Kiwamu Izumi

Abstract DECIGO (DECi-hertz Interferometer Gravitational Wave Observatory) is a space-based gravitational wave antenna concept targeting the 0.1--10 Hz band. It consists of three spacecraft arranged in an equilateral triangle with 1,000 km sides, forming Fabry-P{'e}rot cavities between them. A precursor mission, B-DECIGO, is also planned, featuring a smaller 100 km triangle. Operating these cavities requires ultra-precise formation flying, where inter-mirror distance and alignment must be precisely controlled. Achieving this necessitates a sequential improvement in precision using various sensors and actuators, from the deployment of the spacecraft to laser link acquisition and ultimately to the control of the Fabry-P{'e}rot cavities to maintain resonance. In this paper, we derive the precision requirements at each stage and discuss the feasibility of achieving them. We show that the relative speed between cavity mirrors must be controlled at the sub-micrometer-per-second level and that relative alignment must be maintained at the sub-microradian level to obtain control signals from the Fabry-P{'e}rot cavities of DECIGO and B-DECIGO.

Abstract We propose a mission concept, called the space interferometer laboratory voyaging towards innovative applications (SILVIA), designed to demonstrate ultra-precision formation flying between three spacecraft separated by 100 m. SILVIA aims to achieve submicrometer precision in relative distance control by integrating spacecraft sensors, laser interferometry, low-thrust, and low-noise micro-propulsion for real-time measurement and control of distances and relative orientations between spacecraft. A 100 m scale mission in a near-circular low Earth orbit has been identified as an ideal, cost-effective setting for demonstrating SILVIA, as this configuration maintains a good balance between small relative perturbations and low risk of collision. This mission will fill the current technology gap towards future missions, including gravitational wave observatories such as the decihertz interferometer gravitational wave observatory (DECIGO), designed to detect the primordial gravitational-wave background, and high-contrast nulling infrared interferometers such as the large interferometer for exoplanets (LIFE), designed for direct imaging of thermal emissions from nearby terrestrial planet candidates. The mission concept and its key technologies are outlined, paving the way for the next generation of high-precision space-based observatories.

Abstract Future gravitational wave observation in space will demand improvement in the sensitivity of the local sensor for the drag-free control. This paper presents the proposal, design, and demonstration of a new laser interferometric sensor named Quadrature Interferometric Metrology of Translation and Tilt (QUIMETT) for the drag-free local sensor. QUIMETT enables simultaneous measurements of both translational displacement and tilts of a reflective object with a single interferometer package. QUIMETT offers a characteristic feature where the sensitivity to tilt is independent of the interference condition while maintaining the ability to measure the translational displacement for a range greater than the laser wavelength. The tilt-sensing function has been demonstrated in a prototype experiment. The tilt sensitivity remained unchanged in different interference conditions and stayed at 10 nrad Hz at 0.1 Hz.