The Japan Space Exploration Agency (JAXA) launched its second asteroid probe, the Hayabusa2, in December 2014. The aim: learning more about how the solar system and possibly life on Earth originated. After meeting up with Ryugu, its target asteroid, on 27 June, Hayabusa2 is now decreasing its altitude (to roughly 5 kilometers above the surface) in order to carry out medium altitude observation. By late August, JAXA will decide where on the space rock’s surface Hayabusa2 will land. The agency intends to have it touch down in a September-October time frame.
JAXA’s plans call for Hayabusa2 to land and take off up to three times during an 18-month period, so it can study conditions at different locations on Ryugu. Upon completion of the probe’s mission and its subsequent return voyage, a capsule carrying its precious asteroid samples will detach itself from the spacecraft and a parachute will deploy at about 10 km above the Earth to provide a soft touchdown.
This new space mission was launched four years after its predecessor, Hayabusa, returned to Earth after two landings on the Itokawa asteroid—this despite experiencing a series of equipment glitches. Those setbacks included problems with all four of its ion engines, the failure of two of its three reaction wheels, and a disappointing malfunction of the sampling mechanism.
Despite such technical troubles, JAXA deemed Hayabusa (peregrine falcon in Japanese) an outstanding achievement, because it was still able to return with 1,500 particles from Itokawa—the first time asteroid samples had been captured and brought back to Earth for analysis.
According to Hitoshi Kuninaka, vice president and director general of JAXA’s Institute of Space and Astronautical Science, the agency learned much from the first operation. Kuninaka spoke to the foreign press in Tokyo on Thursday, following Hayabusa2’s rendezvous with Ryugu after a 1,302-day journey through space. He was joined by Makoto Yoshikawa, the mission manager of the Hayabusa2 project.
The asteroid Ryugu.Image: JAXA
Apparently, JAXA made some upgrades in response to the original Hayabusa’s difficulties. New equipment and modifications to existing systems, intended to make the mission more fruitful and less fraught with peril, caused Hayabusa2 to weigh in at 609 kilograms, about 100 kg heavier than its predecessor. But its dimensions and architecture are not much different than those of the first probe.
Kuninaka explained that the craft uses an electric propulsion ion engine system consisting of four units that use microwaves to generate charged ions from xenon gas. The ions are then accelerated using an electric field and expelled at high speed, which provides the thrust to propel the craft forward. He noted that JAXA has made the engine more durable and improved the propellant so it delivers more thrust.
“So, Hayabusa2 can now achieve a velocity of over 30 km a second compared to 5 km a second for conventional chemical propulsion,” says Kuninaka. “And Hayabusa2 is able to reach the asteroid Ryugu and return to earth on just 60 kg of propellant, one-tenth the weight of the craft.”
Concerning communications, mission manager Yoshikawa noted that the first space probe used a large parabolic X-band antenna. Its successor uses two smaller, but equally powerful planar high-gain antennas: an 8-gigahertz Ka-band antenna for ground communications, and a 32 GHz Ka-band antenna to relay scientific observations to Earth after arriving at the asteroid. The latter can transmit roughly four times as much data as the X-band, but transmission can be attenuated during bad weather. In addition, Japan’s tracking stations are not currently set up to receive radio waves in that portion of the spectrum, so JAXA is using NASA and European space agency tracking stations to enable 24-hour communications with Hayabusa2.
Other important equipment on board the craft include a suite of cameras, a near-infrared spectrometer, a thermal infrared camera, a LIDAR laser altimeter to measure the distance between probe and asteroid, asteroid sampling devices, and three small rover robots (the single rover on the first probe was never deployed). Two new additions are an impactor that will be used to make an artificial crater in order to obtain samples of the asteroid’s internal structure, and a small lander containing several scientific instruments.
The craft’s electric power is generated by a two-winged, solar array paddle system consisting of three panels per wing. This produces 1,460 watts, enough to charge 11 inline-mounted 13.2-ampere-hour lithium-ion batteries that supply power to onboard equipment as needed.
Three traveling robots—Rover-1A, Rover-1B, and Rover-2—will explore Ryugu’s surface. They will be deployed via a Minerva-ll minilander. The first two concentric robots weigh approximately 1.1 kilogram, with dimensions of 18 by 7 centimeters. They each contain a wide-angle and a stereo camera, a temperature sensor and photodiode, and an accelerometer and gyro. Power is supplied by solar cells, and movement by means of internal flywheels.
The optional Rover-2 is some 45 percent taller than its counterparts and contains similar equipment but also incorporates four types of mobility systems, two kinds of bucking mechanisms, an eccentric motor microhop mechanism, and a permanent-magnet-type impact generation mechanism.
In addition, Hayabusa2 will deploy a small lander created jointly by the German Aerospace Center and the French National Center for Space Studies. Dubbed the Mobile Asteroid Surface Scout (MASCOT), it will move location once by jumping. It carries a wide-angle camera, spectroscopic microscope, thermal radiometer, and a magnetometer to study composition of the asteroid’s surface.
Yoshikawa noted that JAXA has chosen to study asteroids because they are some of the oldest objects in our solar system. The Itokawa asteroid is an S-type asteroid, meaning it is composed of stony materials. Ryugu is a C-type and is assumed to be composed of carbon and other organic materials containing water—key elements for life on Earth.
NASA is conducting a similar mission with its OSIRIS-Rex spacecraft, which it aims to land on the near-Earth asteroid Bennu and bring back with samples. That mission was launched in September 2016, with a return date of 2023. JAXA and NASA plan to exchange samples to further scientific investigation.
From an engineering perspective, JAXA views these missions as manageable within its budget constraints. What’s more, the agency reaps the benefits of creating new technologies that will further deep space exploration. The budget for the Hayabusa mission was US $250 million, while that of the Hayabusa2 is $300 million. “These amounts include the rockets that launched them,” notes Kuninaka.
Editor’s note: This story was updated on 23 July 2018 to correct the frequency at which Hayabusa2 will broadcast.
