The mission is considered to be one of the most difficult for the probe to accomplish. 

The Japan Aerospace Exploration Agency (JAXA) designed a new impactor specifically for Hayabusa2 to shoot the copper lump at the asteroid, demonstrating the high technology Japan has developed for space exploration.

Going beyond Hayabusa

“We successfully established new means of space exploration,” said Yuichi Tsuda, JAXA’s Hayabusa2 project leader, at a press conference on Friday evening, stressing the significance of the latest achievement which built on the foundations laid down by its predecessor, the original Hayabusa.

The first Hayabusa probe landed on the asteroid Itokawa in 2005. Hayabusa2, which was built using the same basic design, shares its purpose of bringing back samples of rocks, among other materials, from asteroids to Earth. 

But if Hayabusa2 was just a rehash, it would be hard to gain public support for injecting a total of about ¥29 billion (about $260 million) from the state’s coffers into the project.  

Taking this into consideration, Hayabusa2 was additionally given the unprecedented task of using an impactor to create a crater on an asteroid’s surface to enable it to collect samples from the asteroid’s interior that have not deteriorated or been affected by such factors as sunlight. 

The conical small carry-on impactor with a diameter of about 30 centimeters works by ejecting a copper plate attached to its base.

The impactor ejects the copper plate, which is about five millimeters thick and weighs about two kilograms, using explosive power to accelerate its speed to two kilometers per second and strike it against the asteroid’s surface. As the impactor was built specifically for this task, an explosives manufacturer took part in its development. 

Aiming and firing the impactor at a point on the asteroid’s surface required meticulous accuracy. It was “like shooting an arrow on horseback while blindfolded,” according to a person close to the project. 

From analysis of images taken by an observation camera, it is likely that the impactor operated as planned, and it is thought a crater was created on the asteroid’s surface as a result.

The U.S. National Aeronautics and Space Administration has in the past struck a comet with a lump of metal, but Friday’s attempt is the first such achievement on an asteroid. 

“The significance of Hayabusa2’s exploration has grown greater. The rest of the world will look to emulate this achievement,” said Junya Terazono, associate professor at the University of Aizu. 

A space odyssey

One major struggle for the project team scientists in the latest mission was how to protect Hayabusa2’s body from debris from the explosion to catapult the copper lump, as well as fragments ricocheting from the asteroid. 

Hayabusa2 is located about 310 million kilometers from Earth, and it takes about 17 minutes for a signal to reach it, or vice versa, making it impossible to send commands instantaneously. 

For that reason, the team decided to carry out the mission using an automatically-controlled system.

The complicated movement, in which Hayabusa2 evacuates while changing its direction a number of times between horizontal and vertical after releasing the impactor and an observation camera, was all programmed into the system in advance. 

In February, Hayabusa2 touched down precisely on the planned landing site, which is 6 meters in diameter, on Ryugu.

The team members were able to draw from this experience an understanding of the tendencies of each of 12 altitude-controlling reaction wheels installed on Hayabusa2, building up their confidence in probe-control technology. 

Stressing that they learned from the touchdown experience, Takashi Kubota, a member of the team, said, “With the technology that enables the probe to move freely, it can expand the possibilities of exploration in outer space.”

Careful consideration

Hayabusa2 will take about two weeks to return to its home position at a 20-kilometer altitude from Ryugu. Then after that, from April 22 or later, it will descend to the asteroid to confirm whether a crater has been formed on the surface.

At some time as early as May, it will again land on the crater or its vicinity on the asteroid to start collecting samples of fragments.

But whatever happens next, the team believes Hayabusa2 has already managed to collect enough samples from its first landing on the asteroid in February.

It will also be able to gain scientific findings by observing the vicinity of the crater from above. A senior JAXA scientist said, “If there’s a risk that the body of Hayabusa2 may get damage by landing on the asteroid again, it will not be necessary for us to press ahead with it.”

JAXA will weigh up the pros and cons of landing the probe again after carefully assessing the safety of doing so.