined: the surface was rough covered with big rocks. The image really surprised us, because the asteroids we were familiar with from images taken by U.S. explorers always had craters, and therefore I had assumed that this was how all asteroids would look. But in real life, Itokawa looked completely different - there were hardly any craters on the surface.
In addition, all the asteroids the United States has explored are tens of kilometers in diameter, while Itokawa is only 535 meters wide. Itokawa is so different from the ones I’ve seen, maybe because it’s such a small asteroid. Anyway, I was astonished.
And at the same time, I also thought, "There is nowhere to land. What are we going to do?" We had assumed that the asteroid would be covered with craters, which would give HAYABUSA a safe place to land. But in reality, the surface was too rough and rocky for landing. We had to look for a flat spot to prevent the solar paddles from crashing into rocks on landing. Although we were lucky enough to find a large enough area with a smooth surface, we realized that you can never know for sure what a celestial body is like until you get there. Q. What kind of the scientific findings did the HAYABUSA mission make? First, we found evidence that the asteroid Itokawa was essentially a pile of rubble. With spectral analysis, we discovered that the material on Itokawa’s surface is very similar to meteorites that have fallen to Earth - ordinary chondrite. The asteroid’s mass was initially estimated based on the typical density of meteorites, but the mass measured by HAYABUSA was much less than expected, leading to the conclusion that about 40 percent of Itokawa’s interior is hollow. Based on this, we’ve theorized that Itokawa is not monolithic but was formed from rubble created when its main body impacted and was destroyed.
Another finding was that there is not much fine sand or gravel, called regolith, on its surface. Instead there are mostly exposed rocks and stones. This was a great discovery, as the asteroids that had been observed earlier are all covered in regolith, whereas Itokawa is "naked", so to speak, covered in nothing. It is assumed that small bodies such as Itokawa generally aggregate to form larger bodies, so in that sense we have observed a celestial body at an early stage of the formation of the solar system.

HAYABUSA Touched People’s Hearts

Q. How would you like your experience with HAYABUSA to influence HAYABUSA-2?

Asteroid explorer HAYABUSA-2 (courtesy: Akihiro Ikeshita)
Asteroid explorer HAYABUSA-2 (courtesy: Akihiro Ikeshita)

I did indeed experience quite a lot through the HAYABUSA mission, but in particular, the biggest challenge was the operation of the spacecraft itself. To operate the ion engines, I had almost no time to rest while they were in operation, because we needed to stay in daily contact with the spacecraft and make continuous adjustments - deciding the next day’s and the next week’s operation as we confirmed HAYABUSA’s current location and velocity. It was like we were constantly controlling the orbit. So, if the ion engines can be improved for automated operation of HAYABUSA-2, there will be no need for someone to intervene all the time. We would like to reduce the burden on the operators as much as possible.
Also, although HAYABUSA was initially intended to be a four-year mission, its return was delayed by three years due to system malfunctions, and the mission ended up lasting seven years. In the original plan, the condition of the orbit allowed HAYABUSA to stay at Itokawa for only three months. So everything had to be done within that time frame before taking off for return to Earth. We were extremely busy, because we had to finish all the tasks in those three months - from surveying the asteroid, to selecting the landing area, to collecting samples - in a place we had never been before. I think that, in a way, the shortage of time contributed to some of the failures and malfunctions. So for HAYABUSA-2, we have chosen an orbit that allows it to stay on the designated asteroid for about a year and a half after arrival. This way, we will have enough time to observe the asteroid, and to rehearse the landing as many times as fuel allows.

Q. Expectations for HAYABUSA’s successor are rising. How would you like to make use of the project’s popularity?

Dr. Yoshikawa with a model of asteroid Itokawa
Dr. Yoshikawa with a model of asteroid Itokawa

In the beginning, at launch in 2003, HAYABUSA was barely known to the public. Its arrival at Itokawa in 2005 drew some attention, but recognition was still not that high, and only a few space fans cared. HAYABUSA got the public’s full attention when it made its way back to Earth. Frankly speaking, I didn’t expect such attention prior to its return. We are very pleased with the support we received.
I think HAYABUSA became so popular because it was a very challenging and adventurous mission - people are impressed by a "world’s first" mission, which was to travel to and land on an asteroid and return to Earth. HAYABUSA-2 will attempt many new things too, so we’d like to conduct a PR campaign to get the public interested. We will also have many educational and cultural activities to get people interested in space, as well as science and technology in general, through the HAYABUSA-2 mission.

A Space Mission as a Bridge to the Future

Q. Do you have a vision in mind for post-HAYABUSA-2?

Asteroid explorer Hayabusa Mk2 (courtesy: Akihiro Ikeshita)
Asteroid explorer Hayabusa Mk2 (courtesy: Akihiro Ikeshita)

A sample return mission called HAYABUSA Mk2 is under consideration. The spacecraft is a full model change from HAYABUSA, and will be two or three times as big. This is essential because we are aiming for a celestial body at a greater distance from Earth. The candidate destinations are D-type asteroids, or a comet that no longer emits gasses. We don’t know yet what kind of materials they are made of, since there are no meteorites from celestial bodies at such distances. The mission of Hayabusa Mk2 is to bring unknown materials back to Earth, to address the mysteries of the early days of the Solar System. Q. What is your goal now? My present goal is to make HAYABUSA-2 a reality. Once we have the budget and the project begins I’d like to involve as many young scientists and engineers as possible, which will benefit the development of future missions. To move on to HAYABUSA Mk2, we must make HAYABUSA-2 a success.

Makoto Yoshikawa, Ph.D.

Associate Professor, Department of Space Information and Energy, Institute of Space and Astronautical Science, JAXA
HAYABUSA-2 Project Preparation Team Leader, Systems Engineering Office, JAXA Space Exploration Center
Dr. Yoshikawa graduated from the Department of Astronomy and the Graduate School of Science, both at the University of Tokyo. After working as a research fellow at the Japan Society for the Promotion of Science, he was on staff at the Communications Research Laboratory from 1991, and moved to the Institute of Space and Astronautical Science (now part of JAXA) in 1998. Dr. Yoshikawa was a project scientist for the asteroid explorer HAYABUSA. He specializes in celestial mechanics; his research centers on orbital analysis of small Solar System bodies such as asteroids and comets. In addition to research on selecting orbits for artificial satellites and planetary explorers, he also works on analysis of the hazards of Earth impact with celestial bodies.

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