On July 20, 1969, just eight years after President John F. Kennedy threw down the Cold War gauntlet and announced the ambitious goal of “landing a man on the moon and returning him safely to the Earth_,”_ NASA astronauts Neil Armstrong and Buzz Aldrin planted the American flag in the dusty lunar soil.

Below is a timeline of the historic Apollo 11 flight from launch to splashdown.

To overcome the Earth’s orbital gravity, NASA required a rocket 100 times more powerful than the Mercury boosters that launched the first American astronaut into orbit in 1961. The three-stage Saturn V was as big as a Navy destroyer, packed 7.5 million pounds of thrust and could catapult the Apollo 11 astronauts to a maximum velocity of 25,000 mph.

To fuel all that power, the Saturn V was filled to the brim with nearly a million gallons of kerosene, liquid oxygen and liquid hydrogen. Michael Neufeld, a senior curator in the space history department of the Smithsonian National Air and Space Museum, says that the ignition of the Saturn V boosters was the first of many tense moments on Apollo 11.

“If the Saturn V blew up on or near the launch pad, it would have the force of a small nuclear weapon,” says Neufeld.

After firing and jettisoning two of the Saturn V’s three engines, the spacecraft entered Earth’s orbit at nearly 120 miles above the surface. After one swing around the planet, the third-stage J-2 rocket ignited, hurling the Apollo astronauts out of near-Earth orbit and on a trajectory toward the moon.

Next came a truly tricky dance move. Aside from the Saturn V boosters, the Apollo 11 hardware consisted of three vessels: the Lunar Module (LM), codenamed “Eagle,” to transport two astronauts to and from the moon’s surface; the Command Module (CM), codenamed “Columbia,” where all three astronauts hung out during the journey; and the Service Module, which held the propulsion and support systems. (When the Command Module was attached to the Service Module, it was called the CSM.)

To get the vessels in the right order for lunar orbit and landing, the CSM had to eject from inside the tip of the stage three rocket, pull a 180-degree turn and dock head-first with the top of the LM—all while hurtling through space at nearly 20,000 mph.

Once attached, the Apollo 11 spacecraft separated from the Saturn V for good and the Apollo 11 astronauts began their three-day journey across the 238,000-mile expanse between the Earth and the moon.

Once separated from the Saturn V, the Apollo spacecraft was at the mercy of the Service Module engine for mid-course corrections and for the critical maneuver of slipping into the moon’s weaker gravitational orbit.

This last move, known as lunar orbit insertion, went off without a hitch, swinging the astronauts around the moon at 62 miles above the lunar surface.

During the spacecraft’s second pass around the moon, Mission Commander Armstrong and Lunar Module Pilot Aldrin moved from the CSM into the snug confines of the LM to prepare for detachment, leaving Command Module Pilot Michael Collins to anxiously wait and circle in orbit.

Next came the “powered descent” of the LM, what Neufeld calls “the most critical and dangerous part of the flight.” After separating from the CSM, Armstrong and Aldrin piloted the 32,000-pound LM for two hours toward the lunar surface. At the last minute, with fuel supplies running dangerously low, Armstrong realized that the computer’s auto-landing program was dropping them in the middle of a boulder-strewn crater.

“In what’s become a famous moment,” says Neufeld, “Armstrong took over manual control and began maneuvering the spacecraft forward faster so it would skate over the crater to a clear spot beyond it.”

Armstrong, a veteran test pilot, remained cool and collected even as warning alarms blared in the cramped cabin and Mission Control announced only 30 seconds of fuel left in the reserves.

“I think Armstrong was comfortable,” says Neufeld. “It was a tense landing, but he knew he could make it.”

Standing side-by-side and peering out small triangular windows, Armstrong and Aldrin brought the LM to a gentle rest and cut the engines. “The Eagle has landed,” Armstrong reported to a white-knuckled Mission Control.

“Roger, Tranquility. We copy you on the ground,” responded fellow astronaut Charlie Duke in Houston. “You got a bunch of guys about to turn blue. We're breathing again. Thanks a lot.”

As commander, Armstrong had the privilege of being the first astronaut to set foot on the moon. As he stepped off the ladder onto the lunar surface, Armstrong famously radioed back to Earth, "That's one small step for (a) man, one giant leap for mankind." (While Armstrong said "a man..." most heard "small step for man.") Aldrin followed Armstrong down the ladder.

The two men spent the next two hours taking photographs, recording their impressions of the landscape, collecting piles of moon rocks and soil specimens, and deploying a package of scientific experiments, some which would stay on the moon after they left. Those included a seismograph for measuring “moonquakes” and the Laser Ranging Retroreflector for measuring the precise distance of the moon from Earth.

After a meal and a few hours of sleep, it was time for Armstrong and Aldrin to rejoin Collins and the CSM in lunar orbit. Neufeld says that this was another nail-biter moment for folks like him watching at home.

“Lift-off made me nervous,” says Neufeld. “There’s only one ascent engine and it’s got to light. It’s the only way to get back alive.”

The prospect of Armstrong and Aldrin being stranded on the moon was real enough that President Richard Nixon and his speechwriter William Safire had a condolence speech prepared, which began, “Fate has ordained that the men who went to the moon to explore in peace will stay on the moon to rest in peace.”

Thankfully, the ascent engine ignited perfectly and Armstrong and Aldrin cruised into lunar orbit where they pulled off yet another tricky maneuver, docking with the CSM in mid-flight. Armstrong, who had performed the very first successful space docking ever during Gemini 8, proved more than capable for the job.

The three-man crew reunited in the CSM, jettisoned the LM for good and set course for home.

After firing its engines one last time to enter Earth’s orbit, the Service Module was ditched and the three astronauts braced for re-entry inside the cone-shaped Command Module.

This would be the final test for the Apollo 11 crew and the thousands of engineers and test pilots who had made this moment possible. The capsule had to enter the atmosphere at a razor-precise angle.

“When you hit the atmosphere at 24,000 mph, it creates a hell of a fireball,” says Neufeld. “If they came in too steep, they would heat up too fast and spacecraft would burn up. If they came in too shallow, the capsule would skip off the atmosphere like a rock on a pond.”

After a breathless communication blackout of three minutes, Armstrong signaled a successful reentry and the recovery ships made the first visual contact of the capsule with its parachutes deployed.

The Apollo 11 mission concluded exactly eight days, three hours, 18 minutes and 35 seconds after launch with a splashdown landing in the Pacific Ocean, about 800 nautical miles southwest of Hawaii and 12 miles from the recovery ship, the USS Hornet.

The three astronauts emerged from the banged up CM capsule wearing biological contamination suits for fear that they brought back toxic moon bacteria. They would remain inside a mobile medical quarantine facility (resembling a modified Airstream trailer) for 21 days before being cleared to return to their families.