As autonomous space operations continue to evolve, the ability to perform reliable, safe, and repeatable Rendezvous, Proximity Operations, and Docking (RPOD) between maneuverable spacecraft has become increasingly critical. Traditionally, RPOD has been limited to a servicer-client model without real-time communication, relying instead on ground-based coordination. As global participation in space operations grows, the risk of failed rendezvous and potential collisions increases.

The Compliant, Low-profile, Independent, Non-protruding, Genderless and Electronic Rendezvous System (CLINGERS) integrates traditional docking mechanisms with RPOD sensors to enhance safety through cooperation and real-time communication. The University of Southern California Space Engineering Research Center’s CLINGERS project, deployed aboard the ISS, aims to address limitations in the efficiency and responsiveness of RPOD engagements by testing multiple configurations with varying levels of cooperation and communication, ranging from fully collaborative modes with real-time communication to traditional passive client/active servicer operations. Mounted to Astrobees, CLINGERS executes visual-based relative navigation using infrared (IR) LEDs and the Perspective-n-Point (PnP) algorithm, while exchanging pose and state data via Bluetooth. In contrast to traditional RPOD approaches—where one spacecraft remains passive—CLINGERS enables both the client and servicer to actively cooperate in translation, rotation, and control decision-making.

Three configurations have been tested on the International Space Station in initial experiments: one configuration with both CLINGERS communicating in an attempt to dock, and two configurations where one unit stationkeeps while the other attempts maneuvering and docking, each with varying communications functionalities. Accurate relative positioning using PnP is crucial in all three configurations to enable both precise alignment and docking maneuvers. CLINGERS actively communicates with its counterpart, exchanging orientation data and enabling the calculation of the necessary reorientation such that each CLINGERS device is aligned and centered in the field of view of their respective infrared cameras.

Since the CLINGERS units are integrated with the Astrobee flight units, the effectiveness of cooperative docking mechanisms was characterized by the “fuel” usage of the Astrobees. Comparing the relative fuel consumption for the three RPO modes is useful in understanding the efficiency of each configuration. Characterization of the fuel usage of Astrobee was done by analyzing its Force Allocation Module (FAM) data, which includes nozzle angles, commanded nozzle area, and thrust. Using known air properties aboard the ISS, these angles are converted into mass flow rates for each nozzle. The total air usage over a test run is then calculated by integrating the mass flow rates over time. Initial test results have shown that the cooperative RPO mode is the most efficient, as it has lower relative fuel consumption.

The CLINGERS project represents a foundational step toward scalable, autonomous docking systems capable of supporting a diverse range of missions, from on-orbit servicing and inspection to modular construction and long-duration exploration. By successfully demonstrating cooperative RPOD in a dynamic, microgravity environment, this work advances the path toward the next generation of intelligent, modular, and resilient spacecraft systems.