PULSAR achievements: RPS engineering
The objective of the work package 3 was to develop the design of the Radioisotope Power System assembly. Early in the project, potential missions were selected and the specifications were defined for electrical power needs, available geometry, thermal environment, mechanical constraints, etc. (Airbus). Two missions were considered most suitable for the integration of a first European RPS : a continuous power supply for a lunar rover mission, or for a lunar cargo carrier.
In parallel, nuclear safety requirements for launch were defined, considering the perspective of launching the RPS from the Guyana Space Centre (ArianeGroup). Demonstrating compliance with these safety requirements will be part of the licensing process.
Based on these requirements, a conceptual RPS design was developed featuring two Stirling engines facing each other with a centrally positioned heat source (Figure 1). This configuration aligns with the objectives of modularity and resilience to motor failure while maintaining a simple geometry. Most of the heat flux from the heat source is transferred to the engines, and converted to electricity with an expected efficiency of around 20%. The low-quality heat remaining at the end of the cycle is removed at the engine heat sink and evacuated by the RPS radiators.
Engineering studies and design reviews with partners were conducted to further validate the concept and consolidate design choices. This process included sizing and orienting the radiating surfaces, verifying structural integrity against anticipated loading patterns, assessing the dose rate from the radioactive source, and developing mechanical assembly principles (Tractebel studies). System integration on the host spacecraft was performed to evaluate the adequacy of power production over day-night cycles on the Moon in different scenarios (Airbus). A compliance check of the heat source and RPS design was conducted with the safety objectives and the launch authorization process (ArianeGroup).
The 3D mechanical model developed at the end of the project is shown in Figure 2. The assembly comprises independent sub-assemblies for the heat source and the Stirling converters, allowing for the final integration of the source shortly before launch. The model will serve as the basis for further design development, extending the scope and level of details of the engineering files, studying transient modes, failure modes, etc. to reach the necessary higher Technical Readiness Levels.