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The 2001 Winter Issue of Aerospace China

China's Scientific and Technological Test Satellites

By Zhang Yongwei

When starting to develop satellites, China began to develop the series of scientific detection and technological test satellites to make the advanced test of new technology badly needed for space mission, and carry out space environment monitor and space scientific research. Since the 1970s, China has developed and launched the SJ-1 and SJ-2, SJ-4 and SJ-5 satellites, which formed the preliminary series of the SJ scientific detection and technological test satellites. This paper describes in details the SJ-1, SJ-2, SJ-4 and SJ-5 satellites.

The SJ-1, the first satellite of the series was launched within a year after the successful launch of the DFH-1. At the beginning of the 1980s, China made the test of technology for the launch of multiple satellites on one rocket. During the test the SJ-2, SJ-2A and SJ-2B were sent into space with one rocket. Then we developed the SJ-4, a scientific and technological test satellite, which was launched on the maiden flight rocket and mainly used for measuring radiation environment and radiation effect in the geosynchronous transfer orbit. At the end of the 1990s, we developed the SJ-5, a new generation satellite of the series, to improve the service of the satellites?technology for national economy and space scientific research.


The SJ-1 was successfully launched on March 3, 1971. The satellite was placed into an orbit with an apogee of 1826km, a perigee of 266km, inclination of 69.6?and orbit period of 106 min. Its similarly spherical structure with a diameter of 1m was completely covered. There are 14 pieces of silicon solar cell mounted on the trapezoidal planes of upper and lower hemispherical shells. The satellite used the spin-stabilized attitude control system. In the middle of the satellite there is a circular pressurized capsule with short-wave telemetric instruments and the ultrashort- wave beacon transmitter and receiver, and silver-zinc chemical battery. Between the main capsule and outer case there are four auxiliary capsules. They are auxiliary capsule 1 with two sets of nickel-cadmium (Ni-Cd) batteries and small telemetry equipment in it, auxiliary capsule 2 with the limiter and the phase-shifting adjuster network in it, auxiliary capsule 3 with a 5cm responder in it and auxiliary capsule 4 with a 10cm beacon machine.

There were two scientific payloads in the satellite: the G-M counter and BE window integrating ionization chamber. The G-M counter was used for detecting cosmic rays and measuring the total flux of protons with energy of more than 16.4 MeV and the total flux of electrons with energy of more than 0.88MeV. The BE window integrating ionization chamber was used for exploring solar X-rays with measuring wavelength being (1-8)10-2m.

Task of the space technology test of the SJ-1 satellite was to make the long-term space test of satellites?basic technology and systems mainly including silicon solar sell and Ni-Cd battery system, the passive-active thermal control system, and the remote control system.

The SJ-1 had operated normally and properly for 8 years far more than one year designed lifetime. It was few in foreign satellites developed in the 1960s. The SJ-1 provided valuable experiences for the development of satellites with long lifetime. And the long-term power supply system, long-term thermal control system and long-term telemetry system of the SJ-1 satellite won Achievement Prize of the National Science Congress in 1978.


The SJ-2 satellite fleet includes the SJ-2, SJ-2A and SJ-2B. On September 20, 1981 China launched these three satellites on one rocket for the first time, which marked a new breakthrough in space technology.

The SJ-2 Satellite

The weight of the SJ-2 is 250kg, operating in an orbit with an apogee of 1600km, a perigee of 240km and inclination of 50.5? The main body of the satellite is an octahedral pyramid with a circumscribed circle diameter of 615m. On the top of the satellite, the four sides are equipped with four movable solar wings and the other four are equipped with blinds, spinning stabilized toward the sun. There are four explosive bolts with a diameter of 16 mm connected with the launch vehicle.

Two main tasks of SJ-2 were as follows:

(1) To detect space physical environment parameter, for details please see table 1;

(2) To test new technology for the satellite, mainly using the solar panel to supply power for satellite instruments, spin stabilized and directing towards the sun attitude control, the magnetic core memory and delayed telemetry and control technology, ultrashort-wave unified system with tracking and telemetry common use radio channel and passive-active thermal control system for the whole satellite and for the first time using several blinds adjust the temperature of the whole satellite.

The SJ-2A Satellite

The SJ-2A satellite is a beacon transmitter satellite used for the detection of the ionosphere. The mass of the satellite is 480kg, using the silver-zinc cell. High frequencies of the beacon transmitter are 162 MHz and 40.5 MHz. The former one was used for tracking. The principle of the measurement is that the ground station receives Doppler shift and Faraday spin of the two signs passing through the ionosphere to inverse the integrated electronic concentration of the ionosphere.

The SJ-2B Satellite

The SJ-2B is a passive radar calibration test satellite. A balloon with a diameter of 4m was used as a guiding optical beacon connected with a metal ball with a diameter of 0.45m by a 600m silk rope, which was used for the radar's calibration.

The balloon would expand after it was placed into orbit because of sublimate and a little residual gas in it. The polyester aluminum plated surface of the balloon was very bright and guided the radar to find the metal ball. In the first 16 rounds in the orbit, Kashi station for 7010 radar and Zijinshan Observatory acquired 5 targets in orbit and successfully carried out the radar calibration.


On February 8, 1994, A LM-3A placed the SJ-4 satellite into the designed orbit with an apogee of 3600km, a perigee of 200km and inclination of 28.5?

The SJ-4 was used to detect the space radiation environment and radiation effect. The main technical specifications and tested results are shown in table 2.

In order to detect the geosynchronous transfer orbit environment we specially designed a space radiation environment and radiation effect test project. Three instruments were designed for the space radiation environment and radiation effect test project, including a satellite surface potentiometrer and two single particle effect testers (one single particle static monitor and one single particle dynamic monitor).

The working principle of the single particle static and dynamic monitors is as follows: They make the self-checking with the computer's normally working program, check their operation, record faults position and accident time, and correct errors line by line to maintain proper operation. And the system has the ability to restart and record accident time when meeting faults of the whole machine.


The SJ-5satellite was launched into an 870 km similar circle orbit on May 10, 1999. The satellite was designed to operate normally in orbit for three months and carry out a two-layer scientific experiment in microgravity environment, new technology demonstration experiment, and the detection and countermeasure research of the single particle. According to the preset sequence the SJ-5 was launched, tested in orbit, transferred, managed for a long time and tested for lifetime.

The mass of the SJ-5 satellite is 30kg. Its structural configuration is a cube with each side of length being nearly 1.2m when the solar panels are folded and its wingspan is 5m when the solar wings deploy. The satellite was composed of such subsystems as the mechanism and construction, thermal control, attitude control, housekeeping, power and system circuit, measurement and control, antenna, and payload.

The SJ-5 was designed to have the following characteristics:

1. The purpose of the development of the SJ-5 satellite is to develop the common platform;

2. The housekeeping concept is used to conduct the integrated design of the function of onboard electronic equipment;

3. To make multimode test of the attitude control system;

4. Redundant software residency and multi-route information design;

5. For the first time using S-band unified system measurement and control system which is generally used in the world;

6. Use of industrial and commercial devices to make the successful test in orbit for the first time;

7. Using the whole aluminum honeycomb board structure as the main structure for the first time;

8. Using the thermal control design, which is widely suitable;

9. Using high quality power supply with completely adjustment bus;

10. Payload used involved in the modern scientific and technological heat points;

11. Having realized remote operations for the first time;

12.Using the simple and light ground testing system.

The SJ-5 obtained the main following results:

1. Total dose: 12rad(Si) /d;

2. SRAM: (0.54)106SSEU / b/d;

3. DRAM: (0.21) 106SSEU / b/d;

4. Having obtained more than 12000 fluid experiment pictures, and measured and recorded temperature field data for 30 hours;

5. Having obtained a quantity of clear images and perfect data.


The 21st century is a new century in which the world space industry will develop vigorously. According to China's short-term and long-term development targets stated in the Chinese White Paper on China's Space Activities, China will continuously develop the SJ series satellites and improve space scientific and technological exploration and experiments.

For the space science exploration, we will also improve space resolution and time resolution of detecting instruments. And we will also improve the detection of space particle composition and energy spectrum, and further promote the international cooperation.

For space technology we will improve service capability for the new technology test, payload ratio, integration of the electronic system in the satellite and the integration of space and ground.

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