In this paper, we will present the role and subjects of optical sensors in the obstacle detection of the moon lander, that is proposed as the SELENE follow-on mission SELENE-B. For more precise and safe moon landing, optical sensors are the most promising sub-systems, though it has many technical problems before using it as the primary space system sensor. For the optical obstacle sensor, monocular and stereo sensors are possible. Both type optical sensors and many image processing algorithms have good and weak points in their reliability of the results and CPU capabilities for the image processing. Comparison of those algorithms will be reported and a new hybrid system will also be proposed. Keyword: Moon, Landing, Image Processing, Obstacle Detection Introduction For Japanese SELENE-B, that will be the Japan’s first moon lander, the safeties and preciseness of landing are the most significant technological requirements. In 2000, SELENE-B was separated from the SELENE, that Japan’s first moon observing satellite would be launched in 2005, as the results of the project technical evaluation. SELENE-B was started as the research phase program by NASDA, ISAS, and NAL. The lack and immaturity of the safe landing technology were strongly pointed out through this technical evaluation, the landing safety was set as the primary and hardest requirements for SELENE-B study phase. 30 years after the Apollo, there is much drastic progress in the technologies. Especially in the field of information processing and computer technologies, the progress might be almost beyond imagining of the Apollo era’s engineers. The latest laptop PC’s computing capability might easily exceed the whole computing capabilities of the Apollo mission control center in 30 years ago. For our SELENE-B landing, these advanced computer science’s fruits will be fully applied to accomplish the safe and precise moon landing against the severe scientific requirements for the unexplored moon site, such as a vicinity area of a large crater central hill. Landing site From the scientific viewpoint, the unexplored and sciencefull zones were examined as the SELENE-B landing target. After intensive science discussion, a central hill of a large crater is selected as our first exploring target. For the Fig. 1 SELENE-B: Concept of Moon Lander Proceeding of the 7 International Symposium on Artificial Intelligence, Robotics and Automation in Space: i-SAIRAS 2003, NARA, Japan, May 19-23, 2003