The Apollo 1 flight was cancelled after a cabin fire killed the crew and destroyed their command module during a launch rehearsal test.

Of these, nine flew humans to the Moon between 1968 and 1972, and another two performed crewed test flights in low Earth orbit, all as part of the Apollo program.

Finally in 1975, the last flown CSM docked with the Soviet craft Soyuz 19 as part of the international Apollo–Soyuz Test Project.

It would include a large pressurized auxiliary orbital module where the crew would live and work for weeks at a time.

On May 25, 1961 President John F. Kennedy announced the Moon landing goal before 1970, which immediately rendered NASA's Olympus Station plans obsolete.

But the change to lunar orbit rendezvous, plus several technical obstacles encountered in some subsystems (such as environmental control), soon made it clear that substantial redesign would be required.

The inner pressure vessel housed the crew accommodation, equipment bays, controls and displays, and many spacecraft systems.

Part of the area between the inner and outer shells was filled with a layer of fiberglass insulation as additional heat protection.

At about 25,000 feet (7,600 m) during reentry, the forward heat shield was jettisoned to expose the Earth landing equipment and permit deployment of the parachutes.

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.

The portion of the capsule that first contacted the water surface contained four crushable ribs to further mitigate the force of impact.

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.

It was operated by a pump handle, which drove a ratchet mechanism to open or close fifteen latches simultaneously.

These latches allowed a so-called 'soft dock' state and enabled the pitch and yaw movements in the two vehicles to subside.

In undocking, the release of the capture latches was accomplished by electrically energizing tandem-mounted DC rotary solenoids located in the center piston.

In the event of an abort during launch from Earth, the same system would have explosively jettisoned the docking ring and probe from the CM as it separated from the boost protective cover.

The three crew couches were constructed from hollow steel tubing and covered in a heavy, fireproof cloth known as Armalon.

The translation controller was used by the crew member performing the transposition, docking, and extraction maneuver with the LM, usually the CM Pilot.

The couches were supported by eight shock-attenuating struts, designed to ease the impact of touchdown on water or, in case of an emergency landing, on solid ground.

The service propulsion engine nozzle and heat shield increased the total height to 24 feet 7 inches (7.49 m).

The interior was a simple structure consisting of a central tunnel section 44 inches (1.1 m) in diameter, surrounded by six pie-shaped sectors.

[22] A contract was signed in April 1962 for the Aerojet-General company to start developing the engine, resulting in a thrust level twice what was needed to accomplish the lunar orbit rendezvous (LOR) mission mode officially chosen in July of that year.

The propellants were pressure-fed to the engine by 39.2 cubic feet (1.11 m3) of gaseous helium at 3,600 pounds per square inch (25 MPa), carried in two 40-inch (1.0 m) diameter spherical tanks.

[25] Each quad assembly measured 2.2 by 2.7 feet (0.67 by 0.82 m) and had its own fuel, oxidizer, and helium tanks mounted on the inside of an 8-by-2.75-foot (2.44 by 0.84 m) skin panel.

[27] 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.

A steerable unified S-band high-gain antenna for long-range communications with Earth was mounted on the aft bulkhead.

[29] This permitted the addition of some extra RCS propellant to allow for use as a backup for the deorbit burn in case of possible SPS failure.

The command module was also partially painted white, to provide passive thermal control for the extended time it would remain in orbit.

The command module could be modified to carry extra astronauts as passengers by adding jump seat couches in the aft equipment bay.