What difficulties did Qian Xuesen encounter when he returned to China? Use 100 to 200 words to describe the difficulties.

1. The U.S. Under Secretary of the Navy launched a political persecution on the grounds that he knew the core secrets of all U.S. missile projects. The immigration authorities raided his home and detained him for 14 days. They released him only after receiving a huge bail of $15,000 from Caltech. Later, on the grounds that he had confidential materials, the customs confiscated his luggage, including 800 kilograms of books and notebooks;

2. Qian Xuesen was born on December 11, 1911 and died on October 31, 2009 , Han nationality, was born in Shanghai, and his ancestral home is Lin'an, Hangzhou City, Zhejiang Province. World-renowned scientist, aerodynamicist, founder of China's manned spaceflight, "Father of China's scientific system" and "King of Rockets". Since Qian Xuesen returned to China to serve, China's missile and atomic bomb launches have advanced for at least 20 years.