Autonomous Formation Flying using X-Ray Pulsar Based Navigation

The two main purposes of this paper are looking for a navigation plan for formations with total autonomy, good accuracy and least requirements; and examining the aspects of a formation configuration that affect the performance of absolute and relative navigation methods. 1 2 The newly developed X-ray pulsar navigation (XNAV) is employed, and two XNAV modes are introduced: standard XNAV is used for its good autonomy and observability, and relative XNAV is used to examine the effectiveness of relative navigation methods in the navigation of formations. Also crosslink measurement is employed for its great accuracy and low requirement. Two analysis tools are developed to examine the effect of formation configuration on navigation methods. Error amplification factor (EAF) is a useful tool describing the observability levels of navigation plans, and observation variance factor (OVF) is used to evaluate the effectiveness of a navigation method when the formation configuration changes. With the tools and simulations, the effects of the height, tightness and shape of formations on navigation methods are revealed. The performances of relative navigation methods deteriorate as the formation becomes tighter, higher or have a new shape with less relative movements. Under common formation settings, relative navigation methods cannot provide sufficient observability. But the absolute navigation method - standard XNAV is hardly affected by any changes of the formation configuration, with only two pulsars standard XNAV can achieve total observability. The only exception is when the orbit is low enough that the orbit plain rotates fast enough for only one pulsar to achieve total observability. The integrated navigation plan with two pulsars in standard XNAV and crosslink measurement is chosen for its total autonomy, low requirements and good performance. Under various formation settings the positioning accuracy of this plan is within 20m, and the relative accuracy is within 8m. A hardware reduction method by using only one X-ray detector observing multiple pulsars at different periods is proposed and examined with simulations. Comparing to the multiple detectors method, the positioning accuracy is only 10m larger, and the relative accuracy is 6m larger at most. The analysis and simulation results prove that the proposed autonomous integrated navigation plan is suitable for all formation configurations, and it has good accuracy and low requirement, especially after implementing the hardware reduction method.