Vacuum Arc Thrusters Research Articles

Implementation of direct battery driven discharge in triggerless operation of vacuum arc thrusters

The increasing demand for CubeSat missions with limited budgets and constrained timelines necessitates the development of innovative propulsion systems. This paper focuses on vacuum arc thrusters (VATs) and investigates the implementation of battery-driven discharge for triggerless firing. VATs offer a promising alternative for CubeSat propulsion, generating thrust through the pulsed ejection of plasma in a cathode arc discharge. The study explores the feasibility of direct battery-driven discharge in VATs and demonstrates stable and variable-duration pulses. Experimental testing using high C-rating lithium-ion (Li-ion) batteries showcase the advantages and operational benefits of this approach. The results highlight the potential for variable energy pulses, precise control of thrust impulse bit, and improved performance compared to capacitor-driven systems. Future research directions include optimising pulse duration for enhanced lifetime, plume analysis, and erosion rate investigations. The implementation of VATs with battery-driven discharge presents a promising solution to enhance the performance and reliability of CubeSat propulsion systems while ensuring compliance with space sustainability guidelines.

Broadband (kHz–GHz) characterization of instabilities in vacuum arc thruster inside a metallic vacuum chamber

The aim of this paper is to explore the possibility of simultaneously characterizing instabilities in vacuum arc thrusters on a broadband frequency range (kHz–GHz) in situ, meaning in a conventionally used vacuum chamber where vacuum arc thrusters are usually operated. We show in this paper that, despite the reverberant nature of the vacuum metallic chamber, useful information is extracted over a large frequency range from the measurements done with an antenna in this environment. This leads to the first characterization of the self-emission of a vacuum arc thruster in the GHz frequency range.

Space‐charge‐limited current of vacuum arc thruster

AbstractTo optimize thrust performance, the expression of space‐charge‐limited current for vacuum arc thruster is derived from Poisson's equation. The commonly used ring‐type and coaxial‐type vacuum arc thrusters are simplified to the equivalent current sheet in planar geometry and cylindrical capacitor, respectively, for this calculation. Both the spatial distribution and peak magnitude of space‐charge‐limited current are given explicitly, together with their dependences on gap distance, applied voltage, charge number, and ion mass. For typical experimental parameters of the vacuum arc thruster, it is shown that the maximum current density drops significantly when the gap distance becomes large and grows when the applied voltage increases; moreover, a cathode material of lower atomic weight yields a higher current density. The expressions of total current for these two types of vacuum arc thruster are also presented. This work, to our best knowledge, is the first application of space‐charge‐limited current to the vacuum arc thruster and practically very interesting for engineering design.

Discharge characterization of a multi-anode electrode geometry for vacuum arc thruster

Vacuum arc thrusters (VATs) have the potential to be used in nanosatellites and a multi-anode electrode geometry (MAEG) suitable for VATs is proposed in this paper. A unique electric field distribution is formed in the MAEG because of its anode configuration, which is different from conventional electrode geometry (CEG). There exists a region where the electric field vector has opposite directions in the electrode geometry. This region affects the directional drift of electrons in the initial stage of the discharge, thereby changing the process of vacuum breakdown. The variation of the discharge process affects the generation and propagation mechanism of the plasma, forming a plasma plume in favor of the propulsion performance of thrusters. The photographs of the plasma plume are captured and the electron density distributions are measured, which prove the pinch effect on the plasma plume of the MAEG. The propulsion performance of MAEG VATs is found to be superior to CEG VATs with the same discharge condition and increases radically with the increase of discharge power. The impulse bit and thrust-to-power ratio of MAEG VATs have been found to increase by a factor of 26 and 4.5 at most compared with the CEG VAT. It is found that MAEG VATs have a potential application advantage in the field of nanosatellite propulsion.

Micro-propulsion based on vacuum arcs

Micropropulsion systems are rapidly gaining attention from the small satellite community as they can increase the mission lifetime and allow the satellite to perform complex maneuvers and precise attitude control. These systems need to be fully operational with the low power available on satellites. Various thruster concepts based on vacuum arcs are currently under development, predominantly in the pulsed regime due to the power constraints on small spacecraft. Pulsed vacuum arc thrusters are capable of efficiently producing highly-ionized supersonic plasma at very low average power. This Perspective article provides a critical analysis and a review of various aspects of electric propulsion technology based on vacuum arcs. Furthermore, we give a personal assessment of the present status and provide an outlook on the field, including the growing role in small satellites such as CubeSats. Vacuum arc micropropulsion systems could play an important role in mitigating the problem of space debris. Such a system could be integrated with a satellite so that, at the end of its mission and using metal components as solid fuel, it will lower the satellite’s orbit and accelerate reentrance into the atmosphere faster than by its natural decay rate.

A “self-triggered” arc initiation applied in vacuum arc thrusters

The low-voltage vacuum arc initiation is of great importance for the optimization of vacuum arc thrusters (VATs). A low-voltage trigger method is proposed in this paper, which is called “self-triggered” arc initiation. This method uses a special surface flashover to generate the initial plasma and initiate the vacuum metal arc. A carbon fiber material is adopted as the trigger electrode due to its excellent field emission characteristics and it is arranged in series with a current-limiting resistance to avoid the damage caused by a heavy arc current. The experimental results show that this method is able to reduce the arc initiation voltage to several hundred volts, which is below 8% of the vacuum gap breakdown voltage. It has also been found that this trigger method is highly reliable and the trigger number of 104 with a low-melting-point material (Pb) has been performed. In addition, this method is proved to have no effect on the plasma generation characteristics and the impulse bit of the VATs. Therefore, the “self-triggered” method is able to achieve the similar trigger effect with other trigger methods in VATs. It provides an alternative choice for the further optimization of VATs in terms of quality and volume.

Influence of Cathode Shape on Vacuum Arc Thruster Performance and Operation

Vacuum arc thrusters (VATs) are a potentially useful technology for use as microthrusters, given their simplicity, low mass, and low-power requirements. However, further development is still needed to improve and mature their performance and operation. In an effort to improve thruster characteristics, we investigate the use of conically shaped convergent cathode surface profiles in a low-power coaxial VAT design. Experimental measurements of ion current density distribution, thrust, and erosion rate were taken for a range of cathode profiles and materials. Results show that modifying the profile of the cathode face can affect the plasma jet's plume distribution and even improve thrust production in certain cases. One likely cause of the thrust improvement is speculated to be increased charge exchange collisions resulting in a lower average ion charge state of the ejecting plasma.

Direct thrust measurement stand with improved operation and force calibration technique for performance testing of pulsed micro-thrusters

A robust stand for directly measuring pulsed thrust from micro-thrusters is presented. The method of electrostatic discs for in situ calibration was improved upon and simplified to allow convenient and accurate thrust measurement. The novel use of frictionless liquid gallium metal power interfaces for µN-level force measurement stands was also demonstrated. A series of detailed verification tests were performed to characterize the thrust stand’s overall operating range and accuracy. The stand can test single and multiple thrusters with a total mass of up to 10 kg and was found to be capable of resolving impulse bits between 0.27–600 µNs with 2–4% error in the optimal deflection range. Demonstration of the thrust stand’s capability and resilience to electromagnetic interference was accomplished by performing lifetime thrust tests on low-power Vacuum-Arc Thrusters operating with three different cathode fuels.

Determining Vacuum-Arc Thruster Performance Using a Cathode-Spot Model

A simple model of the vacuum-arc cathode-spot and plasma region was developed to predict the performance of vacuum-arc thrusters operating roughly in the arc current range 80–300 A with thrust pulses 250 s. The conventional-based cathode-spot model predicts ion current, average ion velocity, and erosion rate to establish thruster performance. Vacuum-arc properties for a range of materials (Al, Ti, Cr, Fe, Ni, Cu, Ag, Pb, Bi) were determined as well as maximum arc spot currents for Ti, Cr, Fe, Ni, and Bi. Model results generally show good agreement with published data and predicted thruster performance is comparable to literature. Most values of ion-to-arc current ratio were within 10% of published experimental data, ion velocities within about 30%, and erosion rates were within roughly 50%, provided macroparticle ejection was low. The crucial role of the ion-to-arc current ratio on thruster performance is assessed.