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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Apollo command and service module | 3/7 | https://en.wikipedia.org/wiki/Apollo_command_and_service_module | reference | science, encyclopedia | 2026-05-05T12:35:22.001294+00:00 | kb-cron |
The components of the ELS were housed around the forward docking tunnel. The forward compartment was separated from the central by a bulkhead and was divided into 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 24,000 feet (7,300 m), the forward heat shield was jettisoned using four pressurized-gas compression springs. The drogue parachutes were then deployed, slowing the spacecraft to 125 miles per hour (201 kilometres per hour). At 10,700 feet (3,300 m) the drogues were jettisoned and the pilot parachutes, which pulled out the mains, were deployed. These slowed the CM to 22 miles per hour (35 kilometres per hour) 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 93-pound-force (410 N) 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 270 pounds (120 kg) of monomethylhydrazine fuel and nitrogen tetroxide oxidizer, and pressurized by 1.1 pounds (0.50 kg) of helium stored at 4,150 pounds per square inch (28.6 MPa) in two tanks.
=== Hatches === The forward docking hatch was mounted at the top of the docking tunnel. It was 30 inches (76 cm) in diameter and weighed 80 pounds (36 kg), constructed from two machined rings that were weld-joined to a brazed honeycomb panel. The exterior side was covered with 0.5-inch (13 mm) 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 29 inches (74 cm) high, 34 inches (86 cm) wide, and weighed 225 pounds (102 kg). It was operated by a pump handle, which drove a ratchet mechanism to open or close fifteen latches simultaneously.
=== Docking assembly === Apollo's mission required the LM to dock with the CSM on return from the Moon, and also in the transposition, docking, and extraction maneuver at the beginning of the translunar coast. The docking mechanism was a non-androgynous system, consisting of a probe located in the nose of the CSM, which connected to the drogue, a truncated cone located on the lunar module. The probe was extended like a scissor jack to capture the drogue on initial contact, known as soft docking. Then the probe was retracted to pull the vehicles together and establish a firm connection, known as "hard docking". The mechanism was specified by NASA to have the following functions:
Allow the two vehicles to connect, and attenuate excess movement and energy caused by docking Align and center the two vehicles and pull them together for capture Provide a rigid structural connection between both vehicles, and be capable of removal and re-installation by a single crewman Provide a means of remote separation of both vehicles for the return to Earth, using pyrotechnic fasteners at the circumference of the CSM docking collar Provide redundant power and logic circuits for all electrical and pyrotechnic components.
==== Coupling ==== The probe head located in the CSM was self-centering and gimbal-mounted to the probe piston. As the probe head engaged in the opening of the drogue socket, three spring-loaded latches depressed and engaged. These latches allowed a so-called 'soft dock' state and enabled the pitch and yaw movements in the two vehicles to subside. Excess movement in the vehicles during the 'hard dock' process could cause damage to the docking ring and put stress on the upper tunnel. A depressed locking trigger link at each latch allowed a spring-loaded spool to move forward, maintaining the toggle linkage in an over-center locked position. In the upper end of the lunar module tunnel, the drogue, which was constructed of 1-inch-thick aluminum honeycomb core, bonded front and back to aluminum face sheets, was the receiving end of the probe head capture latches.
==== Retraction ==== After the initial capture and stabilization of the vehicles, the probe was capable of exerting a closing force of 1,000 pounds-force (4.4 kN) to draw the vehicles together. This force was generated by gas pressure acting on the center piston within the probe cylinder. Piston retraction compressed the probe and interface seals and actuated the 12 automatic ring latches which were located radially around the inner surface of the CSM docking ring. The latches were manually re-cocked in the docking tunnel by an astronaut after each hard docking event (lunar missions required two dockings).