Last year, Shenzhou 8 approached Tiangong 1 from the rear each time it docked. It withdrew 140 meters from the laboratory to make the second attempt. Shenzhou 9 has been tasked with approaching from ahead, with a plan to return to the 400-meter stopping point before the crew takes over for the second, manual maneuver.
“Shenzhou 8 and Tiangong 1 just created a rigid assembly,” says CAST. “They brought their doors together but didn't open them. So far as the internal environment was concerned, in no real sense did they form a single unit.” This time the astronauts, for the first time in the history of Chinese spacefaring, have moved from one spacecraft to another. Also in preparation for the planned space station, they are shifting stores into the laboratory, while conducting experiments and, above all, just living in it, to prove that they can.
For safety, developers devised more than 300 new fault modes and procedures for the Shenzhou 9 mission, while another 100, relevant to manual control, were improved. Chinese media also report that the spacecraft was modified for greater reliability and fault tolerance.
Experience with Shenzhou 8 suggested improvements to the navigation, guidance and control systems for the current mission. Shenzhou 9 also features a manual backup for what CAST describes as the main recovery switch, presumably meaning the apparatus for initiating and executing the return-to-Earth order normally issued from the ground. The Beijing Aerospace Control Center oversees the missions.
A Long March 2F hurled Shenzhou 9 to orbit. While it is designed to be safe for manned missions, it was also used for Shenzhou 8, showing the importance of keeping the program on the rails.