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Long March 4B lofts latest Ziyuan-3 satellite

The third satellite in the Ziyuan-3 series was orbited by China on Friday at 03:17 UTC using the Long March 4B ‘Chang Zheng-4B’ (Y45) rocket from the Taiyuan Satellite Launch Center’s LC9 launch platform. The new high-resolution remote sensing geological mapping satellite will be used for civil purposes. On its ride to orbit, the new satellite was accompanied by a small Chinese experimental LEO comsat.

The Ziyuan-3 satellites

The new satellite is the third of a series of four high-resolution civilian remote sensing satellites, grown from a project that was initiated in March 2008.

The new satellite carries three high-resolution panchromatic cameras and an infrared multispectral scanner (IRMSS). The cameras are positioned at the front-facing, ground-facing and rear-facing positions.

Two cameras (front-facing and rear-facing) have a spectral resolution of 2.7m and 52.3km ground swath while the ground-facing camera has a spectral resolution of 2.1m and 51.1km ground swath. The IRMSS has a spectral resolution of 6.0m and 51.0km ground swath.

The satellite is equipped with two 3 meters solar arrays for power generation and will orbit a 505.984 km sun-synchronous solar orbit with a 97.421 degree inclination. This orbit will have a re-visit cycle of 5 days.

The operational period will be four years with a possible life extension to five years.
The new satellite will conduct surveys on land resources, help with natural disaster-reduction and prevention and lend assistance to farming, water conservation, urban planning and other sectors, surveying the area between 84 degrees north and 84 degrees south latitude.

The spacecraft is composed of a service module and a payload module. The service module provides supporting functions to the spacecraft such as structure and mechanisms, power generation, control and pointing services, data management subsystem, temperature maintenance, propulsion subsystem, and TT&C (Tracking Telemetry and Command) services.

The payload module includes the sensor complement, the DTS (Data Transmission System), and the image data recording system. The three-line array camera is mounted on top of the spacecraft payload module, pointing toward Earth.

The ZY-3 satellites are designed and constructed by CAST/BISSE (China’s Academy of Space Technology)/Beijing Institute of Spacecraft System Engineering) for the Chinese Ministry of Land and Resources (MLR), using modified ZY-2 platform. The spacecraft is 3-axis stabilized, with the launch mass about 2,630 kg.

The Ziyuan program appears to cover different civil and military earth observation – as well as remote sensing – programs. The ZiYuan-1 program is focused on Earth resources and appears to have two distinct military and civil branches – with this one operated together with Brazil.

The satellites are operated jointly by the Center for Earth Operation and Digital Earth (CEODE) and the Brazilian INPE (Instituto Nacional de Pesquisas Espaciais – National Institute of Space Research).

The Ziyuan-2 program is likely used for aerial surveillance operated by the People’s Liberation Army (PLA) while the new ZiYuan-3 series will be used for stereo mapping, like the TH-1 Tianhui-1 mapping satellite that is operated by the PLA.
ZiYuan-3 will be operated by the State Bureau of Surveying and Mapping.

The Tianqi-10 small satellite

The additional payload on this launch was the Tianqi-10 satellite.

The Tianqi are low-orbit communications satellites operated by Guodian Gaoke for IoT communications, which are also carrying a camera for educational purposes.

The satellites are part of the “Apocalypse Constellation” that provides users with much-needed data collection and transmission services for terrestrial network coverage blind areas, which are widely used in marine, environmental protection, meteorological, forestry, geological, emergency, rescue and smart city industries to enhance China’s global data network coverage and application capabilities are of strategic importance.

Launch vehicle and launch site:

The development of the Chang Zheng-4 began in 1982 based on the Feng Bao-1 launch vehicle. Engineering development was initiated in the following year. Initially, the Chang Zheng-4 served as a back-up launch vehicle for Chang Zheng-3 to launch China’s communications satellites.

Long March 4B via Chinese media

After the successful launch of China’s first DFH-2 communications satellites by Chang Zheng-3, the main mission of the Chang Zheng-4 was shifted to launch sun-synchronous orbit meteorological satellites.

The Chang Zheng-4B launch vehicle was first introduced in May 1999 and also developed by the Shanghai Academy of Space Flight Technology (SAST), based on the Chang Zheng-4.

The rocket is capable of launching 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. Originally, it was scheduled to be commissioned in 1997, but the first launch didn’t take place until late 1999. The modifications introduced on the Chang Zheng-4B included a larger satellite fairing and the replacement of the original mechanical-electrical control on the Chang Zheng-4 with electronic control.

Other modifications include 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; 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. Having 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, a mission command and control center, and a space tracking center.

The stages of the rocket were 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 are 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 are 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).

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