The laser interferometer space antenna (lisa) is a space-based gravitational wave (GW) observatory which will observe GWS between 0.1 and 100 MHZ. This NASA-supported ESA-led flagship mission uses…

The University of Florida Division of Sponsored Research was awarded a $1.24 million grant by the National Aeronautics and Space Administration (NASA) to support testing and verification of prototypes for the Laser Interferometer Space Antenna (LISA) mission. LISA is a NASA-supported European Space Agency-led space-based gravitational wave observatory planned for launch in the mid-2020s. Under the grant, the University of Florida will verify the dimensional stability of LISA telescope structural and engineering development unit models using interferometric length measurements with sub-picometer resolution over months to demonstrate sub-micrometer lifetime stability. The work will also monitor telescope distortions under temperature variations and support development of a compact fiber-based cavity injection system for high-precision internal length measurements. This testing and verification work is critical to maturing LISA telescope prototype designs ahead of a 2023 mission adoption review. The University of Florida is the sole prime contractor on the research grant, which runs from January 2020 through March 2023.

The laser interferometer space antenna (lisa) is a space-based gravitational wave (GW) observatory which will observe GWS between 0.1 and 100 MHZ. This NASA-supported ESA-led flagship mission uses laser interferometry to measure distance fluctuations between three spacecraft separated by 2.5 GM. NASA is currently developing the telescopes which will be within the measurement path between the spacecraft. The main objective of the work proposed here is to verify the dimensional stability of telescope models, starting with the NASA provided structural thermal model (STM) followed by engineering development units (EDU). The verification methods involve interferometric length measurements with sub-PM/rthz sensitivity across the lisa band and NM sensitivity over 3 months to prove sub-UM lifetime (10 YR) stability. The experimental setup also allows to monitor temperature dependent telescope distortions and resulting wavefront errors. These would change the tilt to length coupling and which affects the calibration during flight needed to subtract IT. A third objective is the development of a compact fiber-based cavity injection system for length measurements at the subpm level. This risk reduction activity would result in a very compact system for telescope internal length measurements known as the optical truss interferometer. For objective 1, the STM/EDU will be placed between two mirrors forming a standing wave optical resonator. The frequency of the measurement laser will be locked to this resonator to follow its dimensional changes. A second laser will be stabilized to an ultra-stable reference resonator or to a molecular iodine line for PM and m tests, respectively. Variations in the frequency difference between the lasers are directly proportional to length changes in the STM/EDU. The telescope distortions will be measured using a spatial profile of heterodyne laser beat signals. This approach is often called a phase camera. Our tool will use a differential phase camera approach to isolate telescope distortions from other distortions. While we will likely not be able to measure the absolute wavefront error, we will be able to monitor changes as a function of temperature during the PM-tests. This work also requires a significant modeling effort to extract the telescope distortions from the measured signals. Statement of significance of the proposed work: this work is part of the testing and verification plan of the lisa telescope prototypes (STM and edus) prior to mission adoption which is expected around 2023. The proposed work will also create a well-tested infrastructure and well-trained personnel, which is necessary for the verification of flight units in the future.