Optimization, Test and Diagnostics of Miniaturized Hall Thrusters

The overall goal of this presentation, is to present the methodology involved in the testing of specialized electric propulsion thrusters in a ground based space environment simulation facility. The methods involved feature automated systems which incorporate hardware-software integration to realize smart systems for automated or remote diagnostics and performance evaluation of propulsion modules and other payloads in space. The space propulsion center, Singapore, is a research center at the National Institute of Education, Nanyang Technological University, Singapore.

The test environments developed here include two space environment simulation facilities for different purposes. The scaled space environment simulator is primally employed in lifetime testing of thrusters. Thrusters are fired for extended periods of time in this facility to evaluate effects of plasma damage on distress channels.

and subsequently to infer the lifetime of the thrusters. The quadfilar suspended stage allows for proper visualization of how the propulsion modules as mounted on different payloads may influence in situ maneuver in space. This is simulated through the mounting and suspension of the entire payload on the suspended system.

The thrusters can then be fired and the suspended platform where the modules are mounted on are actuated according to conditions in space. The quadfilar pendulum also expedites the process of leveling, calibration and installation of thrusters and modules for testing in the space environment. With this setup only one operator is required in the test facility to utilize frequency modulation on the torsional wires, to level and calibrate the entire system.

In the large scale space environment simulator apart from the quadfilar suspended thrust stage that enables the in situ derivation of thrust, Modular spatially actuated robotic probes can also be customized for mounting through configurable attachment units. It is also worth noting that the large Space Environment Facility features numerous mounting points and vacuum grip electronic filters to allow for the installation of multiple thrusters and diagnostic equipment for simultaneous performance evaluation. This reduces the downtime incurred when the chamber is evacuated and pumped during access installation and reconfiguration processes if testing were to be done individually.

We will now go through the procedures for installation and calibration of the quadfilar pendulum before testing of propulsion units. First, ensure that all components are installed in the chamber as required for subsequent testing. Test the connectivity of the diagnostic tools externally before sealing the chamber.

Use the integrated facility control to seal the chamber. Turn on the vacuum pumps in cascading order starting from the dry pumps, turbo molecular pumps and then the cryogenic pumps. Use the developed apps to synchronize your devices with the wireless transponders in the chamber.

The synchronization process is complete, when the flashing LED on the transponders stop flashing. Once the desired vacuum has been obtained and initial reading is taken off the laser displacement sensor as a baseline. Use the developed app to trigger the lowering of a calibrated weight for force translation on the quadfilar stage.

Record the displacement from the laser displacement sensor. Repeat the process of lowering the weights and recording of the displacement quadfilar stage until all the calibration weights are expended. Draw a calibration curve to obtain the calibration factor for the system installed on the quadfilar stage.

The thrusters can then be fired and the desired parameters can be captured in real time by data acquisition program written by in house researchers. Alternatively an integrated app can be used to fully automate the calibration process while syncing the actuation sequence from the motors and data acquisition from the sensors accordingly. We will now go through the procedures for independently verifying the obtained thrust parameters to a null measurement and how a spatially actuated proxy can be triggered to obtain plume profiles after thrust measurements have been made.

First, take a baseline reading of the quadfilar pendulum in the equilibrium position. Toggle operational parameters to desired values from the thruster control panel and fire the thruster. Once the trust is fired, wait for the oscillations on the quadfilar pendulum to stabilize.

After stabilization, use the control app for the null measurement system to trigger the lowering of weights. The weights are continually lowered until the quadfilar stage is actuated back into equilibrium. Once the equilibrium position is reached, the actuation sequence is terminated and the force required to bring the quadfilar system back to equilibrium is determined.

A stopper block is then triggered to stop the quadfilar stage from moving. A sweeping sequence is then performed on the spatial measurement probe mount. A synchronized sequence is looped to acquire data from the probe at each spatial location and stored in an array to be analyzed accordingly.

Other probes can be customized to be mounted on the modular attachment to use spatial information on the plume profiles. In this section we will go through typical results obtained from a calibration sequence, as well as typical plume profiles obtained through a faraday probe sweep. Calibration of the quadfilar thrust to measurement stage is done through the employment of that probe motor driven for the translation system.

In order to derive the calibration factors required for derivation of thrust during experimental tasking. A sequence it triggered by an operator of an automated program to lower fine calibration weights that act vertically and translates horizontally to simulate actuation when the thruster is fired. Readings from a high resolution laser displacement sensor are taken at each interval and a calibration curve is then drawn to obtain the calibration factor for subsequent measurements on the system.

In this figure, we see a typical calibration curve drawn during a single automated calibration process. As can be seen, the proper alignment and setup of the quadfilar stage results in a very linear calibration plot yielding a calibration factor of 27.65 milli newtons per volt. In a standardized set up for thrust measurements over a wide range of forces.

The setup can also be modified to fit in calibration weights for extended regimes as shown in this calibration plot. The torsional wires are adjusted for sensitivity and both fine and course calibration weights are included to yield a calibration plot that is linear in both regimes. A sample of the in situ measurements for derived thrust is shown in this figure.

This figure shows how an operator is able to monitor the dependence of thrust on discharge voltage. During the course of the experiment, until the discharge is extinguished. Using the quadfilar thrust measurements stage, we were able to measure the thrust produced by the whole thruster at various input power given by the discharge current and applied voltage.

Through these information, the variation of efficiency and specific impulse with respect to input power can be obtained. These figures show how the thrust and specific impulse vary with input power at four different mass flow rates. And this figure shows how the efficiency depends on the input power.

The results show that the thruster has been optimized to work at input power is below 100 watts, where low flow rates have resulted in efficiencies of almost 30%After the thruster is fired a null measurement sequences is triggered to independently verify the trust obtained from the system. When the thrust is fired, the stage displaces according to the magnitude of propulsion derived out of the system. The null measurement unit is a symmetric system mounted opposite calibration unit, which utilizes a similar force translation system to actuate the stage back into equilibrium.

A laser displacement sensor actively monitors the displacement throughout the measurement and triggers the activation system to activate a sequence which terminates only when baseline equilibrium is achieved. An operator is also able to visualize the in situ plume profiles as shown in this figure. This figure shows how the discharge power influences the magnitude of the peak iron current density and the full width at half maximum accordingly.

Physical processes that are intrinsic to plasma's are known to drive and control self organization and self assembly during material synthesis. at QUT in collaboration with plasma sources and application center, we study how these building blocks are formed, shaped and delivered to surfaces on the different plasma conditions. We hope that by understanding how these plasma form nano structures behave we will be able to design processes that ensure the timely and efficient delivery and incorporation only to add the site where the repair is actually needed.

Providing us with a plasma propulsion systems that are longer serving and more efficient. In this presentation we have presented an overview of the considerations made when designing a facility for testing of propulsion systems and deployable modules in a simulated space environment. Additionally, we have shown the versatility and strengths of using micro controller based systems for in situ data acquisition and analytics, which can be rapidly adapted to perform other modes of evaluation depending on operational mission demands accordingly.