After a three-and-a-half year voyage deep into the asteroid belt, Japan’s second Hayabusa space probe this summer reached the asteroid Ryugu and dropped two robotic rovers on the surface. Their mission: Nothing less than uncovering the mystery of life.
The Hayabusa2 mission follows on the ground-breaking voyage of the original Hayabusa to another asteroid, becoming the first space vehicle to visit another world and return to Earth since the Apollo moon missions.
It was also the longest round-trip – 2,542 days – since the American “star dust” mission [1999-2006] to collect space dust, but that mission did not actually land on a celestial object.
Only a point of light from Earth, the scientists at the Japan Aero Space Exploration Agency (JAXA) were astonished as the first images of Ryugu began to return to Earth.
They revealed a strange diamond-shaped feature, which reminded some people of a child’s toy top. “We didn’t expect this shape,” said project manager Makoto Yoshikawa, in a meeting with the press.
The asteroid is small, only about one km in diameter, or about as tall as the Sky Tree tower in Tokyo. The object is so small and has such as weak gravity that the two rovers actually move about in short leaps and jumps rather then moving on tracks like the Mars probe and others.
If an astronaut could actually get to Ryugu and land safely, he had better watch his step since a wrong jump might literally propel him back into space. Indeed, there is some concern that the asteroid might push the Hayabusa away.
The main purpose of the land rovers is to collect pebbles and dirt from the surface of the asteroid. Later next year a device known as an “impactor” carrying an explosive charge will be detonated on the asteroid’s surface creating a crater.
That would allow the Hayabusa2 to collect materiel from deep below the surface, material that has not been exposed to cosmic rays. The JAXA scientists think this material dates from the very beginning f the solar system, even predating the Earth, which is believed to be more than 4 billion years old.
The asteroid is believed to be about 6 billion years old, which places it at the beginning of the solar system and might provide answers to its origin.
Another success of the mission would be to discover amino acids. Many scientists believe that life-giving acids may have traveled to Earth by “hitching rides” on asteroids or comets.
Hayabusa-1 largely failed in its main mission to recover and bring home samples of the terrain. All that it managed to bring back to Earth were small particles of asteroid dust.
This was just one of many glitches and other malfunctions that the ground crew had to deal with and correct in flight and, of course, re-engineer in order to make the second Hayabusa mission a success.
Three of the four ion thrusters that propel the probe though space stopped working during the trip, a fuel leak rendered the chemical engine inoperable, two of the three attitude control antennas broke down and communication was lost for 50 days after the landing.
Despite these trials and nail-biting moments, the first Hayabusa did in fact return to Earth and landed safely in the far reaches of western Australia following a 600 million km round trip.
According to Hiroshi Kuninaka, a JAXA vice president speaking to reporters, the agency learned a lot from the first Hayabusa mission. A lot of new technology was invented for the second mission, he said.
Small is Beautiful
The motto at JAXA might be small is beautiful. The Hayabusa2 probe itself is not large, 1 x 1.6 meters. The need to save room otherwise used for chemical propellant that takes up space caused the engineers to build an entirely new propulsion system.
Given its small size JAXA engineers developed its own electric ion propulsion engine, using microwaves to generate charged particles (ions) from xenon gas. They are expelled at high speed to provide the thrust that propels the craft forward.
According to JAXA, this type of propulsion provides less raw power than a more conventional chemical-powered spacecraft, But it is highly efficient and can maintain acceleration for a long time. (Of course, the probe is lifted off the Earth on top of a conventional rocket.)
Japan space program is developing its own niche in exploring the smaller objects in the solar system. While others talk and plan bigger and bigger missions to Mars, JAXA is working on a long term plan to land on one or both of Mars’s two satellites, Phobos and Deimos.
Scheduled for 2024, another Hayaubua will probably land on one or the other and collect samples of the surface and return to earth on 2029. The samples could help scientist to understand how these moons originated.
JAXA has more exploratory voyages in the advanced planning stage. In October the European Space Agency and JAXA will team up to jointly launch two spacecraft aimed at the solar System’s smallest planet, Mercury.
The joint expedition will study the planet’s mysterious magnetic field and how it interacts with harsh solar wind, given the proximity to the Sun. It will also observe he planet’s surface and internal composition.
“I’m proud that have established a new method of space exploration for small celestial bodies,” said JAXA project manager Yuichi Tsuda.