Deep Space Navigation of Distributed Small Spacecraft Using Occultations of Celestial X-ray Sources

This program will develop an innovative small spacecraft navigation system using X-ray energy band observations of celestial sources by measuring the photon flux change during the time of the horizon crossing due to occultation by a planetary body, referred to as Occultation X-ray Navigation (OXNAV). Previous work by ASTER Labs has demonstrated concept feasibility of X-ray navigation (XNAV) using periodic source-based algorithms. OXNAV complements XNAVrsquo;s continuous source tracking by providing measurements when sources are obscured by a planetary body. The blended XNAV+OXNAV approach will utilize both the periodic nature of the faint, stable radio and X-ray pulsars when visible, and steady, brighter sources that continually become occulted during a spacecraftrsquo;s orbit. Thus, the operational prototype OXNAV software package and hardware instrument would be capable of frequent measurement updates and continuous, accurate absolute and relative navigation. The baseline instrument is designed for small spacecraft, including larger CubeSats, facilitated by emerging detector materials capabilities, with near-all-sky detection configurations, very good energy resolution, lower energy thresholds for high photon counts, and precise onboard photon timing. Benefits include increased deep space autonomy and formation flight for distributed small spacecraft, while decreasing the burden on the DSN. Phase I will evaluate OXNAV feasibility for relevant NASA applications with system requirements developed based on identified and characterized sources assembled into a catalog. The prototype instrument hardware design will be coupled with data processing navigation algorithms that fuse measurements in a single Extended Kalman filter. ASTER Labsrsquo; XPRESS software and a filter simulation will assess absolute and relative navigation performance under multiple cooperative spacecraft mission scenarios.nbsp;