1. A physical and mathematical model of the processes occurring in the ion-extraction system (IES) of RIT is developed, including the calculation of the electrostatic fields of the electrodes, the trajectories of the primary ion beam, the trajectories of the secondary charge-exchange ions formed in the volume of the primary beam and in the neutralization zone, as well as the rate of erosion of the accelerating grid (AG). Numerical simulation of the processes in the unit cell of the IES of the specified designs (RIT-16 and RIT-45M cases) was conducted. The resource of the AG made from carbon composite at the rated operating modes of the thruster was estimated according to the results simulation with 30,000 hours of a thruster’s operation time.
2. An advanced version of the calculating thermal model of the RIT has been developed, based on the calculation of the power carried out from the gas discharge chamber (GDC) plasma by ion and electron fluxes. The calculations revealed the possibility of a noticeable decrease in the temperature of the GDC and the screen grid (SG), the most critical element of the RIT design in regards to its thermal deformation under thermal loads. The results of the conducted thermal calculations are used as the initial data for calculating the thermal deformation of the IES electrodes.
3. A series of works to refine and adapt the calculated thermomechanical model of the IES unit applied to the RIT with an ion beam diameter of 150...200 mm was conducted. Additional deflections of electrodes made of different materials and having a different initial deflection under thermal loading with a radial temperature gradient of 5 ^{0}/cm were numerically determined.
4. A thermal model of the RIT-8 thruster was developed in the approximation of heat release in a plasma discharge as in a solid element with distributed volumetric electrical conductivity subjected to induction heating. This model automatically implements the equality of the power allocated in the volume and brought to the walls. Thermal modeling was performed via the Comsol Multiphysics ® v4.3b software package.
5. The laboratory models of RIT-10, RIT-16, RIT-16M, RIT-45M were developed.
6. Constructive solutions were found that allowed to significantly reduce the energy cost of an ion and get closer to the world-class. An increase in the characteristics of the RIT model is expected with the implementation of discharge chambers of shorter length, as well as spherical and conical shapes. Currently, these chambers are manufactured and experimental work of their samples is in preparation.
7. The study of physical processes in laboratory models of RIT was carried out in order to obtain the maximum efficient operation mode. It is shown that in order to obtain the maximum efficient operation mode in an inductive discharge with a capacitive coupling, in contrast to the maximum power mode, it is necessary that the RF generator (RFG) impedance is less than the load impedance consisting of a matching circuit, a GDC together with an inductor and their parasitic capacitances. If these recommendations are met, the efficiency of the RFG together with the discharge can exceed 90 %.
8. An equivalent circuit of an inductive discharge with a capacitive coupling, designed to determine the electrical impedance of the GDC together with the inductor, was developed, calculated and analyzed. The results of the analysis prove that the active and reactive parts of the load impedance depend on the main plasma parameters. Detailed calculations were conducted for the RIT-45M and RIT-10 models. Unlike most publications, where a cylindrical inductor is typically considered, the length of which is much larger than the radius, in this paper, the final longitudinal dimensions of the inductor coil are additionally taken into account. Thus, in particular, the analysis for a short inductor was carried out.
9. A laboratory sample of the RFG-3000 was developed and manufactured in order to be used as a part of the RIT series with an ion beam dimension from 100 to 450 mm. The principle of forming a signal with a tunable frequency using a low-power RF, followed by amplification in a broadband amplifier and in a power amplifier, is the basis for the operation of the RFG.
10. The RFG-3000 was tested for a calibrated resistive load in the form of a 62-Ohm coaxial resistor with power dissipation of 1000 W showed that the RFG-3000 in the studied frequency range provides the required power at a resistive load, and the maximum non-linearity of the RF power level readings, according to the generator's switch device, does not exceed 15% in the entire frequency and power range.
11. The developed laboratory model of the RFG-3000 can be used for testing of the RIT series with the dimension of the ion beam from 100 mm to 450 mm in ground conditions. At the same time, it is installed outside of the vacuum test facility, and the RF energy input is carried out using feeder lines. In the case of placing the thruster on a flange with pass-through connectors for the inductor, the control system (CS) is placed outside the vacuum chamber. When the thruter is placed inside of the vacuum chamber, the CS is also placed within the vacuum chamber in the immediate proximity of the inductor terminals.
12. Using the bench RFG-3000, the operating modes of the RIT-10 were studied for three operating frequencies and three values of the propellant volume flow rate. For each of the modes, the voltage on the inductor was adjusted according to the simultaneous ion beam current readings. It was shown that by adjusting the output power of the generator, it is possible to provide an increase in the beam current from 20 mA to 190 mA, which completely covers the possible operating modes of the RIT-10.
13. A method for measuring the electromagnetic field parameters generated during a RIT operation in the frequency range of 1...18 GHz has been developed. The method is based on measuring the power of the noise process (which occurs during the RIT operation) at the output of the measuring antenna, followed by conversion into the electric field strength in the antenna opening. The measurements were taken in the entire frequency band of the measuring antenna and were submitted in a form of graphs of the absolute values of the electric field as a function of the frequency.
14. The developed method of measuring the parameters of the electromagnetic fields generated during the RIT operation is an effective tool for studying the interference emission of the RIT series with an ion beam dimension from 100 mm to 450 mm. Provided this method, it is possible to conduct a study of RF interference emission in the interests of electromagnetic compatibility problems in order to determine the level of their influence on the onboard spacecraft systems.
15. A method for optimizing the multiturn trajectories of the interorbital transfer of a spacecraft with a cruising electric rocket propulsion system (ERPS) was presented. The unique feature of the presented method, in comparison with the results presented in previous reports, is the use of an accurate, non-averaged mathematical model of the undisturbed optimal motion of the spacecraft. Mathematical models and methods for modeling perturbed quasi-optimal flightpaths are developed using the previously obtained quasi-optimal control with feedback. A comparative analysis of the use of RIT and stationary plasma thruster (SPT) on modern and prospective geostationary spacecraft was made. Recommendations on the areas of application of the RIT have been developed. A promising field of application of RITs with an electric power of 2-3 kW is considered to be their use as a part of the geostationary spacecraft correcting ERPS. RITs with a power of about 5 kW in some cases can compete with the SPT-140D thrusters in the tasks of the spacecraft's orbit raising with a cruising ERPS on the GEO according to a combined scheme, with the possibility of increasing the time of the launch. Despite the fact that the specific impulse of the RIT (in contrast to the SPT-140D) is significantly higher than the optimal one for this task, the high efficiency of the RIT makes it possible to compensate for the associated losses during the launch with the correct optimization of the parameters of the spacecraft orbit of separation from the upper stage. Of course, the use of high-power RITs (25...50 kW) as part of prospective reusable interorbital trackers with megawatt-class transport and energy module is promising. It was determined that one tracker like this can provide a modern Russian commercial cargo flow to the GEO for 5...6 years, while reducing the required number of launch vehicles for the implementation of this program by 2.33...3.75 times.
Implemented results of research:
The results of the research were used within research and development works and experimental-design works of the Federal Space Program of the Russian Federation for 2016-2025, approved by the Decree of the Government of the Russian Federation No. 230 of March 23, 2016. The following works have been completed and are being performed: "Ustoichivost’ (from Russian –stability)", "Partitura (from Russian – score)", "DU KA (from Russian – spacecraft propulsion system)", "Forsazh (from Russian – boost)", "Otrabotka (from Russian –testing)" and "Ekspluatatsia MKS (from Russian - operation of the ISS)", etc.
Education and career development:
During the existence of the laboratory, fourteen students received diplomas of higher education, sixteen PhD works were defended with the title of candidates of technical and physical-mathematical sciences, as well as three doctoral works with the title of doctors of technical sciences.
Organizational and structural changes:
The test facility has been modernized and retrofitted, which allows testing and research of working processes of electric rocket engines with a power of up to 50 kW with maintaining a high vacuum at the flow rate of the Xe propellant up to 30 mg/s. The stand was equipped with the power supply systems necessary for the operation of the RIT, systems for supplying working mediums to the thrusters while their operation inside of the vacuum chamber, systems for measuring thrusters’ main parameters (power consumption, working gas consumption, obtained thrust, etc.), systems for automated collection of experimental data.
The test facility is used to study the characteristics of RIT thrusters with two vacuum chambers with a diameter of 2 m and a working length of up to 6.5 m and up to 3.5 m, pumped out by oil-free cryogenic, turbomolecular and forvacuum pumps that provide a residual pressure in the vacuum chamber up to 3,5´10^{-6} Torr and an operation pressure below 5´10^{-5}
Torr when working in the high-pressure chamber (the operation pressure in the vacuum chamber meet the best international standards).
Collaborations:
Joint preparation of a number of Russian-German conferences on the topic of electric propulsion and their applications. Internships of the RIT laboratory employees were conducted simultaneously with the V Russian - German Conference on Electric Rocket Engines (V Russian-German Conference on Electric Propulsion), which took place from 07.09.2014 to 12.09.2014, (Dresden, Germany), as well as with the 34th International Conference on Electric Propulsion (34th International Electric Propulsion Conference), which was held from 04.07.2015 to 10.07.2015, (Kobe, Japan). In cooperation with the University of Giessen. Justus Liebig conducted a research on determining the thermal fields of a RIT with an IES diameter of 80 mm. Also, the supply of the power supply system, the source control unit and the RIT-20 source itself was provided.