When Chinese engineers launched the first part of the country’s permanent space station into the Earth’s orbit late last month President Xi Jinping told them they had achieved a glowing place in the nation’s history.

“[I] hope you can energetically carry forward the spirit of ‘two bombs and a satellite’,” he wrote in a letter to the mission team published in Chinese state media.

He was using Chinese Communist party code for the three major breakthroughs of the 1960s and early 1970s that were considered essential in securing the young People’s Republic — testing a nuclear bomb, placing it on an intercontinental ballistic missile and launching China’s first satellite.