UT Austin's new method simulates cislunar pursuit-evasion games

Researchers from the University of Texas at Austin—Quentin Rommel, Filippos Fotiadis, Cade Armstrong, Luke Peterson, and Ufuk Topcu—have formulated cislunar spacecraft pursuit-evasion as a zero-sum differential game. Published on arXiv (2608.08151), the work uses the circular restricted three-body problem to model the nonlinear, unstable environments spacecraft face near the Moon. Each spacecraft independently controls its thrust and reference orbit phase, allowing motion along periodic orbits and across quasi-periodic tori while staying close to a reference trajectory. The team solves the game with a constrained discrete-time differential dynamic programming (DDP) method that enforces hard input constraints, complemented by a shared time regularization that synchronizes both spacecraft and refines discretization near close lunar passages.

Numerical experiments on periodic and quasi-periodic orbits reveal that phase control significantly improves maneuvering flexibility while limiting departure from the reference orbit. The discrete-time formulation also delivers a large computational advantage over continuous-time methods, making real-time planning more tractable. When comparing quasi-halo and quasi-near-rectilinear halo orbits, the authors found that close lunar passages create larger escape opportunities but also increase the sensitivity of the encounter. These findings highlight that reference orbit geometry is a critical factor in defensive cislunar mission design, offering a new framework for autonomous space defense and collision avoidance in increasingly crowded lunar space.