Numerical simulation of the laser ablative impulse generation onto an aluminum target is carried out. The simulated condition is taken from a recent experiment, in which an aluminum foil is irradiated by the laser pulse which is supplied from an Nd:YAG laser; and the time history of the local impulse generated on the aluminum foil is measured by using a velocity interferometer named VISAR (Velocity Interferometer System for Any Reflector). A computational fluid dynamic method is used, which incorporates the physical modeling for laser ablation phenomenon such as the heating of a solid target including melting and evaporating process and the expansion of the vaporized plume into a near vacuum. The calculation can replicate the measured temporal variation of the local impulse by fitting an effective surface reflectivity on the aluminum target.

View full abstract

Characteristics of compact laser plasma accelerators utilizing high-power laser and thin-target interaction were reviewed as a potential candidate of future spacecraft thrusters capable of generating relativistic plasma beams for interstellar missions. Based on the special theory of relativity, motion of the relativistic plasma beam exhausted from the thruster was formulated. Relationships of thrust, specific impulse, input power and momentum coupling coefficient for the relativistic plasma thruster were derived. It was shown that under relativistic conditions, the thrust could be extremely large even with a small amount of propellant flow rate. Moreover, it was shown that for a given value of input power thrust tended to approach the value of the photon rocket under the relativistic conditions regardless of the propellant flow rate.

View full abstract

A laser propulsion system is expected to be one of the most hopeful next-generation space propulsion systems. In this system, Laser-Supported Plasma (LSP) is an essential phenomenon, because laser energy is mainly absorbed by a hot plasma and then converted into the kinetic energy for propulsion. In this paper, I introduce the analysis model and the calculation methods which I have formulated for numerically simulations on the Laser-Supported Detonation (LSD), which is categorized as one type of LSP, propagating through an inert gas at a room temperature. As a typical geometric model to realize laser propulsion, a conical nozzle, which simplifies the inside of laser propulsion system, is applied. In this analysis, the numerical methods for thermal non-equilibrium plasma flows solved by axisymmetric two dimensional Navier-Stokes equations coupled with laser absorption model, are studied.

View full abstract

A thrust generation model of Microwave Rocket was studied. The model was proposed based on shock wave propagation driven by an atmospheric plasma on the analogy of a pulse detonation engine (PDE), because the pressure histories measured in a thruster tube resembling to those in a PDE. Furthermore, both the shock propagation speed and the ionization front propagation speed were found nearly constant and identical in the tube when they propagated at a supersonic speed with a high microwave power density. Based on the model, thrust impulse was estimated from the pressure history. Estimated thrust showed a good agreement with the result of the flight experiment.

View full abstract

Two basic principles of the ablation plasma expansion, namely a flyer acceleration and an i-BAR (ion beam ablation rocket) arc analyzed to investigate the momentum-producing capability of an ion beam-target interaction. When a target is irradiated with an iron beam, it separates into two parts; one part evaporates forming the ablation plasma, while the unevaporated residue (remaining part) is termed a flyer. This is called a flyer acceleration concept. On the other hand, in the case of the i-BAR, a target is fully-evaporated forming a high momentum ablation plasma driving a spacecraft forward. This paper presents the comparison of the numerical results of both models and evaluates a possible application for space propulsion. In order to explain the hydrodynamic variables and the ablation formation phenomenon, a one-dimensional hydrodynamic model is used and is solved by the Langrangian coordinate. The i-BAR, shows a greater momentum-producing capability than the flyer acceleration concept. In addition, thrust-producing capability over a wide range of ion beam energy densities is investigated.

View full abstract