Study for realization of proximity flyby of asteroid Torifune in the Hayabusa2# mission
Feb. 12, 2025 | Aerospace Project Research Associate, ISAS people
KUSUMOTO Tetsuya / Dept. of Space Flight Systems, ISAS
Research Summary
After bringing samples from asteroid Ryugu back to Earth, the Hayabusa2 spacecraft has continued its cruise as an extended mission named Hayabusa2#. One of the major events in the extended mission is a flyby*1 of the asteroid Torifune (2001 CC21) in July 2026 (Fig. 1). The significance of conducting this flyby is that in addition to obtaining scientific observation data on the asteroid, we will acquire technologies that will contribute to planetary defense*2.
A unique feature of the Hayabusa2# Torifune flyby is that it aims to pass just short of the asteroid with the highest possible guidance accuracy. This is due to the following reasons. Since the nominal mission of Hayabusa2 was to rendezvous with the asteroid, the camera is fixed to the spacecraft. Therefore, as shown in the left figure of Fig. 2, if we try to observe the asteroid at the closest point by tracking the asteroid with the camera, it is necessary to rotate the attitude of the spacecraft, but such a quick attitude change is not realistic for Hayabusa2. Therefore, as shown in the right figure in Fig. 2, we are trying to obtain high-resolution images by reducing the approach distance to the asteroid.
In order to make such an approach, Hayabusa2# is preparing to perform autonomous guidance and navigation. This guidance and navigation means estimating its own position and calculating the amount of fuel injection to reach the target point. In the past, when the spacecraft approached asteroid Ryugu, the spacecraft sent images to the ground and on-ground station sent control inputs back to the spacecraft. However, since the approach speed to the asteroid is large for this flyby, the error also becomes large if we do the guidance and navigation using on-ground stations. Therefore, the spacecraft will attempt to improve its guidance accuracy by doing this autonomously. While Hayabusa2 will not hit Torifune, the technology for accurate guidance is the same technology required to impact an asteroid. Such a maneuver can be used to deflect the trajectory of an asteroid (as demonstrated during the NASA DART mission) and thus this mission can contribute to planetary defense. My team is currently studying and preparing to make this very close flyby happen.
As for my own research, since I was a student, I have been focusing on the target markers that were dropped by Hayabusa2 onto asteroid Ryugu. These target markers are used to guide the spacecraft autonomously to the surface of the asteroid, which is an unknown environment. Based on the experience and knowledge gained from our research to date, we are studying with other team members as to how to achieve high guidance accuracy for the spacecraft during the 2026 flyby. In addition, the ability to perform autonomous, highly accurate guidance and navigation will be a great advantage for rendezvous missions. Therefore, I would like to further promote research on autonomous navigation so that it will be useful for Hayabusa2#'s approach to 1999KY26, which is scheduled to arrive in 2031.
I have been appointed as a project researcher this fiscal year, and as a member of the Hayabusa2# team, I have started to prepare for the flyby. What I have felt most so far is that we have to prepare thoroughly in order to accomplish the mission. The flyby, the exploration itself, is really only an instantaneous process, but I feel that there is a huge amount of consideration and work that goes into it for that one moment. I am sure that many serious and difficult preparations await us for the flyby, but I would like to carefully conduct each part of the research and study the necessary steps one by one. While learning from my seniors who have achieved success on Ryugu, I hope to contribute to the success of the flyby mission and subsequent asteroid exploration missions.
Terminologies
- *1 Flyby : the close approach of a spacecraft to a planet.
- *2 Planetary defense : detecting and reducing the risk of impact from potentially dangerous near-Earth objects.