This work describes the scaling and design attributes of Nested Hall Thrusters (NHT) with extremely large operational envelopes, including a wide range of throttleability in power and specific impulse at high efficiency (>50%). NHTs have the potential to provide the game changing performance, power-processing capabilities, and cost effectiveness required to enable missions that cannot otherwise be accomplished. NHTs were first identified in the electric propulsion community as a path to 100-kW class thrusters for human missions. This study aimed to identify the performance capabilities NHTs can provide for NASA robotic and human missions, with an emphasis on 10-kW class thrusters well-suited for robotic exploration. A key outcome of this work has been the identification of NHTs as nearly constant-efficiency devices over large power throttling ratios, especially in direct-drive power systems. NHT systems sized for robotic solar system exploration are predicted to be capable of high-efficiency operation over nearly their entire power throttling range.
A traditional Annular Hall Thruster (AHT) consists of a single annular discharge chamber where the propellant is ionized and accelerated. In an NHT, multiple annular channels are concentrically stacked. The channels can be operated in unison or individually depending on the available power or required performance. When throttling an AHT, performance must be sacrificed since a single channel cannot satisfy the diverse design attributes needed to maintain high thrust efficiency. NHTs can satisfy these requirements by varying which channels are operated and thereby offer significant benefits in terms of thruster performance, especially under deep power throttling conditions where the efficiency of an AHT suffers since a single channel can only operate efficiently (>50%) over a narrow power throttling ratio (3:1).
Designs for 10-kW class NHTs were developed and compared with AHT systems. Power processing systems were considered using either traditional Power Processing Units (PPU) or Direct Drive Units (DDU). In a PPU-based system, power from the solar arrays is transformed from the low voltage of the arrays to the high voltage needed by the thruster. In a DDU-based system, power from the solar arrays is fed to the thruster without conversion. DDU-based systems are attractive for their simplicity since they eliminate the most complex and expensive part of the propulsion system.
The results point to the strong potential of NHTs operating with either PPUs or DDUs to benefit robotic and human missions through their unprecedented power and specific impulse throttling capabilities. NHTs coupled to traditional PPUs are predicted to offer high-efficiency (>50%) power throttling ratios 320% greater than present capabilities, while NHTs with direct-drive power systems (DDU) could exceed existing capabilities by 340%. Because the NHT-DDU approach is implicitly low-cost, NHT-DDU technology has the potential to radically reduce the cost of SEP-enabled NASA missions while simultaneously enabling unprecedented performance capability.
This work was done by Richard R. Hofer of Caltech for NASA’s Jet Propulsion Laboratory. NPO-48400
This Brief includes a Technical Support Package (TSP).
High-Efficiency Nested Hall Thrusters for Robotic Solar System Exploration
(reference NPO-48400) is currently available for download from the TSP library.
Don't have an account?
Overview
The document discusses advancements in Solar Electric Propulsion (SEP) technology, specifically focusing on High-Efficiency Nested Hall Thrusters (NHTs) developed by NASA's Jet Propulsion Laboratory. These thrusters are designed to enhance the performance of robotic missions in deep space by offering significantly higher specific impulse compared to conventional chemical propulsion systems.
The primary objective of the research is to enable spacecraft to achieve high velocities necessary for ambitious missions, such as NASA's Dawn mission to the asteroids Vesta and Ceres, which requires velocities exceeding 11 km/s. The document emphasizes the importance of power throttling capabilities in Electric Propulsion (EP) systems, which must operate efficiently over a wide range of power levels, typically 10:1 or greater. Traditional Hall thrusters experience a drop in thrust efficiency and specific impulse at lower power levels, which can hinder mission performance.
The NHTs are coupled with Direct-Drive Units (DDUs) that convert low-voltage power from solar arrays (80-160 V) to the higher voltages required by the thrusters (150-800 V). The NHT-DDU configuration is noted for its superior performance, achieving over 40% efficiency across a broad power range (0.3-6.3 kW) and maintaining efficiencies greater than 50% at higher power levels. This results in a predicted 340% improvement in power throttling ratios compared to existing technologies.
The document highlights the potential of NHTs, whether paired with traditional Power Processing Units (PPUs) or DDUs, to revolutionize space missions by providing unprecedented power and specific impulse throttling capabilities. The findings suggest that NHTs could enable 100-kW class thrusters for human missions, significantly enhancing the feasibility and efficiency of future space exploration endeavors.
In conclusion, the research underscores the transformative impact of NHT technology on SEP systems, promising to reduce mission costs while simultaneously improving performance. This advancement is crucial for enabling more ambitious robotic and human exploration missions within our solar system, paving the way for future scientific discoveries. The document serves as a technical support package, providing insights into the development and potential applications of this innovative propulsion technology.
