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China will launch a series of scientific satellites including a retrievable one to probe 'dark matter' later this year, officials said today.The development of four scientific satellites is going well, National Space Science Centre's director Wu Ji under the Chinese Academy of Sciences (CAS) said at an event to mark the 10th anniversary of cooperation between China's Double Star space mission and the European Space Agency's (ESA) Cluster mission to investigate the earth's magnetosphere.The first of the series, the dark matter particle explorer, will be launched from the Jiuquan Satellite Launch Centre in northwest China at the end of this year.All the major tests and experiments have been completed, and a mission control centre for scientific satellites has been set up in Huairou, a northern suburb of Beijing, Wu said.The dark-matter particle explorer satellite will observe the direction, energy and electric charge of high-energy particles in space in search of dark matter, chief scientist of the project Chang Jin said.It will have the widest observation spectrum and highest energy resolution of any dark-matter probe in the world.Dark matter is one of the most important mysteries of physics. Scientists believe in its existence based on the law of universal gravitation, but have never directly detected it."It's very difficult to develop the payload of the satellite. We have overcome many difficulties in making the optical instrument. We are confident of launching it in the first half of next year," state-run Xinhua news agency quoted Wu as saying today.China will launch a satellite for quantum science experiments. SJ-10, a retrievable scientific research satellite will be launched in the first half of 2016. It will carry out research in microgravity and space life science to provide scientific support to manned space missions.The satellite is expected carry out 19 experiments in six fields, microgravity fluid physics, microgravity combustion, space material science, space radiation effect, microgravity biological effect, and space biological techniques.Eight experiments in fluid physics will be conducted in the orbital module and the others will be conducted in the re-entry capsule which is designed to return to earth after 12 days in orbit. The orbital module will keep operating in orbit for three more days, the report said.