Media playback is unsupported on your device Media caption Communications were playing up and fuel was running low

The BBC World Service has launched a special podcast series to mark the 50th anniversary of the Apollo 11 Moon landing. 13 Minutes to the Moon details the final phase of the descent to the lunar surface - and the months and years that led up to those extraordinary moments.

Presenter Kevin Fong recalls meeting the unique cast of characters that contributed to the podcasts, including some of the last surviving Apollo astronauts.

In the making of 13 Minutes to the Moon, we spent the best part of four weeks travelling around the United States looking for the people who, one day in 1969, had somehow got a man safely to the surface of another world.

In Texas, we found Charlie Duke, lunar module pilot on Apollo 16, and Walt Cunningham, who served as command module pilot during Apollo 7, the inaugural test flight.

In Chicago, we interviewed the legendary Jim Lovell, who orbited the Moon in 1968 on the audacious flight of Apollo 8, and of course later commanded the ill-fated Apollo 13.

The very first of our interviews for the series was with Michael Collins who, along with Neil Armstrong and Buzz Aldrin, completed the crew of Apollo 11 on the mission that saw human beings land on the Moon for the very first time in the summer of 1969.

I remember arriving at a cheap hotel somewhere on the western edge of the Everglades in Florida the night before and standing in the car park staring up into the night sky at the waxing Moon, knowing that the next day I'd be talking to someone who had once flown there.

But the astronauts were merely the most visible tip of a gargantuan iceberg.

Image copyright NASA Image caption Buzz Aldrin salutes the US flag: The moonwalkers were the tip of a very long spear

In total, no fewer than 400,000 people were involved in Project Apollo. Nearly all of them felt deeply connected to the mission and, although only a handful of people finally flew to the Moon, in a very real sense the factory workers, engineers, technicians and scientists that worked as part of the Apollo programme felt that, on 20 July 1969, part of them landed on the Moon, too.

We wanted to tell all of those stories, framed by the drama of the last 13 minutes of descent before touchdown on the lunar surface.

That period of the mission was rife with crisis and, as Armstrong would later testify, "rampant with unknowns".

As Armstrong and Aldrin descended from 50,000ft above the Moon, radio communications with Earth broke down; the lunar module was running long on its target landing site; the onboard computer - on which the astronauts absolutely depended - started flashing up error codes that the crew had never before seen; and in the final few seconds, it looked like Armstrong and Aldrin might actually run out of fuel.

In the audio recordings from mission control of those final 13 minutes, you can hear the tension in every spoken word, every phrase and every silence. And so series producer Andrew Luck-Baker and I set about the task of trying to unpick those fraught moments and explain how the furious race to get a crew to the surface of the Moon - before the decade was out - conspired to create those exhilarating final moments.

Growing up in the 1970s, in the afterglow of Project Apollo, I devoured everything I could find that told those stories: every television programme, every book, every magazine.

Later it drove me to pursue science as a career.

I studied astrophysics and then medicine at University College London, and later got the chance to work with Nasa at Johnson Space Center as a doctor and visiting researcher.

That life and the adventures that came with it were driven in no small part by the people who flew to the Moon.

Image copyright NASA Image caption The "Apollo effect": The achievement inspired countless millions around the world

Even as a schoolchild, I think I understood that if people could fire human beings off the surface of our planet, and land them on another world, then surely anything - anything at all - must be possible.

And so when the opportunity came to make this podcast series, I jumped at it.

We interviewed dozens of people from all over the United States and, although it was quite something to spend time sitting in the living rooms of astronauts who had actually flown to and walked on the Moon, it was our interview with former flight controller Stephen Bales that for me stood head and shoulders above all the rest.

I like to think of Steve as the Luke Skywalker of the Apollo programme.

Image copyright NASA Image caption Steve Bales: Like so many of his colleagues, the Iowa man was under 30 years of age

He grew up in a farming community in Iowa but on clear nights he would go outside, stare up into vast dark skies filled with stars and dream of the adventure of space.

Later, equipped with a degree in engineering, he journeyed from rural Iowa to the hustle and bustle of the city of Houston.

He started at first as an intern at Johnson. Little more than an office junior, he gave visiting VIPs tours of mission control. But he stole away from those duties whenever he could, to talk to the flight controllers about their job of running the systems for spacecraft and their human occupants, hurtling through space far above them.

This, he decided, was where he wanted to be, part of the team who ran the missions. And in time his boyish enthusiasm won through.

When President John F Kennedy set his nation on course for the Moon, to arrive in the course of a single decade, Nasa had to scrabble together a workforce capable of delivering that promise. They hired quickly and often without interview, choosing instead to get people who had the requisite skills and then evaluate them on the job.

The flight controllers in mission control were incredibly young - for Project Apollo their average age was just 26 years old. And while it seems strange that such huge responsibility would be given to a bunch of fresh-faced employees, not long out of university, their youth was for the most part regarded as a significant asset.

"It wasn't that they didn't understand the risks," Apollo flight director Gerry Griffin told me, "they just weren't afraid."

Image copyright NASA

Fearless and prepared to give themselves entirely to the task, they were exactly what the space programme needed.

Steve rapidly worked his way up, from a technician's position, supporting missions from the back rooms, to a seat in mission control as a flight controller for Project Gemini. By that time, he was only 23 years old.

In mission control someone was always watching, even if you weren't sure who and, as attention turned from the Gemini's orbital flights to the business of Project Apollo and a landing on the Moon, Steve was assigned to the Guidance, Navigation and Control team. These were the people responsible for shaping the spacecraft's path as it flew through space.

During exhausting simulations in the months leading up to 20 July 1969, Steve continued to impress. As the mission managers began to assemble the team of flight controllers who would be in the room for Apollo 11's historic first attempt at a landing on the Moon, Steve - now all of 26 - found himself somehow in the mix.

For the landing, he would take his seat as the guidance officer, one of mission control's most critical roles. And the enormity of that task was not lost on him.

"Here's some 26-year-old kid," he told me, wide-eyed in disbelief even after 50 years, "a kid who can stop a space mission!"

Image copyright NASA Image caption Inside the "Eagle" Lunar Module, Armstrong and Aldrin were seeing unfamiliar computer codes

In the midst of Armstrong's and Aldrin's descent in those final 13 minutes the crew and their essential support team in mission control were beset by problem after problem.

They were travelling too quickly across the lunar surface and in danger of overshooting their planned landing site.

Their radio communications with Earth became patchy and then, as they sank still closer to the surface, their onboard computer threw up a series of alarms that the crew had never seen before, alarms that they didn't understand.

For the landing on the Moon, the crew depended almost entirely on their onboard auto-pilot - the Apollo Guidance Computer. And although today we like to joke about how limited the processing power of that computer was, at the time it was by far the most complex and sophisticated device aboard the spacecraft. Its ability to assist the astronauts in this near impossible feat was absolutely essential to the success of the mission.

The on-board computer display and keyboard together resembled a giant calculator and its rudimentary display was able to flash up only a series of numbers to display information and help identify problems.

On the mission audio, recorded from the cabin, you can hear Buzz Aldrin and then Neil Armstrong call out the string of digits appearing on the display: 1202, which they read across the void as, "Twelve-oh-two."

In mission control, nobody understood what was happening. Was the computer about to fail? Were they going to have to abort the landing? Were Armstrong's and Aldrin's lives in danger?

There was a pause of a few seconds while the team scrambled to try to find an answer and in that time, the normally ice-cool Neil Armstrong broke into the radio transmission again, almost gabbling the words: "Give me a reading on the twelve-oh-two."

Image copyright NASA Image caption Neil Armstrong: Calm in the most stressful of situations

It is the only time anyone that we spoke to can ever remember hearing a note of urgency in the astronaut's voice.

In the 15 seconds that passed from Armstrong and Aldrin first spotting the alarm, Steve Bales talked with his backroom support team, desperately searching for a response to Armstrong's urgent question.

The seconds ticked by with the lunar module still falling toward the Moon and with the crew still unsure if their vital onboard computer was still up to the task of guiding them through the landing.

This was the essence of mission control. The Apollo flights threw up problems with complex systems, that arose in real time, and which had to be solved by human operators in the moment. And while Armstrong waited all eyes turned to Steve Bales, the boy from Iowa.

From the backroom, Steve's colleague Jack Garman recognised the 1202 code as being similar to something they had seen in a simulation from several weeks earlier.

It told them that the computer was struggling but still working and able to perform its mission-critical tasks.

On that occasion, when the alarm occurred during their dress rehearsal, Steve had aborted the mission unnecessarily and had been admonished for doing so.

So, when the 1202 alarm flashed up during the final minutes of Apollo 11's descent, Steve Bales quickly had an answer: "We're go on that flight." And the rest of course is history.

Image copyright NASA

We spoke to flight controllers and directors about Steve Bales. They painted a picture of an irrepressible young man, brimming over with enthusiasm but who was nevertheless highly capable and absolutely dependable.

Having grown up dreaming about the stars, that night in the summer of 1969, he somehow found himself in the middle of one of the most difficult and critical decisions of the whole Apollo programme and made a split-second judgement that saved the mission.

Afterwards, when the crew were safely on the surface, flight director Gene Kranz led him out to join him at a frenzied press conference. And when his shift in mission control was finally done he wove his way down the long corridors that led from the mission operations control room into the blazing Houston sunshine.

Bleary-eyed he stood there blinking. The boy from Iowa who had helped put a human being on the Moon.

Media playback is unsupported on your device Media caption Thirteen facts about one of the greatest events in history

Our road trip across America in search of the people and stories that together were the essence of the Apollo programme was a labour of pure love.

Everywhere we turned there were stories just like Steve's, with the safety and success of the mission perpetually in the balance.

Someone once said of Neil Armstrong that he's one of the few people of the 20th Century who has a chance of being remembered in the 30th Century. But Armstrong was merely the tip of the spear, and our podcast series gives us a chance to celebrate not only him and his astronaut brethren, but also the genuinely remarkable army of people without whom we would never have set foot on the Moon.

The first episode of 13 Minutes To The Moon will be available for download on 13 May, with further episodes released every Monday, culminating in a final edition on 20 July, the anniversary of the Apollo 11 landing itself. The podcasts can be downloaded from the BBC and from leading platforms around the globe.