The present paper reports optomechanical and quantum electronical analyses of the mechanism of photonic laser thruster (PLT) in achieving spacecraft velocities on the order of by using macroscale laser-like optical resonators. One remarkable result is that the resonance condition of the PLT optical cavity imposes the magnitude of the dynamic frequency shift of the circulating laser beam wavefunction by the moving mirror to equal that of the single-reflection Doppler shift of a nonresonant laser beam. However, their mechanisms are proven completely different. The optomechanical dynamics of PLT was analytically investigated and the chief results are as follows: 1) the maximum achievable PLT spacecraft velocity with existing laser technologies is estimated to be ; 2) for interplanetary propulsion applications the optimum range of the intrinsic PLT cavity power loss factors from absorption, scattering, and diffraction is ; and 3) the efficiency of transforming the laser energy to the spacecraft kinetic energy increases over 40% at velocities greater than . The present results validate the theoretical feasibility of PLT to enable unprecedentedly fast interplanetary transportation systems, such as the Photonic Railways. The required engineering and manufacturing capabilities for implementing the interplanetary PLT are discussed.