This project seeks to understand how non-equilibrium plasma chemistry influences the nonlinear behavior of molecular plasma flows under conditions relevant to electric propulsion applications. Experiments will be performed on our modular radio frequency (RF) plasma test cell with an adaptive magnetic field geometry and multi-gas mixing manifold and injector. Infrared laser absorption spectroscopy will be used to examine how molecular plasma chemistry influences nonlinear RF helicon mode transitions. Particular emphasis will be given to understanding how the additional reaction pathways influence mass and energy transport near the mode transition onset. As the capabilities of the RF test cell mature, additional nonlinear dynamics will be explored including natural and driven oscillations. 

SPACE Lab’s neutral beam source will be used to expose advanced, low-drag spacecraft coatings to high-velocity atomic oxygen flows characteristic of LEO-like environments. To minimize background pressure effects, the neutral beam source will be moved to a recently completed, high-pumping-speed vacuum chamber (STF 2). Early work will focus on characterizing the beam quality and AO fluence using a variety of diagnostics. Drag and erosion measurements will then be completed for samples prepared in the Bergsman Research Lab. Finally, to examine the coupled processes of AO exposure and thermal cycling, in situ thermal cycling (from -35 C to +70 C) of the sample will be performed between AO exposure tests.

This project will provide the first detailed investigation and proof-of-concept of inductive pulsed plasma thrusters (IPPTs) for air-breathing electric propulsion (ABEP). Our research approach combines reduced-order modeling with laboratory experimentation to examine the fundamental physics, scaling, and performance of AB-IPPTs for vLEO spacecraft. Key open questions that will be examined include: how does air plasma chemistry influence current sheet formation and thruster optimization? What are the dominant power loss mechanisms for an AB-IPPT? How does performance (Isp, thrust-to-drag, etc.) scale with altitude? What limits thruster lifetime? The resulting discoveries will provide the foundational knowledge needed to develop and test a proof-of-concept thruster for ABEP applications.

This project seeks to provide proof-of-concept for a self-neutralizing surface-mount electric thruster. Self-neutralization refers to an exhaust plume that consists of equal parts positive and negative ions. This capability removes the need for a neutralizing hollow cathode, drastically simplifying the system and improving robustness to atmospheric oxygen. To avoid this problem, are researching a new thruster architecture that combines elements of a dielectric barrier discharge (DBD) with those of a Hall effect thruster (HET). To achieve the necessary flows, we apply a magnetic field perpendicular to the DBD electrodes that strengthens the electric field and confines it to a narrow region optimized for ion acceleration. Tuning of the DBD voltage waveform (dV/dt) allows control over both the direction of the accelerating electric field and electron temperature, and therefore also the negative and positive ion production and acceleration rates.

This project seeks to understand and leverage mini-magnetospheres as a means to extract useful quantities of power from the action of the solar wind against Lunar magnetic anomalies. The interaction between the solar wind and Lunar magnetic anomalies generates small-scale (~100’s of km) magnetospheric plasma structures. A key feature of these structures is a relatively strong (~0.1-1 V/m) polarization electric field. It is possible to extract power from this field using electrodes placed on either side of the potential drop, however, the current draw would be severely limited due to low solar wind particle fluxes in this region. To overcome this challenge, we are researching a novel configuration wherein a virtual plasma cathode is used to increase current draw by many orders of magnitude.

This project focuses on the use of machine learning for optimizing electric thrusters. An active control system, capable of mapping and optimizing Hall thrusters, has been built to quickly and efficiently characterize thruster systems. To facilitate this, a novel rapid thrust measurement technique was developed to enable thrust measurements at significantly faster rates compared to traditional methods. This allows for fast and accurate thrust measurement while minimizing the effects of long-term thermal drift. Fast mapping of a Hall thruster’s operation was demonstrated at 72 test points per hour, a significant improvement over standard IVB mapping techniques. The combination of rapid thrust measurement and thruster-in-the-loop control were used to automate thruster optimization. Various optimization schemes are currently being tested.

The erosion of ceramic channel insulators in Hall thrusters has been the most dominant cause of end-of-life since the first Hall thrusters first flew in 1971. Recent developments in magnetic shielding, a new magnetic field geometry where field lines are tangential to the insulator at the front of the thruster, have reduced channel erosion to negligible levels. However, the switch to a magnetically shielded configuration significantly increases plume divergence and creates complex optimizations of the field geometry. The ACME thruster has adjustable pole, anode, and cathode positioning to allow for significant changes while maintaining the shielded shape, allowing magnetic shielding across a variety of geometries. The influence of the inner magnetic pole position on thruster performance has been investigated with Faraday probe, retarding potential analyzer, and thrust stand measurements.