The nation’s Hayabusa2 space probe, launched in December 2014, will make its closest approach to the Earth on Thursday as it performs a swing-by to set it on a course toward its target asteroid, 300 million kilometers away.
The probe, which has until now had an orbit similar to the Earth’s orbit around the sun, will reach an altitude of only 3,100 km shortly after 7 p.m., the space agency said. Gravity will then cause it to change direction and pick up speed — a method used by spacecraft to save fuel on long missions.
To put Hayabusa2 on the correct orbit with the swing-by requires precise maneuvering. This is like “aiming at a bug at the top of Mount Fuji from Tokyo,” Hiroshi Takeuchi of the Japan Aerospace Exploration Agency said. The 3,776-meter mountain is Japan’s highest peak.
The probe will be over Hawaii when it makes its closest approach to the Earth, but experts say it will be invisible to the naked eye at that time.
Before then, astronomical observatories in Japan may have a chance to observe the probe by telescope. It measures 4 meters by 6 meters when its solar panels are spread.
Hayabusa2 was launched in December 2014 on an H-2A rocket with a mission to reach and collect rock samples from a 900-meter-wide asteroid that was later named Ryugu. The probe is expected to reach the asteroid in 2018 and return to Earth in late 2020.
The probe is a successor to the Hayabusa asteroid explorer, which brought the first ever asteroid samples to Earth in 2010.
Launched in 2003, Hayabusa had a journey of 6 billion km to and from the asteroid Itokawa. The voyage was plagued with difficulties, including failures of its engines and gyroscopes, and at one point a loss of communications.
The roughly 600-kg Hayabusa2 has various improvements on its predecessor, include more durable ion engines.
The probe is expected to land on Ryugu and release rovers. It will dig a crater with a metal impactor to access materials undisturbed by radiation from the sun and other bodies.