The Mammoth Book of Space Exploration and Disasters

“Descent orbit insertion” was a 29.8-second burn of our descent engine that would drop the perilune, the lowest point in our orbit, to eight miles above the surface. If everything still looked good at that point, Houston would approve powered descent initiation (FDI). Twelve minutes later Neil and I would either be on the moon or would have aborted the landing attempt.

The LM flew backward, with our two cabin windows parallel to the gray surface of the moon. The DOI burn was so smooth that I didn’t even feel a vibration through my boots, only a slow sagging in my knees as the deceleration mounted when we throttled up from 10 percent to 100 percent thrust. Before the throttle-up was finished, I could tell from the landing radar data that our orbit was already bending. Neil turned a page in the flight plan and grinned at me through his helmet.

The moon rolled by silently outside my window. The craters were slowly becoming more distinct as we descended. There wasn’t much to do except monitor the instruments and wait for AOS (acquisition of signal). As we got closer; the moon’s color changed from beige to bleached gray. The hissing crackle of Houston’s signal returned to our earphones. “Eagle, Houston,” Charlie Duke called through the static. “If you read, you’re go for powered descent. Over.”

Neil nodded, his tired eyes warm with anticipation. I was grinning like a kid. We were going to land on the moon.

Mission Control was quiet. The terracelike rows of consoles descended to the front rank, the “trench.” Plaques from all of NASA’s manned missions were hung along the walls. Wide data-projection screens covering the front wall “scribed” the Eagle’s descent trajectory toward the surface of the moon.

Flight director Gene Kranz hunched over his console in the second row listening to his team’s callouts. Their acronyms had become nicknames: FIDO (flight dynamics officer) and GUIDO (guidance officer), and this shift’s capcom was Charlie Duke. Eagle was descending through 42,000 feet and had just yawed around to its pre-programmed attitude. GUIDO, a 26-year-old engineer named Steve Bales sitting at the middle console in the trench, gave Kranz the intermediate “go.”

“Capcom,” Kranz told Charlie, “they are go.”

“Eagle, Houston,” Charlie Duke called. “You are go. Take it all at four minutes. You are go to continue powered descent.”

The data on the consoles showed that the LM’s pitchover was correct. But when the digits 1202 suddenly appeared on Bales’s screen, he knew the same alarm was flashing on Eagle’s DSKY.

“Twelve-oh-two,” I called. “Twelve-oh-two.”

The 12 01 and 12 02 codes were called “executive overflow,” meaning that the LM’s onboard computer was overloaded with data. We didn’t necessarily have to abort on this signal – not yet, at least. Bales saw that Eagle’s computer was recycling, so the hardware was probably still in good condition. But with the LM a quarter million miles away, dropping toward the moon’s surface, he couldn’t be 100 percent certain this wasn’t an indication that something else was wrong.

“Give us the reading on the twelve-oh-two program alarm,” Neil Armstrong called, his voice strained.

“GUIDO?” Kranz asked.

Bales again scanned his data, and then replied, “Go.”

Charlie Duke frowned. “We’ve got… we’re go on that alarm.”

In the back row, Bob Gilruth, Chris Kraft, George Low, and Sam Phillips stared at their consoles. Kraft was the only one who knew anything about the program alarms. A man with close-cropped white hair sat alone at the far end of the row It was John Houbolt, the Langley mathematician who had successfully backed Lunar Orbit Rendezvous.

Eagle was approaching 4,000 feet. Gene Kranz leaned forward to speak into his microphone. He had a crewcut and wore narrow black ties that made him look like he’d successfully avoided the 1960s altogether.

“All flight controllers, coming up on go-no go for landing,” he told his officers. “FIDO?”

“Go!”

“GUIDO,” Kranz asked, “you happy?”

Bales had to either fish or cut bait. The program alarms were popping up again, though they weren’t signaling an obvious problem with the hardware. But he just couldn’t be certain Eagle would have a good computer for ascent the next day. “Go!” he answered.

“Eagle,” Charlie Duke called, “you’re go for landing.”

Twenty seconds later, Eagle passed through 2,000 feet and another program alarm flashed.

“Twelve alarm,” Neil called. “Twelve-oh-one.”

“Roger,” Charlie acknowledged. “Twelve-oh-one alarm.”

“GUIDO?” Kranz asked. Even his voice was strained.

Deke Slayton was sitting next to Kranz, and he was almost doubled over with tension, dragging deeply on a cigarillo.

Bales looked at the data on his screen. “Go.”

“We’re go,” Charlie Duke told Eagle. “Hang tight, we’re go.”