Long March 4C lofts Gaofen-5

by Rui C. Barbosa

China launched a new remote sensing satellite called Gaofen-5 via a Long March 4C from the Taiyuan Satellite Launch Center on Tuesday. Launch took place at 18:28 from the LC9 launch complex.

The Gaofen civilian high-resolution remote sensing satellites (gao fen = high-resolution) are part of a program that is one of the 16 main programs announced by the State Council in a 15 year plan of Chinese national science and technology programs between 2006 and 2020.

This program will become the main civilian Earth observation project of China in the next years, combining the use of satellites as well as airplanes and even stratosphere balloons.

The program was started in 2010 and at least 14 satellites are planned, forming a near-real-time, all-weather, global surveillance network for agricultural planning, disaster relief, environment protection, and security purposes.

In May 2010, China officially initiated the development China High-Resolution Earth Observation System (CHEOS), which is established as one of the major national science and technology projects. The Earth Observation System and Data Center of China National Space Administration (EOSDC-CNSA) is responsible for organizing the construction of the CHEOS.

The Earth Observation System and Data Center, China National Space Administration was established in Mar 2010. The Center is principally responsible for organizing and implementing as well as managing CHEOS. It is also responsible for EO application services, commercial development, technology consultant and international cooperation.

By following an arrangement of integral observation from space, air and ground, the CHEOS develops space-based system, near space system, aerial system, ground system and application system as a whole to materialize earth observation at high temporal, spatial and spectral resolution, which is now in smooth progress. Overall, to meet the strategic demands of the national economic development and social progress.

The initial plan presented five satellites.  Gaofen-1 employs a CAST2000 bus, configured with one 2 meter panchromatic / 8 meter multi-spectral camera and one 16m multispectral medium-resolution and wide-view camera. The satellite realizes an integration of imaging capacity at medium and high spatial resolution and with large swath, with designed lifespan of over 5 years. It was launched on April 26, 2013.

Gaofen-2 employs CS-L3000A bus, configured with one 1 meter panchromatic/4m multi-spectral camera, with designed lifespan of over 5 years. The satellite was launched on August 19, 2014.

Gaofen-3 employs CS-L3000B bus, configured with multi-polarized C band SAR at meter-level resolution, with designed lifespan of 8 years. Gaofen-3 was launched on August 9, 2016.

Gaofen-4 is China’s first geosynchronous orbit remote sensing satellite featuring a visible light and infra-red staring optical imager with a common optical system. The optical resolution is better than 50 meters, while the infrared resolution is better than 400 meters.


GF-4 can provide an imaging area of 7,000 km × 7,000 km with individual scene covering an area of 400 km × 400 km, and with capacity for high temporal resolution remote sensing monitor at minute-level. The satellite was launched on December 28, 2015 – from the Xichang Satellite Launch Center using a Long March-3B/G2.

Gaofen-5 is configured with six payloads, including a VIS and SWIR (Shortwave Infrared) hyperspectral camera, spectral imager, greenhouse gas detector, atmospheric environment infrared detector at very high spectral resolution, differential absorption spectrometer for atmospheric trace gas, and a multi-angle polarization detector.

It is based on the SAST-5000B satellite platform developed by the Shanghai Academy of Spaceflight Technology.

The six payloads on Gaofen-5 are the Advanced Hyperspectral Imager (AHSI); the Visual and Infrared Multispectral Sensor (VIMS); the Greenhouse-gases Monitoring Instrument (GMI); the Atmospheric Infrared Ultraspectral (AIUS); the Environment Monitoring Instrument (EMI); and the Directional Polarization Camera (DPC).

A slide on GMI from CEOS

The Atmospheric Infrared Ultraspectral (AIUS) will study the atmospheric chemistry, primary addressing the contents of O3, H2O, NO, N2O, NO2, CO and CO2 on our planet’s atmosphere. This instrument is a SWIR/MWIR/TIR spectrometer with a spectral range of 2.4-13.3 μm (750-4100 cm-1) and spectral resolution of 0.03 cm-1. It will use a scanning technique of limb sounding by sun occultation with horizontal coverage +/- 10 degrees and vertical resolution of 1.25 mrad.

The Directional Polarization Camera (DPC) will measure the aerosol and cloud microphysical parameters using the Bidirectional Reflectance Distribution Function (BRDF). Measurements will be made on 8 VIS/NIR wavelengths, with 3 polarisations at 3 wavelengths, totaling 14 channels. The instrument will use 512 x 512 CCD arrays, 2400 km swath, each Earth’s spot viewed from up to 9 directions as the satellite moves.

The instrument will measure the Aerosol Optical Depth, aerosol column burden and effective radius, aerosol mass mixing ratio and type, aerosol volcanic ash, amount of biomass; cloud cover, optical depth, top height and type; the Earth surface albedo; the Fraction of Absorbed PAR (FAPAR); Photosynthetically Active Radiation (PAR), and Upward short-wave irradiance at TOA.

Gaofen-5 during testing.

The Environment Monitoring Instrument (EMI) will measure the Ozone profile and total-column or gross profile of other species, including BrO, ClO H2O, HCHO, NO, NO2, O3, SO2 and aerosol. The instrument is a UV/VIS grating imaging spectrometer with four bands, totaling 1536 channels. It will use the Pushbroom scanning technique with a cross-track swath of 2,500 km. Resolution is 13 km along-track x 48 km cross-track.

Greenhouse-gases Monitoring Instrument will study the CO2 and CH4 profiles using a 4-band NIR/SWIR grating spectrometer with a mechanical cross-track scanning, getting five cross-track samples at about 150 km distance, along-track sampling at about 130 km distance. Scanning swath is about 800 km and resolution of 10.3 km.

The Shanghai Academy of Spaceflight Technology is subordinate of China Aerospace Science and Technology Corporation (CASC), being referred as The Eighth Division of CASC. The academy was established in August 1961 as Shanghai Bureau 2. In 1993 was renamed as the Shanghai Academy of Spaceflight Technology.

With its main commonality matched to the Long March-4B, the Long March-4C first stage has a 24.65 meter length with a 3.35 meter diameter, consuming 183,340 kg of N2O4/UDMH (gross mass of 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 Long March 4C

It includes 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 TSLC launch site

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 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 centre 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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