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Hayabusa2# is an extended mission of Hayabusa2, which will spend another decade conducting various scientific and engineering investigations highlighted by a flyby at Asteroid (98943) Torifune in 2026 and a rendezvous with Asteroid 1998 KY26 in 2031. Our space flight operations have continuously performed cruise science investigations of exoplanets, comets, and zodiacal light. Recently, the mission has also weighed our efforts more to plan flyby operation sequences at its target, (98943) Torifune, formerly 2001 CC21. Planned to be in July 2026, the flyby observation is an excellent opportunity to detail this asteroid geologically. Unlike a rendezvous observation, however, the flyby at an encounter speed of 5.3 km/s challenges detailed scientific observations. Regardless of the spacecraft's tight system constraints, maximizing scientific return is essential to address our science objectives.
Hayabusa2 #'s science objective for the Torifune flyby is to determine the asteroid's taxonomy, shape, and morphological features as much as possible under extremely limited fast-flyby conditions to constrain its contribution to material transfer and demonstrate critical Planetary Defense technologies. The measurement requirements to achieve this objective specify the necessary performances of the onboard remote-sensing instruments: the Optical Navigation Camera Telescope (ONC-T), Thermal Infrared Imager (TIR), Near Infrared Spectrometer (NIRS3), and Laser Altimeter (LIDAR). Given highly tight constraints, while ONC-T and TIR will challenge their resolution limits, NIRS3 and LIDAR will attempt to detect at least one data sample.
The science operation planning divides science observation sequences into two phases. The first phase targets observations relatively far from Torifune 5 minutes before the closest approach (T-5 min to the CA). Because this phase actively controls the spacecraft via optical navigation, guidance, and control, science observations are expected to be limited and must meet zero conflicts with the planned system sequences using ONC-T for optical navigation. Limited scientific observation chances also challenge the simultaneous use of multiple remote-sensing instruments for science operations.
Conversely, the second phase can focus more on science investigations from T-5 min until the CA. This phase is planned to have more time for science observations. The primary discussion among the science team is about how to use the available time to maximize science return. The second phase also needs to determine the view geometry and CA timing for science observations based on Torifune's shape and rotational state. The mission's system team gave the science team flexibility regarding the timing and approach direction at the CA. We are currently identifying a sequential plan that can characterize the asteroid's geological and thermal conditions at most but can still satisfy the system constraints.
Considering all possible conditions, the Hayabusa2# team offers a holistic science observation plan for the Torifune flyby. This paper summarizes the current status of the mission's science operation planning.