Mission Concept for Demonstrating Small-Spacecraft True Anomaly Estimation Using Millisecond X-Ray Pulsars

Mission Concept for Demonstrating Small-Spacecraft True Anomaly Estimation Using Millisecond X-Ray Pulsars

Utah State University, Logan, UT

Navigation based on X-ray pulsars was first suggested in 1981 for deep space navigation as an alternative to the conventional Deep Space Network (DSN) which is inaccurate at large distances from the Earth. This idea was recently demonstrated using the NICER/SEXTANT instrument onboard the ISS. X-ray pulsar-based navigation is of of great interest as it eliminates the reliance on Earth-based systems, and is yet to be implemented as an autonomous navigation system for deep space missions. For the purpose of navigation, X-ray millisecond pulsars are the most appropriate celestial sources. They emit unique, stable and periodic radiation that exhibits high timing stability comparable to atomic clocks, thus making them suitable as navigational beacons. The phase difference between the pulsar’s pulse profile obtained at the satellite and a reference profile is tied to the position of the satellite with respect to the chosen reference location, typically considered to be the Solar System Barycenter (SSB). Measurements from at least four pulsars are required to estimate the 3D position, velocity, and time of the satellite. This article describes a small satellite mission concept being developed at the Small-spacecraft Systems and PAyload CEntre (SSPACE) at the Indian Institute of Space Science and Technology (IIST) that aims to demonstrate navigation in space using X-ray millisecond pulsars. The satellite contains a miniaturized X-ray timing detector payload, which extracts accurate pulse profiles from detected pulsar signals. A mission-specific algorithm is developed that uses measurements from a single pulsar to estimate only the true anomaly of the satellite, since given the orbital insertion, the other orbital elements are assumed to be stationary. Additionally, the process of pulsar selection is presented, where pulsars are ranked according to the weighted parameters of stable time periods, visibility from the chosen orbital configuration, and high signal-to-noise ratio with respect to the diffuse X-ray background. This is followed by details of the instrument design and concept of operations of this technology demonstration mission. The article concludes with an overview of the systems architecture of the small-satellite, which has a standard 6U CubeSat form factor and details regarding the various subsystems including the On Board Computer, Electrical Power System, Communication system, and Attitude Determination and Control System are discussed. A successful demonstration of this mission will pave the way for future small-satellite missions, where 3D position estimation can be carried out using multiple X-ray pulsar detectors.