Why Apollo 10 Stopped Just 47,000 Feet From the Moon

Soon we will recognize the 50th anniversary of the first humans to walk on the moon.

We remember and celebrate the heroism of the Apollo 11 crew: the humility of Neil Armstrong making those first bootprints; the cool bravado of Buzz Aldrin during the critical moments of the Eagle lander’s final descent; and, the lonely vigil of Michael Collins in orbit above his mates, waiting to bring them back home.

But we also need to celebrate the many pathfinders who made this historic mission possible. Among the most critical were the crew of Apollo 10, who were asked to perform a full dress-rehearsal of the Apollo 11 mission just two months beforehand. Commander Thomas P. Stafford; John W. Young, the command module pilot; and Eugene A. Cernan, lunar module pilot, did almost everything that Aldrin, Armstrong and Collins did, but they stopped just before landing on the moon.

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Imagine if Ferdinand and Isabella had sent a ship to the New World in 1491 and asked its captain and crew to find new lands to the west without getting out of the ship to set foot on them, because the next captain and crew were scheduled to do that in 1492.

Or picture President Thomas Jefferson sending a party to scout passage to the Pacific Ocean in 1803, then saying, don’t touch a thing, especially not the ocean — because Lewis and Clark are scheduled to do that the following year.

It seems unfathomable, to go all that way, to take all of those risks and then pull back, not grabbing the brass ring and reaping the rewards. In a sense, though, those were the instructions, and that was the burden, borne by the relatively unheralded crew of Apollo 10 fifty years ago this month.

Spurred by President John F. Kennedy’s 1961 speech challenging the nation to “commit itself to achieving the goal, before this decade is out, of landing a man on the moon and returning him safely to the Earth,” NASA went on an 8-year lunar sprint. This bold endeavor would employ close to a half million engineers, technicians, scientists and others both in government and industry. It also cost the lives of three heroic astronauts — Gus Grissom, Ed White, and Roger Chaffee — who perished in the 1967 Apollo 1 fire.

Successive Apollo flights had to become both safer and more daring at the same time to meet Kennedy’s deadline. Delays in the completion of the lunar lander, also known as the Lunar Excursion Module, meant that Apollo 8 would be the first crewed lunar mission to fly the command module only, from which 1968’s famed “Earthrise” photo was taken. It fell to the crew of Apollo 9 in March 1969, to fly the first test mission of the lander into space, spending 10 days in Earth orbit.

The stage was set, then for a full dress rehearsal by the next crew to the launchpad. Apollo 10’s officers had all earned astronaut wings during Project Gemini, NASA’s precursor to Apollo. Their mission aboard was simple: Practice and work out the kinks and set the stage for a successful landing on the moon (and safe return to Earth).

But there was one critical order: don’t actually land on the moon.

It would be the first time the moon lander was flown in the environment for which it was built. All of the risks that they would take to prove out the equipment and procedures — launching; Earth-orbital docking; the three-day Earth to Moon cruise; lunar orbit undocking; descent of the lander nicknamed Snoopy almost to the surface; reascending and re-docking; three more days back to Earth; then a Pacific Ocean splashdown — were the same risks the Apollo 11 crew would have to take, with one distinction. A moon landing was not to be.

They executed the rehearsal flawlessly. While Young circled above them in the command and service module nicknamed Charlie Brown, Stafford and Cernan undocked for their descent toward the landing site in the smooth, dark volcanic plains of the Sea of Tranquillity.

“You’ll never know how big this thing is when there ain’t nobody in here but one guy,” Young told his departing friends from his lonely outpost. As they began to fall toward the surface, Cernan quipped back, “You’ll never know how small it looks when you’re as far away as we are.”

They would eventually guide the lander to within only about 47,000 feet above the surface — close enough to test the landing radar and around the same maximum altitude of commercial aircraft above Earth’s surface. While relaying their reactions and perspective back to Young aboard Charlie Brown, Cernan called out, “Oh Charlie! We just saw Earthrise and it’s got to be magnificent!”

The view of the stark lunar landscape below them from that altitude, scarred by billions of years of impact cratering, was just as stunning to the crew. Transcripts of their conversations reveal that they didn’t have much free time to admire it though, given the intense concentration (and occasional computer glitch repair) needed to fly Snoopy.

Still, at one point Stafford remarked, “It looks like we’re getting so close all you have to do is put your tail hook down and we’re there.” Cernan was just as excited, exclaiming, “We are close, babe! This is, like, it!”

Snapping photos out the window and noting the many boulders that they could clearly see, Stafford proclaimed, “Tell Jack Schmitt,” referring to their geologist-astronaut colleague and future Apollo 17 moon walker, “that there’s enough boulders down here to fill up Galveston Bay too!”

What ran through their minds when the command finally came from Houston to fire the ascent engine and head back up? It must have been so tempting to go for a landing. Cernan was wistful: “The spacecraft is looking good and there are no problems, Charlie, except it would be nice to be around here more often …”

But Snoopy didn’t have enough fuel to land on the moon and then blast off again. According to Craig Nelson, author of the book “Rocket Men,” Cernan speculated that the lander’s ascent module had been short-fueled on purpose: “A lot of people thought about the kind of people we were: ‘Don’t give those guys an opportunity to land, ‘cause they might!’”

Two months later as the entire world looked on, human footsteps were at last emblazoned on the dusty surface of the moon by Neil and Buzz.

The willingness of the Apollo 10 crew to serve as something like stand-ins instead of the stars of the show would in time be generously rewarded by NASA.

Young descended those final few miles to the moon’s surface as commander of Apollo 16, and later commanded the first flight of the space shuttle. Cernan, too, made it to the surface as the commander of Apollo 17 in 1972, and is still the last person to have walked on the moon.

Although Stafford never again returned to the moon, he was the American commander of the Apollo-Soyuz Test Project in 1975, docking with Soviet counterparts in Earth orbit in a joint effort to redirect the space race toward an emerging détente between the world’s superpowers.

In the annals of history, the mission of Apollo 10 has been overshadowed by later journeys to the lunar surface. But the astronauts of Apollo 10 were trailblazers, and their story adds richness and humanity to the history of the race to the moon. Their achievements, and the risks that they took to help America to win that sprint, deserve to be remembered and celebrated.


Jim Bell is a professor in the School of Earth and Space Exploration at Arizona State University and president of The Planetary Society, the world’s largest public space advocacy organization. His most recent book is “The Earth Book” (Sterling, 2019), a photo-rich history of Earth Science.

[1] https://www.nytimes.com/2019/05/13/science/apollo-10-moon-nasa.html?partner=rss&emc=rss

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