(Press-News.org)
As lunar exploration intensifies, the cislunar space is experiencing increasing congestion. Traditional two-body Keplerian elements, which have long been the standard for Earth-orbiting objects, prove insufficient for accurately describing the complex orbits near the Earth–Moon Lagrange points due to the chaotic and non-integrable nature of three-body dynamics. This fundamental deficiency has hindered the development of an effective space situational awareness (SSA) framework for this strategically vital region. A research team from the National University of Defense Technology (NUDT) has successfully developed a novel parameterization method (published in the Chinese Journal of Aeronautics, https://doi.org/10.1016/j.cja.2025.103869) for orbits near collinear libration points. This advancement enables the systematic cataloging and robust identification of cislunar objects, representing a critical enabler for the safety and sustainability of future space operations.
Professor Leping Yang, the team's lead scientist, underscored the practical imperatives driving this investigation: "With the lunar economy on the horizon, libration point regions face inevitable congestion. We need an efficient and intuitive cataloging method, analogous to the systems currently employed for Earth orbits, to accurately characterize the situation of cislunar space. Our work aims to build the foundational lexicon for describing orbital mechanics within this emerging domain."
The core contribution of this research involves deriving a new set of dynamical parameters. The study, led by doctoral researchers Chenyuan Qiao and Xi Long, leverages canonical transformations and center manifold theory within the Circular Restricted Three-Body Problem (CRTBP) framework. This procedure effectively translates the complex dynamics near libration points into a set of intuitive parameters.
These parameters distinctly characterize motion along two directions. The hyperbolic parameters (q₁, p₁) function as a monitor, signaling when a spacecraft transits into or out of a libration point orbit and precisely identifying its associated invariant manifold. "This is crucial for understanding spacecraft maneuvers," Chenyuan Qiao explained, "Since many fuel-efficient transfers in cislunar space utilize these invariant manifolds, our parameters provide direct insight into transfer events and subsequent orbital changes."
The center manifold parameters (I₂, θ₂, I₃, θ₃) characterize the quasi-periodic motion of a spacecraft around the libration point. To facilitate the visualization and analysis of this motion, the team employed Poincaré sections, which effectively project the complex four-dimensional phase space onto a two-dimensional plane. "The Poincaré section serves as our cataloging chart," said Chenyuan Qiao, "It establishes a one-to-one correspondence between an orbit's physical characteristics—specifically its amplitudes in the horizontal and vertical directions—and a unique point on the map. Consequently, classic orbital families such as Lyapunov, Halo, and Lissajous orbits each occupy a distinct and identifiable location."
This framework directly enables orbit identification. Given a segment of a spacecraft's observed trajectory, the method determines the best-matching CRTBP reference orbit by minimizing the discrepancy between their respective action variables. The team conducted a sensitivity analysis to demonstrate the method's robustness, showing reliable identification performance, achieving success with position errors up to 100 km and velocity errors below 1 m/s. Notably, the findings suggest that improving velocity measurement accuracy is paramount for the development of future cislunar tracking systems.
While the developed framework represents a significant leap forward, its current applicability is restricted primarily to the collinear libration points (L1 and L2) within the simplified CRTBP. Professor Yanwei Zhu from the team acknowledges the next major challenge explicitly, "The dynamics near the triangular libration points L4 and L5 are significantly influenced by solar gravity, which cannot be ignored. The assumptions underpinning our current model become inadequate there."
The researchers' immediate next step involves extending this parameterization method to a more realistic, non-autonomous ephemeris model that incorporates the gravitational perturbations from the Sun. The ultimate goal is ambitious but critical: to establish a single, unified parameterization and cataloging system applicable to all libration points within the Earth-Moon system. Achieving this comprehensive framework would provide a standardized "common language" for cislunar SSA, which is essential for effectively managing the safe and efficient utilization of the cislunar space in the decades to come.
Original Source
C. QIAO, X. LONG, L. YANG, Y. ZHU, P. WANG, Orbital parameter characterization and objects cataloging for Earth-Moon collinear libration points, Chinese Journal of Aeronautics , 2025, https://doi.org/10.1016/j.cja.2025.103869
About Chinese Journal of Aeronautics
Chinese Journal of Aeronautics (CJA) is an open access, peer-reviewed international journal covering all aspects of aerospace engineering, monthly published by Elsevier. The Journal reports the scientific and technological achievements and frontiers in aeronautic engineering and astronautic engineering, in both theory and practice. CJA is indexed in SCI (IF = 5.7, Q1), EI, IAA, AJ, CSA, Scopus.
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