In a surprise launch, China orbited two environmental and disaster management satellites from the Taiyuan Satellite Launch Center on early Sunday. Huanjing-2A (HJ-2A) and Huanjing-2B (HJ-2B) were launched from the LC9 Launch Complex at 03:23UTC using the Long March-4B – Chang Zheng-4B – (Y42) rocket.
Developed by the China Academy of Space Technology (CAST), the two new satellites will replace the Huanjing-1A and Huanjing-1B (launched in 2008) to provide services concerning environmental protection, natural resources, water conservancy, agriculture, and forestry.
Both satellites are 16-meter optical satellites with high mobility, precision control, and stability, as well as strong load adaptability and long lifespans.
HJ-2A and HJ-2B have the same identical instrument suite. These are upgraded versions of the original HJ-1 instruments with the addition of an atmospheric correction instrument.
The two satellites during processing – Chinese State MediaThe two vehicles can provide 16-meter multispectral, 48-meter hyperspectral and infrared image data to support the monitorization of natural disasters and land utilization, regulation and protection of water resources, dynamic monitoring of crop areas, and assessment of yield – as well as quake emergency rescue.
Both satellites are based on the CAST-2000 satellite platform bus. This is a compact satellite platform characterized by its high performance, expandability, and flexibility.
It is fitted with an S-band TT&C sub-system, X-band data transmission sub-system, and 3-axis attitude stabilization. It can offer highly precise control, large-range sway maneuver, flexible orbit maneuver, highly integrated housekeeping, and highly effective power supply.
The feasibility study of the CZ-4 Chang Zheng-4 began in 1982 based on the FB-1 Feng Bao-1 launch vehicle. Engineering development was initiated in the following year. Initially, the Chang Zheng-4 served as a backup launch vehicle for Chang Zheng-3 to launch China’s communications satellites.
After the successful launch of China’s first DFH-2 communications satellites by Chang Zheng-3, the primary mission of the Chang Zheng-4 was shifted to launch sun-synchronous orbit meteorological satellites. On the other hand, the Chang Zheng-4B launch vehicle was first introduced in May 1999 and developed by the Shanghai Academy of Space Flight Technology (SAST), based on the Chang Zheng-4.
The rocket can launch a 2,800 kg satellite into low Earth orbit, developing 2,971 kN at launch. With a mass of 248,470 kg, the CZ-4B is 45.58 meters long and has a diameter of 3.35 meters.
SAST began to develop the Chang Zheng-4B in February 1989. Initially, it was scheduled to be commissioned in 1997, but the first launch didn’t occur until late 1999. The modifications introduced on the Chang Zheng-4B included a larger satellite fairing and replacing the original mechanical-electrical control on the Chang Zheng-4 with electronic control.
Other modifications were improved telemetry, tracking, control, and self-destruction systems with smaller size and lighter weight, a revised nozzle design in the second stage for better high-altitude performance. Other improvements included a propellant management system for the second stage to reduce the spare propellant amount, thus increasing the vehicle’s payload capability and a propellant jettison system on the third-stage.
The first stage has a 24.65-meter length with a 3.35-meter diameter, consuming 183,340 kg of N2O4/UDMH (gross mass of the first stage is 193.330 kg).
The vehicle is equipped with a YF-21B engine capable of a ground thrust of 2,971 kN and a ground specific impulse of 2,550 Ns/kg. The second stage has a 10.40-meter length with a 3.35-meter diameter and 38,326 kg, consuming 35,374 kg of N2O4/UDMH.
The vehicle is equipped with a YF-22B main engine capable of a vacuum thrust of 742 kN and four YF-23B vernier engines with a vacuum thrust of 47.1 kN (specific impulses of 2,922 Ns/kg and 2,834 Ns/kg, respectively).
The third stage has a 4.93-meter length with a 2.9-meter diameter, consuming 12,814 kg of N2O4/UDMH. With a gross mass of 14,560 kg, it is equipped with a YF-40 engine capable of a vacuum thrust of 100.8 kN and a specific impulse in a vacuum of 2,971 Ns/kg.
Situated in the Kelan County in the northwest part of the Shanxi Province, the Taiyuan Satellite Launch Center (TSLC) is also known by the Wuzhai designation. It is used mainly for polar launches (meteorological, Earth resources, and scientific satellites).
The launch center has two single-pad launch complexes, a technical area for rocket and spacecraft preparations, a communications center, mission command and control center, and a space tracking center.
The stages of the rocket are transported to the launch center by railway and offloaded at a transit station south of the launch complex. They were then transported by road to the technical area for checkout procedures.
The launch vehicles were assembled on the launch pad by using a crane at the top of the umbilical tower to hoist each stage of the vehicle in place. Satellites were airlifted to the Taiyuan Wusu Airport about 300km away and then transported to the center by road.
The TT&C Centre, also known as Lüliang Command Post, is headquartered in the city of Taiyuan. It has four subordinate radar tracking stations in Yangqu (Shanxi), Lishi (Shanxi), Yulin (Shaanxi), and Hancheng (Shaanxi).