The module was 23 m long, and consisted, from fore to aft, an 8 m long unpressurized hangar housing the Earth Entry Module re-entry vehicle; a tunnel providing crew access to the EEM; a four-floor pressurized crew compartment, 6.7 m in diameter and 8 m long, a cross of pressurized tunnels leading to two lateral Logistic Vehicle docking ports and aft to the Mars Excursion Module, and a flared section that mated with the 10.06 m diameter MEM interstage.
One floor of the Crew Compartment contained the experiments. A second floor provided a radiation shelter for the crew in the event a period of high solar radiation was encountered. The third floor was the control center, and the fourth floor was the living area. Total floor area was approximately 130 sq m, or about the size of a three-bedroom house. However, 23 metric tons of equipment was also located in the crew compartment. When the floor area for this equipment was subtracted, the usable floor area for the crew was closer to 90 sq m - not much for a six-man crew for periods of up to three years. The mission module total mass was a function of mission time, since consumables and spare parts would vary according to the mission length. Minimum would be 37,600 kg for a Mars opposition mission of 460 days duration; maximum would be 52,300 kg for a Mars conjunction mission of 1040 days.
AKA: Mission Module.
Gross mass: 37,600 kg (82,800 lb).
Height: 23.00 m (75.00 ft).
Diameter: 6.70 m (21.90 ft).