China’s space programme, including the recoverable satellite project, was seriously disrupted when the political turmoil during the ‘Culture Revolution’ that began in 1966. Under the direct order of Chinese Premier Zhou Enlai, in 1968 the personnel and organisations working on the satellite development were transferred from the CAS to the China Academy of Space Technology (CAST, or the 5th Academy), a military institution that was later placed under the Seventh Ministry of Machinery Industry.
The recoverable satellite development made little progress over the next two years, as CAST focused most of its resources on the DFH-1 mission. This only changed in 1970, when the DFH-1 satellite development had concluded. In February 1970, the recoverable satellite was listed by the State Council as one of the country’s top-priority industrial projects. The NDSTC demanded for a 1,800 kg mass satellite to be ready by the end of 1970 for the DF-5 ICBM test flight, but it soon become clear that this timeframe was unrealistic.
One of the key technologies on the recoverable satellite was its thermal protection system (TPS). An ablative heat shield was developed for the protection of the capsule’s blunt nose tip, which endures the strongest heat flux during re-entry. The heat shield was made of a carbon-based composite material known as ‘XF’. The re-entry capsule with its heat shield was tested inside CAST’s KM-3 thermal vacuum chamber, to ensure that the shield remained intact in temperatures between -100°C to 120°C.
The bottom of the re-entry capsule was originally fitted with an aluminium-alloy radiatively-cooled TPS. However, the TPS was badly damaged during re-entry in the first mission. An ablative heat shield also made of the ‘XF’ material was adopted on all subsequent missions, at the expense of an increased weight in the TPS.
Another breakthrough on the recoverable satellite was its three-axis stabilised altitude control, which was required for precision orbit insertion, imaging operations, and re-entry pitching. The altitude control system, designed and developed by CAST Beijing Institute of Control Engineering (502 Institute), used a gyroscope-based inertial system, coupled with an infrared Earth horizon sensor developed by CAS Shanghai Institute of Technical Physics (SITP). The infrared Earth horizon sensor was fitted on the T-7A sounding rocket for two launches in June-July 1969 to demonstrate its technology.
The satellite’s retro-fire rocket was developed by the 4th Academy of the Seventh Ministry of Machinery Industry, which also developed most solid-fuelled rocket motors in the early years of the Chinese missile and space programme. The parachute system was developed by CAST Beijing Institute of Aerospace Machinery and Electronics (508 Institute). The onboard cameras (Earth-observation and star tracker) were developed by a joint project team (Project 6711) from CAS Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP), 811 Factory of the Ministry of Public Security, and Beijing Institute of Technology, under the direction of Wang Daheng.
Five test articles (spaceframe I, spaceframe II, thermal control, electric test, and launch simulation) were produced during the development phase. Between November 1970 and January 1971, CAST conducted a desktop simulation of the onboard electronic systems, with over 80 engineers and technicians from 7 organisations taking part. The test identified and resolved over 100 design flaws and faults, including radio communication interference and film jamming. The electric prototype test was completed by January 1972. The flight simulation to test the interface between the satellite and the ground tracking and control systems was completed in the summer of 1972.
A full-size mock-up identical to that of the final article was produced to undergo a test to simulate the vibration during launch, orbital flight, and re-entry. The test was conducted on a shaking table imported from Japan. The only available shaking table at the time was situated inside a workshop that was only 9 m in height and 70 square metres in size. The crane in the workshop was incapable of hoisting the 1,800 kg satellite onto the 3 m tall shaking table. The technicians had to place a heavy truck crane next to the workshop and stick the boom through the window into the workshop to lift the satellite.
Between April and December 1973, the mock-up satellite underwent the vibration, noise, jettison impact and thermal vacuum tests, which allowed the satellite design to be fully tested in the simulated environment. A number of design flaws were identified and rectified, allowing improvements to be made on the final design. The development of the flying example of the satellite began in early 1973, with the first launch scheduled for November 1974.