Korolyov, Russia - When sending a rocket ship to the moon first became possible, Soviet scientists proposed setting off a nuclear blast there to show the world its scientific prowess.
"In 1958 there was a plan to send an atomic bomb to the moon, so that astronomers across the world could photograph its explosion on film," said Boris Chertok, 87, a leading rocket scientist from the earliest days of the Soviet space programme.
"That way no one would have doubted that the Soviet Union was capable of landing on the surface of the moon," he said in an interview. "But the idea was rejected as physicists decided the flash would be so short lived because of the lack of an atmosphere on the moon that it might not register on film."
The Soviet leadership eventually set its sights on sending a man to the moon, setting off on a decade-long race with the United States that ended with an American taking the first step 30 years ago this month on July 20, 1969.
For engineers and cosmonauts involved in the Soviet effort, the anniversary revives often-bitter memories of a high-profile loss and contradictory explanations of what went wrong.
Vasily Mishin(82), who headed the Soviet moon programme from 1966 to 1974, now says the race was an unfair contest, pitting the vast financial resources of the United States against a far-weaker Soviet Union.
"It was not a fair race. First of all, America was richer than we were, especially then - and Russia was weakened by the fight against German fascism and by the costs of the arms race."
"As soon as America began the moon race, we understood we could not win," he said.
Despite these disadvantages, the Soviets achieved impressive results in putting their mark on the moon.
They were the first to hit the moon with a probe in 1959 and to land an unmanned spacecraft in 1966. The unmanned Soviet Luna 10 first orbited the moon later that year, broadcasting the "Internationale" to the Communist Party Congress in Moscow.
In 1968, the Soviet Union sent the first space ship to orbit the moon with life abroad, returning turtles back to Earth.
The United States space agency NASA took the Soviet challenge very seriously, and in 1968 sped up their programme as a result.
When the day came that Neil Armstrong was ready to step out of the lunar module Eagle and make his historic walk on the moon, top Soviet scientists and cosmonauts gathered to view the event via a bootleg cable hook-up from Europe.
"We were delighted as engineers as they had done wonderful work," said Chertok, deputy for 20 years to Sergei Korolyov, the father of the Soviet rocket programme. "But on the other hand we felt disappointment. Why them and not us? It was bitter."
Soviet television did not broadcast live images of Armstrong on the moon on what was already July 21, 1969, in Moscow.
The Soviet daily Pravda provided a small mention of the historic walk on the front page. Inside, after extensive coverage of 25 years of Polish socialism, the paper offered another article and a fuzzy photo taken from a television image of Armstrong and Buzz Aldrin on the moon.
Soviet authorities explained they were not first to the moon by denying they had even been trying to get there. The secrecy surrounding the moon effort at the time was such that Mishin was often airbrushed out of photos. The official line also said America took needless risks to put a man on the moon.
Mishin, who is now finishing an updated memoir, says he no longer remembers the day the Americans landed on the moon, but still feels the blow of losing.
"Of course it pains me," said Mishin. "We made mistakes."
After the end of the Cold War and collapse of the Soviet Union in 1991, deep secrets of the moon quest began to emerge, including the atomic blast idea Chertok described in an interview this month.
Those involved in the Soviet moon programme still disagree - often strongly - about what went wrong.
The rocket scientists say they were not close to landing a man on the moon as they lagged in devising a way of getting a cosmonaut from the moon's orbit to the surface and back.
However, they were close to flying a man around the moon, but lost that race to Apollo in December 1968.
Alexei Leonov, the cosmonaut who might have been the first human on the moon if Mishin's efforts had succeeded, is still bitter three decades later about the programme's failures.
"Some people today say there wasn't enough money. Nothing of the kind. We had the money, but we only needed to spend it properly." Leonov said.
"Mishin says the Defence Ministry didn't give us money. This is not true," he said. "We did not properly analyse things and do not move further. That was his mistake. Bad organisation."
Mishin's response? "Leonov is a mouse. He doesn't understand anything," he said.
In addition to money woes, Mishin says he lost time with rocket design mistakes and said the Soviet leadership wasted resources by running competing space programmes. Soviet rocket scientists, unlike their NASA counterparts, also had the burden of building nuclear missiles as well as space rockets.
Leonov and others say the Soviet moon effort never recovered from the death of Korolyov in 1966.
"We had everything to fly around the moon. We had the rockets, the space ship, the crew was ready, but we didn't have Korolyov," said Leonov, who keeps small framed US and Soviet flags flown on Apollo 11 on his office wall.
"But even with Korolyov, we would not have beaten the Americans to be the first on the moon."
The men who took over from Korolyov still live in his shadow. Mishin has a home in a town near Moscow named after the scientist, and Chertok lives on a Moscow street honouring him.
For the cosmonauts who trained for moon missions, the Soviet failure could not erase their longing to take a closer look.
"Sometimes I take out binoculars and look at the moon," said Vitaly Sevastyanov, who trained to make a trip around the moon. "And of course the thought arises: could it have happened that I would have flown close by?
"I don't allow myself to say perhaps I could have landed on the moon," said the former cosmonaut, who is now a member of parliament. "That couldn't have happened, but perhaps I could have flown around the moon, but it didn't work out. Of course there is a certain regret." - Reuters