Introduction of laser pointing scheme in the Taiji program

To realize scientific measurement of gravitational waves in the space gravitational wave detection, after launching into a predetermined orbit, the satellites must first construct a 100-km laser link. Furthermore, to prevent the gravitational wave signal from being flooded by laser pointing noise, the laser pointing stability must reach a magnitude of nrad/Hz. Therefore, a sophisticated laser pointing scheme has to be adopted. In this paper, based on the Taiji program, we will discuss the design of such a scheme, which can be divided into two phases. Laser acquisition will be the first process. A star sensor(STR) and a charge coupled device (CCD) will be used as auxiliary capture detectors to decrease the laser pointing uncertainty region to sub-mu rad levels. After that will be the laser fine pointing process, which uses differential wavefront sensitive (DWS) technology to accurately control pointing direction. The requirements of the acquisition sensors will be proposed based on the Taiji program while the feasibility of the DWS technique in the laser fine pointing phase will be discussed. The conclusions of this paper can be regarded as the basis and principle of related experiments and will give a reference for system construction in the laser pointing scheme of the Taiji program.