. These combined hydrogen and oxygen to generate electrical power, and produced drinkable water as a byproduct. The cells were fed by two hemispherical-cylindrical diameter tanks, each holding of liquid hydrogen, and two spherical diameter tanks, each holding of liquid oxygen (which also supplied the environmental control system). On the flight of Apollo 13, the EPS was disabled by an explosive rupture of one oxygen tank, which punctured the second tank and led to the loss of all oxygen. After the accident, a third oxygen tank was added to obviate operation below 50% tank capacity. That allowed the elimination of the tank's internal stirring-fan equipment, which had contributed to the failure. Also starting with Apollo 14, a 400 Ah auxiliary battery was added to the SM for emergency use. Apollo 13 had drawn heavily on its entry batteries in the first hours after the explosion, and while this new battery could not power the CM for more than 5–10 hours it would buy time in the event of a temporary loss of all three fuel cells. Such an event had occurred when Apollo 12 was struck twice by lightning during launch. Environmental control system Cabin atmosphere was maintained at of pure oxygen from the same liquid oxygen tanks that fed the electrical power system's fuel cells. Potable water supplied by the fuel cells was stored for drinking and food preparation. A thermal control system using a mixture of water and ethylene glycol as coolant dumped waste heat from the CM cabin and electronics to outer space via two radiators located on the lower section of the exterior walls, one covering sectors 2 and 3 and the other covering sectors 5 and 6. Communications system Short-range communications between the CSM and LM employed two VHF scimitar antennas mounted on the SM just above the ECS radiators. These antennas were originally located on the Block I command module and performed a double function as aerodynamic strakes to stabilize the capsule after a launch abort. The antennas were moved to the Block II service module when this function was found unnecessary. A steerable unified S-band high-gain antenna for long-range communications with Earth was mounted on the aft bulkhead. This was an array of four diameter reflectors surrounding a single square reflector. During launch it was folded down parallel to the main engine to fit inside the Spacecraft-to-LM Adapter (SLA). After CSM separation from