The transition from old space to new space along with increasing commercialization has a major impact on space flight, in general, and on electric propulsion (EP) by ion thrusters, in particular Ion thrusters are nowadays used as primary propulsion systems in space This article describes how these changes related to new space affect various aspects that are important for the development of EP systems Starting with a historical overview of the development of space flight and of the technology of EP systems, a number of important missions with EP and the underlying technologies are presented The focus of our discussion is the technology of the radio frequency ion thruster as a prominent member of the gridded ion engine family Based on this discussion, we give an overview of important research topics such as the search for alternative propellants, the development of reliable neutralizer concepts based on novel insert materials, as well as promising neutralizer-free propulsion concepts In addition, aspects of thruster modeling and requirements for test facilities are discussed Furthermore, we address aspects of space electronics with regard to the development of highly efficient electronic components as well as aspects of electromagnetic compatibility and radiation hardness This article concludes with a presentation of the interaction of EP systems with the spacecraft

Ion thrusters for electric propulsion: Scientific issues developing a niche technology into a game changer.

Direct thrust measurements of an electron cyclotron resonance plasma thruster are performed with a thrust balance. The thruster performances are deduced, and the influence of power and mass-flow rate is studied. The measured thrust is around 1 mN for 50 W of microwave power input and 0.1  mg/s of xenon, corresponding to 1000 s of specific impulse and 11% of total efficiency. It is found that the thrust is increased by 25% when the walls of the plasma source are covered with a dielectric layer. Comparisons are made between the direct thrust measurements and the indirect thrust measurements obtained with electrostatic probes in the plasma beam.

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Direct Thrust Measurement of an Electron Cyclotron Resonance Plasma Thruster

This paper presents the development of an electrostatic calibration system that produces consistent and reproducible calibration force over three orders of magnitude in the range 30 $\mu \text{N}$ –3.4 mN with a deviation error of less than 2%. In the proposed approach, the electrostatic force is generated using a pair of heat sinks that is electrically charged with high voltage and engaged at a particular distance. Precise control of the high-voltage pulses applied to the calibrator produces calibration impulse bit in the range 7–340 $\mu $ Ns. The calibrator is used to tune a torsional thrust stand that performs measurements of constant and impulsive force from any micropropulsion system.

Development of an Electrostatic Calibration System for a Torsional Micronewton Thrust Stand

Operations of a three-channel 100-kW class nested Hall thruster at total power levels from 5 to 102 kW and discharge currents from 16 to 247 A were successful. The thruster was operated in all seven available channel combinations at discharge voltages of 300, 400, and 500 V and at current densities that were 0.60 and 0.95 of the nominal value. Additional test points were also collected at 1.20 the nominal current density. The thruster was throttled through a total of forty-six unique operating conditions. At each condition, thruster performance was measured using a high-power thrust stand designed to measure up to 8 N of thrust. From these thrust measurements, specific impulse and efficiency were calculated. All seven channel combinations showed similar performance at a given discharge voltage and current density. The largest thrust recorded was 5.42 N at 99 kW, 400 V discharge voltage. Total efficiency values 0.54 to 0.67, and total specific impulse ranged from 1800 seconds to 2650 seconds. Discharge current oscillations were also measured. Generally these oscillations increased on the inner and middle channels during multi-channel mode but stayed roughly a constant fraction of the channel discharge current for the outer channel in both single- and multi-channel operation. We also found that the thrust of the three channels firing together was not significantly higher than the sum of each channel _ring individually, a result that differs from what was found previously for nested Hall thrusters.

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High-Power Performance of a 100-kW Class Nested Hall Thruster

The performance of many Hall thrusters has been shown to exhibit sensitivity to background pressure in ground-based test facilities, and this property can have an impact on the prediction of in-spa...

Effects of Background Pressure on SPT-140 Hall Thruster Performance

The accurate, direct measurement of thrust or impulse is one of the most critical elements of electric thruster characterization, and it is one of the most difficult measurements to make. This pape...

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Recommended Practice for Thrust Measurement in Electric Propulsion Testing

Accurate, direct measurement of thrust or impulse is one of the most critical elements of electric thruster characterization, and one of the most difficult measurements to make. The American Institute of Aeronautics and Astronautics has started an initiative to develop standards for many important measurement processes in electric propulsion, including thrust measurements. This paper summarizes recommended practices for the design, calibration, and operation of pendulum thrust stands, which are widely recognized as the best approach for measuring micro N- to mN-level thrust and micro Ns-level impulse bits. The fundamentals of pendulum thrust stand operation are reviewed, along with its implementation in hanging pendulum, inverted pendulum, and torsional balance configurations. Methods of calibration and recommendations for calibration processes are presented. Sources of error are identified and methods for data processing and uncertainty analysis are discussed. This review is intended to be the first step toward a recommended practices document to help the community produce high quality thrust measurements.

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Joseph Blakely

Papers

Recommended Practice for Thrust Measurement in Electric Propulsion Testing

Recommended Practices in Thrust Measurements