Trajectory Analysis of the Hayabusa2 Capsule from a Single Airborne Observation

The reentry trajectory of the Hayabusa2 capsule has been measured using a single video stream captured during the Australian Airborne Observation of the Hayabusa2 capsule. A new analysis methodology was required, and developed, to enable the trajectory to be determined from a single viewpoint. The method developed used the star-field background visible in the video stream, combined with the aircraft Global Positioning System data, to establish lines of sight along which the capsule was measured in time. A set of common sense criteria including altitude and velocity limits were then used to exclude impossible trajectories. The remaining trajectories were then examined and evaluated using a least-squares fitting routine to analyze candidate ballistic trajectories. The trajectories were ranked based on the fit parameter, enabling the determination of the single most likely trajectory and a family of most probable trajectories. The most probable Hayabusa2 capsule trajectory inferred from the measurements passed 10 km west of Coober Pedy and traveled at a heading of 150 deg. Evaluation of other highly probable trajectories showed they all passed Coober Pedy at a similar distance; however, they tended toward a slightly higher heading, approaching 155 deg. The distance between the measurement aircraft and the capsule remained relatively constant at approximately 180 km throughout the measurement period. This work demonstrates a new method for determining the trajectory of an object measured with a star-field background. Importantly, we have used this to establish the Hayabusa2 reentry capsule trajectory, and hence the distance from our aircraft, which will allow the detailed analysis of our spectral data.