The speed of Apollo 11 constantly changed throughout the mission due to propulsion efforts and the gravitational forces of both Earth and the Moon. Engineers used precisely timed engine burns and orbital mechanics to achieve the specific velocities needed for each phase, from escaping Earth’s gravity to returning home.
Escaping Earth’s Gravity
The journey began with the Saturn V rocket. After the initial launch, the first two stages boosted the craft into a temporary orbit around Earth, reaching approximately 17,500 miles per hour (28,000 kilometers per hour). This velocity was necessary to maintain a stable, low Earth orbit and prevent the spacecraft from falling back into the atmosphere.
Once systems checks were complete, the Saturn V’s third stage, the S-IVB, fired again in the Trans-Lunar Injection (TLI) burn. This burn provided the thrust needed to accelerate the spacecraft past Earth’s escape velocity. At the completion of the TLI burn, Apollo 11 reached its maximum outbound velocity of roughly 24,200 miles per hour (39,000 kilometers per hour), the minimum speed required to overcome Earth’s gravitational pull and set a trajectory toward the Moon.
The Journey to the Moon
After the TLI burn, the spacecraft began coasting toward its destination, and its speed immediately began to decrease. Earth’s gravity acted as a constant brake, steadily slowing the spacecraft’s forward momentum throughout the three-day transit phase.
The slowest point of the journey occurred at the “neutral point,” where the gravitational pull of Earth and the Moon were roughly equal. At this crossover point, approximately 80% of the way to the Moon, Apollo 11’s velocity had dropped significantly to around 2,300 miles per hour (3,700 kilometers per hour). Once past this point, the Moon’s gravity dominated, and the spacecraft started to accelerate again as it fell toward its target.
Speed in Lunar Orbit
Upon reaching the Moon, the spacecraft was traveling too fast to be captured into a stable orbit, risking flying past its destination. The crew executed a precisely timed rocket firing called the Lunar Orbit Insertion (LOI) burn to slow down.
The LOI burn used the main Service Propulsion System engine to change the spacecraft’s trajectory from a hyperbolic path to a stable, elliptical orbit around the Moon. This maneuver brought the speed down to approximately 3,700 miles per hour (6,000 kilometers per hour). This velocity was required to maintain a low-altitude orbit without falling to the lunar surface or escaping the Moon’s weaker gravitational field.
Fastest Moment: Reentry Velocity
The absolute maximum speed achieved during the entire eight-day mission occurred on the return trip to Earth. As the command module separated and began its final descent, Earth’s gravity violently accelerated the capsule.
The Apollo 11 command module hit the atmosphere at its peak velocity of approximately 24,678 miles per hour (39,700 kilometers per hour). This velocity, known as “skip velocity,” was the fastest point of the entire mission, slightly exceeding the TLI speed.
The friction generated by this hypersonic speed created immense heat, raising the temperature on the heat shield’s surface to approximately 5,000 degrees Fahrenheit. The ablative heat shield was designed to intentionally burn away, protecting the crew as the atmosphere rapidly decelerated the capsule to speeds low enough for parachute deployment.