KeywordsAsteroid Regolith Sample return
Hayabusa (“peregrine falcon” in Japanese) is a scientific space mission developed by JAXA to explore a near-Earth asteroid and to return asteroidal soil, while validating new engineering technologies (propulsion, landing, and atmospheric reentry). Launched in May 2003, the Hayabusa-1 rendezvous with asteroid Itokawa was in September 2005. After 2 months of close observations, it descended and attempted to collect surface grains. It departed in 2007 and cruised back to Earth. The sample canister returned safely in July 2010. JAXA has confirmed the presence of tiny dust particles sampled on Itokawa. Hayabusa-2 is now planned, targeting the C-type asteroid 1993JU3 (launch in late 2014).
The Hayabusa-1 spacecraft consisted of a core (1 × 1.6 × 2 m) and two solar paddles (5.7 m width), with a total mass of ∼530 kg, including its propellant (for chemical propulsion) and xenon (for electrical propulsion). It carried four scientific instruments, the AMICA imaging camera, the NIRS near-infrared spectrometer, the LiDAR laser ranging instrument, and the XRS X-ray fluorescence spectrometer. In addition, the probe embarked three instruments for navigation: an optical camera (ONC), an electromagnetic sensor (FBS), and a laser emitter to control the attitude during descent (LRF). As an engineering spacecraft, Hayabusa-1 tested two new developments, xenon ion engines and an autonomous navigation system, which both performed successfully.
The mission was quite complex and faced major issues. Hayabusa-1 was launched on May 9, 2003, from Kagoshima Space Center (now called Uchinoura), with an MV-5 solid propellant rocket. Soon after, it was hit by a large solar flare that damaged the solar cells, reducing the electrical power and the efficiency of the ion engines. After an Earth swing-by in May 2004, Hayabusa arrived close to the targeted asteroid (25143) Itokawa in mid-September 2005 and performed its thorough remote characterization. In November 2005, it released the Minerva mini-lander, which unfortunately escaped Itokawa’s gravitational pull and was lost in space. Hayabusa then attempted twice to touch down on the surface of the asteroid, after having deployed a sampling horn, later sealed after having tentatively collected asteroidal dust. Hayabusa-1’s return maneuver started in April 2007, for a 3-year cruise back to the Earth. The return capsule, released from the main spacecraft 3 h before reentering the Earth atmosphere, landed safely near Woomera, Australia, on June 13, 2010. It was transferred to the JAXA curation facility. Preliminary analyses have confirmed that most of the collected particles, which have sizes below 10 μm, have come from Itokawa.
The scientific observations made while Hayabusa-1 was hovering above Itokawa have established that it is a very small body (major axes 530 × 290 × 210 m, with a density of (1,925 ± 160) kg m−3), indicative of a rather high porosity of about 40 %. This may suggest that it is built from loose-packed rocks, held together by their gravity. Itokawa presents a significant topographic diversity, with a variety of rough terrains scattered with boulders, as well as featureless central areas, which likely result from fine dust particles forming a smooth regolith that has accumulated in local gravitational lows. Its shape may suggest that it is a contact binary. Such results are to be taken into account when considering the orbital deflection techniques that should and could be implemented if a similar asteroid was discovered on a collision course with the Earth.
Following the overall success of this pioneering mission, Hayabusa-2 is now planned, for a launch in 2014, to rendezvous with a primitive C-type asteroid (162173), 1993 JU3, with similar goals and instruments. A major added contribution still under consideration is a hoping lander, provided by DLR and CNES, designed to monitor the potential magnetic field of the asteroid and to perform in situ a microscopic characterization of the composition of the asteroid, at a grain scale.