A Novel Method of Acquisition and Tracking between the Twin Spacecrafts of "Taiji-2"

“Taiji” is a space-based gravitational wave (GW) detection program proposed by Chinese Academy of Sciences (CAS), aiming to detect GW with lower frequencies to observe celestial bodies with greater mass or located farther away in the universe. “Taiji-2” is the inheritor of “Taiji-1”, aiming to validate the technologies required by the final “Taiji” program, which includes the verification of super-far distance satellite to satellite (SS) laser link acquisition and tracking, non-orthogonal multiple degrees of freedom (DoF) drag free control (DFC), ultra-stable ultra-clean satellite platform and so on. SS acquisition and pointing are prerequisites for inter-satellite laser interferometer, which is the foundation of GW detection. “Taiji-2” is a spacecraft formation with two identical satellites, carrying two suit of gravitational reference sensors (GRS) subsystem, two telescopes, two suit of scientific interferometer subsystem, one suit of DFC subsystem as the payloads in each spacecraft. First, the error source tree of the relative pointing uncertainty between the twin spacecrafts is built and its characteristic are analyzed. Second, the method to calibrate the deviation of the line of each telescope is introduced, and the final uncertainty cone is determined. Then, four different acquisition strategies and the detail acquisition procedures are constructed according to the operating modes. After that, a novel acquisition guidance law is proposed to scan the receiving spacecraft, which can meet the torque and angular velocity limit in engineering implementation, and a fifth order polynomials is adopted to design the recovery guidance law after scanning for the sending spacecraft. Last, simulations based on MATLAB environment are conducted to validate the effectiveness of the acquisition algorithms, the results show that the two spacecrafts can acquire the laser signal each other during tens of minutes. Based on the preliminary analysis, the conclusions are given and some suggestions are provided for the design of the SS link establishment and keeping subsystem of “Taiji-2.