Trajectory reconstruction of Hayabusa's atmospheric reentry

Abstract

The Hayabusa mission of the Japan Aerospace Exploration Agency ended on 13 June, 2010, with the planned atmospheric reentry of the main spacecraft and asteroid sample return capsule. These objects reentered the atmosphere at night, creating bright fireballs in the sky over the Woomera Prohibited Area in the Australian desert. The main spacecraft disintegrated in the atmosphere, and the capsule reentered nominally and landed approximately 1 km from its targeted landing point. This paper describes the work that was done to: operate an optical measurement system to observe the reentry; identify the capsule; and estimate the capsule's trajectory using an Extended Kalman Filter (EKF). The measurements consisted of unit line-of-sight vectors from optical measurements from ground-based cameras. Using this system, the capsule was distinguishable from the main spacecraft fragments from approximately 52 to 37 km altitude. The preliminary post-flight trajectory reconstruction results described in this paper agree closely with the nominal trajectory. The position (velocity) difference between the nominal and estimated trajectories is approximately 2 km (200 m/s) averaged over the measurement span. The state error covariances from the EKF are underestimated because of the presence of measurement biases on the order of 10 −3 rad; several likely causes for these measurement biases are discussed.