Conrad, also known as Pete, was commander of the Apollo 12 mission in 1969.

He was killed while riding with friends

Along with fellow astronaut Alan Bean, he spent seven hours and 45 minutes on the lunar surface collecting samples and retrieving parts of an unmanned craft which had landed two years earlier.

He died in hospital on Thursday after crashing on a turn while riding with friends.

The aeronautical engineer, who lived in Huntington Beach near Los Angeles, was selected by Nasa as an astronaut in 1962. He was the pilot of the Gemini 5 mission in 1965 which set an endurance record in orbiting the earth.

A year later, he commanded Gemini 11, which docked with another craft and featured space walks by another pilot.

Skylab mission

Charles Conrad, who joined the US Navy as a pilot after graduating from Princeton University, also took part in the first manned Skylab mission in 1973.

Conrad practising for the second lunar landing

During this flight, he established a personal endurance record for time in space, with 1,179 hours and 38 minutes.

After retiring from Nasa and the navy, Conrad worked as chief operating officer of American Television and Communications Corp in Denver and later for McDonnell Douglas Corporation, the aviation manufacturer.

In 1995, he formed his own company called Universal Space Lines and several sister companies with the goal of commercialising space.

"He was going back to space as an entrepreneur, trying to create ways for rockets to launch inexpensively and manage satellites," said his widow, Nancy.