Fundamental Challenges of Self-Guided Beamed Propulsion and Prospects for Near-Term Experiments

Author: Chris Limbach, PhD, Assistant Professor, Texas A&M University

Abstract Background: Beamed propulsion concepts based on laser or particle beams are affected by finite beam divergence due to diffraction or thermal spreading of the beam particles, respectively. These effects, in addition to the low thrust provided by photons, often result in large-scale transmitter systems and very light payloads.

Abstract Objectives: A combination of laser and particle beams, exploiting optical dipole forces and refraction, has recently been proposed to mitigate beam spreading and provide increased thrust from the particle beam. This study examines the conditions for self- guiding and applicable scaling laws for future laboratory experiments.

Abstract Methods: Determination of self-propagating modes and simulation of guided propagation have been performed by numerically solving the paraxial wave equation and gas-kinetic equation (Boltzmann equation), with and without optical coupling. Stationary solutions for self-guiding are obtained from an iterative method for the paraxial Helmholtz equation and the method of characteristics solution of the 2D, axisymmetric, collisionless Boltzmann equation.

Abstract Results: Self-guiding solutions for the laser intensity and particle density profiles have been found to exist over a range of parameterizations of the phase-space distribution function and the waveguide V-parameter. Application of fundamental scaling laws show these modes can be observed in the laboratory. The effect of collisions and light scattering are also considered in the context of planned experiments.

TRL Assessment: The present study continues the TRL advancement of self-guided beamed propulsion from TRL 2 to towards TRL 3.

Abstract Development: Challenges and potential solutions to larger-scale ground testing are described, with the goal of defining a roadmap to TRL 5.Challenges and potential solutions to larger-scale ground testing are described, with the goal of defining a roadmap to TRL 5.

Abstract Near-Term Technical Milestones: Observation and study of self-guiding should be feasible over the next several years, necessitating only commercially available lasers and cold atomic beams produced through conventional laser-cooling techniques. Development of predictive computational models will be helpful to design such experimental demonstrations and understand optimal operating conditions.

Observation and study of self-guiding should be feasible over the next several years, necessitating only commercially available lasers and cold atomic beams produced through conventional laser-cooling techniques. Development of predictive computational models will be helpful to design such experimental demonstrations and understand optimal operating conditions.

Abstract Conclusions: Analysis of the governing equations suggests that direct observation of self-guiding and validation of numerical simulations could be achievable in near-term lab-scale experiments. Indeed, laser and atomic beam propagation over several tens of meters may be used, by virtue of scaling laws, to simulate and study self-guided propagation of high energy atomic beams over thousands of kilometers.