Simulation Study of Relations Between Design Parameters
and Velocity Measurement Accuracy in the Lunar Landing Radar

Seisuke Fukuda1, Tomohiko Sakai1, Teppei Sato2,1, and Takahide Mizuno1
1ISAS/JAXA, 2Tokyo University of Science

Abstract
A radar for navigation in future Japanese lunar landing missions (e.g., SELENE-2) is being developed in the ISAS/JAXA. The ability of pinpoint soft landing on lunar surfaces, where we want to examine, broad-ens the range of scientific and exploration missions. In order to perform the pinpoint landing, measurement of relative velocity against the surfaces is considered to be essential. So the C-band pulse radar provides not only altitude but also velocity information. Required accuracy of the velocity measurement is less than 5% or 10 cm/s. Until now, we have proposed a novel method based on the Doppler measurement at multi-ple points within a received pulse. While the Doppler frequency at each point has a kind of ambiguity, the most probable velocity can be estimated by fitting the multi-point measurement with a theoretical curve in the plane of range time and the Doppler frequency. The multi-points method was implemented on our de-veloping radar BBM (Bread Board Model), and tested in the helicopter-based field experiments. On the start of the next development phases (i.e., EM and PFM) soon, it is important to understand how the pa-rameters in the radar design affect the accuracy of the velocity measurement. We have developed a radar simulator, with which we can examine the relations between the measurement accuracy and several design parameters: Beam width (range/azimuth), beam tilt angle, pulse width, A/D sampling frequency, point se-lection, and so on. In this paper, the results of the simulation study are shown in detail. The results are also helpful in the actual radar operation such as a kind of mode switching.


月探査機搭載着陸レーダにおける各種設計パラメータと
速度測定精度の関係に関するシミュレーション検討

福田盛介1，坂井智彦1，佐藤哲平2,1，水野貴秀1
1宇宙航空研究開発機構 宇宙科学研究本部，　2東京理科大学

摘要
ISAS/JAXA では，将来の月惑星着陸ミッションに用いる誘導航法用センサとして，C バンドのパルスレーダを開発している．所定の地点へピンポイントで軟着陸するミッションを考える場合，着陸レーダには，対地高度のみならず，表面に対する水平方向速度を5%あるいは10cm/sといった高い精度で測定することが求められる．これに対し，著者らは，受信パルス内の複数の時間サンプルにおいてドップラ周波数を測定するアイデアに基づく，新たな速度測定の方法を提案している（複数サンプル方式）．本稿では，ビーム傾斜角やビーム幅，あるいはパルス幅などのレーダ設計に係る種々のパラメータと複数サンプル方式の速度測定精度の関係について，シミュレータを開発して定量的に検討した結果について報告する．