Inter-satellite laser ranging for time-delay interferometry in space- based gravitational-wave detection

In the mission of space-based gravitational wave detection, laser interferometry is utilized to achieve the precision of tenpicometer level in the displacement measurement between drag-free proof masses. Laser frequency noise is the dominant noise in the measurement, and the spaceborne stabilized laser cannot meet the requirement of the laser noise budget in the foreseeable future. In the European Laser Interferometer Space Antenna (LISA) project for gravitational-wave detection, the technique of time-delay interferometry (TDI) is utilized to cancel the laser noise and sampling clock noise by time-delaying and linearly combining the phase measurement data on the three satellites. However, TDI algorithm requires sub-meter precision of the absolute ranging over the inter-satellite distance of several million kilometers for effectively cancelling the laser noise and clock noise. In this paper, the laser ranging scheme for TDI is analyzed and the code shift keying (CSK) modulation is proposed in which the ranging code and communication code are temporally divided. Comparing to the direct sequence spread spectrum (DS/SS) modulation in LISA scheme, the CSK proposal is advantageous in correlation performance of the ranging code and the transmission speed of the communication code, providing a competitive solution for the laser absolute ranging towards TDI algorithm.