Qian Xuesen was twenty-four years old in 1935, a fresh graduate of Shanghai Jiaotong University, when he used a scholarship to get to M.I.T. A year later, he moved to Caltech to earn his doctorate, and Theodore von Karman, a legendary Caltech professor, pronounced Qian an “undisputed genius.” When the U.S. went to war, he joined American scientists in the study of jet propulsion, and helped produce technology to counter German rockets. Then he joined the Manhattan Project.

In 1949, just as he was being named the first director of Caltech’s jet propulsion lab, the Chinese Communist Party rose to power in his homeland, and Qian was accused of being a Communist sympathizer; he acknowledged attending social gatherings with others who had been accused, but he firmly denied any political involvement. When he applied for U.S. citizenship, his application was denied. He lost his security clearance. When he applied to leave America, he was detained, because he was said to know too much about the American weapons system. Finally, in 1955, Qian was allowed to return to China.

“I do not plan to come back,” Qian told reporters at the time. “I have no reason to come back…. I plan to do my best to help the Chinese people build up the nation to where they can live with dignity and happiness.”

He never returned.

“It was the stupidest thing this country ever did,” former Navy Secretary Dan Kimball said later. “He was no more a Communist than I was, and we forced him to go.”

Qian was greeted in China as a hero. He became director of China’s rocket research and was named to the Central Committee of the Communist Party. In 1964, China tested its first nuclear weapon, an extraordinary measure of its development, and a moment that gave a symbolic jumpstart to a rapid modernization of science and technology.

Qian died last week, at the age of ninety-eight. The late Iris Chang, who wrote a book about Qian, concluded that the Immigration and Naturalization Service had no concrete evidence to back up its charge that Qian was a Communist. The L.A. Times writes, “Few can agree on the question of whether Qian was a spy. An examination of the papers Qian packed away failed to turn up any classified documents.” Caltech has long stood behind him; in 1979, the university gave him its distinguished alumni award in recognition of his pioneering work in rocket science, and this week it said, “No evidence was produced to substantiate the allegations, and [Qian] and his colleagues in academia, government, and industry protested that they were nonsense.”

These days, China is moving ahead on its plan to put a man on the moon in the next decade. Qian is being widely credited for his leadership of the space and missile program. There are few people who ever made such a lasting impression on these two countries—whether Qian ever intended to be one of them or not.