伊藤 琢博

Precise satellite formation flying is a promising technology that enables unprecedented astronomical observations. For comprehensive astronomical missions, preliminary small satellite missions in low Earth orbit (LEO) have been proposed. However, various perturbation sources in LEO can disturb rigid and precise formation control. This study proposes an approach that combines feedforward and feedback controls to attain precise formation flying in LEO. The developed feedforward control can compensate for major gravitational perturbations, predicted from the absolute position and velocity of spacecraft. In addition, the feedback control can address uncertain and unmodeled perturbations. Consequently, the hybrid approach can yield a smaller tracking error than feedback control alone. This novel approach is reliable and robust against environmental uncertainties—including atmospheric density, high-order Earth gravitational potentials, and third-body gravity—and systematic uncertainties—including atmospheric and solar radiation coefficients and thrust errors of spacecraft. Indeed, closed-loop control simulations of a linear astronomical interferometer under such uncertainties reveal a significant reduction in tracking error and feedback controller load using feedforward control, potentially making precise and reliable formation flying in LEO much achievable.

We propose SILVIA (Space Interferometer Laboratory Voyaging towards Innovative Applications), a mission concept designed to demonstrate ultra-precision formation flying between three spacecraft separated by 100 m. SILVIA aims to achieve sub-micrometer 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-meter-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 for collision. This mission will fill the current technology gap towards future missions, including gravitational wave observatories such as DECIGO (DECihertz Interferometer Gravitational wave Observatory), designed to detect the primordial gravitational wave background, and high-contrast nulling infrared interferometers like LIFE (Large Interferometer for Exoplanets), 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.