Thermal Design of the CAESAR Multi-Degree-of-Freedom Robotic Arm for On-Orbit Servicing

Kurzfassung

The Compliant Assistance and Exploration SpAce Robot (CAESAR) is a seven-degree-of-freedom robotic arm developed at the Institute of Robotics and Mechatronics (RM) of the German Aerospace Center (DLR) as a servicing asset for missions in LEO, GEO and beyond. CAESAR's upcoming flight application is the European Robotic Orbital Support Services - Servicing Component (EROSS SC) on-orbit servicing mission, whose demanding LEO environment and operational scenarios drive the arm's thermal requirements. This paper presents the thermal architecture and modeling approach for CAESAR, building on its multi-orbit servicing design and adapting it into mission-ready hardware for EROSS SC. The thermal design combines multi-layer insulation, radiators and distributed heaters to control temperatures and gradients in joints, electronics and structure. The arm must remain functional across a broad Sun-synchronous orbit (SSO) envelope, with varying altitudes and environmental conditions, as well as servicer attitudes and arm configurations, while performing close-range capture and manipulation of an unprepared or prepared client satellite and Orbital Replacement Unit (ORU) transfer operations. The combination of seven robotic joints and varying illumination conditions creates a multidimensional configuration space that challenges traditional sizing approaches based on limited analysis cases. To address this, a kinematically configurable ESATAN-TMS model of the arm has been developed and applied to initial chasing-mode orbital cases with selected arm postures. These cases are used to size heater zones, assess margins to temperature limits, and identify gradients along the arm. The paper summarizes the modeling approach, worst-case environments and design trades for chasing operations, including radiator self-viewing and arm-servicer heat exchange, and shows its applicability to future articulated servicing arms. The segment-level results indicate compliance for the assessed cases, with self-shadowing configurations being particularly sensitive due to reduced heat rejection. Future work will address proximity operations and coupled thermal interactions between the servicer and the client satellite.