four 90-degree wedges. The ELS consisted of two drogue parachutes with mortars, three main parachutes, three pilot parachutes to deploy the mains, three inflation bags for uprighting the capsule if necessary, a sea recovery cable, a dye marker, and a swimmer umbilical. The command module's center of mass was offset a foot or so from the center of pressure (along the symmetry axis). This provided a rotational moment during reentry, angling the capsule and providing some lift (a lift to drag ratio of about 0.368). The capsule was then steered by rotating the capsule using thrusters; when no steering was required, the capsule was spun slowly, and the lift effects cancelled out. This system greatly reduced the g-force experienced by the astronauts, permitted a reasonable amount of directional control and allowed the capsule's splashdown point to be targeted within a few miles. At , the forward heat shield was jettisoned using four pressurized-gas compression springs. The drogue parachutes were then deployed, slowing the spacecraft to . At the drogues were jettisoned and the pilot parachutes, which pulled out the mains, were deployed. These slowed the CM to for splashdown. The portion of the capsule that first contacted the water surface contained four crushable ribs to further mitigate the force of impact. The command module could safely parachute to an ocean landing with only two parachutes deployed (as occurred on Apollo 15), the third parachute being a safety precaution. Reaction control system The command module attitude control system consisted of twelve attitude control thrusters, ten of which were located in the aft compartment, plus two in the forward compartment. These were supplied by four tanks storing of monomethylhydrazine fuel and nitrogen tetroxide oxidizer, and pressurized by of helium stored at in two tanks. Hatches The forward docking hatch was mounted at the top of the docking tunnel. It was in diameter and weighed , constructed from two machined rings that were weld-joined to a brazed honeycomb panel. The exterior side was covered with of insulation and a layer of aluminum foil. It was latched in six places and operated by a pump handle. The hatch contained a valve in its center, used to equalize the pressure between the tunnel and the CM so the hatch could be removed. The unified crew hatch (UCH) measured high, wide, and weighed . It was operated by a pump handle, which drove a ratchet mechanism