The science showing that flight to the moon was possible was worked out in the 17th century, but it took until the mid-20th century for engineering and technology to advance enough to make it happen.
Imagine throwing a ball off of a high mountain. The Earth's gravity will pull the ball down to the ground.
If the ball could be thrown at 24,000 feet per second (7,300 meters per second), it would fall continuously around the curve of the Earth. This is a circular orbit. [Saturn V Rockets & Apollo Spacecraft Explained]
If the ball is thrown faster, it continues to gain altitude and will be in an elliptical orbit.
A ball launched really fast — about 36,745 feet/s (11,200 m/s) — is said to have achieved escape velocity. The ball is no longer in orbit around Earth, but it will still be orbiting the sun.
Once in orbit, the rockets can be turned off. Objects in space remain traveling at whatever speed they were going when they stopped accelerating.
On the other side of the world from the launch point, Earth's gravity finally wins out over the ball's velocity, and the ball starts to fall back again toward its origin.
Going to the moon requires getting into a high elliptical orbit (dashed line in diagram). A speed of 35,505 feet/s (10,822 m/s) must be achieved when the booster engine is shut down. If nothing else were done, Apollo 11 would pass behind the moon and then fall back to Earth (a "free return" trajectory). Instead, firing a rocket engine firings puts Apollo into orbit around the moon.
To maneuver in space, a rocket must change its velocity. This change is termed Δv (delta-v). Much of the delta-v required to go anywhere in the solar system is devoted to simply getting off the Earth. A velocity change of about 30,500 feet/s (9,300 m/s) is needed to get into Earth orbit. A smaller delta-v is required to get from Earth orbit to lunar orbit.
The Saturn V rocket used the largest and most powerful rocket engines that had been developed. The first stage contained five F-1 engines. The second stage used five J-2s, and the third stage had one J-2.
A large rocket such as the Saturn V is built in segments called stages. As each stage runs out of fuel or has served its purpose, it is discarded. That way, the remaining part of the vehicle does not have to continue to boost the dead weight of unused engines, tanks and structures.
The conical command module (CM) was the only part of the huge rocket to return to Earth. The cylindrical service module (SM) contained propellant tanks, the main rocket engine, breathing oxygen and electrical power generators.
The three crew couches could be folded up to create more room in the command module. The back of the command module (opposite the entry hatch) was a station for taking measurements of the stars with a telescope for guidance and navigation (G&N).
The two-part lunar module flew only in the vacuum of space. The faceted upper half, the ascent stage, had its own rocket engine to return the crew to lunar orbit.
The only part of the LM that was habitable was the small pressurized cabin in the ascent stage. Astronauts stood at their controls, as seats were deemed irrelevant in the low gravity of the moon. For sleep, the crew hung hammocks across the cabin.
The octagonal landing stage was in the form of an "X"-shaped box containing propellant tanks and the main rocket engine. The four remaining wedge-shaped sections (quadrants) contained surface equipment, experiments and, on later missions, a folded-up lunar rover.
Most of the time during the flight, the crew wore sensors, a constant-wear garment containing medical and communications gear, and overalls. At launch, landing and during critical maneuvers, the astronauts wore a space suit called the pressure garment assembly.
When exiting the spaceship, the crew wore additional gear. The constant-wear garment was replaced by liquid-cooled long underwear. A pressure suit provided life support. A visor and sunshade assembly (LEVA) covered the astronauts’ polycarbonate plastic pressure helmet. The backpack (PLSS) contained a supply of oxygen, cooling water and the radio equipment. A smaller pack on top (oxygen purge system) contained a 30-minute emergency supply of O2. The remote control unit strapped to the chest (PLSS RCU) allowed the astronaut to regulate the life-support system and operate the radio.
The final three Apollo missions each spent three days on the surface. Every day, the crew would take photos, place experiment packages, collect samples and drive their moon car, the lunar rover, to new locations.Follow us @Spacedotcom, Facebook and Google+