HAYABUSA's seven-year journey in space Case Studies for Society

May 9th, 2003
An asteroid probe departed Earth on a round-trip journey that spanned billions of kilometers to search for secrets behind the birth of our solar system.
The probe's name was "Hayabusa".
Under the direction of JAXA, the Japan Aerospace Exploration Agency, NEC was involved in the project as a system integrator. The journey was a miraculous achievement made possible by leading-edge technologies and teamwork between human beings and machines.

Hayabusa's target was Itokawa, an asteroid located between the orbits of Earth and Mars. To enter the asteroid orbit, Hayabusa employed an Earth swing-by navigation technique developed by JAXA and NEC over many years.
(Mr. Kominato)
"Usually, spacecrafts use a powerful engine for propulsion, but, Hayabusa uses a combination of ion engines and Earth swing-by for its orbit control.
First, Hayabusa traveled all the way around Earth along approximately the same orbit as Earth, which took a year. The ion engines provided continuous thrust during this time. When the probe got close to Earth again, it performed a swing-by to use the gravity of Earth so as to increase the probe's acceleration.
Hayabusa's Earth swing-by required extremely precise adjustments and other calculations. These requirements included an altitude of 3,700 km, a positional error of 1 km or less, and a velocity error of 1 cm/s or less when the probe got close to Earth again. Hayabusa succeeded in meeting these requirements.
An orbit control engineer at NASA sent us an email to say "congratulations," on an "outstanding job". We were happy about that. Getting an email from NASA made us feel like we really accomplished something."
In this way, Hayabusa changed its orbit to that of the asteroid Itokawa.

As Itokawa has almost no gravitational pull, landing on it is not possible, so Hayabusa had to collect a sample by simply touching down on the asteroid.
(Mr. Hagino)
"When looking from Earth, Itokawa is behind the sun and twice as far away from the Earth as the sun. At this distance, we could only control Hayabusa about once every hour. Therefore, once it approached the asteroid surface, Hayabusa had to look at the terrain on its own, determine which way to tilt, and decide how Itokawa's rotation affected the probe position."
Hayabusa successfully touched down by using various new methods and technologies, including a laser altimeter, a target marker, and a high sensitivity camera.

Unfortunately, after the successful touchdown and asteroid takeoff, terrible events awaited: Hayabusa lost its attitude control due to fuel leakage from its chemical engine, and communication with the probe was lost.
However, those on Earth maintained their faith that Hayabusa would respond.
Seven silent weeks passed.

(beacon)
(Mr. Hagino)
"We believed that, once sunlight could strike the solar arrays, a command would reach Hayabusa and we would hear back from it. However, although we were happy to hear from the probe, our first thought was that we needed to figure out how to fix it."
By this time, it was no longer possible to use the chemical engine, which had lost its fuel, to control the attitude, so Hayabusa used its ion engines and solar power to start its return.

(Mr. Shirakawa)
"At that time, Hayabusa was returning with most of its attitude control capabilities lost, and our only available option was to use the neutralizers attached to the ion engines to generate a weak force, so we continuously used this force for a while to control and maintain the attitude.
We used this extremely weak force, the force of solar radiation, and other forces that could gradually change the attitude over time. This was a continuous process. If we tried to tilt the probe right, for example, we wouldn't know the results until the next day, so we would have come back the next day, check whether the probe was moving as we expected, and then apply force in the opposite direction if it wasn't.
I sometimes felt it was our duty to keep the light of Hayabusa from going out."

After a seven-year journey, Hayabusa returned to Earth, and its mission came to an end.
NEC provided total support for the Hayabusa project, including the development of the ion engines and various other devices, orbit design, and space navigation operations. The know-how obtained through the many challenges overcome during this project will be extremely valuable in taking the next step in space development.
The achievements of Hayabusa continue to inspire us, guiding us into the future.

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