Procurement of the beam alignment mechanism (bam) for lisas interferometric detection system (ids)

The Laser Interferometer Space Antenna (LISA) is the L3 mission in ESA's Cosmic Vision 2015- 2025 Programme, which has been adoptedby the Science Programme Committee in January 2024 with an expected launch date in 2035. LISA is made of a constellation of three spacecrafts tasked with detecting and measuring gravitational waves with precision. It will become the first ever space gravitationalwave observatory, aiming at delivering world-class science, granting a significant public and strategic impact. The three spacecrafts will be launched from the Guiana Space Centre, Kourou, with the Ariane 6.4 vehicle into a direct escape trajectory towards the operational heliocentric orbit at one Astronomical Unit (AU). The scientific payloads of LISA will be the result of the collaboration of subsystems developed with NASA and other European partners under the lead of ESA. Each of the three satellites will consist of two telescopes, two lasers, two interferometric detection systems with their associated optical benches, and two gravitational reference systems. Integrated on the Optical Bench Assembly (OBA), the Beam Alignment Mechanism (BAM) is a fundamental element of the Interferometric Detection System (IDS), the subsystem conceived to provide the interferometric readout of the laser phases, enabling the extraction of the key information needed to achieve the scientific goals of the LISA mission.The alignment of optical components,both within the IDS (on the OBA) and external to it, plays a crucial role in minimizing unwanted effects on the optical path lengthwithin the system. Spurious changes in the optical path length manifest as noise in the final interferometer measurements, with tilt-to-length (TTL) coupling being a significant contributor to the LISA noise budget.The suppression of this noise source is fundamental, and it is gained through different steps. Among them the implementation of a dedicated device, the BAM, enabling the adjustment of the optical alignment between the OBA and the Telescope after their integration on the spacecraft and during the in-orbit operations covers an essential role. The BAMs are mounted on the Optical Bench (OB) between the transmit and receive pupils and the optical interface to the telescope, allowing the global alignment between the OB and the Telescope to be adjusted as needed.The major functions of the BAM are:allowing the lateral displacement of the transmitted beam, working as the primary means for the TTL compensation;maintaining its position and its calibrated compensation throughout the mission lifetime;when necessary, operating in flight and correcting the newly induced TTL.A separate BAM for each of the two beams is hosted by the OBA, and it comprises two main units: the BAM Mechanism (BAM-M), integrated on the OBA and responsible for beam translation through the movement of the internaloptical elements, and the BAM Front End Electronics (BAM-FEE), integrated on the spacecraft and in charge of the sensing and the control of the BAM-M elements.The BAM, in line with the approved Multi-Lateral Agreement for LISA, was considered as a Belgian national contribution. Because of funding difficulties, the Executive have accepted responsibility for the procurement of this item. In order to have a reliable cost estimate and an overview of the expected development time, the Agency issued a Request for Information (RFI) in Q4 2024, the results of which will be considered in the preparation of the relevant Invitation to Tender (ITT).Consideringthe accumulated delays with this item (given that the mission was adopted 12 months ago), it is intended to release an ITT no laterthan April 2025 and start the development activities of the BAM in Q3 2025. Further to the application of the Agency wide preference clause, the Agency will reserve the right to give preference to offers contributing to contain either under return or over return situations in the SCI Programme.