Geometrodynamics research in the Sun-Earth-Moon system with laster retroreflectors and laser sabers.

by Simone Dell'Agnello (Istituto Nazionale di Fisica Nucleare)

Monday 17 Jun 2024, 14:30 → 16:00 Europe/Rome

Aula Conversi (Dipartimento di Fisica- Ed. G. Marconi)

We will present over 10 flight laser retroreflector instruments with TRL ≥ 7 (Technology Readiness Level), either flown or delivered and accepted for flight for the whole solar system: Mars, Phobos, Didymos asteroid, Galileo 2nd Generation, medium and low Earth orbits, Earth Observation, and more. We work for several space missions in deep space equipped with a laser saber or within observable distance of the International Laser Ranging Service (ILRS, ground-based laser sabers).

Then we will focus on current and imminent missions to the far and near side of the Moon, for the precise geometrodynamics of the Sun-Earth-Moon system.

Since 1969 Apollo and Luna missions deployed Laser Retroreflector Arrays (LRAs) of Cube Corner Retroreflectors (CCRs) on the Moon. These LRAs reflect the incoming incident light back to the emitter. Thanks to a technique known as Lunar Laser Ranging (LLR), high precision distance measurements of the Moon have been performed, by firing short laser pulses from Earth ground stations to these LRAs and measuring the two-way time of flight (ToF) of the light. LLR outputs include accurate tests of General Relativity (GR), information on the internal structure of the Moon, its ephemerides and geocentric positions and motions of Earth ground stations. Over the past 55 years, Earth ground stations LLR capabilities have significantly improved, and nowadays the lunar CCRs represent the main limitation for achieving more accurate/precise measurements of ToFs. The main problem affecting the Apollo and Lunokhod LRAs is represented by the lunar librations, resulting from the eccentricity and inclination of the Moon orbit around the Earth. For this reason, the Moon Laser Instrumentation for General relativity High-accuracy Tests (MoonLIGHT) instrument was envisaged at the Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali di Frascati (INFN-LNF), aiming at designing, prototyping, manufacturing and qualifying the next-generation of lunar laser retroreflectors, moving from a multi (small) CCR LRA geometry to a single (large, 100 mm) CCR, unaffected by lunar librations. The MoonLIGHT field of view is a cone with an opening angle of about 30˚ (with apex at the CCR vertex) and it must be pointed accurately to the Earth within 3˚. Since landers do not guarantee this accurate pointing, INFN-LNF proposed the MoonLIGHT Pointing Actuator (MPAc) hardware to ESA in 2018. MPAc was then selected by ESA for development. In 2021 ESA signed with NASA an MoU to launch MPAc to the Reiner Gamma swirl on the Moon, with a lander of the Commercial Lunar Payload Services (CLPS) program, the 3rd mission granted by NASA to Intuitive Machines (IM). This IM-3 launch is currently foreseen by NASA for 2025 [3], delayed due to recent failures / partial successes of the first two NASA returns to the Moon. Chang’E-6 landed OK.

MPAc will perform two perpendicular rotations to accurately point MoonLIGHT to Earth, operating in Ultra High Vacuum and in a wide temperature range. MoonLIGHT+MPAc was integrated, successfully qualified and delivered in 2023. The instrument was accepted by ESA in November 2023, by NASA and IM in December 2023, and now it is storage in Houston, ready for lunch on IM-3.