Gaofen (High Resolution)
Gaofen (GF, “High Resolution”) is a series of civilian Earth observation satellites developed and launched for the China High-definition Earth Observation System (CHEOS), a state-sponsored programme aimed to develop a near-real time, all-weather, global surveillance network consisting of satellite, near-space (stratosphere) airships, and aerial observation platforms. Originally proposed in 2006, the CHEOS programme was officially approved by the Chinese government in May 2010. As many as 14 satellites equipped with CCD camera, multi-spectrum imagers and SAR radar are set for launch between 2013 to 2020.
The CHEOS is one of the 16 key science and technology programmes initiated under the Chinese government’s Medium- to Long-term Development Plan for Science and Technology (2006—2020). The State Administration of Science, Technology and Industry for National Defence (SASTIND) oversees the implementation of the CHEOS plan. The China Aerospace Science & Technology Corporation (CASC) consortium is responsible for the development of its space segment, and the Centre for Resources Satellite Data and Application (CRESDA) operates the ground segment.
The Earth imagery supplied by the Gaofen series satellites are used for a wide range of applications including agricultural planning, disaster relief, climate change monitoring, geographical mapping, environmental and resource surveying, maritime surveillance, and national security. The major users of the observation data are the Ministry of Land and Resources, Ministry of Environmental Protection, and the Ministry of Agriculture.
Gaofen 1 (GF-1) is a medium-resolution Earth observation satellite operating in a 650 km Sun Synchronous Orbit (SSO). It is equipped with two multispectral cameras and four multispectral wide-field cameras. The multispectral cameras are able to capture Earth images with a spatial resolution of 2 metres in the panchromatic or black and white mode, or 8 metres in the multispectral or colour imagery. The wide-field cameras offer a spatial resolution of 16 metres and ground swath width of 800 km, allowing the satellite to collect the imagery of entire globe in only 4 days.
The satellite is based on the CAST2000 small satellite bus designed and developed by the Beijing-based China SpaceSat Co. Ltd. (also referred to as DFH Satellite Co. Ltd.), the commercial subsidiary of CAST (Chinese Academy of Space Technology). The satellite is equipped with a pair of solar panel wings, each with three solar panels, and has a launch mass of 1,080 kg. The satellite’s Attitude Determination and Control Sub-system (ADCS) uses a 3-axis star tracker, gyroscope, infrared earth sensors and digital sun sensors. Actuators are reaction wheels, magnetic torques, solar array drivers with BAPTA (Bearing And Power Transfer Assembly) and a propulsion subsystem with 8 years’ fuel.
Gaofen 1 was lofted into a 650 km SSO by a CZ-2D launch vehicle on 26 April 2013 from the Jiuquan Satellite Launch Centre.
Contractor..........CAST (Prime), 508 Institute (Imaging) Satellite bus:......CAST2000 Mass:...............1,080 kg Dimensions:.........N/A Solar panel span:...N/A Orbit:..............650 km Inclination:........98.36º Stabilisation.......3-axis Designed life.......5 to 8 years Launch vehicle......CZ-2D Launch site.........Jiuquan Missions............Gaofen 1 (2013-018A)
Gaofen 2 is a follow-up mission to Gaofen 1. The satellite is equipped with two high-resolution multispectral cameras, which are capable of capturing Earth images with a spatial resolution of 0.81 metre in the panchromatic or black and white mode, or 3.24 metres in the multispectral or colour imagery, with a ground swath width of 45 km. The satellite has a designed orbital life of 5 to 8 years.
The satellite is based on the CS-L3000A satellite bus designed and developed by Chinese Academy of Space Technology (CAST). The satellite features a high-stability and rapid-roll attitude control, achieved by an indigenous high-precision APS (Active Pixel Sensor) star sensor, MWs (Momentum Wheels) and CMGs (Control Moment Gyros) for its ADCS (Attitude Determination and Control Subsystem). While orbiting the Earth, four momentum wheels balance the whole satellite momentum, and keep its 3-axis ADCS stable with respect to the nadir direction. The mixed MWs and CMGs attitude control model, the optimized attitude steering and stabilization algorithm, especially the finely designed “avoidance of excited vibration of flexible body” algorithm, allow the high precision and high stability attitude control and rapid roll of the satellite.
The spacecraft is 2,870 mm in width and 3,792 mm in length (excluding the solar panel wings), with a launch mass of 2,200 kg. The solar panels are 11 m in span, and provides an output of 3.2 kW. The satellite has a unified S-band (USB) telemetry, tracking and control (TT&C) sub-system, which can transmit data directly to ground tracking stations, or via China’s tracking and data relay satellite (TDRS). The images captured by the payload is transmitted in X-band at rate of 450 Mbit/s for each camera. There is also an onboard data storage capable of holding 3.756 TB of data.
Gaofen 2 was lofted into a 620 km SSO by a CZ-4B launch vehicle on 19 August 2014 from the Taiyuan Satellite Launch Centre.
Contractor..........CAST (Prime), 508 Institute (Imaging) Satellite bus:......CS-L3000A Mass:...............2,200 kg Dimensions:.........2.87 m x 3.79 m Solar panel span:...11 m Orbit:..............620 km Inclination:........98º Stabilisation.......3-axis Designed life.......5 to 8 years Launch vehicle......CZ-4B Launch site.........Taiyuan Missions............Gaofen 2 (2014-049A)
Gaofen 3 is an ocean surveillance satellite, equipped with a multi-polarized C-band Synthetic Aperture Radar (SAR) at meter-level resolution. Pre-research of the satellite was initiated in December 2010, and the engineering development began in September 2013. The satellite was completed in March 2016. The satellite was launched by a CZ-4C launch vehicle from the Taiyuan Satellite Launch Centre at 06:55 CST on 10 August 2016.
The primary user of the satellite is the State Oceanic Administration (SOA), the China Meteorological Administration (CMA), the Ministry of Civil Affairs, and the Ministry of Water Resources.
Gaofen 3 carries a Synthetic Aperture Radar (SAR) imager operating in C-band, capable of providing earth images up to 1 m resolution (with 10 km ground swath). SAR technology sends microwaves that penetrate the clouds, and then captures and records the images that are echoed back. These images are downloaded through a high-rate data transmission link. Unlike conventional electro-optical imagery satellites, SAR satellites can operate in all-weather, day/night conditions, and can even capture images of underwater and underground targets. The SAR package of Gaofen 3, featuring a large radar antenna 18 m in length, was developed by the Institute of Electronics of the China Academy of Sciences (CAS).
Gaofen 3’s SAR package can operate in 12 different working modes, from high-resolution (1 m) to large-swatch (650 km), and from maritime imaging to combined land/water imaging. The 2,950 kg mass satellite operate on a 755 km LEO (98º inclination), with a designed operational life of 8 years. The package is capable of working for up to an hour.
Contractor..........CAST (Prime) Satellite bus:......CS-L3000B Mass:...............2,950 kg Dimensions:.........N/A Solar panel span:...N/A Orbit:..............755 km Inclination:........98º Stabilisation.......3-axis Designed life.......8 years Launch vehicle......CZ-4C Launch site.........Taiyuan Missions............1
Gaofen 4 is a geostationary Earth observation satellite. Unlike most Earth observation satellites which all operate in highly inclined polar orbits, Gaofen 4 operates from geostationary Earth orbit (GEO), which allows uninterrupted coverage of the same area on the ground 24 hours a day. Gaofen 4’s imaging payload, developed by Beijing Institute of Space Machinery & Electronics (508 Institute), consists of two staring optical imagers, one operating in visible light and one in infrared, sharing a common optical system. The spatial resolution is 50 m for the visible light imager and 400 m for the infrared imager. Operating from GEO, the imaging package allows the observation of China and its surrounding areas within an area of 7,000 km x 7,000 km, with each individual frame covering an area of 400 km x 400 km, and a capacity for minute-level temporal resolution monitoring.
The satellite was developed by China Academy of Space Technology (CAST), based on their new GEO remote-sensing satellite bus. It has orbital mass of 4,600 kg, and was designed for a life span of 8 years. The satellite was placed into orbit by a CZ-3B launch vehicle from the Xichang Satellite Launch Centre on 29 December 2015. After four orbital manoeuvres, the satellite was positioned at 105.6° E on GEO on 4 January 2016.
Contractor..........CAST (Prime), 508 Institute (Imaging) Satellite bus:......GEO remote-sensing satellite bus Mass:...............4,600 kg Dimensions:.........N/A Solar panel span:...N/A Orbit:..............GEO Position:...........105.5º E Stabilisation.......3-axis Designed life.......5 to 8 years Launch vehicle......CZ-3B Launch site.........Xichang Missions............Gaofen 4 (2015-083A)
Based on the SAST5000B bus, Gaofen 5 will carry six types of payloads, including visible and short-wave infra hyper-spectral camera, spectral imager, greenhouse gas detector, atmospheric environment infrared detector at very high spectral resolution, differential absorption spectrometer for atmospheric trace gas, and multi-angle polarization detector. The satellite has a designed life of 8 years and is scheduled to launch in 2016—17.
Contractor..........SAST (Prime), 508 Institute (Imaging) Satellite bus:......SAST5000B Mass:...............N/A Dimensions:.........N/A Solar panel span:...N/A Orbit:..............N/A Inclination:........N/A Stabilisation.......N/A Designed life.......8 years Launch vehicle......N/A Launch site.........N/A Missions............None
Gaofen 8 is an optical satellite with a high-resolution imaging payload, designed for country surveying, disaster response, agriculture mapping, city planning, land ownership marking and road network planning. There has been a lack of public sourced information regarding the technical details of the mission, but the satellite is speculated to have been developed from the Yaogan 26 reconnaissance satellite, with an imaging payload developed by Changchun Institute of Optics, Fine Machinery and Physics (CIOMP) of the China Academy of Sciences (CAS). Gaofen 8 was lofted into a 490 km polar orbit inclined at 97.3° by a CZ-4B launch vehicle from the Taiyuan Satellite Launch Centre on 26 June 2015.
Gaofen 9 is China’s first agile earth-observing satellite, with three-dimensional freedom for acquiring Earth imagery, giving opportunities for a more efficient scheduling of observations. The satellite’s imaging payload, developed by Beijing Institute of Space Machinery and Electronics (508 Institute), is capable of capturing Earth images with a spatial resolution of 0.5 metres in the panchromatic (black and white) mode, or 2 metres in the multispectral (colour imagery). The satellite was launched atop a CZ-2D launch vehicle from the Jiuquan Satellite Launch Centre on 14 September 2014, and operates on a 650 km polar orbit inclined at 98°.
* The CZ-4C launcher failed to place the satellite into orbit