Long March 4B lofts new Gaofen satellite

by Rui C. Barbosa

China launched a new remote sensing satellite on Friday from the Taiyuan Satellite Launch Center. Launch of the Gaofen multi-mode integrated imaging satellite took place at 03:10 UTC from the LC9 launch Complex using the Long March-4B (Y43) rocket. The new remote sensing satellite was accompanied by the small Xibaipo (BY 70-2) on its ride to orbit.

According to the official Chinese media, the satellite is a civil-use optical remote-sensing vehicle with a resolution up to the sub-meter level. It will operate in Sun-synchronous orbit.

The satellite will be widely used in many industries such as surveying and mapping, agriculture, environmental protection, forestry, etc., to further meet the high requirements of natural resources, survey monitoring, development and utilization, geological survey, and emergency disaster reduction, agricultural survey, housing construction monitoring, forestry protection and other fields.

In fact, this is the first use of the ‘Agility’ remote sensing medium satellite platform. This platform can be used by various remote sensing satellites orbiting between 500 km and 1,500 km.

The new platform has an agile attitude maneuver capability, higher attitude and orbit measurement and pointing accuracy of 10 m without control points, spacecraft body pointing capability of ±45º in all directions and movement time of < 20 s in rotating POV by 25º.

The platform offers better micro-vibration attenuation, a longer designed lifetime of 8 years and can support various agility imaging modes.
The platform has a modularized structure providing top-installed and side-installed designs for all kinds of optical and microwave payloads. The agile maneuver attitude is capable trough big moment CMG and wide range three-floated gyroscopes.

Its high geolocation accuracy is able through extremely accurate star sensors and using dual-frequency/dual-mode navigation receiver.

The medium size platform structure has the characteristics of modularization and generalization. It can be adapted to transport optical, SAR and other payloads through the appropriate design of payload adaptative structure, meeting the requirements of high stability. It has a powerful task management ability by the adoption of international standard space data system technology.

The large-caliber, long-focus high-resolution camera carried by the high-resolution multi-mode satellite is capable of full-color images with sub-meter resolution and images with meter resolution. The camera obtains multi-spectral images with multiple spectral bands such as dark blue, blue, green, yellow, red, etc., and ensures that the image texture has extremely high definition, which fully meets user needs.

The 1 meter diameter camera also has an important atmospheric synchronization calibrator. With this artifact, even in the fog and haze, it can still perceive the autumn, as if shooting high-definition images on a sunny day.

The small Xibaipo (BY 70-2) will carry out science experiments such as image and voice data transmission from orbit. Mainly used for the promotion of youth space science education, the satellite is equipped with programmable educational software, a small remote sensing camera and a sky-to-earth comparison experiment payload, which can realize the function of comparing ground image data with satellite remote sensing data and physical experiment data.
Both satellites were developed by the 5th Academy of China Aerospace Science and Technology Corporation.

Launch Vehicle and Launch Site:

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 main 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 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 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; 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 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 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 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).

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