Tributes are being paid to "one of the great unsung heroes of the space age".
Tecwyn Roberts, from Anglesey, helped set up mission control rooms and enabled astronaut Neil Armstrong to communicate with Earth from the Moon.
Experts have hailed Roberts' expertise as events are held to mark the 50 years since Nasa's second lunar landing.
A flag will be placed on his grave during the anniversary of Apollo 12 which flew from 14-24 November 1969.
"Without Tec[wyn], Nasa and mission control as it exists today would probably not have happened," said Nick Howes, a fellow of the Royal Astronomical Society.
"Tecwyn Roberts could rightly be labelled as one of the great unsung heroes of the space age."
Mr Howes was speaking in an interview published by Nasa's Goddard Space Flight Center in Greenbelt, Maryland, which has also hailed Roberts as a "pioneer".
He was chief of the network engineering division by the time of the first landing on the Moon and helped to ensure there was communication with astronauts.
Roberts, who also helped establish the Satellite Servicing Control Center at Goddard, was born in Llanddaniel Fab in 1925.
He was educated on Anglesey where he took up an engineering apprenticeship.
He then studied aeronautical engineering at university before taking a job with an aircraft manufacturing company in Toronto, Canada, and later joining Nasa.
Gary Morse, a former Nasa space shuttle network director, said Roberts "essentially invented" the flight director position.
"He didn't say much but when he did it was very important," he said.
Roberts received several accolades during his career, including being awarded the exceptional service medal by Nasa.
Mr Howes, who has sent the Welsh flag to the US, said he hoped Roberts' career would inspire the next generation of engineers as he rose "from humble beginnings in such a small town so very far away".