Space-Based Gravitational Wave Detection (Taiji/TianQin)

China is developing two independent space-based gravitational wave detection programs. Taiji, led by the Chinese Academy of Sciences, will deploy three satellites in a triangular formation in heliocentric orbit, with arm lengths of 3 million kilometers. TianQin, led by Sun Yat-sen University, uses a similar three-satellite configuration but in Earth orbit with 170,000-km arms. Both target the millihertz frequency band — gravitational waves from supermassive black hole mergers that ground-based detectors like LIGO cannot observe.

Taiji-1, a pathfinder satellite, launched successfully in 2019 and validated key technologies including optical metrology and drag-free control systems. Taiji-2 (two satellites for inter-satellite laser link testing) was planned for 2023-2025, with the full three-satellite constellation (Taiji-3) targeting ~2030. TianQin's pathfinder mission TianQin-1 launched in 2019 as well. The dual-program approach provides redundancy and competition.

The only comparable Western project is ESA's LISA mission, also targeting ~2035 launch. China's parallel development of two gravitational wave observatories — when no other country is building even one independently — illustrates its strategy of pursuing frontier science as a matter of national prestige and eventual practical application. Space-based gravitational wave detection is pure science today, but the precision laser interferometry, drag-free satellite control, and inter-satellite ranging technologies have applications in next-generation navigation and geodesy.