A total of 640 experiment days were scheduled between 2007 and 2011, divided into three stages of differing length. During each stage, the crew of volunteers lived and worked in a mockup spacecraft. Communication with the outside world was limited, and was conducted with a realistic time delay of up to 25 minutes, to simulate the real-life communications lag between Mars and Earth. Similarly, a realistically limited supply of on-board consumables was provided for the volunteers. Some conditions, such as weightlessness and cosmic radiation, could not be simulated.