RF Helicon-based Inductive Plasma Thruster (IPT) Design for an Atmosphere-Breathing Electric Propulsion system (ABEP) (2007.06397v2)

Abstract: Challenging space missions include those at very low altitudes, where the atmosphere is source of aerodynamic drag on the spacecraft. To extend such missions lifetime, an efficient propulsion system is required. One solution is Atmosphere-Breathing Electric Propulsion (ABEP). It collects atmospheric particles to be used as propellant for an electric thruster. The system would minimize the requirement of limited propellant availability and can also be applied to any planet with atmosphere, enabling new mission at low altitude ranges for longer times. Challenging is also the presence of reactive chemical species, such as atomic oxygen in Earth orbit. Such species cause erosion of (not only) propulsion system components, i.e. acceleration grids, electrodes, and discharge channels of conventional EP systems. IRS is developing within the DISCOVERER project, an intake and a thruster for an ABEP system. The paper describes the design and implementation of the RF helicon-based inductive plasma thruster (IPT). This paper deals in particular with the design and implementation of a novel antenna called the birdcage antenna, a device well known in magnetic resonance imaging (MRI), and also lately employed for helicon-wave based plasma sources in fusion research. The IPT is based on RF electrodeless operation aided by an externally applied static magnetic field. The IPT is composed by an antenna, a discharge channel, a movable injector, and a solenoid. By changing the operational parameters along with the novel antenna design, the aim is to minimize losses in the RF circuit, and accelerate a quasi-neutral plasma plume. This is also to be aided by the formation of helicon waves within the plasma that are to improve the overall efficiency and achieve higher exhaust velocities. Finally, the designed IPT with a particular focus on the birdcage antenna design procedure is presented

• The paper introduces an innovative RF helicon-based IPT design that employs a birdcage antenna for efficient plasma ionization in ABEP systems.
• The paper details numerical simulations using XFdtd® to optimize antenna resonance and helicon wave formation for improved thrust production.
• The paper demonstrates that utilizing in-situ atmospheric particles significantly reduces onboard propellant needs while extending mission lifetimes in VLEO.

Overview of the RF Helicon-Based Inductive Plasma Thruster for Atmosphere-Breathing Electric Propulsion Systems

The paper presents a comprehensive design and implementation analysis of an RF helicon-based inductive plasma thruster (IPT) proposed as a cornerstone technology for Atmosphere-Breathing Electric Propulsion (ABEP) systems. Developed by researchers at the Institute of Space Systems (IRS), within the framework of the DISCOVERER project, this paper examines how IPT could enhance spacecraft missions in very low Earth orbits (VLEO), which necessitate propulsion systems adept at compensating significant atmospheric drag without reliance on large quantities of onboard propellant.

Design and Theoretical Implications

The IPT's design capitalizes on a novel application of the birdcage antenna—an innovation typically employed in magnetic resonance imaging. This specific antenna design, coupled with an RF electrodeless operational mode, functions to ionize atmospheric particles gathered by the ABEP system, subsequently accelerating them to produce thrust while maintaining a quasi-neutral plasma plume. Such design mitigates the traditional erosion challenges of thrust components seen with reactive species like atomic oxygen, especially relevant for prolonged missions at VLEO where atmospheric gases such as \ce{N2} and \ce{O} are prevalent.

Numerical and Engineering Insights

The implementation of the birdcage antenna, which operates at a targeted frequency of 40.68 MHz, aims to optimize RF circuit energy transfer while minimizing losses. The IPT's architecture is supported by the use of numerical tools like XFdtd® for modeling electromagnetic interactions, ensuring resonance of the antenna's EM field. The antenna resonance induces helicon waves within the plasma, thus enhancing ionization efficiency and aiding the acceleration mechanism. The inclusion of a static magnetic field completes the operational configuration, creating favorable conditions for helicon wave formation and resultant efficient thrust production without the need for a neutraliser.

Operational and Practical Implications

The paper's results underscore the IPT’s ability to function continuously in VLEO by utilizing in-situ atmospheric particles as propellant, thereby substantially reducing mission propellant requirements and extending operational lifetimes. This technology has broader implications for exploring other planetary atmospheres, enabling new mission profiles that were previously limited by propellant storage constraints.

Future Directions and Speculations

Looking ahead, the integration of IPT into ABEP systems suggests transformative changes in spacecraft propulsion capabilities, particularly for long-duration missions and applications requiring sustained low thrust. Further experimental validation and in-space demonstrations would bolster confidence in transitioning from theoretical design to practical deployment. Advances in materials resistant to atomic oxygen erosion and adaptive control of plasma dynamics will further enhance system reliability and performance.

This work not only contributes to the specific field of electric space propulsion but also sets the stage for interdisciplinary collaborations aiming to leverage atmospheric resources in various planetary environments. Future research could explore hybrid systems incorporating IPTs for flexibility across mission stages and environments, delivering scalable propulsion solutions across a range of mission architectures.