* * *
—
Anders had imagined he would watch the Moon closing in, as the pilots did in the film 2001: A Space Odyssey, until it filled the sky. Instead, he saw emptiness. Even Lovell, with the wide field of view from his telescope and sextant, couldn’t catch a glimpse of the Moon. Due to the position of the Sun (and the glare it caused) and the position of the spacecraft’s windows (facing mostly toward black space), it had been all but impossible for the crew to spot its target.
“As a matter of interest, we have as yet to see the Moon,” Lovell radioed to Houston.
“What else are you seeing?” asked CapCom Jerry Carr.
“Nothing,” Anders replied. “It’s like being on the inside of a submarine.”
In Houston, in the middle of the night, the astronauts’ wives turned their squawk boxes just loud enough to hear without awakening friends and family who were curled up on couches and in chairs throughout their homes. One by one, these supporters awoke to help the wives through Lunar Orbit Insertion. In the fog of nerves and excitement, few realized that it was now officially Christmas Eve.
Despite the hour, approaching four in the morning in Houston, visitors began to crowd into the viewing room at Mission Control. A hundred people sardined themselves into this room designed for far fewer, but all respected the flashing sign that requested QUIET PLEASE as Lunar Orbit Insertion drew near.
It was time for Mission Control to make a final decision. One by one, Flight Director Glynn Lunney polled each of his controllers, looking for a simple Go or No Go. One by one, they gave him their answer. Lunney looked at Carr, who radioed to the spacecraft, now just over three thousand miles from the Moon.
“Apollo 8, this is Houston. At 68:04, you’re Go for LOI.”
“Okay,” Borman answered. “Apollo 8 is Go.”
“You are riding the best bird we can find,” Carr said.
Thirty minutes remained until Lunar Orbit Insertion. Controllers continued to make final checks of the spacecraft and its systems, and to grow more nervous by the minute.
George Mueller had thought 69 miles was cutting it far too close to approach or orbit the Moon. “You don’t know that you’re that accurate,” Mueller had told Kraft when the mission was planned. “You don’t know that you can hit the Moon within sixty-nine miles as you’re aiming at this thing two hundred and forty thousand miles away. You don’t know that your radar is that good. You don’t know that your tracking is that good.” Kraft agreed that orbiting at a higher altitude would decrease the chance of error and catastrophe. But that wouldn’t have allowed NASA to best prepare for a lunar landing. So 69 miles it would be.
Mueller wasn’t the only one worried. Pacing the back row at Mission Control, the lead flight director, Cliff Charlesworth, who was off duty at the time, kept thinking, I know all our guidance systems are accurate, and we tracked it properly, and all the mathematicians in the world have looked at this thing. But sixty-nine miles is pretty close…
In a back room, John Mayer, chief of the Mission Planning and Analysis Division, began to receive visitors—Bob Gilruth, George Low, and other top managers, who’d arrived with a pressing, semiserious question:
“How sure are you we’re going to miss the Moon?”
On board Apollo 8, the crew had the same concern. Their spacecraft was now traveling more than 5,000 miles per hour. For its part, the Moon, 2,160 miles in diameter, was moving at more than 2,000 miles per hour. Could anyone really guarantee the ship wasn’t going to end up smashing into the massive orb?
At one console, Flight Dynamics Officer Ed Pavelka calculated the SPS burn data Apollo 8 required for its Lunar Orbit Insertion. Nearby, Jerry Bostick, chief of the flight dynamics program, the team responsible for the trajectory and guidance of the spacecraft, watched him check and recheck his calculations, not once or twice but nine or ten times, before passing them along to Carr for transmission to the astronauts.
Five minutes remained until Apollo 8 met the Moon. At home, Susan, Marilyn, and Valerie hung on every word from the squawk box.
“Apollo 8, Houston. Five minutes…all systems Go. Over,” Carr radioed to the crew.
“Thank you. Houston, Apollo 8,” Borman replied.
“Roger, Frank,” Carr said. “The custard is in the oven at three fifty. Over.”
That was a secret message from Susan to Frank. Long ago, he’d told her, “You worry about the custard and I’ll worry about the flying”—separating their duties was the only way to survive the toll a test pilot’s career exacted from a marriage and family. She’d wanted to let him know that all was good at home at a time he might need to hear it most.
“No comprendo,” Borman told Carr.
Susan couldn’t tell whether Frank hadn’t understood the words or had forgotten the reference. All she knew for sure was that she couldn’t reach him.
Two minutes remained until the spacecraft, now moving at 5,125 miles per hour, went behind the Moon. Since lift-off, Apollo 8 had traveled 240,000 miles, and the Moon had traveled 150,000 miles, to make this rendezvous.
“One minute to LOS [loss of signal],” Carr radioed to Apollo 8. “All systems Go.”
“We’ll see you on the other side,” Lovell said.
Outside Anders’s window, any trace of sunlight had disappeared, and as his eyes adapted to the intense darkness he began to see stars, it seemed like a million of them, so many he couldn’t even pick out constellations. The sight took his breath away. He looked to his right, through the window beside him, hungry for more, but suddenly there were no stars anymore—all of them had gone dark. There was just a giant black hole, as if part of the universe had vanished. The hair on the back of Anders’s neck stood up, and for a moment it felt as if his heart had stopped, until he realized that he wasn’t looking at a missing piece of the universe at all.
He was looking at the Moon.
A few seconds after that, Apollo 8 disappeared behind it.
THE MOON IS APPROXIMATELY 4.5 BILLION years old, about the same age as Earth. The Moon is not a planet but a satellite, and a unique one in the solar system, much larger than other satellites that orbit solid, rocky planets (usually such giant moons revolve around gaseous bodies).
While the Moon is one-quarter the size of Earth, its mass is only about 1 percent of that of Earth. Gravity on the Moon acts with just one-sixth the strength that it does on Earth. Every year, the Moon drifts about an inch and a half farther from Earth as a result of the acceleration effects of Earth’s ocean tides. As a result, the rotation rate of Earth is gradually reducing.
Unlike Earth, which currently rotates every twenty-four hours, the Moon rotates around its axis just once a month. Because it also circles Earth once a month, the Moon’s near side is always the side facing Earth. It wasn’t until 1959, when an unmanned Soviet spacecraft snapped grainy photographs of the far side, that anyone had any idea what it looked like. If all went according to plan, the crew of Apollo 8 would become the first humans ever to lay eyes on the far side of the Moon.
The far side is often referred to as the dark side, but that is a misnomer. All sides of the Moon receive sunlight and experience days and nights. The Moon’s slow rotation on its axis does mean that areas can stay in sunlight, or in darkness, for nearly two weeks.
In many ways, the story of the Moon is a story of its two sides. The near side, which has been facing Earth for billions of years, is marked by dramatic contrast between light and dark sections, which can easily be seen from Earth with the naked eye. The light areas are the highlands, covered with craters and rolling with hills and mountains that can rise miles above the surface. The dark areas are called mare (mare is Latin for “sea”; the plural is maria). The maria cover about one-third of the near side and are much smoother than the highlands, with far fewer craters, an unusual coda to a violent story.
For billions of yea
rs, the Moon was bombarded by asteroids, comets, and other debris. The lunar surface is a record of those impacts, each of its round craters, with its sharp rim and rising edges, a snapshot of a collision. Some of the most massive impacts excavated huge basins with fractured floors that allowed molten magma to ooze up from the Moon’s mantle and fill them in, solidifying into a dark, smooth basalt that became the maria. These giant impacts were the climax of an era of bombardment that marked the Moon’s initial evolution. The formation of the maria occurred long after the basins were formed, in some cases perhaps by a half billion years or more, so they are younger than the light-colored highlands. The maria are also relatively free of craters, suggesting that the lunar landscape appears much the same today as it did three billion years ago.
The far side of the Moon is very different from the near side.
It has almost no maria—just 1 percent of its surface area is dark “sea” compared to 30 percent on the near side. Instead, almost the entire far side is covered in heavily cratered, light-colored highlands. Many scientists think this is the result of a lesser concentration on the far side of radioactive elements, which produced the volcanic activity that created the maria on the near side. Experts also believe that the far side has a thicker crust, which would have made it more difficult for even the largest asteroids and comets to break through to reach the magma below.
The far side is also more mountainous, with its highlands rising higher above the surface than on the near side. And it is more heavily cratered because it has so few maria, the “seas” of hardened magma that covered over so many impacts on the near side.
Once the differences between the near and far sides are accounted for, it becomes easy to describe the Moon as a whole. Perhaps the Moon’s most distinctive feature is its craters. These range in size from microscopic to the South Pole–Aitken basin, which measures 1,550 miles across and 5 miles deep. There are possibly more than a million craters at least a half mile wide on the Moon. Even at close range, and with optical instruments, the crew of Apollo 8 would never be able to count all the craters on the Moon.
The current impact rate from meteoroids and other debris is just about one ten-thousandth of what it was during the late heavy bombardment period about four billion years ago, when the basins formed. Today, that equates to about a hundred impacts a year by objects weighing between a fraction of a pound and a ton.
As a result of the constant bombardment of asteroids and comets, the vast majority of the lunar surface is coated in a mixture of powdery dust and pulverized rock fragments known as regolith. This top layer might be as shallow as six feet at the maria, or as deep as thirty feet in the highlands. For years, NASA planners worried about whether a spacecraft, or even an astronaut, might sink beneath the regolith and disappear. In the mid- to late 1960s, unmanned probes sent by NASA answered that question: The regolith was sturdy enough to support lunar landings, even if spacecraft would settle into it a bit and men might make footprints with their boots.
The Moon’s crust—its rocky, rigid outer layer—is much thicker (35–60 miles) than Earth’s (3–20 miles), remarkable given the relative sizes of the two bodies. The opposite is true of the Moon’s core, which is much smaller and lighter (3 percent of total mass) than Earth’s (one-third of total mass).
The Moon isn’t a perfect sphere. It’s difficult to see from Earth, but the Moon is a bit squashed at the poles, with a slight bulge at the equator, which points toward Earth. That bulge is evidence of Earth’s grip on the Moon. The Moon’s gravitational pull on Earth is equally important; without it, Earth would wobble on its axis and lose its moderate climate. Summer temperatures could exceed 200 degrees Fahrenheit. Much of Earth could sink beneath water. Spinning faster without the Moon’s grip, Earth days might last just eight hours, winds would reach hurricane strengths, and life would be difficult, if not impossible.
There is essentially no atmosphere on the Moon; its gravity isn’t strong enough to keep hold of an envelope of gases. Without an atmosphere, the Moon cannot trap or filter heat. On the side facing the Sun, temperatures can rise to 240 degrees Fahrenheit; on the other side, they can plummet to minus 290 degrees Fahrenheit. The lunar surface and surroundings are in a vacuum, which should make the Moon absolutely dry and devoid of water. Yet recent probes proved that there is water ice in the regolith of craters at the lunar south pole, which exists in eternal shadow. If humans someday set up a colony on the Moon, they’d probably start at these craters, where water is most likely to be.
On Earth, there is little sign of the bombardment the planet has received from meteorites and other space debris. Rain, wind, plate tectonics, glaciers—all of these factors have worked over eons to erode or bury the evidence of these impacts on Earth. On the Moon, nothing is churned or worn away. The scars from objects that strike the Moon are preserved; this is true even for objects that arrived during the earliest days of the solar system. Examining particles blown onto the Moon by the solar wind might reveal much about the young Sun, when that star was just born. And examining particles thrown off by Earth onto the Moon would tell us about our own history—and ourselves.
Little is known about Earth’s first billion years, the time when primitive life originated on the planet. Earth meteorites preserved on the Moon could provide a window back to that time, giving us a glimpse of the ages from which we came, the stuff from which we are made. But there would be no way to examine Earth meteorites embedded in the Moon without space travelers who could bring them back to us—without humans brave enough to climb into a spacecraft, light an engine with the power of a nuclear bomb below them, and land on our most ancient companion. And one must wonder if, in the future, a similar push by bold adventurers, this time beyond the Moon and into the universe, might bring back another kind of knowledge about ourselves, one that we might not yet have the capacity to imagine but that might transform us fundamentally.
FOR MONTHS, BORMAN HAD BEEN FIXATED on a particular moment in the flight plan: the instant when Apollo 8 would lose radio contact with Earth as it slipped behind the Moon. This would not be the first time a space mission lost contact with Earth. In fact, every Earth orbital flight (Mercury, Gemini, and Apollo 7, as well as the Soviet flights) had long periods when the spacecraft was out of touch with all the ground stations due to Earth’s curvature. Since the planet was not covered with ground stations, the crews on those missions spent most of their time in radio silence. But that was far different from losing contact with the home planet because another world got in the way, which was just about to happen with Apollo 8. NASA had calculated, to the second, when it expected its communications with Apollo 8 to go dead. If the planners were correct, it meant the ship was on its proper trajectory and was where it should be.
If radio contact lasted too long, however, it likely meant Apollo 8 had been traveling too fast and had arrived at its rendezvous point with the Moon before the Moon had a chance to get there and block the transmissions. If the arrival was just a little early, the spacecraft might still be whipped around the Moon by lunar gravity, but at a much higher orbit than desired. If the arrival was earlier than that, Apollo 8 might head off in a trajectory away from the Moon that it couldn’t reverse for lack of sufficient onboard propellant.
If, on the other hand, radio contact ended prematurely, it likely meant Apollo 8 had taken too long to reach its rendezvous point with the Moon. If the lateness of arrival was slight, the spacecraft would zoom past the lunar surface at an altitude lower than NASA had planned or deemed safe for the mission. If it arrived much later, Apollo 8 would smash into the Moon.
So it was with great anticipation—and some dread—that the astronauts focused on the clock as the spacecraft flew backward, its cone-shaped nose and windows facing away from the direction of travel, into blackness. At the Anders residence, Valerie listened with friends, her living room dark except for the glow of a Christmas tree and a crackling fire. At her home
, Susan Borman huddled in the breakfast nook and put her ear to the squawk box.
With just one second to go before predicted loss of signal, Apollo 8 was still in contact with Houston.
Borman’s stomach tightened.
Lovell and Anders stared at the clock.
The view out the windows became even darker.
The astronauts’ headsets went silent.
Borman looked at the clock.
“Jeez,” he said.
Radio contact had been lost at precisely the second NASA had calculated.
Borman could hardly believe it. Anders joked, “Chris [Kraft] probably said, ‘No matter what happens, turn it off.’ ”
Anders had seen how concerned—obsessed—Borman had been about this moment during training. It took a second for Borman to realize Anders was kidding. After that, Borman couldn’t stop smiling. Another critical hurdle in the Apollo 8 mission had been cleared.
In Houston, controllers looked at each other with a sense of wonder and relief, shaking their heads and then shaking hands. Orbital mechanics—the way the universe ordered and moved itself—worked. And man had figured it out to the split second.
The relief at Mission Control was short-lived. In ten minutes, Apollo 8 would fire its Service Propulsion System engine in order to slow itself enough to achieve lunar orbit. The SPS had to work perfectly. And everyone remembered how the engine had fallen short of optimal performance during its brief test firing on the way to the Moon.
Ordinarily, controllers in Houston could rely on their consoles and readouts to provide reassurance that all was well with the spacecraft. But that wasn’t possible with Apollo 8 behind the Moon. No one on Earth would know how well the SPS engine had performed, or even if it had ignited, until Apollo 8 came around and reappeared on the near side of the Moon. If all went well, that would happen in thirty-six minutes.
“Okay, this is a good time to take a break,” Flight Director Glynn Lunney said. He wanted everyone back in twenty minutes.
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