Shenzhou 9 should build confidence as China plans to assemble a space station
By last year, China's manned space program had launched its Shenzhou spacecraft eight times, three of them with astronauts aboard. Yet only now, with 13 years of cautiously accumulated experience behind the program, has a Shenzhou crew been given responsibility for controlling the movement of their spacecraft.
So while Shenzhou 8 last year showed that the Chinese manned space program had the technology for automatically bringing one spacecraft up to another and linking them, Shenzhou 9 has set out to prove that if the autonomous system were unavailable, then the crew could do the job manually. If they succeed, planned missions to assemble a space station around the end of the decade will not be hostage to the reliability of the automatic rendezvous and docking equipment.
Shenzhou 9, with three astronauts, has proved that equipment a third time, adding to the two docking maneuvers that the unmanned Shenzhou 8 executed. On June 18, the latest spacecraft brought itself toward the Tiangong 1 orbital laboratory, then stopped at a range of 5,000 meters (16,400 ft.) while controllers on the ground assessed its progress. A few minutes later, it began moving on its target again until it stopped once more at a range of 400 meters. With a microwave radar and laser rangefinder supplying data, the spacecraft repeated its procedure down to 140 meters, then 30 meters before finally moving right up to Tiangong 1 and docking with it.
In pushing ahead with their military-led program, the Chinese have had to reinvent such technologies because Western nations have been largely unwilling to cooperate (see p. 18).
All Shenzhou craft have been fitted with manual flight controls, but until Shenzhou 9 the commands to fire maneuvering thrusters were all issued from the ground. Astronauts on previous Chinese missions “just sat in the cabin,” says government spacecraft and rocket builder CAST. “They did not control the spacecraft.”
Another major task of Shenzhou 9 is to prove that Tiangong 1 can support life. The three astronauts are due to spend 10 days of the 13-day mission in the quarters provided by the linked craft. When they left the Jiuquan space base on June 16, they had supplies for 15 days. (Shenzhou, pronounced shen-jo, means “divine craft” and is a homonym of an old name for China. Tiangong, pronounced tian-gong, means “palace of the heavens.”)
Engineers are progressively improving the Shenzhou craft with physical changes and new procedures and failure modes. The current mission's most obvious differences from Shenzhou 8 are the addition of procedures for manual control and equipment for carrying three people, including China's first female astronaut. Beyond that, its test of the automatic rendezvous and docking system was more severe, because it executed the maneuver entirely in sunlight. Shenzhou 8 shielded its systems from some light interference by completing the process in shadow. “The rendezvous and docking equipment must accept a severe and unusual test,” CAST said in a report carried by the Xinhua news agency before the maneuver.
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.