As humanity sets its sights on long duration missions to the Moon, Mars, and beyond, keeping astronauts healthy will be as critical as building rockets or habitats. In the harsh environment of space, the human body faces challenges that Earth never prepared us for including isolation, microgravity, and radiation that disrupt the immune system, increasing the risk of infection, chronic inflammation, and disease. Interestingly, new research on HIV is revealing lessons that could help future explorers live sustainably, regenerate resources in closed-loop systems, and even produce custom medicine far from Earth.