Due to harsh and inaccessible operating environments, space computing presents many unique challenges and constraints that limit onboard computing performance. However, the increasing need for real-time sensor and autonomous processing, coupled with limited communication bandwidth with ground stations, is increasing onboard computing demands for next-generation space missions. Because currently available space-grade processors cannot satisfy this growing demand, research into various processors is conducted to ensure that potential new processors are based upon architectures that will best meet the computing needs of space missions. Device metrics are used to measure and compare the theoretical capabilities of processors based upon vendor-provided data and tools, enabling the study of large and diverse sets of architectures. Architectural tradeoffs are determined that can be considered when comparing or designing space-grade processors. Results demonstrate how onboard computing capabilities are increasing due to emerging architectures that support high levels of parallelism in terms of computational units, internal memories, and input/output resources; and that performance varies between applications, depending on the compute-intensive kernels used. Furthermore, the overheads incurred by radiation hardening are quantified and used to analyze low-power commercial-off-the-shelf processors for potential hardening and use in future space missions.