Core Points - The Shenzhou 21 astronaut crew, including payload expert Zhang Hongzhang, is preparing for a mission, highlighting the importance of scientists in space exploration [1] - Payload experts are selected based on their specific scientific backgrounds and undergo extensive training to conduct important experiments in space [2] - The physical and psychological requirements for astronauts vary, with payload experts having lower physical demands but higher expectations in scientific and experimental capabilities [3][4] Group 1: Role of Scientists in Space - Scientists, particularly payload experts, perform critical experiments in space that cannot be conducted on Earth, requiring a combination of research and space adaptation skills [2] - Zhang Hongzhang, a scholar in high-energy battery technology, will conduct experiments related to space power systems during the Shenzhou 21 mission [2] Group 2: Selection and Training of Payload Experts - The selection process for payload experts involves a rigorous two-and-a-half-year training program covering spacecraft structure, emergency skills, and specific mission training [5] - Even after completing training, candidates must pass additional evaluations to ensure they can handle the physical and psychological demands of space missions [6]