Apollo spacecraft configuration with CSM (right) and LM docked I - Lunar module descent stage; II - Lunar module ascent stage; III - Command module; IV - Service module. 1 LM descent engine skirt; 2 LM landing gear; 3 LM ladder; 4 Egress platform; 5 Forward hatch; 6 LM reaction control system quad; 7 S-band inflight antenna (2); 8 Rendezvous radar antenna; 9 S-band steerable antenna; 10 Command Module crew compartment; 11 Electrical power system radiators; 12 SM reaction control system quad; 13 Environmental control system radiator; 14 S-band steerable high gain antenna; 15 Nozzle extension; 16 Docking window; 17 VHF antenna; 18 Docking target; 19 LM overhead hatch; 20 CSM combined tunnel hatch; 21 Viewing windows; 22 Aft heatshield