The Apollo 11 mission’s journey to the Moon and back involved a complex series of maneuvers, each requiring precise control over the spacecraft’s speed. Its trajectory was not defined by a single constant velocity but rather a dynamic array of speeds, adapting to different phases of travel, from overcoming Earth’s gravity to navigating the lunar environment and returning safely home.
Blasting Off and Orbital Velocity
The journey began with the powerful Saturn V rocket lifting off from the launchpad. Initially, the acceleration was about 0.25 times the force of Earth’s gravity, or 0.25g. As the rocket consumed its massive fuel load, its mass decreased, causing the acceleration to climb, peaking at nearly 4g during the first stage’s burnout. This immense thrust was necessary to overcome Earth’s strong gravitational pull.
The Saturn V’s first stage propelled the spacecraft to speeds around 6,164 mph. Following the separation of the first stage, the second stage continued to accelerate the vehicle, reaching approximately 15,647 mph. The third stage then provided the final push, inserting the Apollo spacecraft into a parking orbit around Earth. At this point, the spacecraft was traveling at approximately 17,500 mph (28,000 km/h). This speed, known as orbital velocity, balanced the spacecraft’s forward motion and Earth’s gravitational pull, allowing it to continuously fall around the planet without re-entering the atmosphere.
Journey to the Moon and Lunar Orbit
After completing nearly two orbits around Earth, the Saturn V’s third stage re-ignited for Trans-Lunar Injection (TLI). This five-minute, 48-second burn increased the spacecraft’s speed, propelling it out of Earth orbit and towards the Moon. At the conclusion of this burn, Apollo 11 reached a peak velocity of approximately 25,000 mph (around 40,200 km/h) relative to Earth.
Following the TLI burn, the spacecraft began its three-and-a-half-day coast towards the Moon. During this long journey, its speed was not constant; it gradually slowed down as Earth’s gravity exerted a diminishing pull. As Apollo 11 neared the point where the Moon’s gravitational influence became stronger than Earth’s, its speed had decreased to about 2,400 mph. Subsequently, the Moon’s gravity began to accelerate the spacecraft, drawing it closer.
Upon reaching the Moon, the spacecraft executed the Lunar Orbit Insertion (LOI) burn. This maneuver involved firing the engine to slow down, allowing the Moon’s gravity to capture the spacecraft into orbit. Apollo 11 entered an elliptical lunar orbit, then adjusted to a nearly circular orbit at a speed of approximately 3,600 mph (5,800 km/h). Maintaining this speed ensured a stable orbit around the Moon, preparing for the next phase of the mission.
Descent to the Surface and Liftoff
From lunar orbit, the Lunar Module (LM) Eagle began its powered descent towards the Moon’s surface. The descent initiated from an orbital speed of about 3,600 mph (5,800 km/h). During this phase, the LM’s descent engine fired to steadily reduce its horizontal and vertical velocity. The goal was to transition from orbiting the Moon to a controlled, vertical landing.
As the LM approached the lunar surface, its speed continued to decrease. In the final moments before touchdown, the descent rate slowed to a few feet per second, allowing the astronauts to make adjustments for a soft landing. The landing speed itself was effectively zero, ensuring the module settled gently onto the dusty surface. This control was necessary for a successful landing on an extraterrestrial body.
After completing their tasks on the Moon, the astronauts prepared for liftoff from the lunar surface. The LM’s ascent stage fired its engine, accelerating from a standstill to achieve lunar orbital velocity. This engine, though smaller than those used for Earth launch, was powerful enough in the Moon’s weaker gravity to accelerate the ascent stage to approximately 3,756 mph (about 1,600 meters per second). This speed was necessary to rendezvous and dock with the Command Module, which remained in lunar orbit.
Homeward Bound and Splashdown
With the crew reunited in the Command Module, Apollo 11 prepared for its journey back to Earth with the Trans-Earth Injection (TEI) burn. This maneuver, performed while behind the Moon, accelerated the spacecraft to escape the Moon’s gravitational pull and set it on a course for home. The speed achieved during TEI was approximately 4,400 mph (7,080 km/h).
As Apollo 11 neared Earth, its speed increased due to the planet’s gravitational acceleration. Just before entering Earth’s atmosphere, the Command Module was traveling at an extraordinary speed of about 24,000 to 25,000 mph (around 38,600 to 40,200 km/h). The fastest speed Apollo 11 achieved was 24,678 mph (39,715 km/h) during re-entry. This extreme velocity required a precise re-entry angle to prevent the spacecraft from either burning up due to excessive friction or bouncing off the atmosphere into deep space.
Atmospheric drag rapidly decelerated the Command Module, generating intense heat and rapidly reducing its speed from tens of thousands of miles per hour to hundreds. Parachutes deployed at lower altitudes further slowed the capsule for a controlled descent. The final splashdown speed into the Pacific Ocean was relatively gentle, around 20 mph (32 km/h). This final reduction in speed completed the Apollo 11 mission, bringing the astronauts safely back to Earth.