Technological heritage exploitation of the experience of the LISA Pathfinder release mechanism

Gravitational waves, which are ripples in space-time predicted by Einstein's General Theory of Relativity, have revolutionized our understanding of the universe since their first-ever direct detection in 2015 by the Advanced Laser Interferometer Gravitational Wave Observatory (Advanced LIGO), the most sensitive on-ground gravitational wave detector ever built. The detection of gravitational waves marked a monumental milestone in scientific achievement, providing a new observational tool to probe some of the most enigmatic phenomena in the universe. The successful detection of gravitational waves has not only validated Einstein's theory but has also opened a new window onto the universe, allowing scientists to explore phenomena that were previously hidden from traditional electromagnetic observations. Moreover, gravitational wave astronomy promises to shed light on fundamental questions regarding the nature of gravity, the origin of compact objects, and the evolution of the universe itself. However, the on-ground detection of gravitational waves is affected by some factors limiting the measurement sensitivity, mainly the presence of a relatively high background noise due to the Earth environment. As a result, innovative technologies to detect gravitational waves from space are being developed, since the outer space environment is less noisy compared to Earth. The inaugural space-based detector, known as the Laser Interferometer Space Antenna (LISA), is being developed and its launch is currently scheduled for 2034. Given the mission complexity, a dedicated precursory mission known as LISA Pathfinder (LPF) was launched in 2015 and operated until 2017. LISA Pathfinder aimed at demonstrating the feasibility of gravitational waves detection directly from space by measuring the noise affecting the relative acceleration of two free falling test masses (TMs) enclosed in the same spacecraft. The scientific goal of the mission was fulfilled, proving that a requirement on the TMs relative acceleration 10 times more demanding than the one set was met. The mission was a scientific success, however some difficulties had to be faced, particularly during the release of the TMs into free fall. The mission telemetry data shows that, for the majority of the in-flight releases, all linear and rotational TMs velocity components were not compliant with the requirements. Given these anomalies, an additional dedicated TMs release campaign was carried out at the end of the mission phase to test different release strategies. The analysis of the extended mission campaign telemetry data supports the hypothesis that the separation of the mechanism responsible for the TM release from the TM caused the TMs to assume unexpected states. The research work outlined in the thesis arises in this context: understanding what happened at the TMs releases is critical since the mechanism in charge of the release will also be employed in LISA. Starting from three extensive on-ground experimental campaigns, through a methodical exploration of the campaigns results, the TM release into free fall function is assessed, providing guidelines for the design of the release mechanism units for LISA. The factors contributing to the momentum acquired by the TMs at the release are identified and analyzed, demonstrating that the nominal release dynamics is compliant with the LPF design requirements. The results are considered for possible application in future space missions relying on very accurate precision sensors or accelerometers for spacecraft navigation and scientific measurements study.