The first International Symposium on Gravitational Waves (ISGW2017) was held from May 26 to 28 on the Yanqi campus of the University of Chinese Academy of Sciences (UCAS), Beijing, China. Nearly 120 participants from 11 countries and over 66 universities, institutions and international organizations attended the symposium. This symposium has been paid great attention by the Chinese Academy of Sciences，Ministry of Science and Technology，National Natural Science Foundation of China.The main topics of the symposium include• Gravitational Wave Physics• Missions, Strategies and Plans of Gravitational Wave Detection• Frontiers of Science and Technology in Gravitational Wave Detection• International Collaborations on Gravitational Wave DetectionThe aim of the symposium is to bring together leading experts in gravitational wave physics and gravitational wave detection to present the latest research advances and to discuss possible collaborations on gravitational wave detection. During the three-day symposium, 55 scientists (23 invited speakers and 22 parallel speakers) gave their wonderful talks. As the science and education area of the “one nuclear four area” of Huairou Science City, UCAS has attracted the attention of the world’s gravitational wave researchers for Huairou Science City this time.AsChinese Academy of Sciences has previously announced, UCAS is also the relying on unit of Chinese “Taiji Program” in Space. More than ten domestic scientific research institutions haveset up “Taiji Union” (Consortium of Gravitational Wave Detection Program in Space) during this symposium.Since the frequency of the gravitational wave signal is between 35Hz and 250Hz (the human ear can capture the sound frequency of 20Hz-20000Hz), we can use the ear to hear the magic of the gravitational wave. “The era of GW Astronomy has come, let’s start listening to the sounds of the cosmic jungle!” As professor Bernard F. Schutz said in the talk, the direct detection of gravitational waves opens a new window to explore our universe and indicates the coming of a new era of gravitational-wave astronomy.
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中国青年报客户端北京1月8日电（中青报·中青网记者 孙庆玲）今天，微重力技术实验卫星“太极一号”在轨交付于中国科学院大学（以下简称“国科大”）。作为这颗卫星的主要用户，国科大将接手接下来的科学实验计划的制订、拓展实验安排、科学实验数据处理、科学产品发布等“攻关”任务。微重力技术实验卫星“太极一号”是中国科学院空间科学（二期）战略性先导科技专项首发卫星，也是我国首颗空间引力波探测技术实验卫星，旨在探测中低频段的引力波信号，从而发现天体质量更大、距离更遥远的引力波波源，揭示更为丰富的天体物理过程。“引力波是非常微弱的，对探测器的精确度要求非常高。”国科大副校长吴岳良院士做了个比喻，“这相当于拿一个西瓜在极弱的推力下碰撞一下喜玛拉雅山，我们要去测这时喜马拉雅山产生的加速度”。由于地球力场的影响，这种对引力波的探测实验在地面上是不可能实现的，所以把它放在了卫星上，去宇宙空间中进行实验、探测。而“太极一号”只是空间引力波探测的第一步，后续还将有“太极二号”“太极三号”。这颗卫星于2019年8月31日发射成功。当天，适逢国科大2019级新生开学典礼，中国科学院院长、国科大名誉校长白春礼在现场分享了这一消息，并指出“这颗卫星的主要用户是中国科学院大学”。杨天鹏 ／摄据悉，国科大是空间引力波探测“太极联盟”的牵头单位，负责空间引力波探测“太极计划”项目的整体规划及协调，并承担了“太极一号”的科学应用系统研制和霍尔微推进系统研制等任务。历经半年的在轨测试，目前“太极一号”已经达到了研制任务书的要求，满足在轨交付条件，并于今天正式交付于国科大使用。“目前相当于搭建好了一个平台，交给了用户单位，用户单位可以进行技术验证、技术成果产出等。”吴岳良介绍，这颗卫星将主要用于对空间引力波探测、地球重力场反演、超高精度惯性导航等相关的技术进行验证和研究。这其中涉及到众多领域的技术及其应用，国科大可以利用 “科教融合”这一优势为联合中国科学院相关科研院所搭建起一座沟通的桥梁，整合多方的研究力量和资源，集中优势力量共同进行技术攻关。
China's first satellite to conduct experiments on key technologies related to space-based gravitational wave detection, Taiji-1, has successfully completed its in-orbit tests, the Chinese Academy of Sciences (CAS) announced Wednesday.The satellite, sent into orbit on Aug. 31, 2019, is China's first such kind of satellite, and has completed its in-orbit experiments, making a breakthrough in the country's gravitational wave detection, said Wu Yueliang, chief scientist of the project.After four months of tests and experiments, it was proved that the satellite system has performed well in orbit and completed all the experiments required for research, Wu added.With the success of Taiji-1's in-orbit tests, the first goal of CAS's three-step strategy to implement the program has been successfully achieved.Taiji-1 will conduct more expansion experiments in the next stage, said Wu.
On November 24, space gravitational wave detection Taiji consortium 2019 annual meeting held successfully at University of Chinese Academy of Sciences (UCAS). The UNESCO International Centre for Theoretical Physics Asia-Pacific (ICTP-AP), and Taiji consortium jointly sponsored this meeting. The conference focused on the research of gravitational wave physics and the detection technology. It has attracted active participation of more than 160 experts and scholars from 36 institutions to discuss the latest scientific results and future development of gravitational wave detection.Yanfen Wang (vice-president of UCAS), Wenrui Hu (chief scientific adviser of Taiji Programme, Institute of Mechanics CAS), Min Huang (deputy commissioner of Bureau of Frontier Science and Education CAS), Xiaolong Dong (deputy director of National Space Science Center CAS) and Zijie Li (deputy chief of Photoelectric and Universe Section of Bureau of Major R&D Programs CAS) on behalf of Yingjie-Yu commissioner attended the meeting and delivered speeches.Yanfen Wang, on behalf of UCAS, extended a sincere welcome to all the representatives and congratulated the convening of the 2019 Taiji consortium meeting. In her speech, she stressed that Taiji consortium is not only an important platform for all-round and multi-disciplinary scientific cooperation among academic institutions but also important support for the cultivation of innovative talents in related fields.In May 2017, Taiji working group initiated and founded the ‘Taiji Consortium’ on the International Symposium on Space Gravitational Wave Detection. As an academic consortium, it brought experts in related fields together to carry out the research of gravitational wave space exploration.Taiji-01, the first satellite of Taiji programme, successfully launched into orbit on 31 August 2019. This means that the first step of the ‘three-step development’ strategy of ‘Taiji Program’ was initiated. The on-orbit test and data analysis results of Taiji-01 shows that:The first-stage in-orbit test showed that the accuracy of displacement measurement of the laser interferometer on Taiji-01 could reach a 100-picometer order of magnitude, equivalent to the size of an atom.The accuracy of the gravitational reference sensor on the satellite reached ten billionths of the magnitude of the earth's gravitational acceleration, equivalent to the acceleration produced by an ant pushing the Taiji-01 satellite.The thrust resolution of the micro-thruster on the satellite reached a scale equivalent to one-ten thousandth of the weight of a sesame grain.Taiji-01 Achieved: China’s highest accuracy of spatial laser interferometry. China’s first on-orbit drag free control technology test. Firstly and internationally on-orbit verification of micro-newton level radio frequency ion propulsion technology and dual mode hall-effect micro thruster technology.As the chief scientist of Taiji programme, professor Yueliang Wu, vice-president of UCAS, director of ICTP-AP, made a scientific interpretation of gravitational wave detection, and reported the progress of the orbit test of Taiji-01.Professor Jianyu Wang, president of Shanghai Branch of CAS and chief engineer of Taiji-01 project, reported and summarized the Taiji-01 satellite project.Professor Ronggen Cai, deputy director of the Institute of Theoretical Physics CAS introduced the relevant knowledge of gravitational waves and the significance of exploring gravitational waves from the perspective of fundamental physics research.Professor Weidou Ni from the National Astronomical Observatories CAS introduced his views on the future planning of the world's gravitational wave exploration and the discussion of the Taiji space gravitational wave detection mission.32 experts and scholars from 21 scientific institutions made academic reports on the relevant research of Taiji programme. This annual meeting provides a platform for cooperation and communication among members of Taiji consortium. It promotes in-depth exploration of scientific connotation and improves the influence of Taiji plan. Moreover, it also promotes interdisciplinary integration and the achievement of China's goal of space gravitational wave detection.
The early morning of August 31st witnessed the successful launching of a satellite for experiments under microgravity from Jiuquan Satellite Launching Center in northwestern China. Later named “Taiji-1”, this satellite marks the first under the Phase-II of the Strategic Priority Program on Space Science (SPPSS-II) sponsored by the Chinese Academy of Sciences (CAS). As confirmed by the National Space Science Center (NSSC), CAS in late September, the experiments aboard are so far in smooth operation, and the satellite in proper status with all test results reported normal. Model of Taiji-1, the first experiment satellite for space detection of gravitational waves. This announces the successful completion of the first stage of in-orbit tests and starts a journey to detect gravitational waves (GW) from space.Taiji-1, the first experiment satellite for space detection of gravitational waves (GW), got its name from Taiji Program, a space mission proposed by CAS to detect GWs when orbiting the Sun accompanying the Earth. Comprising of three satellites, it is designed to form an equilateral triangle flying 18 to 22 degrees ahead of the Earth, with each side spanning a distance of 3.0 million km. Scheduled to fly in around 2033, the conception of the mission can be traced back to 2008, when the Academy took the lead in China to explore the feasibility to detect gravitational waves from space. The following years saw it develop into a three-stage layout and roadmap, with its first stage featuring one satellite as a pathfinder, followed by a double-star and a trio-star stage. In August 2018, the single-star project for Taiji Program was officially adopted by SPPSS-II, taking the first step toward implementing the program. It took the satellite development team, consisting of experts from the CAS Innovation Academy for Microsatellites, only one year to develop and build the satellite. As indicated by the first results from the in-orbit tests and data analysis of Taiji-1, the interferometer aboard has achieved a measuring precision of hundred picometer level, making it able to discern a distance as small as the diameter of an atom. Besides, the gravitational reference sensor aboard is now able to detect fluctuations in Earth gravity as trivial as trillionths of the gravitational acceleration; and the resolution of its micro-thruster can tune its impulses less than one µN a time. The success lays a firm foundation for future detection of GWs in space.The GW is a type of matter wave originated from radical motion and change in mass and energy. As early as about 100 years ago, Albert Einstein predicted its existence based on his theory of general gravity. Not until 2015, however, did humankind first directly detect this space-time oscillation from Earth ground – LIGO (Laser Interferometer Gravitational-wave Observatory) eventually succeeded in picking up the weak, vague signals from the merger of binary black holes, after decades of efforts. Since then, human beings not only can “see” the cosmos via electromagnetic waves, but also “hear” its voices by virtue of GWs – this revolutionary experiment has invited one more “messenger” to tell the story of the cosmos.GWs of different frequencies give clues about various astrophysical processes occurring in different stages of cosmic evolution. The GWs detected from space fall in the mid- and low-frequency bands of the spectrum. Such space-time ripples are set off by more massive celestials compared to those of higher frequencies as detectable from the Earth ground. Free from the complexity of noise on the ground, space-based GW detectors might be able to capture weaker signals and find out more distant sources of them. This will help us reveal much enriched astrophysical phenomena and better understand how our universe works.Signals of GWs are extremely weak, however. This poses a great challenge on space detection of them and pushes it to the limits of existing human technologies for precise measurement and control. Taiji-1 has meant to test the feasibility of existing key technologies and verify their in-orbit implementation.Under the framework of SPPSS-II, CAS plans to fly a series of missions for various science goals, including the Gravitational Wave Electromagnetic Counterpart All-sky Monitor (GECAM), the Advanced Space-borne Solar Observatory (ASO-S), the Einstein Probe (EP) and the Solar wind Magnetosphere Ionosphere Link Explorer (SMILE), to detect electromagnetic signals from GW sources, black holes, fluctuations in solar activities, aimed at understanding the mechanisms underlying solar activities and the origin and evolution of the universe. All the above missions are to be launched by 2023.
HELSINKI — China launched a new meteorological satellite from Jiuquan late Sept. 24, adding to a series of recent government and commercial missions.The Yunhai-1 (02) satellite launched from Jiuquan in the Gobi Desert atop a Long March 2D hypergolic rocket at 8:54 p.m. Eastern Tuesday, making it Chinese five launches in under a month.The new Yunhai-1 series of satellites will be used mainly used for “detecting the atmospheric and marine environment and space environment, as well as disaster control and other scientific experiments”, according to state media.The satellites were developed by the Shanghai Academy of Spaceflight Technology (SAST), a subsidiary of the China Aerospace Science and Technology Corp. (CASC). CASC, the state-owned main contractor for Chinese space programs, stated in January that it aimed to carry out over 30 launches during 2019. The second half of the calendar year typically sees the majority of Chinese launch activity.The Tuesday mission took the Chinese orbital launch tally for the year to 20, including a failed Long March 4C launch. That number also includes one failed private launch and the first Chinese private launch to reach orbit.Liftoff despite prior earthquakeA Long March 3B lifted off from the Xichang Satellite Launch Center, southwestern China, Sept. 22, despite a nearby 3.5 magnitude earthquake just over a day prior.The launch used a Yuanzheng-1 upper stage to insert two Beidou navigation and positioning satellites into medium Earth orbits (MEO). A piece of a rocket engine, apparently resulting from the launch, was found downrange and posted on Chinese social media.This was the tenth launch of pairs of Beidou satellites to MEO, as China pushes to complete its own answer to the U.S. GPS. Further Beidou launches, to MEO and inclined geosynchronous orbits, are expected before the end of 2019. China aims to complete the 35-satellite Beidou constellation—which is named after the Big Dipper asterism—in the first half of 2020.The Wenchang Satellite Launch Center, located on Hainan island, also participated in the launch activities, according to reports.Wenchang hosts launches of China’s new, large cryogenic launch vehicles. The exercises may indicate ongoing ground preparations for the return-to-flight of the Long March 5, which could launch before the end of 2019. The Long March 5 is required for major projects, including the Chinese Space Station and upcoming lunar and Mars missions. It has been grounded since a launch failure in July 2017.Remote sensing, experimental polar, deorbit missionsEarlier this month a solid propellant Long March 11 carried five Zhuhai-1 remote sensing satellites into roughly 500-kilometer-altitude Sun synchronous orbits.The four hyperspectral and one video satellites are part of the development of the Zhuhai-1 commercial remote sensing constellation planned by Zhuhai Orbita Aerospace Science and Technology Co. Ltd. The launch took place at 02:42 a.m. Eastern Sept. 19 at the Jiuquan Satellite Launch Center and saw stage wreckage fall to Earth in Myanmar.Sept. 11 saw the return to action of the Long March 4 series following a May failure. Carrying the Ziyuan-1 (02) remote sensing satellite, the launch left wreckage downrange.Also aboard was the BNU-1 (Jingshi-1) small, experimental polar observation satellite from Beijing Normal University, and Taurus-1 (Jinniuzuo-1) a 3U CubeSat developed by Shanghai Aerospace Science and Technology Co., Ltd., also known as ASES Space. The latter carries a 2.5-square-meter deployable sail for deorbit tests for debris mitigation.Gravitational wave detectionA commercial Kuaizhou-1A launch Aug. 31 carried two payloads into orbit. The Chinese Academy of Sciences has now revealed that the satellite initially designated KX-09 is named Taiji-1. Furthermore the small has completed first-stage on-orbit experiments for space-based gravitational wave detection. Taiji-1 carried out on-orbit space laser interference measurements and will be joined in the coming years by two further satellites. The trio will aim to detect gravitational waves, described as “ripples” in space-time, caused by extremely violent events. These include merging black holes, colliding binary stars and supernovae.
On 20 September, the Chinese Academy of Sciences held a regular press conference, announcing that the first phase of the on-orbit test of the launched satellite of Taiji Program in Space has been successfully completed. At the conference, Xianglibin, vice president of the Chinese Academy of Sciences (CAS), officially named the satellite "Taiji-01".Prof. Bin Xiang-LiWith the efforts of all the members of Taiji-01, it only took one year for the development and launch of the satellite. The satellite successfully launched into orbit on 31 August 2019. This means that the first step of the ‘three-step development’ strategy of ‘Taiji Program’ was initiated.Taiji-01 Launched SuccessfullyIn Taiji-01 project, the University of Chinese Academy of Sciences (UCAS) is responsible for overall management of the science mission system and development of the micro hall-effect thruster system.Prof. Yue-Liang WuDuring the press conference, the chief scientist of ‘Taiji’ program, vice president of UCAS, director of International Centre of Theoretical Physics-Asia Pacific (ICTP-AP), Yue-Liang Wu interpreted the on-orbit test and data analysis results of the first phase of Taiji-01. The results show that: The measurement accuracy of laser interferometer reaches 100 pm. The measurement accuracy of gravitational reference sensor reaches a billionth . The thrust resolution ratio of micro thruster reaches sub-scale.Taiji-01 Achieved: China’s highest accuracy of spatial laser interferometry. China’s first on-orbit drag free control technology test. Firstly and internationally on-orbit verification of micro-newton level radio frequency ion propulsion technology and dual mode hall-effect micro thruster technology. Professor Wu introduced that, in 1916, Einstein predicted the existence of gravitational waves based on general relativity. It is a kind of matter wave generated by the violent movement and change of matter and energy. The research on gravitational waves will provide a new important window for observing the universe and promote humans understanding of the unknown world.Prof. Xiao-Long DongProf. Xiao-Long Dong, general manager of the project, introduced the development process, organization, and implementation of the Taiji-01 project. After that, Prof. Hua-Wang Li, introduced the platform and payload of the satellite system.Prof. Hua-Wang LiTaiji-01 has taken the first step in the exploration of space gravitational waves in China，and promoted the breakthrough of key technologies in the detection of space gravitational waves in China. ICTP-AP will also provide sustained support to the Taiji project and contribute to space gravitational waves detection.
BEIJING, Sept. 20 (Xinhua) -- A recently-launched Chinese satellite has conducted in-orbit experiments on the key technologies related to space-based gravitational wave detection, the Chinese Academy of Sciences (CAS) announced on Friday.The satellite, sent into orbit on Aug. 31, is China's first such kind of satellite, and has completed its first stage tests in orbit, laying a solid foundation for future gravitational wave observation in space, said Xiangli Bin, vice president of CAS."This is the first step of China's space-based gravitational wave detection. But there is still a long way to go to realize detecting gravitational waves in space. Chinese scientists will continue to contribute Chinese wisdom to the exploration and human progress," Xiangli said.The satellite has been named Taiji-1. As a Chinese term for the "supreme ultimate," Taiji is well-known as the black and white circular symbol representing yin and yang. The pattern of Taiji also resembles a binary star system composed by objects like neutron stars or black holes.Gravitational waves are "ripples" in space-time caused by some of the most violent and energetic processes in the universe. Albert Einstein predicted the existence of gravitational waves in 1916 in his general theory of relativity.The strongest gravitational waves are produced by catastrophic events such as colliding black holes, supernovae, coalescing neutron stars or white dwarf stars and possibly even the remnants of gravitational radiation created by the birth of the universe itself.The first discovery of gravitational waves by the LIGO Collaboration in 2015 has opened a new window to observe the universe and encouraged scientists worldwide to accelerate their research.CAS has announced the research program "Taiji" that will study gravitational waves from the merging of binary black holes and other celestial bodies.Unlike the LIGO research conducted from a ground-based observatory, Taiji will conduct space-based detection on the gravitational waves with lower frequencies to observe celestial bodies with greater mass or located farther away in the universe, said Wu Yueliang, chief scientist of the Taiji program and an academician of CAS.However, the gravitational wave signals from those celestial bodies are extremely weak, posing great challenges for detection. Scientists need to break through the limit of current precise measurement and control technology, Wu said.Taiji-1 aims to test the key technologies such as high-precision and ultra-stable laser interferometer, gravitational reference sensor, ultra-high precision drag-free control and ultra-stable and ultra-static satellite platform, according to Wu.Taiji-1 has realized China's most accurate space laser interference measurement and the first in-orbit drag-free control technology test. It also carried out electric propulsion technology experiments, Xiangli said.The first-stage in-orbit test showed that the accuracy of displacement measurement of the laser interferometer on Taiji-1 could reach a 100-picometer order of magnitude, equivalent to the size of an atom."The accuracy of the gravitational reference sensor on the satellite reached ten billionths of the magnitude of the earth's gravitational acceleration, equivalent to the acceleration produced by an ant pushing the Taiji-1 satellite," Wu explained.The thrust resolution of the micro-thruster on the satellite reached a scale equivalent to one-ten thousandth of the weight of a sesame grain, Wu said.However, the technological requirements for detecting gravitational waves in space are much higher, scientists say.CAS set a three-step strategy to implement the Taiji program. It took the research team about one year to develop Taiji-1, the first satellite of the program. It is expected to launch another two satellites in the second step after 2023, and three more satellites in the third step around 2033, according to Wu.Over the past few years, China has sent a series of space science satellites into space, including the DAMPE to search for dark matter, the world's first quantum satellite and the HXMT, China's first X-ray space telescope.In the coming three to four years, China plans to launch new space science satellites including the Gravitational Wave Electromagnetic Counterpart All-sky Monitor (GECAM), the Advanced Space-borne Solar Observatory (ASO-S), the Einstein-Probe (EP) and the Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) to study gravitational waves, black holes, the relationship between the solar system and humanity and the origin and evolution of the universe.
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2019年8月31日，中国科学院空间科学（二期）战略性先导科技专项首发星——微重力技术实验卫星在酒泉卫星发射中心成功发射。卫星在轨测试正在按计划有序开展，截至目前，卫星状态正常，各项测试结果正常，第一阶段在轨测试任务顺利完成。作为我国首颗空间引力波探测技术实验卫星，该卫星被正式命名为“太极一号”。引力波是物质和能量的剧烈运动和变化所产生的一种物质波，它提供了有别于电磁波的一个全新的观测宇宙的重要窗口，成为人类探索和认识宇宙的新的途径和手段。爱因斯坦一个世纪前基于广义相对论预言了引力波的存在。双黑洞并合产生的引力波已在2015年首次在地面被直接观测到。不同频率引力波反映了宇宙的不同时期和不同的天体物理过程。有别于地基探测，在空间能够探测到中低频段的引力波信号，能够发现天体质量更大、距离更遥远的引力波波源，揭示更为丰富的天体物理过程。然而，由于引力波信号极其微弱，实施空间引力波探测挑战巨大，需要突破目前人类精密测量和控制技术的极限。所涉及的核心技术包括高精度超稳激光干涉仪、引力参考传感器、超高精度无拖曳控制、微牛级推进器、超稳超静卫星平台等。“‘太极一号’正是瞄准这一重大科技前沿，对这些核心技术的可行性和实现途径进行在轨验证。” 中国科学院院士、工程首席科学家吴岳良说，“目前，“太极一号”实现了我国迄今为止最高精度的空间激光干涉测量，成功进行了我国首次在轨无拖曳控制技术试验，并在国际上首次实现了微牛级射频离子和双模霍尔电推进技术的在轨验证。” 据介绍，中科院从2008年开始前瞻论证我国空间引力波探测的可行性，经过多年科学前沿研究，提出了我国空间引力波探测“太极计划”，确定了“单星、双星、三星”“三步走”的发展战略和路线图，并于2018年8月在空间科学（二期）战略性先导科技专项中立项实施 “太极计划”单星工程任务，启动了三步走中的第一步。中国科学院副院长、党组成员相里斌说：“太极一号”的成功发射和第一阶段在轨测试任务的顺利完成，迈出了我国空间引力波探测的第一步，为我国在空间引力波探测领域率先取得突破奠定了基础。”来源：吴月辉 人民日报
Taiji-1 satellite [Photo/Xinhua]BEIJING - A recently-launched Chinese satellite has conducted in-orbit experiments on the key technologies related to space-based gravitational wave detection, the Chinese Academy of Sciences (CAS) announced on Friday.The satellite, sent into orbit on Aug 31, is China's first such kind of satellite, and has completed its first stage tests in orbit, laying a solid foundation for future gravitational wave observation in space, said Xiangli Bin, vice president of CAS."This is the first step of China's space-based gravitational wave detection. But there is still a long way to go to realize detecting gravitational waves in space. Chinese scientists will continue to contribute Chinese wisdom to the exploration and human progress," Xiangli said.The satellite has been named Taiji-1. As a Chinese term for the "supreme ultimate," Taiji is well-known as the black and white circular symbol representing yin and yang. The pattern of Taiji also resembles a binary star system composed by objects like neutron stars or black holes.Gravitational waves are "ripples" in space-time caused by some of the most violent and energetic processes in the universe. Albert Einstein predicted the existence of gravitational waves in 1916 in his general theory of relativity.The strongest gravitational waves are produced by catastrophic events such as colliding black holes, supernovae, coalescing neutron stars or white dwarf stars and possibly even the remnants of gravitational radiation created by the birth of the universe itself.The first discovery of gravitational waves by the LIGO Collaboration in 2015 has opened a new window to observe the universe and encouraged scientists worldwide to accelerate their research.CAS has announced the research program "Taiji" that will study gravitational waves from the merging of binary black holes and other celestial bodies.Unlike the LIGO research conducted from a ground-based observatory, Taiji will conduct space-based detection on the gravitational waves with lower frequencies to observe celestial bodies with greater mass or located farther away in the universe, said Wu Yueliang, chief scientist of the Taiji program and an academician of CAS.However, the gravitational wave signals from those celestial bodies are extremely weak, posing great challenges for detection. Scientists need to break through the limit of current precise measurement and control technology, Wu said.Taiji-1 aims to test the key technologies such as high-precision and ultra-stable laser interferometer, gravitational reference sensor, ultra-high precision drag-free control and ultra-stable and ultra-static satellite platform, according to Wu.Taiji-1 has realized China's most accurate space laser interference measurement and the first in-orbit drag-free control technology test. It also carried out electric propulsion technology experiments, Xiangli said.The first-stage in-orbit test showed that the accuracy of displacement measurement of the laser interferometer on Taiji-1 could reach a 100-picometer order of magnitude, equivalent to the size of an atom."The accuracy of the gravitational reference sensor on the satellite reached ten billionths of the magnitude of the earth's gravitational acceleration, equivalent to the acceleration produced by an ant pushing the Taiji-1 satellite," Wu explained.The thrust resolution of the micro-thruster on the satellite reached a scale equivalent to one-ten thousandth of the weight of a sesame grain, Wu said.However, the technological requirements for detecting gravitational waves in space are much higher, scientists say.CAS set a three-step strategy to implement the Taiji program. It took the research team about one year to develop Taiji-1, the first satellite of the program. It is expected to launch another two satellites in the second step after 2023, and three more satellites in the third step around 2033, according to Wu.Over the past few years, China has sent a series of space science satellites into space, including the DAMPE to search for dark matter, the world's first quantum satellite and the HXMT, China's first X-ray space telescope.In the coming three to four years, China plans to launch new space science satellites including the Gravitational Wave Electromagnetic Counterpart All-sky Monitor (GECAM), the Advanced Space-borne Solar Observatory (ASO-S), the Einstein-Probe (EP) and the Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) to study gravitational waves, black holes, the relationship between the solar system and humanity and the origin and evolution of the universe.
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