Measurements of Reflection Characteristics of the Lunar Surface for Radio Propagation

Numerous Moon missions are currently being planned for the 2030s and beyond. Communications traffic among astronauts, rovers, robots, satellites, etc. will increase exponentially. Mobile communications technologies such as 5G systems and WiFi on the Earth seem able to support such communications on the Moon. However, radio propagation characteristics on the Moon may be different from those on Earth because the lunar surface is covered by a regolith consisting of metal compounds. To determine radio propagation characteristics there, we investigated the reflection coefficient of a flat surface with a regolith simulant (also called simulated lunar soil) at five frequency bands defined in the latest SFCG (Space Frequency Coordination Group) recommendation, i.e., the 2.4 GHz, 5.6 GHz, and 25 GHz bands for lunar surface to lunar surface communication and used for 5G and WiFi, as well as 7 GHz and the 8.5 GHz bands for lunar orbit to lunar surface communications. The reflection coefficient of concrete blocks, which are widely used on Earth, were also measured and compared. The results indicate that the design methods used for coverage areas of mobile communications systems on Earth can be applicable on the Moon with minimal adjustments.