Japan’s Hayabusa2 Spacecraft Creeps Up on the Ryugu Asteroid
Posted June 25, 2018 2:37 p.m. EDT
Here is the mission for Japan’s Hayabusa2 spacecraft in a nutshell: Fly to a carbon-rich asteroid between the orbits of Earth and Mars, study it for a year and a half and then bring back some pieces for additional study on Earth.
Like most space missions, that is much easier said than done. Launched in 2014, Hayabusa2 is just now approaching its target, Ryugu, an asteroid about a half-mile wide. The Japanese astronomers studying it say it has the shape of a top or even an abacus bead.
That is a big improvement from earlier in June when it sent back a picture taken at a distance of about 1,600 miles — the asteroid then was just three pixels across and looked like something drawn in the blocky style of Minecraft.
— Why did it take so long to get there?
Hayabusa2 is powered by ion engines, which accelerate charged atoms of xenon with an electric field to generate thrust.
Ion engines are a very efficient form of propulsion but not very powerful. That means Hayabusa2 can carry much less fuel than traditional thrusters would require, but it also means that it could not take a quick, direct route. The spacecraft used a flyby of Earth in December 2015 to accelerate and match its trajectory with the tilted orbit of the asteroid.
Hayabusa is the Japanese word for peregrine falcon.
— When will the spacecraft reach Ryugu?
As of Monday, the spacecraft is about 15 miles away, and it is scheduled to arrive around Wednesday coming within 12.5 miles of the space rock. It is currently creeping up to Ryugu at a relative velocity of about 4 inches per second.
— Why are they studying this asteroid?
Asteroids are bits and pieces leftover from the disc of gas and dust that formed around the young sun and never quite coalesced into a planet. They contain some almost pristine compounds that help tell what the early solar system was like 4.5 billion years ago.
Ryugu, as dark as coal, is a C-type, or carbonaceous, asteroid, meaning it is full of carbon molecules known as organics including possibly amino acids, the building blocks of proteins. Such molecules are not always associated with biology and can form from chemical reactions in deep space, but asteroids could have seeded Earth with the organic matter that led to life.
About three-quarters of asteroids in the solar system fall into the C-type. And the time it takes for Ryugu to rotate came as a surprise to the scientists who are studying it.
“Up to now we know several top-shaped asteroids, but all of them have a short spin period around 3 hours,” said Makoto Yoshikawa, the Hayabusa2 mission’s manager. “The spin period of Ryugu is about 7.5 hours, so this issue is quite interesting from the point of science.”
This space rock was discovered in 1999 and not given a name until 2015. Ryugu is named after Ryugu-jo, or dragon’s palace — a magical undersea palace in a Japanese folk tale.
— What will it do once it gets there?
If the spacecraft is able to keep its schedule, by the end of July, Hayabusa2 will descend within 3.1 miles of Ryugu’s surface to measure the gravity field around the asteroid. In September or October, Hayabusa2 is scheduled to make its first “touchdown operation” on the asteroid.
At that point, it may deploy one or more of the five tiny rovers it is carrying. It may also deploy a European-built lander then.
Then it will take a hiatus in November and December, because the sun will be directly between Ryugu and Earth, blocking communications.
After that, the spacecraft will make a couple more touchdowns, as well as dropping a copper projectile into the asteroid to create a crater. That will allow the spacecraft to collect some material from beneath the surface. (The projectile is made of copper, because that metal is easily distinguishable from what the asteroid is made of.)
At the end of 2019, Hayabusa2 is to leave the asteroid and head back to Earth. As it flies by in 2020, it will drop off a capsule with the asteroid samples.
— Isn’t NASA doing something like this too?
Yes. The Osiris-Rex spacecraft is currently heading to another carbon-rich asteroid known as Bennu, and it too will collect samples and return them to Earth. Bennu is even smaller than Ryugu, about 500 yards wide. Osiris-Rex will begin its approach of Bennu in August, and start surveying the asteroid at a distance in October; it will not return with its samples until 2023.
NASA and Japanese scientists plan to exchange samples of the two asteroids to compare the similarities and differences.
— Has Japan done this before?
As the 2 in Hayabusa2 indicates, this is the second time that JAXA, the Japanese space agency has sent a spacecraft to an asteroid.
Hayabusa2 is an improved version of Hayabusa, which visited a stony asteroid, Itokawa, in 2005. Despite several technical problems at Itokawa, Hayabusa returned a capsule to Earth in 2010 containing 1,500 particles from the asteroid.