Modelling Radio Frequency Interference on the Lunar Farside

Abstract

Technological progress is a double-edged sword in the world of radio astronomy: improvements in antennas, receivers, and digital backends increase sensitivity, but rapid growth in terrestrial and orbital communications has caused a steep rise in radio-frequency interference (RFI). Modern datasets have become increasingly contaminated by RFI that is difficult to remove and can mimic or obscure astrophysical signals, complicating the search for objects such fast radio bursts (FRBs), pulsars, and technosignatures. The lunar farside has such been proposed as a site for radio-quiet observations, motivating missions such as the Lunar Farside Transients and Technology Telescope (LFT3) and others. However, planned lunar missions may introduce intended and unintended radio emissions into this protected environment. We use a LFT3-like instrument to model the evolution of the apparent lunar farside RFI environment over the coming years. Using a planned lunar mission catalogue and models for intended and unintended emissions, we estimate the received RFI over the 0.1-2700 MHz frequency range. We find that while intended emissions are concentrated near communications bands, particularly 2.4-2.6 GHz, unintended emissions contaminate broad regions of the LFT3 band. We further find that, under the assumptions of our model, uniform UEMR shielding of at least 30 dB is required to place the maximum interference below the sensitivity of a LFT3-like instrument; more sensitive telescopes would require higher UEMR shielding. We predict that the lunar farside will remain usable for LFT3-like observations, but will become increasingly contaminated as the lunar satellite population grows. This highlights the decreasing window of opportunity for measurements of the lunar farside's radio quiet environment and should inform future mission design and policy choices for the protection of Moon-based radio science.