Astronauts are affected by various physical and chemical factors during spaceflight, resulting in a series of pathological and physiological changes. Many studies have shown that spaceflight causes oxidative stress and induces brain disorder in astronauts, negatively affecting neuronal function and brain structure. However, the underlying mechanisms and the countermeasures need to be further explored. Moreover, it is observed that hydrogen has preventative and curative effects on ischemia–reperfusion injury, ionizing radiation injury, inflammatory diseases, and metabolic and neurodegenerative diseases. Increasing evidence demonstrated that hydrogen can act as a therapeutic antioxidant. In a research paper recently published in Space: Science & Technology,…