China state-run Xinhua new agency announced on 27 April 2006 that a new satellite named Remote Sensing Satellite 1 (or YaoGan WeiXing 1 in its Chinese translation) was successfully launched by a CZ-4B (Batch-02) launch vehicle from Taiyuan Satellite Launch Centre (TSLC). While the report about the purposes and technical details of the satellites was very brief, it is understood that this 2,700kg satellite was in fact China’s first space-based synthetic aperture radar (SAR) system, with a military designation JianBing 5 (JB-5).
Synthetic aperture radar (SAR) is an active microwave instrument producing high-resolution imagery of the Earth’s surface in all-weather, day/night conditions. A SAR instrument can measure both intensity and phase of the reflected microwave radiation, resulting not only in a high sensitivity to texture, but also in some three-dimensional capabilities. While conventional optical imagery intelligence systems are less effective in night and bad weather (e.g. cloudy) conditions, the SAR generates its own microwave radiation that can penetrate cloud, haze, shallow water, or even ground surface to obtain high-resolution images of the Earth surface as well as underwater and underground.
China first began to develop the SAR technology in the late 1970s, with the first operational airborne X-band mono-polarisation SAR system introduced in 1981 by the Electronic Research Institute of the China Academy of Science (CAS). The multi-polarisation SAR system was introduced in the early 1990s for flood monitoring. The first operational real-time airborne SAR system which can analyse the images using onboard equipment and transmit the image data to ground stations via datalink communication was introduced in 1994.
For over a decade China had been planning to put a high-resolution SAR satellite in orbit for all-weather targeting applications, particularly the location of naval forces in the Taiwan Strait. China has also taken an interest in the potential civil applications of such a system in the aftermath of the flooding, landslides, and typhoon damage in 1994. While China has used optical and infrared imaging space-based civil remote-sensing systems, there is particular interest in active microwave imagery that can penetrate southern China's constant cloud cover. It is believed that China’s space-based SAR system development has benefited from its co-operation with Russia and Europe in this field.
The People’s Liberation Army (PLA) views SAR satellite imagery as vital in its ability to achieve information dominance in future warfare. Unlike the conventional passive optical imagery satellites, the space-based SAR system can see through clouds, rain, fog and dust in order to detect targets on the ground or underground, and in or under the ocean. In addition, SAR satellites are extremely useful in tracking moving targets, and can be useful in satisfying military mapping requirements. Chinese engineers have been examining SAR satellites as a means to track enemy submarines in shallow waters.
Preliminary research and development on China’s first-generation space-based SAR system was initiated in the late 1980s, and the model R&D began in 1991. In May 1995, the State Science & Technology Committee (SSTC) and COSTIND approved the finalised design and work on associated high speed data transmission. A ground simulation system for the SAR satellite was developed by CAS and BUAA in the late 1990s. Even before the launch of the first-generation SAR satellite, preliminary research had already began on the second-generation SAR satellite system. According to a BUAA report, the second-generation SAR satellite programme had been listed in China’s 11th Five-Year Development Plan (2006~2010).
JB-5 Launch: A CZ-4B (02) launch vehicle carrying the JB-5 satellite blasts off from Taiyuan Satellite Launch Centre (Source: Chinese Internet)
The main contractors for the SAR satellite system include China Academy of Science’s Institute of Electronics (SAR instruments), Shanghai Academy of Spaceflight Technology (SAST, also known as Shanghai Space Bureau or 8th Space Academy) (spacecraft general design and CZ-4B launch vehicle), China Academy of Space Technology (CAST, also known as 5th Space Academy)’s 501 and 504 Institutes, China Electronics Technology Group Corporation (CETC)’s Nanjing Research Institute of Electronic Technology (also known as 14 Institute) and Southwest Institute of Electronic Equipment (SWIEE, also known as 29th Institute), and Beijing University of Aeronautics & Astronautics (BUAA).
According to the Chinese media reports, the Remote Sensing Satellite-1 launched on 27 April 2006 weights 2,700kg. The satellite housed in an enlarged fairing (diameter 3.8m; length 10m) on top of the three-stage CZ-4B launch vehicle, which lifted off at 18:48 Beijing Time (10:48 GMT). The payload was released into a near-polar sun-synchronous orbit some 603km high. The reports also confirmed that the launch vehicle used in the mission was an improved CZ-4B Batch-02 model.
Another report confirmed that the JB-5/Remote Sensing Satellite-1 is fitted with a electronic motor-powered solar panel which expanded under the command from the ground control station. The onboard radar It is not known which band the JB-5’s radar is working, and what kind of resolution the radar image can achieve.
The second satellite debuted Yaogan Weixing-3 was launched by a CZ-4C launch vehicle from Taiyuan on 12 November 2007.
The CAS Electronic Research Institute has been tasked under “Project 863”—China’s high-tech development plan—to develop an indigenous satellite-based SAR system since the late 1980s. Little details are available regarding the SAR system carried by the JianBing-5, but a CAS leaflet has revealed some information on a prototype system introduced in the late 1990s for ground simulation. The system later formed the core technology of the SAR carried by JianBing-5.
According to the leaflet, the SAR prototype works in L-band and has two resolution options. In the high-resolution mode the system has a discrimination of 5m X 5m target and a observation capability at 40km. In the low-resolution mode the system has a discrimination of 20m X 20m and a observation capability at 100km. The prototype system was tested onboard a plane and its result was said to be satisfactory.
JB-5 in the Orbit: An artist impression of the JB-5 satellite in the orbit (Source: Chinese Internet)
