Saturday, July 17, 1999 Published at 08:28 GMT 09:28 UK
Astronauts call for Mars mission
Astronauts plant a flag on the surface of the Moon
Three of the 12 American astronauts who flew to the Moon in the Apollo missions have called for a commitment to a manned mission to Mars.
Neil Armstrong, who made the first historic Moon-walk, said the Apollo missions had demonstrated that "humanity was not forever chained to this planet", and that opportunity was unlimited.
"To put together the effort that it takes to get there once, twice, three times, and then turn our backs on it would be very sad for me and I would not like to see that happen," said Aldrin.
"We could do it in 2020 if we committed to it today, added Armstrong. "So the real question is: When are you going to commit to it?"
'We came in peace'
The four days of celebrations are expected to culminate on Tuesday - exactly 30 years to the day after Armstrong's Moon-walk.
After completing their work on the Moon's surface, the Apollo 11 crew left behind a plaque that read: "Here Men From Planet Earth First Set Foot Upon the Moon July 1969 AD. We Came In Peace For All Mankind."
David Baker, a space consultant, says it was a very significant event which cut mankind's umbilical cord to Earth.
"We felt at the time that mankind was being born as a true cosmic force. Around the far side of the Moon, those men were totally alone for the first time since humans evolved," Mr Baker told the BBC.
The mission was fuelled by the Cold War and American fears of Soviet domination in space exploration.
A silent death
The heroism of the three-man crew was highlighted this year by the release of a memo written to then-President Nixon at the time of the landings.
Under contingency plans, if Armstrong and Aldrin's lunar module had not been able to blast off from the Moon's surface to hook up with the command module on return, communications would have been cut and they would have been left either to commit suicide or die slowly.
The anniversary comes at a time when interest in space exploration is again growing.
This time businesses, not governments, are looking to space and they hope to exploit opportunities for satellite launches and space tourism.
Last year private investment in the space industry exceeded public investment for the first time.