3D plume modeling of SPT-100

Hall thrusters are a spacecraft propulsion device for orbit maintenance and north-south station keeping. One of the concerns about Hall thrusters is the sputtering of high energy ions which could result in the erosion of sensitive surface coatings used for solar cell elements and thermal control. In this thesis, a 3D DSMC-PIC hybrid kinetic simulation of a well known, stationary plasma thruster SPT-100 plume modeling was performed using a hybrid MPI-GPU AMR code CHAOS. Xe atoms, Xe+, and Xe+2 ions are modeled using a kinetic approach. Modeling electrons using a kinetic approach is not feasible in today's computational power for a Hall thruster plume. Thus three different models are used to compute the plasma potential. First, Boltzmann and polytropic models are used for electric potential calculations. Current density values obtained from both electron models are compared with previous experimental measurements and simulations in the literature. It was seen that the polytropic model shows better agreement with the experimental measurements than the Boltzmann model and previous studies. In order to implement more detailed models, an electron fluid model is implemented and is solved on an AMR octree grid using the preconditioned conjugate gradient method. Current density comparisons of the electron fluid model with the experimental measurements showed a worse comparison than the polytropic model for the selected parameters. The implemented electron fluid model is then compared with ion energy distributions from flight measurements and previous simulations and showed good agreement for the chosen parameters. In order to investigate the influence of solar panel voltage on a spacecraft plume, simulations using the electron fluid and the polytropic models were compared. It was seen that the spatial distribution of ions in the core plume and in the backflow region are similar for both electron models. Finally, sputtering calculations were performed and it was seen that the energies of ions that hit the solar panel are smaller than the threshold energy of aluminum, and so that there would be insignificant sputtering. This is because neutralized particles in the vicinity of the solar panel create a shield that protects the solar panel from the high energy CEX ions

Controlling a CyberOctopus Soft Arm with Muscle-like Actuation

This paper presents an application of the energy shaping methodology to control a flexible, elastic Cosserat rod model of a single octopus arm. The novel contributions of this work are two-fold: (i) a control-oriented modeling of the anatomically realistic internal muscular architecture of an octopus arm; and (ii) the integration of these muscle models into the energy shaping control methodology. The control-oriented modeling takes inspiration in equal parts from theories of nonlinear elasticity and energy shaping control. By introducing a stored energy function for muscles, the difficulties associated with explicitly solving the matching conditions of the energy shaping methodology are avoided. The overall control design problem is posed as a bilevel optimization problem. Its solution is obtained through iterative algorithms. The methodology is numerically implemented and demonstrated in a full-scale dynamic simulation environment Elastica. Two bio-inspired numerical experiments involving the control of octopus arms are reported

Energy Shaping Control of a CyberOctopus Soft Arm

This paper entails application of the energy shaping methodology to control a flexible, elastic Cosserat rod model. Recent interest in such continuum models stems from applications in soft robotics, and from the growing recognition of the role of mechanics and embodiment in biological control strategies: octopuses are often regarded as iconic examples of this interplay. Here, the dynamics of the Cosserat rod, modeling a single octopus arm, are treated as a Hamiltonian system and the internal muscle actuators are modeled as distributed forces and couples. The proposed energy shaping control design procedure involves two steps: (1) a potential energy is designed such that its minimizer is the desired equilibrium configuration; (2) an energy shaping control law is implemented to reach the desired equilibrium. By interpreting the controlled Hamiltonian as a Lyapunov function, asymptotic stability of the equilibrium configuration is deduced. The energy shaping control law is shown to require only the deformations of the equilibrium configuration. A forward-backward algorithm is proposed to compute these deformations in an online iterative manner. The overall control design methodology is implemented and demonstrated in a dynamic simulation environment. Results of several bio-inspired numerical experiments involving the control of octopus arms are reported

Tracking control of spacecraft attitude on time dependent trajectories

A spacecraft attitude control which uses the quaternion parametrization, is proposed. The derivative of the to-go quaternion is obtained where the desired attitude is a time dependent function. Using this new attitude formulation, a Lyapunov function based feed-back control law that takes the time derivative of the desired attitude into account is proposed. The simulation results demonstrate the success of the new algorithm in tracking the desired attitude trajectory

3D plume modeling of SPT-100

Hall thrusters are a spacecraft propulsion device for orbit maintenance and north-south station keeping. One of the concerns about Hall thrusters is the sputtering of high energy ions which could result in the erosion of sensitive surface coatings used for solar cell elements and thermal control. In this thesis, a 3D DSMC-PIC hybrid kinetic simulation of a well known, stationary plasma thruster SPT-100 plume modeling was performed using a hybrid MPI-GPU AMR code CHAOS. Xe atoms, Xe+, and Xe+2 ions are modeled using a kinetic approach. Modeling electrons using a kinetic approach is not feasible in today's computational power for a Hall thruster plume. Thus three different models are used to compute the plasma potential. First, Boltzmann and polytropic models are used for electric potential calculations. Current density values obtained from both electron models are compared with previous experimental measurements and simulations in the literature. It was seen that the polytropic model shows better agreement with the experimental measurements than the Boltzmann model and previous studies. In order to implement more detailed models, an electron fluid model is implemented and is solved on an AMR octree grid using the preconditioned conjugate gradient method. Current density comparisons of the electron fluid model with the experimental measurements showed a worse comparison than the polytropic model for the selected parameters. The implemented electron fluid model is then compared with ion energy distributions from flight measurements and previous simulations and showed good agreement for the chosen parameters. In order to investigate the influence of solar panel voltage on a spacecraft plume, simulations using the electron fluid and the polytropic models were compared. It was seen that the spatial distribution of ions in the core plume and in the backflow region are similar for both electron models. Finally, sputtering calculations were performed and it was seen that the energies of ions that hit the solar panel are smaller than the threshold energy of aluminum, and so that there would be insignificant sputtering. This is because neutralized particles in the vicinity of the solar panel create a shield that protects the solar panel from the high energy CEX ions