Systems and methods for multi-mode radiation hardened multi-core microprocessors are disclosed. In some embodiments, a triplicated circuit includes a first core logic, a second core logic, a third core logic, and bus arbitration and control circuitry. The triplicated circuit is configurable to operate in both a Triple-Modular Redundant (TMR) mode of operation and a multi-threaded mode of operation. In some embodiments, there is essentially no overhead in soft mode and low overhead (power only) in hard mode. In most applications, it is expected that portions of missions require very hard systems (e.g., landing) where a failure is catastrophic. However, other portions require essentially no hardening (digital signal processor and signal processing activities) but much better throughput. Consequently, there is a huge opportunity to develop computer processors with low overhead in soft mode and unprecedented hardness in hard mode.