The Apollo spacecraft was designed as part of the Apollo Program, by the United States in the early 1960s to land men on the moon before 1970 and return them safely to earth. This goal was set forth by President Kennedy after the first flight of the Mercury Space Program. The spacecraft was made up of multiple units or stages that worked together to perform the mission of landing on the moon and returning safely to earth. The main components of the Apollo spacecraft were (going from top to bottom) the launch escape system, the Command Module, the Service Module, the Lunar Module and the lunar module adapter. These stages together would sit atop the launch vehicle.
The principle was Lunar Orbit Rendezvous: A rocket would launch the spacecraft to the moon. The spacecraft would fly to the moon and orbit it. A smaller portion of the spacecraft would land on the moon and return to lunar orbit. Then a portion of the spacecraft would return to earth.
The purpose of the Apollo launch escape system was to pull the Command Module (which contained the crew cabin) away from the launch vehicle in an abort situation.
The emergency could be a pad fire, exploding launch vehicle or a launch vehicle going off course.
The Launch Escape System would work automatically (or through manual activation) to fire a solid fuel escape rocket and open a canard system to direct the Command Module away from, and off the path of, a launch vehicle in trouble. The Launch Escape System would then jettison and the Command Module would land with its parachute recovery system.
If the emergency happened on the launch pad, the Launch Escape System would lift the Command Module to a sufficient height to allow the recovery parachutes to deploy safely before coming in contact with the ground.
The Command Module was the control center for the Apollo spacecraft and living quarters for the crew. It contained the pressurized main crew cabin, crew couches, control and instrument panel, optical and electronic guidance systems, communications systems, environmental control system, batteries, heat shield, reaction control system, forward docking hatch, side hatch, five windows and the parachute recovery system.
The Service Module was a portion of the spacecraft that was unpressurized and contained fuel cells, batteries, high gain antenna, radiators, water, oxygen, hydrogen, reaction control system and propellant to enter and leave lunar orbit, and service propulsion systems. On Apollo 15, 16 and 17 it also carried a scientific instrument package, mapping camera and a small sub-satellite to study the moon.
A major portion of the service module was taken up by propellant and the main rocket engine that placed the Apollo spacecraft into and out of lunar orbit. The main rocket engine was also used for mid-course corrections between the earth and the moon. It was capable of multiple restarts. During Apollo 13, a tank heater thermostat fused closed, causing gases in an oxygen tank to vaporize and melted the casing on the wires to the tank stirring fan. During flight when the tank fan was turned on, a spark from short caused the gas to ignite. It remained attached to the Command Module throughout the mission. It was jettisoned just prior to reentry into the earth's atmosphere.
The Lunar Module was the portion of the Apollo spacecraft that landed on the moon and returned to lunar orbit and was the first true "spaceship" since it was designed to only fly in the vacuum of space. It is divided into two major parts, the Descent Module and the Ascent Module. It was designed specifically for flight in space. It supplied life support systems for two astronauts for a total of four to five days. The spacecraft was designed and manufactured by the Grumman Aircraft Company led by Tom Kelly.
The Descent Module contains the landing gear, landing radar antenna, descent rocket engine, and fuel to land on the moon. It also had several cargo compartments used to carry among other things, the Apollo Lunar Surface Experiment Packages ALSEP, Mobile Equipment Cart (a hand pulled equipment cart - Apollo 14) the Lunar Rover (moon car - Apollo 15, 16 and 17), surface television camera, surface tools and lunar sample collection boxes.
The Ascent Module contains the crew cabin, instrument panels, overhead hatch/docking port, forward hatch, optical and electronic guidance systems, reaction control system, radar and communications antennas, ascent rocket engine and fuel to return to lunar orbit and rendezvous with the Apollo Command and Service Modules.
The Spacecraft Lunar Module Adapter (SLA) was a conical aluminum structure which supported the Service Module above the Saturn S-IVB rocket stage. It protected the Lunar Module, the Service Propulsion System engine nozzle, and the launch vehicle to Service Module umbilical during launch and ascent through the atmosphere.
The SLA was composed of four fixed seven foot long panels bolted to the Instrument Unit on top of the S-IVB stage, which were connected via hinges to four twenty-one foot long panels which would open from the top similar to flower petals.
The SLA was made from 1.7 inch (42.5 mm) thick aluminum honeycomb material. The exterior of the SLA was covered by a thin (0.03–0.2 inch, 1–5 mm) layer of cork and painted white to minimize thermal stresses during launch and ascent.
The Service Module was bolted to a flange at the top of the longer panels, and power to the SLA multiply-redundant pyrotechnics was provided by an umbilical. Because a failure to separate from the S-IVB stage could leave the crew stranded in orbit, the separation system used multiple signal paths, multiple detonators and multiple explosive charges where the detonation of one charge would set off another even if the detonator on that charge failed to function.
Once in space, the astronauts pressed the 'CSM/LV Sep' button on the control panel to separate the Command and Service Module from the launch vehicle. Detonating cord was ignited around the flange between the Service Module and SLA, and along the joints between the four SLA panels, releasing the Service Module and blowing apart the connections between the panels. Dual-redundant pyrotechnic thrusters at the lower end of the SLA panels then fired to rotate them around the hinges at 30-60 degrees per second.
On the Apollo 7 flight the SLA panels were retained on the S-IVB, but concerns about collision between the CSM and the SLA panels when docking with the Lunar Module led to a decision that the Saturn V launches would release the panels during the separation process. When they opened to an angle of approximately 45 degrees the hinges connecting the moving panels to the fixed panels disengaged, and springs pushed the panels away from the S-IVB at a velocity of around five miles per hour. Hence by the time the astronauts had rotated the Command/Service Module through one hundred and eighty degrees in preparation for docking, the panels were a safe distance away with no chance of a collision occurring.
The Lunar Module was connected to the SLA at four points around the lower panels. After the astronauts docked the CSM to the LEM, they blew charges to separate those connections and a guillotine severed the LEM to Instrument Unit umbilical. After the charges fired, springs pushed the LEM away from the S-IVB and the astronauts were free to continue their trip to the Moon.
Apollo 5 Lunar Module - Burned up in Earth's atmosphere
Apollo 9 Lunar Module "Spider" -Burned up in Earth's atmosphere
Apollo 10 Lunar Module "Snoopy" - Descent stage jettisoned, impacted moon, site unknown; ascent stage in heliocentric orbit
Apollo 13 Lunar Module "Aquarius" -Burned up in Earth's atmosphere
Note 1: The service modules for all Apollo spacecraft were jettisoned before earth re-entry, so all have burned up in the earth's atmosphere.
Note 2: Lunar orbits are generally unstable, so spacecraft jettisoned in lunar orbit would eventually impact the moon. However, the impact sites would be unknown.