Complex sentence: The Advanced Stirling Radioisotope Generator (ASRG) is a radioisotope power system using Stirling power conversion technology currently being developed under joint sponsorship by the United States Department of Energy and NASA for potential future space missions.
Split into simpler sentences: The Advanced Stirling Radioisotope Generator (ASRG) was a radioisotope power system under development for NASA. Development was undertaken under joint sponsorship by the United States Department of Energy and NASA for potential future space missions.