The Lunar Electromagnetic Monitor in X-rays (LEM-X): optimization of the instrument layout and trade-off study for the observatory location on the Moon surface

The Lunar Electromagnetic Monitor in X-rays (LEM-X) is a proposed observatory for high-energy transients to be placed on the surface of the Moon and it is being developed in the context of the Earth-Moon-Mars project of the Italian National Recovery and Resilience Plan. The fundamental components of the LEM-X instrument are pairs of compact and lightweight coded aperture cameras. In this paper, we present a tradeoff analysis ultimately aimed at defining the configuration of the experiment and its best location on the Moon surface. We first optimized the number and configuration of cameras and designed a concept of their support structure, to ensure best effective sky coverage while minimizing complexity, volume, and mass. Then, by using NASA’s SPICE toolkit, simulations were carried out to assess the effective sky coverage of the proposed instrument configuration across the lunar day, as well as the solar incidence angle. We provide results for a selection of potential lunar surface locations, along with considerations about thermal management and solar power. These initial findings lay the groundwork for future mission implementation studies.