Zhangheng 1 - China Seismo-Electromagnetic Satellite (CSES)
China on 02 February 2018 launched its first seismo-electromagnetic satellite to study seismic precursors, which could help establish a ground-space earthquake monitoring and forecasting network in the future. A Long March-2D rocket was launched at 15:51 from Jiuquan Satellite Launch Center, in northwest China's Gobi Desert, carrying the 730-kilogram China Seismo-Electromagnetic Satellite (CSES) into a sun-synchronous orbit at an altitude of about 500 kilometers. Known as Zhangheng 1 in Chinese, it has an expected mission life of five years, said Zhao Jian, a senior official with China National Space Administration (CNSA).
The satellite is named after Zhang Heng, a renowned scholar of the Eastern Han Dynasty (25-220), who pioneered earthquake studies by inventing the first ever seismoscope in the year 132. Zhangheng 1 will record electromagnetic data associated with earthquakes above 6 magnitude in China and those above 7 magnitude around the world, in a bid to identify patterns in the electromagnetic disturbances in the near-Earth environment, Zhao said.
The satellite will focus on the Chinese mainland, areas within 1,000 kilometers of China's land borders and two major global earthquake belts. Zhangheng 1 was funded by CNSA, developed by China Earthquake Administration (CEA) and produced by DFH Satellite Company, a subsidiary of China Academy of Space Technology (CAST). Zhangheng 1 has a single solar panel and six booms, which will deploy and keep electromagnetic detectors more than four meters away from the satellite, said Zhou Feng, a senior manager with DFH Satellite Company.
China is one of the countries most affected by dynamic earthquakes, which are often spread over a wide terrain, high in magnitude and have a shallow epicenter. However, scientists are still unable to predict earthquakes despite efforts by various countries since the 1950s. In recent years, more efforts have been focused on monitoring seismo-electromagnetic anomalies in the near-Earth environment.
Research shows that just before a quake, tectonic forces acting on the Earth's crust emit electromagnetic waves and twist magnetic field lines. But such phenomena are relatively weak and need further study to be useful.
The data accumulated by Zhangheng 1 will help the research of seismic precursors, Zhao said. "Zhangheng 1 cannot be used to predict earthquakes directly, but it will help prepare the research and technology for a ground-space earthquake monitoring and forecasting system in the future," he noted.
Shen Xuhui, deputy chief designer of Zhangheng 1, said it will gather enough data to build models of the Earth's geomagnetic field and ionosphere, which are still unknown to China. "Zhangheng 1, with a wider coverage and better electromagnetic environment from space, will be an important supplement to earthquake monitoring in the Qinghai-Tibet Plateau and sea areas that cannot be fully covered by the ground observation network," said Shen, who is also chief engineer of the Institute of Crustal Dynamics of the CEA.
In order to accumulate data effectively, Zhangheng 1 must be extremely clean, which means the sensors must be free of disturbances from magnetic fields and charging effects. "We used hinged booms of nearly five meters with detectors on the far ends so as to decrease disturbances from the satellite platform. We also limited the use of magnetic materials, and ran strict simulation and magnetic tests to calibrate its data," said Yuan Shigeng, general director and chief designer of the satellite with CAST.
Engineers in charge of the data transmission subsystem spent four years minimizing its electromagnetic emissions, making sure the collected data would return to researchers accurately. "Before the launch, satellites in orbit with high magnetic cleanness had all been developed by other countries, and Zhangheng 1 fills this gap," Yuan Shigeng said.
As well as requiring magnetic cleanness, engineers had to find suitable special materials to enable the booms to withstand the enormous pressure of the launch, Yuan said. "In space, the booms must remain still, and the location of their far ends cannot move more than 2 millimeters, about the thickness of a coin, in temperature changes of over 200 degrees Celsius," he said.
The booms help broaden the distance between the sensors from two meters to over 10 meters, giving the small satellite platform more room for its payloads. Four of the outstretched sensors are electric field probes, similar to antennas, and will detect changes in the electric field in three dimensions. Zhangheng 1 will run in-orbit tests for about six months to assess its data quality before it is formally put into service. A second seismo-electromagnetic satellite is under evaluation, said Zhao Jian, the senior official with CNSA.
Zhangheng 1 will also provide data services for weather forecasts, aerospace and navigation communications, space physics and geophysics research.
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