Direct Position Estimation Framework for Lunar Positioning, Navigation, and Timing

With the increasing volume of lunar missions planned by international space agencies in the near future, precise and reliable Positioning, Navigation, and Timing (PNT) for lunar operations have become essential for successful launches and exploration. Recent research has focused on leveraging the Global Navigation Satellite System (GNSS) for lunar positioning. However, one of the primary challenges of employing GNSS for lunar PNT is the significantly low signal power, caused by the long propagation distance and the side-lobe beam pattern of GNSS signals. In this work, we introduce the Direct Position Estimation (DPE) framework for GNSS-based lunar positioning. DPE is a high-sensitivity receiver design which is capable of operating the weak signal for positioning. It has been shown that the DPE approach outperforms the traditional two-step (2SP) approach, especially when working under harsh environments. Besides, we present GNSSLunarSim, a simple, flexible, and controllable signal simulator designed to generate GNSS baseband signals on the Moon for PNT solution validation. Simulation results demonstrate that the DPE framework achieves higher positioning accuracy than the 2SP approach under various conditions, highlighting its strong potential for lunar PNT applications.