Hayabusa2 Re-Entry Capsule Tracking by Marine Radars

In the Hayabusa2 re-entry capsule recovery operation, marine radars were used to estimate the landing point of the capsule. These radars were commercial products for ships and were used with some modifications for this operation. The radars tracked the instrument module (I/M) containing the asteroid samples for 18 min, along with other equipment. The maximum observed distance was 31.55 km, and the tracking was accurate up to 240 m near the I/M landing point. This article describes the marine radar system, reports the tracking results of the operation, and discusses the considerations made for future missions. One consideration is to estimate the altitude by using multiple search radars in order to more accurately predict the landing point. Another is to estimate the radar cross-section of the I/M during descent. This article demonstrates that the altitude can be estimated by the search radars, and the radar cross-section fluctuates by approximately. 10 times depending on the elevation angle relative to the radar. The results of this article suggest the possibility of cooperative search by using multiple small radars. This feature may contribute to reductions in mission costs and to expanding the choice of landing areas.