Psychological and sociological effects of space flight are important to understanding how to successfully achieve the goals of long-duration expeditionary missions. Although robotic spacecraft have landed on Mars, plans have also been discussed for a human expedition, perhaps in the 2030s, or as early as 2024 for a return mission. In October 2015, the NASA Office of Inspector General issued a health hazards report related to human spaceflight, including a human mission to Mars.