China Advances Space-Based Gravitational-Wave Detection with Taiji Optical Core Test

Researchers at the Institute of Mechanics, Chinese Academy of Sciences, have completed ground-based validation of the optical core for the Taiji space-based gravitational-wave observatory. The test demonstrated that the interferometer meets the mission’s precision requirements, marking the transition from theoretical design to operational hardware.

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Gravitational waves are ripples in spacetime generated by cataclysmic events such as black-hole mergers. Ground-based detectors like LIGO first observed these signals in 2015, but are limited to higher-frequency bands. Space-based platforms such as Taiji aim to detect lower-frequency millihertz waves, complementing projects like ESA’s LISA.

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The optical core was engineered by the Institute of Mechanics, part of the Chinese Academy of Sciences. The development is part of the national Taiji program, a space-based gravitational-wave project. The team’s findings were published in the international journal *Research*.

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• Taiji-1 launched in August 2019 to test laser interferometry and drag-free control in orbit.

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• Taiji-2 will incorporate the newly validated optical core and involve two spacecraft in a demonstration mission.

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• Taiji-3 envisions a full three-satellite array and is planned for deployment in the 2030s.

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Ground testing recorded picometer-level precision, enabling detection of displacements as small as one ten-thousandth of a human hair’s diameter. Temperature-induced interference was suppressed, and measurement stability improved tenfold while overall noise levels were substantially reduced.

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By targeting the millihertz band, Taiji could observe mergers of intermediate-mass black holes, probe the early universe, and test general relativity on cosmological scales. The mission expands China’s capability in space-based astrophysics and adds to the suite of large-scale gravitational-wave detectors being developed internationally.

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The Institute of Mechanics team reported that the optical core’s ground tests satisfied all mission-critical parameters, confirming readiness for integration into the Taiji-2 flight segment. They emphasized that the results demonstrate a shift from conceptual design to functional hardware suitable for space deployment.

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• “The ground tests [of the optical core] were a success, and all the key numbers met the strict demands of the mission.” — Science and Technology Daily report

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• “That means that the core measurement system of Taiji has officially moved from [theory] to real hardware.” — Science and Technology Daily report

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• “Incredibly, this means it is capable of detecting displacements as small as one ten-thousandth of the diameter of a human hair.” — Researchers, Institute of Mechanics, Chinese Academy of Sciences

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The validated optical core will be incorporated into the upcoming Taiji-2 demonstration mission, which will involve two spacecraft. After Taiji-2, the full three-satellite Taiji-3 observatory is planned for deployment in the 2030s, adding to the suite of large-scale gravitational-wave detectors being developed internationally.

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