Formation-flying interferometry in geocentric orbits

Spacecraft formation flying serves as a method of astronomical instrumentation that enables the construction of large virtual structures in space. The formation-flying interferometry generally requires very-high control accuracy, and beyond-Earth orbits are typically selected. By contrast, this study proposes the use of geocentric orbits for formation-flying interferometry. A geocentric orbit is beneficial because of its economic accessibility and the availability of flight-proven technologies for formation-flying autonomy, safety, and management. Its feasibility depends on the existence of specific orbits that satisfy a small-disturbance environment with favorable observation conditions. This theory, developed based on celestial mechanics, indicates that small-perturbation regions tend to appear in higher-altitude and shorter-separation regions. Candidate orbits are identified in high Earth orbit for the triangular laser-interferometric gravitational-wave telescope, which is 100 km in size, and in medium Earth orbit for the linear astronomical interferometer, which is 0.5 km in size. A low Earth orbit with a separation of approximately 0.1 km may be suitable for experimental purposes. As shown in these examples, geocentric orbits are potentially applicable for various types of formation-flying interferometry.