Relative navigation for formation flying spacecrafts using X-ray pulsars

Relative navigation for spacecrafts has received a great deal of attention recently because of its importance for space applications, especially for formation flights. One approach of relative navigtion is to use the Global Positioning System (GPS). However, GPS signals are not available for deep space missions. Hence, an alternative solution is needed. A possibility is to use the signals emitted from X-ray celestial sources. One of the most reliable X-ray sources is pulsars. Relative navigation of spacecrafts may be accomplished by observing X-ray sources and indirectly determining the spacecrafts´ relative position. This paper investigates the algorithm of relative navigation for formation flying spacecrafts using X-ray pulsars. A novel relative navigation algorithm for multiple-satellite formation using X-ray pulsars measurements is proposed. The problem of relative navigation between formation flights utilizing X-ray pulsars measurements is investigated. The time difference of signal arrival (TDOA) is estimated by signal´s cross-correlated processing, which is further used as measurement to achieve the relative navigation. An Extended Kalman filter is employed to estimate the relative positions and velocities between the formation flights. Numerical simulations are performed to assess the proposed navigation algorithm. Furthermore, errors of the navigation are analyzed in order to improve the accuracy of this method.