Research and Development of Space High-impulse High-frequency Plasmadynamic Electric Rocket Thrusters

Scientific results:

1. A physical and mathematical model has been developed that describes the processes occurring in the ion optical system (IOS) of a radio-frequency ion thruster (RIT), including a computation of the electrostatic fields of the electrodes, the trajectories of motion of the primary ion beam, the trajectories of secondary charge-exchange ions formed in the volume of the primary beam and in the neutralization zone as well as the speed of erosion of the accelerating electrode (AE). A numerical modeling of the processes in an elementary cell of IOS of specified geometries that correspond to the structure of VChID-16 and VChID-45M. The operational life of an AE made of carbon composite at nominal operation modes of the thruster is 30000 hours according to the results of a modeling.
2. An enhanced version of a thermal computational model of a RIT based on a calculation of the power carried out from plasma in the gas discharge chamber (GDC) by flows of ions and electrons has been developed. The computations identified the possibility of significantly decreasing the temperature of the GDC and the EE, the most critical element of the structure of a RIT in terms of its thermal deformation under heat loading. The results of the completed thermal computations have been used as source data for performing computations of the thermal deformation of electrodes in an IOS.
3. Our researchers have conducted a series of works to refine and adapt a computational thermomechanical model of an IOS node with regard to RITs with diameters of the ion beam of 150-200 mm. We have numerically determined additional deflections of electrodes made of various materials that have different initial deflections under thermal loading with a radial temperature gradient of 5 ⁰/cm.
4. A thermal model of the VchID-8 thruster has been developed in the approximation of the thermal emission in the volume of plasma as in a solid element with distributed  volume electrical conductivity that is susceptible to induction heading. Such a model automatically implements the equality of the power produced in the volume and supplied to the walls. The thermal modeling has been conducted using the software complex Comsol Multiphysics® v4.3b.
5. Laboratory models of VChID-10, VChID-16, VChID-16М, VChID-45М have been developed.
6. We have found design solutions that allow to significantly reduce the cost per ion and approach the world level. An improvement of the characteristics of the RIT model is expected to occur during transition to chambers of smaller length which will also be spherical and conical in shape. These chambers have already been manufactured and we are preparing to test models involving those chambers.
7. Our researchers have conducted a study of the physical processes in laboratory RIT models to find the maximum efficiency mode. It has been demonstrated that to find the maximum efficiency mode in an inductive capacitive coupling, discharge in contrast with the maximum power mode, it is necessary that the impedance of the radio-frequency generator is lower than the impedance of the load comprised of the matching circuit, the GDC together with the inductor and their parasitic capacitances. If the specified recommendations are applied, the efficiency factor of RITs in conjunction with the discharge can exceed 90 per cent.
8. We have developed, computed and analyzed an equivalent-circuit model of an inductive capacitive coupling discharge. The model was designed to determine the electrical impedance of the GDC in conjunction with the inductor. The results of the analysis demonstrate that the active and the reactive part of the impedance of the load depends on the main plasma parameters. Detailed computations have been conducted for the models of VChID-45M and VChID-10. Unlike the majority of publications, where, as a rule, a cylindrical inductor is considered, whose length is much greater than its radius, in this work we  additionally considered the finite longitudinal size, in particular, we conducted an analysis for a short inductor.
9. VchD-3000 has been designed and produced for use as part of a series of RITs with ion beam dimensions ranging from 100 to 450 mm. The operation of the radio-frequency generator relies on the principle of the formation of signals with configurable frequencies using a low-power master clock generator with subsequent amplification in a wideband amplifier and in a power amplifier.
10. Our Laboratory has conducted tests of VChG-3000 using a calibrated resistive load comprised of a co-axial resistor with a resistance of 62 Ohm and a dissipated power of 1000 W. The tests have demonstrated that VChG-3000 ensures the required power output with a resistive load in the researched frequency range while the maximum non-linearity of the indicators of the level of radio-frequency power, according to data from the dial instrument of the generator in the whole range of frequencies and power outputs, does not exceed 15 per cent.
11. The laboratory sample of VChG-3000 can be used to refine a series of RITs with ion beam dimensions ranging from 100 to 450 mm in field conditions. The thruster was placed outside of the vacuum chamber and radio-frequency energy was provided over feeder lines. If a thruster is placed on the flange with bulkhead connectors for the inductor, the control system is placed outside of the vacuum chamber. If a thruster is placed directly in the vacuum chamber, the control system is also placed in the vacuum chamber in the direct vicinity of the inductor outputs.
12. Using the VChG-3000 test rig, we have conducted a research of the operation modes of VChID-10 for three operation frequencies and three values of fuel volume flow rate. For each of the above-mentioned modes, we changed the current on the inductor while simultaneously controlling the current of the beam. It has been demonstrated that by regulating the output power of the generator it is possible to change the current of the beam from 20 mA to 190 mA, which completely covers the possible operation modes of VChID-10.
13. A methodology has been developed for the measurement of the parameters of electromagnetic fields created by the operation of RITs in the frequency range between 1 and 18 GHz. The methodology is based on the measurement of the power of the noise process (occurring during the operation of RITs) at the output of the measuring antenna with subsequent re-calculation as electric-field strength in the aperture of the antenna. The measurements were made in the whole range of frequencies of the measuring antenna and are represented as graphs of dependencies of the absolute values of the intensity of the electric field on the frequency.
14. The developed methodology for the measurement of the parameters of electromagnetic fields created by the operation of RITs is an efficient tool for the research of the noise emission of a series of RITs with the dimensions of the ion beam dimensions ranging from 100 to 450 mm. Using this methodology, it is possible to research the noise emission of RITs for the problems of electromagnetic compatibility to determine the degree of their influence on onboard systems of spacecraft.
15. A methodology has been presented for the optimization of multi-orbit trajectories of spacecraft with sustainer electric propulsion units. In contrast with the results presented in earlier reports, the proposed methodology features the use of a precise unaveraged mathematical model of the unperturbed optimal movement of spacecraft. Mathematical models and methods have been developed for the modeling of perturbed quasi-optimal flight trajectories using the stable quasi-optimal control mode with feedback proposed earlier. Our researchers have presented a comparative analysis of the use of radio-frequency ion thrusters and stationary plasma thrusters installed on modern and future spacecraft. Recommendations have been compiled on the scope of the applicability of RITs. It turned out that a promising area of use of RITs with electrical outputs of 2 – 3 kW is their use as part of the trajectory correction electric propulsion units of geostationary spacecraft. In a number of cases, RITs with power outputs of about 5 kW can compete with the SPD-140D thruster in the task of raising spacecraft with electric sustainers to a geostationary orbit using a combined scheme with the possibility of increasing the duration of transport operations. Despite the fact that the specific impulse of RITs (as opposed to SPD-140D) is significantly higher than the optimal value for this task, the high efficiency factor of RITs allows to compensate for the losses caused by this in terms of the duration of the orbit insertion in case the parameters of the orbit of the separation from the upper stage are correctly optimized. Undoubtedly, one of the promising applications of high-power RITs (25…50 kW) is installation on future reusable interorbital transfer vehicles featuring megawatt-class transport and energy modules. It has been determined that one such vehicle will be able to fulfil the needs of modern commercial cargo delivery to the geostationary orbit performed by Russia in 5 to 6 years while reducing the number of required launches of carrier rockets by the factor of 2,33 to 3,75.
16. A mathematical model has been developed that describes an ion beam during its outflow into vacuum and allows to refine the requirements for radio-frequencyy ion sources intended for implementing the contactless method of deflection of space debris and develop source data for ballistic computations and modeling control of movement of  a service spacecraft.
17. Mathematical models have been developed that describe interaction of an ion beam with orbital debris close in shape to a parallelepiped or a cylinder in terms of shape in various angular orientations with respect to the ion beam.
18. We have determined the parameters of an electric rocket propulsion unit and an ion source that ensure efficient deflection of space debris with masses ranging from 750 to 2200 kg while the relative distance of the objects is 20 m or more.
19. The evolution of an orbit of a space debris object after deflection from the region of the geostationary orbit to a graveyard orbit has been investigated.
20. We have corrected software for ballistic computations accounting for a stricter model of  the interaction of a beam with space debris.
21. Computations have been conducted to deflect 10 space debris objects involving  repeated maneuvering accounting for the limitations of the stored volume of the operational body of the electric rocket propulsion unit and the ion beam injection system.

Implemented results of research:

• The results of our research have been used in R&D for the Federal space programme of the Russian Federation for 2016 – 2025 designated by the Decree of the Government of the Russian Federation No. 230 of 23 March 2016. The following parts of the programme have been already implemented or are currently being implemented:: «Stability», «Sheet music», «Spacecraft propulsion units», «Afterburner», «Refinement», «ISS operations» and others.
• «Information Satellite Systems Reshetnev» JSC has purchased rights for the patent «Gas-electric isolation of a gas-discharge unit of an ion source and a method for manufacturing base parts thereof».
• Patent RU 2 752 857 C1 – IPC: H01J 27/00, H05H 1/54, F03H 1/00. – Application of 12 August 2021. Published on 11 August 2021 Authors: Andrey I Mogulkin, Victor V. Balashov, Vladislav V. Nigmatzyamov, Oleg D. Peysakhovich, Valentin A. Ryabiy, Viktoriya V. Svotina, Serget A. Sitnikov. 

Education and career development:

• 14 bachelor's degree theses, 3 Doctor of Science and 16 Candidate of Science   dissertations have been prepared and defended.

• The Laboratory regularly conducts summer internships of students of the institute No. 2 «Aircraft, rocket engines and power units» of the Moscow Aviation Institute. 

Organizational and structural changes: 

We have modernized and retrofitted the experimental benches that allow to practice and research the operational processes of electric rocket thrusters with power outputs of up to 50 kW that support deep vacuum while expending 30 mg of the Xe working substance per second. The experimental bench was equipped with electric power supply systems necessary for the operation of RITs, systems supplying working gas to thrusters working in the chamber, systems for measuring the main parameters of thrusters (power consumption, working gas consumption, produced thrust and others), systems for automated accumulation of experimental data. 

Collaborations:

Justus Liebig University Giessen: (Germany): collaboration for the assessment of thermal fields of RITs with diameters of the operational part of 80 mm, as well as the delivery of a power supply system, a source control system and a RIM-20 source itself.