Photonic Laser Propulsion (PLP): Photon Propulsion Using an Active Resonant Optical Cavity

Abstract

We present an innovative Photonic Propulsion concept, Photonic Laser Propulsion (PLP), which uses direct momentum transfer of photons for thrust generation, and exploits a novel photon thrust amplification scheme that increases the thrust to power ratio by orders of magnitudes. The amplification is accomplished by trapping or bouncing photons between two high reflectance mirrors located separately in spacecraft platforms. With this enhanced photon thrust the thrust to power ratio of PLP engines is competitive with the conventional electric thrusters. PLP provides Isp = 3x10 7 sec, and is propellantless, thus theoretically, it can accelerate spacecraft to the velocities orders of magnitude larger than conventional rocket velocities. In addition, PLP can provide ultrahigh precision in thrust as well as thrust vector pointing. This aspect permits the usage of PLP in precision control of spacecraft clusters or precision docking of spacecraft. We have recently successfully demonstrated the proof-of-concept of PLP in the sub-scale laboratory setup. The maximum photon thruster achieved so far in this setup was 35 µN at the laser output of 1.7 W with the use of high reflectance mirror with a 0.99967 reflectance, corresponding to an apparent photon thrust amplification factor of ~3,000. The results on this demonstration are presented in a concurrent session. The crucial aspect of the current innovation is in the usage of an active resonant optical cavity in which the laser cavity is directly formed between a pair of space platforms. During the PLP demonstration, we have discovered that the optical gain medium can rapidly adapt to any changes in the optical cavity parameters by amplifying the resonant photon waves at a given cavity condition, thus the cavity becomes robust against changes in the cavity length or acceleration of cavity mirrors. The reason for this is that the optical gain medium is within the optical cavity, and the cavity is operated in multifrequency oscillation.