Future spaceborne platforms will require expanded onboard processing payloads to meet increasing mission performance and autonomy requirements. Recently proposed spacecraft systems plan to deploy networked processors configured much like commodity clusters for high-performance computing (HPC). Just as robust job management services have been developed and are required to optimize the performance of ground-based systems, so too will spaceborne clusters require similar management services, especially to meet real-time mission deadlines. In order to gain insight into how best to address the challenge of job management in high-performance, embedded space systems, a management service has been developed for a NASA New Millennium Program (NMP) experiment for the ST-8 mission slated for launch in 2009. This paper presents an overview and analysis of the effects on overall mission performance of adding priority and preemption to a baseline gang scheduler employing opportunistic loadbalancing (OLB) on a heterogeneous processing system for space. Experiments are conducted with two mission scenarios including planetary mapping and object tracking.