President Richard M. Nixon speaks at Hickam Air Force Base prior to presenting the nation's highest civilian award to the Apollo 13 crew. Photo: NASA/JSC

In a colourful half hour ceremony at Houston, President Nixon, accompanied by Mrs Nixon, presented the Medal of Freedom, America's highest civil award, to the NASA Manned Spacecraft Center in recognition of their achievement in bringing Apollo 13 safely home.

It was less than 24 hours after splashdown. But overnight the vivid green lawns of the Center had been provided with stands and enclosures. Dr Paine, NASA's head, greeted the President and disclosed that throughout the 4-day crisis there had been an open line from Houston to the White House.

Nixon, who described Apollo 13's safe return as the most exciting day of his life, was slighty ruffled by a demonstration. Twenty men and women had been allowed to display placards reading: "Space shot a success: The welfare System a big Zero" were hustled away when they started shouting as he spoke.

The President then collected the wives and children of Jim Lovell and Fred Haise, and Jack Swigert's parents, and departed in the Presidential jet to Honolulu, where he also presented Medals of Freedom to Jim Lovell, Fred Haise and Jack Swigert.

I stayed at Houston until April 23, when the three astronauts arrived home, looking extraordinarily fit (even though Lovell had lost a whole stone during the flight) and told us their own stories. Fred Haise said he had calculated "on the back of an envelope" that they had had a 1-hour margin of consumables to get them home. They all said they were willing to make another attempt to land on the moon - but of course, not one of them ever did return to space.

Grumman, the company which had built the Lunar Module, at that time presented the contractors for the Command and Service Modules with a salvage bill for about half a billion dollars for towing the crippled spacecraft all the way home from the moon. I suspected it was not entirely a joke.

By then NASA had already dropped earlier suggestions that the Service Module explosion might have been due to a meteorite collision, and accepted that there must have been an internal cause. But they pressed on with the moonlanding programme with much more courage and determination than when the Space Shuttle hit trouble in 1986. Apollo 14 was launched only nine months after Apollo 13 and the programme was completed with Apollo 17 in December 1972.

Post-flight test at the NASA Manned Spacecraft Center (MSC) shows Teflon insulation burning in supercritical oxygen at earth gravity. Photo: NASA/JSC

One reason was the political pressures they faced to cut costs. Before Apollo 13 the number of moonlandings had already been cut from 10 to nine, and after it two more were cancelled, so that in end only six took place, carrying 12 men to the lunar surface.

Not until five years later, in the official Apollo history, did Lovell himself give the full details of how Oxygen Tank No.2 overheated and blew up (putting No.1 out of action as well) because its heater switches had been welded shut during excessive pre-launch tests. "Warning signs during testing went unheeded, and the tank, damaged from eight hours of overheating, was a potential bomb," he wrote. "That bomb exploded on April 13, 1970, 200,000 miles from earth."

Had anybody told me, amid the euphoria of Apollo 13's safe landing, and after the complete success of the later missions, that another 50 years was likely to pass after Apollo ended before humans returned to the moon, I would have been incredulous indeed. Dr Wernher von Braun, whose rockets had made lunar travel possible, had shown me his plans for a Lunar Base occupied by 100 people before the end of the 20th century. I share the acute disappointment of those early Apollo astronauts that all that preparatory work was never followed up!