Formation Flying (FF) is a revolutionary technology used for several satellites which maintain a specific position relative to each other. This technology enables us to achieve various missions, for example, X-ray telescopes, infrared interferometers and gravitational wave observatories, because it overcomes the constraint of satellites' physical dimensions. We are currently examining the precise FF technology needed for X-ray telescopes, called Formation Flight All Sky Telescope (FFAST). This paper describes the system analysis and design needed for precise FF guidance and control systems.