Asteroid Explorer Hayabusa2 sets a new record for closest approach during a Solar System body flyby mission

Japan Aerospace Exploration Agency
SPACE ENGINEERING DEVELOPMENT Co., Ltd.
NEC Networks & System Integration Corporation
Systems Engineering Consultants Co., Ltd.
DAIKO XTECH,Ltd.
Chiba Institute of Technology
Toshiba Electronic Technologies Corporation
NEC Corporation
NEC Aerospace Systems, Ltd.
Japan Spaceguard Association
Fujitsu Ltd.
Fujitsu Defense & National Security Ltd.
National Institute of Technology, Matsue College

 After closely examining the spacecraft operations and scientific data collected during the flyby exploration of asteroid Torifune by the asteroid explorer Hayabusa2, the Japan Aerospace Exploration Agency (JAXA) has found that the minimum distance between the spacecraft and asteroid centre was approximately 744 m. The time at which Hayabusa2 passed the point of closest approach was 18:30:00.31±0.03 seconds on 5 July 2026.
 The minimum distance to the surface of Torifune was approximately 400 m. This distance represents the closest pass to a celestial body among all flyby explorations of Solar System bodies conducted to data (Figure 1).

 Regarding the guidance, navigation and control of Hayabusa2, the deviation from the target point at the location of closest approach was 120 m. This confirms that the combined radio-optical navigation on the ground and the control by the newly developed onboard navigation and guidance software functioned largely as planned (Figure 2). The navigation and guidance result confirms the demonstration of the control technology capable of causing a spacecraft to collide with a small asteroid, marking a major step forward in Japan’s planetary defence.

 Torifune is estimated to have a major axis of approximately 840 m, a minor axis of approximately 340 m, and an average diameter of 540 m. Regarding the accuracy of the estimated orbit of Torifune, the error around the time of the flyby was 49.5 km (3σ) before the flyby, but reduced to 0.78 km (3σ) after the flyby. Being able to estimate the size and orbit of an asteroid with extremely high accuracy constitutes an important achievement for planetary defence. If future analysis of the scientific data makes it possible to estimate the physical properties of Torifune, the information yielded will be even more useful to planetary defence.