Human exploration of space is a high-risk, high-stress endeavor. Thus, human error must be guarded against at every juncture. We have implemented a portable system, the MiniCog Rapid Assessment Battery, to assess quickly and accurately nine cognitive functions (including attention, working memory, and problem-solving). This system is intended to provide an "early warning," indicating when an astronaut or other type of worker is suffering from stress-related deficits that may affect performance. The results can be used to warn a worker to pay additional attention or take a countermeasure (even if only a brief rest). At present, the MiniCog platform is fully functional; it includes software for administering cognitive tests on a hand-held device and providing immediate user feedback, as well as desktop software for authoring new tests and scoring results in detail. Studies are underway to assess the utility of the MiniCog Rapid Assessment Battery for measuring impaired cognitive performance induced by a variety of stressors, for evaluating countermeasures, and for predicting performance on more complex tasks. We hope that this tool will allow quick and easy self-diagnosis of cognitive impairment, encouraging better mental health and facilitating safer on-the-job (and recreational) performance.