The Mars Desert Research Station (MDRS) is the second of four planned simulated Mars surface exploration habitats (or Mars Analogue Research Stations) owned and operated by the Mars Society. Built in the western United States in the early 2000s, it is typically manned by small crews who visit the site for short periods of time to conduct scientific research. Besides a large building that serves as the center of activities, the complex includes a greenhouse, an observatory, and assorted open areas.