Connor Segal, EO Solutions & Virginia Polytechnic Institute and State University; Kevin Schroeder, Virginia Polytechnic Institute and State University
Keywords: Cislunar Space, Poincaré Map, Persistent Monitoring, Space Domain Awareness, Search
Abstract:
The growing interest in Cislunar space has accompanied a surge in missions to the Moon and beyond by government, scientific, and commercial stakeholders alike. Although the motivations for their interests differ, the result of an increased presence in this regime remains. During the early days of spaceflight, a poignant lack of consideration was initially given to the ramifications of rapid growth in the space domain when it came to Low Earth Orbit (LEO). The vastness of space, combined with the extreme costs required to achieve orbit at the time, made it unnecessary to closely consider the positions of satellites, their relative proximities, or operational intentions. This mindset has dramatically shifted since then with the explosion of satellites operating from LEO to Geostationary Earth Orbit (GEO). As a result, the field of Space Domain Awareness (SDA) arose to tackle these new challenges.
The same SDA considerations for orbits solely around Earth must now be taken into account for those in the Cislunar domain. However, the specific challenges for Cislunar space differ from those of near-Earth orbiting objects. To maintain SDA, the requisite search volume of the Cislunar regime is over 1000 times greater than that of the GEO regime. Additionally, a majority of the sensors used for consistently monitoring Resident Space Objects (RSOs) are only designed for operational ranges up to GEO, severely limiting the resources available to be proactive about SDA in the Cislunar domain. Lastly, the dynamics of the region allow the existence of trajectories from periodic orbits that require very little fuel expenditure to go from the farthest regions around Lagrange points back to Earth.
Many proposed solutions for maintaining Cislunar SDA from the current literature involve placing space-based Cislunar assets on periodic trajectories where a significant variety of periodic orbits exist and possess great advantages due to their diverse geometries. However, building satellites with the correct capabilities, getting them to these exotic orbits, and maintaining the orbits are an extreme investment of time and money that may not be practical in the near-term. Repurposing currently operational infrastructure has the potential to begin tackling the problem immediately and address the growing SDA concerns in Cislunar space.
Poincaré Maps (PMs) offer a solution to the volume search problem that the Cislunar region raises. PMs are mathematical surfaces placed within a physical representation of space corresponding to a discrete dynamical system. Using PMs, surfaces can be placed in strategic locations to chart where bodies subject to the defining system dynamics cross the map surface. In the context of this paper, a PM is placed at a spherical distance of 4X GEO centered around the Earth. The choice of 4X GEO as the location of the PM is motivated by the strategic implications of the aforementioned free return trajectories to Earth and the nearby orbital regimes of interest. By enabling search of a sphere at a distance 4 times that of GEO, this gives decision makers the lead-time required to assess threats and react accordingly in a decisive manner, and by focusing on a subset of the Cislunar volume to search, the daunting task of maintaining Cislunar SDA becomes much more tenable.
Utilizing the Circular Restricted Three-Body Problem (CR3BP) to represent the dynamics and all 272,008 periodic orbits for the Earth-Moon system contained within the JPL Three-Body Periodic Orbit catalog, a reachability analysis is conducted. 25 equally spaced points in time around each periodic orbit are given small delta V’s of 1-10 m/s and one positional translation, typically used to calculate manifold trajectories, and are propagated for one year. The points where each trajectory crosses the 4X GEO PM are recorded. A representative range of the total number of crossing points, defined by a +/- 36 degrees latitude spherical segment from the Earth-Moon plane, in addition to the first boundary crossings are analyzed to highlight the underlying patterns the sum of these transfers from Cislunar loitering trajectories display on their near-Earth fly-bys.
Using the total of these crossing points, the complete 4 pi steradian search space is reduced by up to 85.3% to a mere 0.587 pi steradians. Additionally, this search space of the unreduced crossings covers 100% of the span of the GEO belt that is either currently monitored or desired to be monitored. In other words, at the bare minimum, accomplishing the goal of total persistent monitoring of GEO would also succeed at monitoring a large swath of crossing points from possible loitering locations in Cislunar space.
Utilizing these crossing points, studies will be conducted using the optical sensors employed within the Space Surveillance Network (SSN) to determine the performance of these sensors working collaboratively to search the 4X GEO PM crossing region for all crossing points, the 4X GEO PM crossing region for the first crossings, and finally compare them to the performance of the unreduced search space.
In addition, a supplemental study is conducted in which a typical catalog maintenance methodology for searching the currently desired regions of the GEO belt is employed and the 4X GEO PM first crossing points that are captured within the background of that search are recorded. From this simulation, this study demonstrates the possibility of maintaining Cislunar SDA through current GEO catalog maintenance operations.
Adoption of monitoring any of these reduced-area search spaces by the United States Space Force (USSF) and other partners will provide the initial steps needed towards building up the required capabilities for maintaining Cislunar SDA. Additionally, as shown by the practical application towards current operations, its adoption and use will accomplish the goal of tactical persistent GEO monitoring that is currently desired.
Date of Conference: September 16-19, 2025
Track: Cislunar SDA