The pilot of Taiji program — From the ground to Taiji-2

The Taiji-1 satellite is a pilot satellite mission of Taiji program, which is used to verify Taiji’s key technology and also to testify the feasibility of Taiji roadmap. Taiji-1 was launched on 31st August 2019 and its designed mission was completed. The results of Taiji-1 first scientific run are briefly introduced. A detailed analysis on how Taiji-1 can bridge the gap between ground experiment and Taiji pathfinder is presented. To report current progresses and achievements on Taiji program made by Taiji scientific collaboration, we publish this special issue with including 26 articles.