and a waste storage compartment. The aft storage bay, behind the crew couches. This housed the 70 mm camera equipment, the astronaut's garments, tool sets, storage bags, a fire extinguisher, CO2 absorbers, sleep restraint ropes, spacesuit maintenance kits, 16mm camera equipment, and the contingency lunar sample container. The CM had five windows. The two side windows measured square next to the left and right-hand couches. Two forward-facing triangular rendezvous windows measured , used to aid in rendezvous and docking with the LM. The circular hatch window was in diameter located directly over the center couch. Each window assembly consisted of three thick panes of glass. The inner two panes, which were made of aluminosilicate, made up part of the module's pressure vessel. The fused silica outer pane served as both a debris shield and as part of the heat shield. Each pane had an anti-reflective coating and a blue-red reflective coating on the inner surface. Specifications Crew: 3 Crew cabin volume: living space, pressurized Length: Diameter: Mass: Structure mass: Heat shield mass: RCS engine mass: 12 × Recovery equipment mass: Navigation equipment mass: Telemetry equipment mass: Electrical equipment mass: Communications systems mass: Crew couches and provisions mass: Environmental Control System mass: Misc. contingency mass: RCS: twelve thrusters, firing in pairs RCS propellants: MMH/ RCS propellant mass: Drinking water capacity: Waste water capacity: CO2 scrubber: lithium hydroxide Odor absorber: activated charcoal Electric system batteries: three 40 ampere-hour silver-zinc batteries; two 0.75 ampere-hour silver-zinc pyrotechnic batteries Parachutes: two conical ribbon drogue parachutes; three ringslot pilot parachutes; three ringsail main parachutes Sources: Service module (SM) Construction The service module was an unpressurized cylindrical structure with a diameter of and long. The service propulsion engine nozzle and heat shield increased the total height to . The interior was a simple structure consisting of a central tunnel section in diameter, surrounded by six pie-shaped sectors. The sectors were topped by a forward bulkhead and fairing, separated by six radial beams, covered on the outside by four honeycomb panels, and supported by an aft bulkhead and engine heat shield. The sectors were not all equal 60° angles, but varied according to required size. Sector 1 (50°) was originally unused, so it was filled with ballast to maintain the SM's center-of gravity. On the last three lunar landing (I-J class) missions, it carried the scientific instrument module (SIM) with a powerful Itek focal length camera originally developed