NeXosim, An Open-Source, Rust-Based Digital Twinning Framework for Hardware-In-The-Loop Testing and Virtual FlatSats

NeXosim, An Open-Source, Rust-Based Digital Twinning Framework for Hardware-In-The-Loop Testing and Virtual FlatSats

Salt Palace Convention Center, Salt Lake City, UT

Digital twinning has become a cornerstone of modern space systems, enabling robust in-orbit operations and ground verification and validation. For over two decades, major spacecraft manufacturers and space agencies have relied on Discrete Event Simulation (DES) to achieve these goals. The C++-based Simulation Modelling Platform (SMP), now an ECSS standard, has emerged as a unifying framework for these efforts. Despite the tremendous benefits of simulation-assisted spacecraft development, the complexity, rigidity, and lack of vendor-neutral implementations of SMP have limited its adoption in academia and the NewSpace sector. This gap is particularly concerning given the high failure rate of SmallSat missions, where flexibility, ease of use, and cost efficiency are critical to success. To address these challenges, we present NeXosim, an open-source DES framework designed to streamline spacecraft digital twinning. Built on Rust—a modern, memory-safe programming language widely regarded as a superior alternative to C++ for high-performance, reliable software—NeXosim combines ease of use and flexibility. NeXosim is the first auto-parallelizing DES in the space industry, leveraging Rust's native support for multithreading and asynchronous programming. In spite of this, NeXosim remains far more accessible than traditional C++-based simulators. It is strongly optimized for low-latency Hardware-in-the-Loop (HIL) testing, addressing a key use case in modern space systems development. NeXosim's core simulation concepts are presented, including its inter-model communication primitives and asynchronous architecture, followed by an illustration of real-world applications within industry and academic projects.