１．Abstract

Lunar Excursion Vehicle (LEV)-1 is one of the rovers mounted on the Smart Lander for Investigating Moon (SLIM). Figure 1 shows the appearance of LEV-1, a 2.3 kg robot. Its objectives include demonstrating rough terrain mobility suitable for small rovers, autonomous functions, observing the lander’s status after landing, and directly transmitting data to Earth through an independent communication system. Additionally, LEV-1 serves as a data relay for another rover, LEV-2. As shown in Figure 2, LEV-1 was separated from SLIM just before lunar landing and began operating autonomously. LEV-1 successfully transmitted locomotion, environmental, and image data captured by the camera on LEV-2 directly to Earth without relying on the SLIM.

Fig. 1. Appearance of LEV-1

Fig. 2. LEV-1 Deployment and Activity on the Lunar Surface

２．Technical Details

LEV-1 is a hopping rover equipped with a jump mechanism at the rear of its body. Its primary mode of locomotion is hopping. It has a single wheel to aid posture recovery after jumping. LEV-1 adopts hopping locomotion instead of continuous wheeled movement to explore new mobility mechanisms. Additionally, obstacles such as lunar boulders are relatively large for small robots, and hopping is well-suited for overcoming them.

LEV-1 stores energy in a spring and converts it into kinetic energy to perform jumps. Figure 3 illustrates the hopping motion. Energy is stored in the spring by pulling the hopping pad’s string using a winch mechanism. The stored energy propels the pad when the string is released. This generates momentum, enabling the rover to hop.

Fig. 3 Hopping motion of LEV-1

LEV-1’s wheel is octagonal and designed for direction and posture control. A polygonal wheel was chosen to achieve sufficient traction and minimal sinkage. The octagonal shape helps balance these requirements, enabling effective maneuverability on the lunar terrain.

The design of LEV-1 incorporates mechanisms that enable continuous operation on uneven terrain with a minimal number of motors, preventing deadlock. Since small rovers cannot always be guaranteed continuous remote operation, the mechanical system itself needed to support full autonomy. LEV-1 can transition from any posture to a jump-ready position by rotating its wheel in one direction without requiring feedback control. This feature reduces the complexity of autonomous operations.

LEV-1 demonstrated a novel locomotion mechanism, offering a new option for small exploration rovers. It also validated key technologies like direct Moon-Earth communication, full autonomy, and multi-rover exploration. These achievements are essential to an era where numerous rovers can operate on the lunar surface.

Takao Maeda
Member，Tokyo University of Agriculture and Technology (〒184-8588 2-24-16, Naka-cho, Koganei, Tokyo Japan)

Kent Yoshikawa
Member，Japan Aerospace Exploration Agency (〒252-5210 3-1-1, Yoshinodai, Chuo-ku, Sagamihara, Kanagawa, Japan)

Masatsugu Otsuki
Member，Japan Aerospace Exploration Agency (〒252-5210 3-1-1, Yoshinodai, Chuo-ku, Sagamihara, Kanagawa, Japan)

Tetsuo Yoshimitsu
Japan Aerospace Exploration Agency (〒252-5210 3-1-1, Yoshinodai, Chuo-ku, Sagamihara, Kanagawa, Japan)

Yasuharu Kunii
Member，Chuo University (〒112-8551 1-13-27, Kasuga, Bunkyo-ku, Tokyo, Japan)