Lunar rotation and tides with Same-Beam Interferometry: Results of numerical simulations

In recent years, a rapidly increasing number of missions have targeted the Moon, with the number expected to increase even more in the near future, presenting an unprecedented amount of flight opportunities for science payloads. Furthermore, lunar Positioning, Navigation and Timing (PNT) networks that would support this rapidly increasing number of missions are in development by space agencies. Together, they present exciting opportunities for multi-lander radio science experiments by utilizing either dedicated payloads or the built-in spacecraft communications systems. Up to date, the principal source of data on lunar tides, orientation and ephemeris has been Lunar Laser Ranging (LLR), which utilizes retroreflectors left on the surface of the Moon by the Apollo and Luna missions, and which provides several decades of data, with centimeter-level precision achieved in the recent years. An alternative technique called Same-Beam Interferometry (SBI) has been proposed for the Moon in Bender 1994, and later explored in Gregnanin et al. 2012. Here, we take their research further and investigate the possibility of measuring the lunar orientation and tides using SBI observations for various mission configurations, reflecting the proposed future lunar missions. We discuss the relationship between the rotation and tides of the Moon and its interior and evolution models. We conduct numerical simulations to identify the limitations of this and other radiometric techniques, and identify the mission requirements and optimal architectures and locations. We compare our results to those obtained by LLR and spacecraft data, as well as to the expected performance of the recently-proposed Differential Lunar Laser Ranging (DLLR) (Zhang et al. 2023). Finally, we investigate the possibility of using the ROB's LaRa instrument and its future iterations for lunar radio science.

References:

Bender, P. L. (1994). “Proposed microwave transponders for early lunar robotic landers”. In: Advances in Space Research 14.
Gregnanin, M. et al. (2012). “Same beam interferometry as a tool for the investigation of the lunar interior”. In: Planetary and Space Science 74.
Zhang, M. et al. (2024). “Advantages of combining Lunar Laser Ranging and Differential Lunar Laser Ranging”. In: Astronomy & Astrophysics 681.