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Gridded ion thrusters (GITs) are an established technology that, by covering a wide range of power class, allows one to accomplish a lot of space mission types. Many analysis tools and analytical models describing the physics of GITs are present in the open literature, while there is a lack of tools for preliminary design, considering the mission requirements (i.e., thrust or power). Thus, in this work, a tool that takes as input thrust or power and that combines analytical formulas, describing GITs' physics; a curve-fitting approach, exploiting data from different ion thrusters present in the open literature; and an FEMM (finite element method magnetics) simulation has been developed and validated against known medium-low-power (<5 kW) gridded ion thrusters (e.g., NSTAR, XIPS, ETS-8). Some of the main outputs of the developed tool are its specific impulse, efficiencies, voltages, and propellant flow rate. The results obtained by the tool have been in good agreement with the real performance and working parameters of the thrusters selected for the validation, obtaining an average error of less than 5–10%. The tool has been also compared with a tool proposed in the literature as a possible design tool, which makes use of a simple macroscopic plasma-source simulation (SMPS) code with a genetic algorithm (GA) and obtains slightly more accurate results on average. Finally, the tool has been exploited for the design of a very low-power GIT (100 W) that is able to produce 2 mN of thrust, as the interest of the scientific community in miniaturizing electric engines has recently grown because they could enable new space missions. [ABSTRACT FROM AUTHOR]

Abstract The lifetime of electric propulsion (EP) thrusters depends particularly on the erosion characteristics of operation relevant components, for instance, the grid hole erosion of gridded ion thrusters or the channel wall erosion of Hall effect thrusters. Here two tools for in situ erosion measurements are presented, a triangular laser head for surface profiling and a telemicroscope for high-resolution optical imaging. Both can give access to radial and axial erosion parameters. The measurements can be done in situ without the need for breaking the vacuum and dismounting the thruster, which reduces thruster testing time considerably. In situ measurements can also help to ensure reproducibility of thruster performance conditions and can improve statistics of thruster characterization. The present work describes the fundamentals of both techniques in detail, selected experimental setups are presented, their performance is characterized and critically evaluated. The capabilities and limitations related to erosion measurements of EP thrusters are, exemplary, demonstrated for a gridded ion thruster RIT-22 and a Hall effect thruster SPT-100D.

Gridded ion thrusters (GITs) are an established technology that, by covering a wide range of power class, allows one to accomplish a lot of space mission types. Many analysis tools and analytical models describing the physics of GITs are present in the open literature, while there is a lack of tools for preliminary design, considering the mission requirements (i.e., thrust or power). Thus, in this work, a tool that takes as input thrust or power and that combines analytical formulas, describing GITs’ physics; a curve-fitting approach, exploiting data from different ion thrusters present in the open literature; and an FEMM (finite element method magnetics) simulation has been developed and validated against known medium-low-power (

The work deals with indirect optimization of minimum-time and minimum-fuel interplanetary trajectories when gridded ion thruster models are considered. Using an accurate model of solar electric propulsion is beneficial in preliminary mission design, and allows including operational constraints. The maximum thrust and the specific impulse are expressed as a function of thruster input power, which is achieved by means of point-fitting lines that match the performance capabilities of the thrusters. Minimum-time and minimum-fuel problems are formulated to be solved by indirect optimization. In order to increase the accuracy and robustness of the shooting procedure, analytic Jacobians are derived, and a hybrid switching detection technique is used to improve the integration accuracy for minimum-fuel problems. Two examples of Earth-to-Mars transfer and Near-Earth rendezvous mission using the realistic NASA's Evolutionary Xenon Thruster (NEXT) are given to substantiate the feasibility and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The lifetime of electric propulsion (EP) thrusters depends particularly on the erosion characteristics of operation relevant components, for instance, the grid hole erosion of gridded ion thrusters or the channel wall erosion of Hall effect thrusters. Here two tools for in situ erosion measurements are presented, a triangular laser head for surface profiling and a telemicroscope for high-resolution optical imaging. Both can give access to radial and axial erosion parameters. The measurements can be done in situ without the need for breaking the vacuum and dismounting the thruster, which reduces thruster testing time considerably. In situ measurements can also help to ensure reproducibility of thruster performance conditions and can improve statistics of thruster characterization. The present work describes the fundamentals of both techniques in detail, selected experimental setups are presented, their performance is characterized and critically evaluated. The capabilities and limitations related to erosion measurements of EP thrusters are, exemplary, demonstrated for a gridded ion thruster RIT-22 and a Hall effect thruster SPT-100D. [ABSTRACT FROM AUTHOR]

The research challenges for electric propulsion technologies are examined in the context of s-curve development cycles. It is shown that the need for research is driven both by the application as well as relative maturity of the technology. For flight qualified systems such as moderately-powered Hall thrusters and gridded ion thrusters, there are open questions related to testing fidelity and predictive modeling. For less developed technologies like large-scale electrospray arrays and pulsed inductive thrusters, the challenges include scalability and realizing theoretical performance. Strategies are discussed to address the challenges of both mature and developed technologies. With the aid of targeted numerical and experimental facility effects studies, the application of data-driven analyses, and the development of advanced power systems, many of these hurdles can be overcome in the near future.

In gridded ion thrusters, it is generally known that the ion extraction from the grid significantly decreases the neutral density. However, because it is difficult to measure the density inside thruster, it has not been revealed how the local density decreases including the inhomogeneous effects (e.g., gas injection, ionization, and ion recombination). To investigate these inhomogeneous effects, two-photon laser-induced fluorescence (TALIF) and Direct Simulation Monte Carlo (DSMC) applied to a gridded microwave discharge ion thruster. First, the TALIF directly measured the density distribution. Second, the DSMC reproduced the measured density distribution. From these results, the main effect of the ion extraction is the decrease of ion recombination at the grid. This decrease makes the density distribution more sensitive to the ionization distribution and increases the inhomogeneity. Based on this knowledge, we propose improvement against 'simulated experiment without ion extraction' and 'decoupled numerical simulation' which reproduce the density distribution of ion extraction under the condition without ion extraction by decreasing flow rate. Specifically, we suggest that the grid transparency is expanded and the rest discrepancy is adjusted by the flow rate because the difference of the inhomogeneous effect due to gas injection can be reduced. • Measurement of neutral density distribution inside gridded ion thruster by TALIF. • Comparison of neutral density distribution between without and with ion extraction. • DSMC simulation was performed to reproduce TALIF measurement. • Inhomogeneity of gas injection, ionization, and ion recombination on neutral density. • Expansion of grid transparency is better solution to reproduce sate of ion extraction. [ABSTRACT FROM AUTHOR]

The research challenges for electric propulsion technologies are examined in the context of s-curve development cycles. It is shown that the need for research is driven both by the application as well as relative maturity of the technology. For flight qualified systems such as moderately-powered Hall thrusters and gridded ion thrusters, there are open questions related to testing fidelity and predictive modeling. For less developed technologies like large-scale electrospray arrays and pulsed inductive thrusters, the challenges include scalability and realizing theoretical performance. Strategies are discussed to address the challenges of both mature and developed technologies. With the aid of targeted numerical and experimental facility effects studies, the application of data-driven analyses, and the development of advanced power systems, many of these hurdles can be overcome in the near future. [ABSTRACT FROM AUTHOR]