WASHINGTON – It was Dec. 21, 1968, the end of a tumultuous year wracked by political, racial and generational strife.

The number of U.S. troops killed in action in Vietnam had surged past 30,000. Brutal riots outside the Democratic National Convention played out on televisions across the country. The assassinations of Martin Luther King in April and Bobby Kennedy in June added to the despair and division.

The three Americans occupying the module of the Saturn V rocket that Saturday morning 50 years ago at Florida's Kennedy Space Center weren't thinking of the turbulence on Earth. Frank Borman, Jim Lovell and Bill Anders were focused on something else: becoming the first humans to reach the moon's orbit and return safely.

The Apollo 8 mission, which paved the way for Apollo 11's historic lunar landing seven months later, was fraught with risk. The urgency created by the Soviet Union's efforts to reach the moon forced NASA to compress the time frame and take a number of calculated gambles.

The mission took 16 weeks from conception to launch, compared to similar ones that took at least a year to execute. Flight simulators couldn't be used because they weren't finished. It was the first time Saturn V would be carrying humans – and one of its two previous test flights had failed. It would fly without a lunar module that serves as the backup engine in case of a problem.

“Now they’re going to put, on only the third (Saturn V) flight ever, three men aboard this thing," said Robert Kurson, author of 'Rocket Men: The Daring Odyssey of Apollo 8 and the Astronauts Who Made Man's First Journey to the Moon.'

"And they’re not going to send it 100 miles away to Earth’s orbit, or 853 miles which was the world altitude record at the time, they’re going to send it 240,000 miles away," he said. "And they’re going with no redundancy. No lifeboat.”

Many of the millions who watched the countdown that Saturday and heard the astronauts' broadcast as they orbited the moon probably weren't aware of the risks involved. They were likely looking for a respite from the chaos and acrimony that had enveloped their country, Kurson said.

And NASA delivered.

The six-day mission was a roaring success, orbiting the moon 10 times and testing out the "trans-lunar injection" system and other electronic networks that would allow future missions to land on the moon over the next three years. Anders' iconic photo (known as the "Earthrise" image) of a partially shaded bright blue Earth graced a U.S. stamp and is credited in part with being a catalyst for the environmental movement. The astronauts were feted with a ticker-tape parade in New York City.

The mission gradually lost a measure of prominence after Apollo 11 carried Neil Armstrong, Buzz Aldrin and Michael Collins to the lunar surface the following year. Other missions also grabbed the public's attention, including the Apollo 13 mission Lovell commanded in 1970 that failed and became the subject of a Hollywood movie.

But Lovell, 90, who lives in Lake Forest, Illinois, said the success of Apollo proved to be just what an ailing country needed.

"I thought it was necessary just for the importance of giving the American public a boost." he told USA TODAY. "The year 1968 was undoubtedly one of the worst we had. The American public needed an uplift, and this came just in the nick of time."

In separate interviews, USA TODAY spoke with Kurson, Lovell and Borman, 90, of Billings, Montana, about the historic mission and it's significance 50 years later. (The Q&A has been lightly edited for clarity.)

Question: What do you remember most about the mission?

Frank Borman: Looking back at the Earth over the lunar horizon, that picture that Bill Anders took (will stay with me) until my dying day.

Jim Lovell: Going into lunar orbit and seeing the far side of the moon for the first time, meaning that we were the first three people (to do so).

Q: Given the risks, did you think you wouldn't return?

Borman: I never thought that at all. I was absolutely confident in the hardware. If I didn’t think it was 100 percent certain about it, I wouldn’t have gone.

Lovell: It was a bit risky, there’s no doubt about it. My two companions wrote goodbye letters to their wives. I didn’t. I knew I was coming back home. If I had to sit down and write a goodbye letter to my wife, I wouldn’t have gone.

Q: The mission brought a high note to a turbulent year. What if it had been a failure?

Robert Kurson: (Then-NASA administrator) James Webb said, "(1968) has been the worst year anybody has ever lived through. But Christmas is that one day when you get a few hours just to exhale and forget the troubles of the world. If something happens to these men at Christmas at the moon, nothing will ever be the same again."

Q: How much did the Soviet threat of reaching the moon first motivate your desire to accomplish the mission?

Lovell: I could have cared less whether we beat the Russians to the moon. This was, to me, a mini Lewis and Clark expedition. We were going to look at parts of the moon that had never been seen before live by humans.

Borman:The Apollo program wasn’t designed to be a great scientific venture or means of exploration. It was a battle of the Cold War. We were in a desperate battle with the Soviets, and that’s why we were pressing.

USA TODAY: What would it have meant if the Soviets had sent cosmonauts to the moon before you got there?

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Borman: It might have changed the whole nature of the post-World War landscape. I’m not certain we would have had the dissolution of the Soviet empire. I’d like to think that the success of the Apollo program was an important first step in the end of the Soviets.

Q: There’s a refocus on the moon now after the Obama administration had placed more of an emphasis on Mars. Is a lunar return the right call?

Lovell: Definitely. Going back to the moon is really important because what you can do is really start to explore the moon itself and build up confidence. Eventually, if there is a strong push to go to Mars, they can build on the architecture of what we did going to the moon.

Borman: I think we should go back because the been-there-done-that was to beat the Soviets. Now we need to go back and try to understand more about the moon and how it can help us go to Mars. I don’t believe there’ll ever be a colony of human beings on Mars. That’s nonsense.