On October 31st, 2009, Chinese famous scientist Qian Xuesen, died in Beijing when he was 98 years old. He is famous as "the country's father of space technology and king of rocketry". Qian was born in 1911 in Hangzhou. He left for the United States after winning a scholarship to graduate school in 1936. He studied at the Massachusetts Institute of Technology and later at the California Institute of Technology. Qian began his career in the US and was regarded as one of the brightest minds in the new field of aeronautics  before returning to China in 1955. After he returned, Qian set up the first missile and rocket research institute  of China. The institute later helped start Chinese space program. He led the development of China's first nuclear-armed ballistic missile   and worked on its first satellite. He retired in the year before Chinese manned space program was launched in 1992. But his research formed the basis for the Long March CZ -2F rocket that carried astronaut Yang Liwei into orbit in 2003. In August, 2009, Chinese Premier Wen Jiabao visited Qian and _ him for devoting his life to Chinese defense technologies. Qian told him, "I'm trying to live to be 100 years old". When did Qian Xuesen retire?
In 1970. In 1991. In 1992. In 2009.