Recoverable satellites

Chapter 4 tells the story of the Chinese Fanhui Shi Weixing (FSW) recoverable satellite series. This began in 1975 and, since then, China has carried out 23 recoverable missions, including one recently in the Shi Jian series, called “the seeds satellite”. These satellites have been important for testing new technologies, Earth observations, and biology.

PROJECT 911

China was the third country to recover a satellite from orbit. The idea of a recoverable Earth satellite in China went back to 1964 and the work of engineers in the Shanghai design team. They had been inspired by what they read of the American Discoverer series of recoverable satellites in the early 1960s. The concept was first formally proposed in the Chinese Academy of Sciences’ Proposal on Plan and Program of Development Work of Our Artificial Satellites, approved in August 1965, and hardened up during a design conference in March 1966. The Shanghai bureau was awarded the task and it was named project 911.

Design studies began immediately and were settled in the course of a three-day conference in September 1967. It was agreed to build a satellite with a weight of 1,800 kg (payload was 150 kg) and a typical orbit of 173-493 km, 91 min, 59.5°. It was given the name in Chinese Fanhui Shi Weixing, or “recoverable experimental satellite”. Apart from verifying the ability to recover satelhtes from orbit, the precise purpose of the program has never been entirely clear. The American Discoverer, although promoted as a research program, was actually a military photo­reconnaissance program designed to photograph Soviet military facilities and the Chinese later announced that the FSWs carried out Earth observation work, its cameras having a resolution of 10 m and a length of 2,000 m of film [1]. At the same time, another purpose of the FSW was probably to pave the way for an early manned flight (see Chapter 8). Whatever its original purpose, later versions of the FSW were also used to conduct a range of microgravity experiments in orbit. Whether this was because of an improvement in the international climate, or the Umited military reconnaissance value achieved from the FSW missions, or a form of

B. Harvey, China in Space: The Great Leap Forward, Springer Praxis Books,

DOI 10.1007/978-l-4614-5043-6_4, © Springer Science+Business Media New York 2013

diversification is a matter of guesswork. The military intelligence benefit from orbiting a recoverable cabin collecting 10-m-resolution images for a week every year is probably quite limited. Ultimately, the lasting achievements of the program were in civilian applications.

The use of photography for military reconnaissance was developed in the 1960s by both the Americans (Discoverer) and the Russians {Zenit, Yantar). Both had flown high-quality film, which was then returned to the Earth in a descent cabin for developing and interpretation, also called wet-film technology. The principal drawback of the system was that no data could be examined until the cabin returned, which reduced its value in following a rapidly evolving military situation. From the 1970s, the Americans moved to digital imaging, with photographs relayed electronically from orbit, but the Russians persisted with high-quality film – recoverable technology right into the 2010s {Kobalt). Eventually, the Chinese would move to digital technology (Zi Yuan and Yaogan).

The task of developing the project fell to the China Academy for Space Technology (CAST), while a new rocket, the Long March 2, was developed by the China Academy for Launcher Technology (CALT). Just as the civil version of the Dong Feng 4 missile had been the Long March 1, so in this case was the Long March 2 related to the Dong Feng 5. Progress was held up by the later phases of the cultural revolution but for which the first launch might have appeared several years earher than it eventually did. Recovering satellites posed difficult engineering challenges: devising a protective heat shield to ensure the capsule survives re-entry temperatures of 1,200°C, the development of retro rockets, a very precise attitude control system, quality ground tracking to prepare the cabin for the precise moment of re-entry, and search-and-recovery systems. These engineering challenges required the development of ever more sophisticated ground-testing equipment. A thermal vacuum chamber called the KM3 was constructed by the Institute of Environment Test Engineering and the Lanzhou Institute of Physics, achieving a vacuum level of КГ9 torr. The Xian Satellite Surveying and Control Centre was built so as to follow the satellite in orbit.

The Chinese had no previous experience of making heat shields. They did not wish to use ablative heat shields of the type developed by the US and Soviet Union in the 1960s, in which the material progressively burned off during the descent, enough remaining for the cabin to survive, but they were very heavy. Equally, they knew they did not have the capacity to go straight to light, low-density foam-type shielding of the type subsequently used by the American and Soviet shuttles (tiling). They eventually found a non-ablative material whose qualities lay somewhere in between – a carbon composite material called XF, able to withstand re-entry temperatures of 2,000°C. Contrary to some Western reports, the shields were not made of wooden oak planks (Europe’s Atmospheric Reentry Demonstrator (ARD) did use resin processed from Cork oak).

The recoverable series required a relatively advanced level of automation: a new three-axis attitude control system using an infrared horizon scanner and a gyrocompass, with analog computers, Sun and Earth orientation sensors, an inertial measurement unit, and a cold gas thruster system to orient the spacecraft. A camera

system was developed by the Changchun Institute of Optics and Fine Systems, comprising cameras for ground photography and side-pointing cameras for stellar photography (so as to work out the precise position of the spacecraft in orbit). To come out of orbit, a solid-fuel rocket was developed. The parachute system proved problematical and four air-dropped cabins were lost in tests when the parachute failed to open.

The FSW satellites were a quantum leap in size and scale beyond the first two satellites. Coming in at just under 2 tonnes, the cabin itself was beehive-shaped, 3.1 m tall, and ranging from 1.4 m in diameter at the forward end to 2.25 m in diameter at the large end. The satellites comprised a blunt cone capsule placed on a service module. During the mission, the nose was pointed in the direction of travel. At the end of its mission, when it reached Chinese territory, the spacecraft was swiveled through 100°, pointed nose down directly toward the Earth, and the sohd retro-rocket was fired, to descend almost vertically from orbit. This was a crude means of returning to the Earth – one that used up a substantial amount of fuel, but had the advantage of ensuring that retro-fire could be commanded over China and recovery would take place in China (by contrast, Russian spacecraft made a gentler descent, but with retro-fire commanded far away over the South Atlantic). On the other hand, such a retro-fire maneuver required a big velocity change of 650 m/sec, much more than the standard Russian or American re-entry profiles (about 175 m/ sec), while the angle of retro-fire must be very accurate, for each degree out meant a 300-km difference in the landing spot. At 16 km, the FSW dropped its heat shield and retrorockets, a parachute opened, and the cabin came down at 14 m/sec in Sichuan province in southern China. The Chinese landing technique, guaranteeing

landing in China, was important if sensitive film were on board (the Russians fitted self-destruct devices to their spacecraft to stop theirs falling into unfriendly hands). To help rescuers find it, the cabin was equipped with a transponder and two location beacons.

Sichuan province in the south-west of the country was chosen as the recovery zone, although it is hilly and often subject to thick clouds and mists. Photographs from the recovery area have frequently shown Mil-type recovery helicopters hovering against a background of mountains, follow­ing the descent craft down, and then lifting it away for post-flight exam­ination. The scene is one of the space cabin lying on the hillside, its red – and-white parachute streamed out alongside, the recovery teams safing and checking the cabin, and rural workers gathering on the nearby hills to watch the excitement.

The chief designer of the rocket to carry the FSW, the Long March 2, was Tu Shoue and the rocket remains in service 40 years later (see Chapter 3). Made of high – strength aluminum copper alloy, it was the first Chinese launcher to use full computer guidance and gimbaled engines. Its lightweight medium-speed, small – capacity digital computer was the first of its kind in China. A particular feature of the ascent was interstage glide: once the second-stage engine had completed its burn, the maneuvering vernier engines would continue to fire as a main engine, which enabled an extra 500 kg of payload to be carried.

Chief designer of the FSW cabin was Wang Xiji, born in 1921 in Dali, Yunnan, a graduate of Xian University who went on to Virginia Institute of Technology, where he was awarded a doctorate in 1949, returning to China the following year and becoming director of the Shanghai Institute of Mechanical Engineering and Design in 1958.