This work was supported in part by OSTIn-SRP/EDB, the National Research Foundation (Singapore), Academic Research Fund AcRF Tier 1 RP 6/16 (Singapore), and the George Washington Institute for Nanotechnology (USA). I. L. acknowledges the support from the School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology.

Here we present the protocols for the thrust calibration procedure and performance evaluation, independent thrust verification via null measurement and plume profilometry through spatial in situ data sensing.
1. Thrust calibration procedure and thrust performance evaluation
<ol>
	<li>Ensure that all components are installed in the chamber as shown in Figure 5.</li>
	<li>Test the connectivity of the diagnostic tools externally before sealing the chamber.</li>
	<li>Use the integrated facility control to seal the chamber.</li>
	<li>Turn on the vacuum pumps in cascading order starting from the dry pumps (until the chamber reaches 1 Pa), turbo-molecular pumps (until it reaches ~5 x 10-4 Pa), and then the cryogenic pumps. 
	NOTE: PSAC is left to pump down to high vacuum (&#60; ~10-5 Pa) to simulate space environment. The protocol can be paused here.</li>
	<li>Use the developed apps to synchronize the devices with the wireless transponder in the chamber. The synchronization process is complete when the light-emitting diode (LED) on the transponder stops flashing.</li>
	<li>Once the desired vacuum has been obtained, take an initial reading (analog voltage) off the laser displacement sensor as a baseline.</li>
	<li>Use the developed app to trigger the lowering of a weight (of a precisely known and calibrated mass of copper loop) for force translation on the quadfilar stage. 
	NOTE: The mass of each copper loop depends on the intended sensitivity of the quadfilar stage being used. In this case, the mass of each copper loop was in the order of 100 mg for the extended calibration regime and 10 mg for the fine calibration regime. See the representative results for more information.</li>
	<li>Record the displacement (analog voltage) from the laser displacement sensor when it is triggered after the mass is fully lowered and its weight is translated into a horizontal force.</li>
	<li>Repeat the process (steps 1.7 and 1.8) of lowering the weights and recording of the displacement of the quadfilar stage until all the calibrations weights are expanded. All the weights will be automatically returned to the equilibrium position by the calibration unit after the sequence is completed to allow the quadfilar stage to reach an equilibrium position before thruster can be fired. Save the calibration factor ( File | Save as | &#34;Factor.txt&#34;).</li>
	<li>Draw a calibration curve to obtain the calibration factor for the system installed on the quadfilar stage, where the calibration factor (in mN/V) is the gradient of the force/voltage graph.</li>
	<li>Record a baseline analog voltage from the laser displacement sensor again before firing the thruster.</li>
	<li>Activate the in situ MATLAB program for calculating thrust instantaneously using Equation 3 (see the representative results) and input the calibration factor derived in step 1.9 ( File | Open | &#34;Factor.txt&#34;).</li>
	<li>The thrusters can then be fired again. Capture the desired parameters in real time using the in-house data acquisition program. 
	NOTE: Alternatively, an integrated app can be used to fully automate the calibration process while synchronizing the actuation sequence from the motors, and data acquisition from the sensors accordingly.</li>
</ol>
2. Null measurement protocol for independent thrust verification
<ol>
	<li>First, take a baseline (analog voltage) reading (from the laser displacement sensor) of the thruster in equilibrium position.</li>
	<li>Toggle operational parameters to desired values from the thruster control panel and fire the thruster.</li>
	<li>Once the thruster is fired, wait for the oscillations on the quadfilar pendulum to stabilize.</li>
	<li>After the quadfilar stabilizes to a steady state, use the control app for the null measurement system to trigger the lowering of weights. Readings from the laser displacement sensor are monitored simultaneously. The weights are continually lowered until the quadfilar stage is actuated back into equilibrium.</li>
	<li>Once the equilibrium position is reached, terminate the actuation sequence, and determine the force required to bring the quadfilar system back to equilibrium.</li>
	<li>Trigger a stopper block to stop the quadfilar stage from moving.</li>
	<li>Compute mass corresponding to the horizontal force required to pull the system back into equilibrium.</li>
</ol>
3. Actuation of robotic turrets for spatial in situ data sensing and plume profilometry
NOTE: During operation of the thruster, an operator may choose to actuate the system manually to desired angles to obtain plume characteristics at particular locations or trigger an automated sequence.
<ol>
	<li>Mount the thruster on a moving stage (as in the case of PSAC) before starting the experiment.</li>
	<li>Activate the stop-bar mechanism to prevent the stage from actuating during the experiment.</li>
	<li>Trigger the measurement protocol and servo motor to actuate the probe to the 0&#176; position.</li>
	<li>Acquire a measurement from the probe. 
	NOTE: Depending on the type of probes installed, the measurement processes can be varied according to the programmable sequence for obtaining complete spatial plume profiles of the discharge. (a) If a Faraday probe is mounted, a reading off a source meter is taken (where a bias of -30 V is continuously applied to the guard rings). (b) If a Langmuir probe is mounted, a sawtooth voltage waveform is supplied to the probe and the I-V characteristics are obtained and interpreted. (c) If an RPA is mounted, a sawtooth voltage waveform is applied to the discriminating grid, and the I-V characteristics are obtained and interpreted.</li>
	<li>Trigger the servo motor using the microcontroller, to move to the next angular position where the probe sequence is triggered to make a measurement again.</li>
	<li>Save the measurements in individually marked arrays in a data matrix.</li>
	<li>Repeat steps 3.5 and 3.6 until a full sweep up to 180&#176; has been performed, and the probe is brought back to 0&#176;.</li>
	<li>Analyze the saved data.</li>
</ol>

The authors declare no competing financial or other interests.

Typical Hall-type thrusters44 are relatively simple, cheap and highly efficient devices that could accelerate an ion flux to the velocities of several tens of km/s, providing thrust required for accelerating satellites and spacecraft, as well as for maneuvering, orientation, position and attitude control, and de-orbiting at the end of their operation service life. Application of Hall thrusters on satellites and other orbital payloads enhance mission lifetime, allow orbital transfer and formation/c...

Renewed interest in the space industry has in part been catalyzed by highly efficient electric propulsion systems that deliver enhanced mission capabilities at increasingly reduced launch costs1,2,3. Many different types of space electric propulsion devices have recently been proposed and tested4,5,6,7,8&#160;supported by the present-day interest in space exploration9,10. Among them, gridded ion11,12 and Hall-type thrusters13,14 are of primary interest due to their ability to reach very high efficiency of about 80%, exceeding that of any chemical thruster, including the most efficient oxygen-hydrogen systems, the efficiency of which is limited to about 5000 m/s by the principal physical laws15,16,17,18.
Comprehensive, reliable testing of miniaturized space thrusters typically requires a large complex of test facilities that include test chambers, vacuum facilities (pumps), control and diagnostics instruments, a system for measurement of plasma parameters19, and a wide range of auxiliary equipment that sustain the operation of the thruster, such as an electric power supply system, propellant supply unit, thrust measurement stand and many others20,21. Moreover, a typical space propulsion thruster consists of several units which separately influence the efficiency and service life of the whole thrust system, and therefore, could be tested both separately and as part of the thruster assembly22,23. This significantly complicates test procedures and implies long test periods24,25. Reliability of a thruster&#39;s cathode unit, as well as operation of thrusters when different propellants are used also requires special consideration26,27.
To quantify performance of an electric propulsion system, and to qualify modules for operational deployment in space missions, ground testing facilities which enable simulation of realistic space environments are needed for testing of multi-scaled propulsion units28,29,30. An example of such a system is a large scaled space environment simulation chamber located at the Space Propulsion Centre-Singapore (SPC-S, Figure 1a,b)31. When developing such a simulation environment, the following primary and secondary considerations need to be taken into account. Primary concerns are that the thus-created space environment must accurately and reliably simulate a realistic space environment, and the in-built diagnostic systems must provide precise and accurate diagnostics during performance evaluation of a system. Secondary concerns are that the simulated space environments must be highly customizable to enable rapid installation and testing of different propulsion and diagnostic modules, and the environment must be able to accommodate high throughput testing to optimize discharge and operational conditions of multiple units simultaneously.
Space environment simulators and pumping facilities
Here, we illustrate two simulation facilities at SPC-S that have been implemented for the testing of miniaturized electric propulsion systems, as well as integrated modules. These two facilities are of different scales, and primarily have different roles in the process of performance evaluation, as outlined below.
Large plasma space actuation chamber (PSAC)
The PSAC has dimensions of 4.75 m (Length) x 2.3 m (Diameter) and has a vacuum pumping suite which comprises of numerous high capacity pumps working in tandem. It is able to achieve a base pressure lower than 10-6 Pa. It has an integrated vacuum control readout and pump activation/purge system for evacuation and purging of the chamber. It is equipped with numerous customizable flanges, electrical feedthroughs and visual diagnostic portholes to provide line test facility. This, together with a full-suite of diagnostics capabilities mounted internally, allows it to be rapidly modified for multi-modal diagnostics. The scale of PSAC also allows for testing of completely integrated modules for applications in a simulated environment.
PSAC is the SPC-S flagship space environment simulation facility (Figure 1c,d). Its sheer size allows for testing of complete modules of up to a few U&#39;s mounted on a quadfilar stage. The advantage of this method would be in the real-time visualization of how the propulsion modules as mounted on different payloads may influence in situ maneuvering of payloads in space. This is simulated through the mounting and suspension of the entire payload on a proprietary quadfilar thrust measurement platform. The thruster can then be fired, and the suspended platform with the thruster and payload would be tested according to space conditions. Propellant gas feedstocks which enter the test environment via the electric propulsion modules are pumped out efficiently by the vacuum suite to ensure that the chamber&#39;s overall pressure is not altered, thus, maintaining a realistic space environment32,33,34. Furthermore, electric propulsion systems typically involve the production of plasmas and exploit the manipulation of trajectories of charged particles exiting the system in order to generate thrust35. In smaller simulation environments, the buildup of charge or plasma sheaths on the wall may affect the discharge performance through plasma-wall interactions due to its proximity to the propulsion system, especially for micropropulsion where typical thrust values are in the order of millinewtons. Therefore, special attention and emphasis must be made to account for and marginalize contributions from such factors36. The PSAC&#39;s large size minimizes plasma-wall interactions, rendering them negligible, giving a more accurate representation of discharge parameters and enabling monitoring of plume profiles in electric propulsion modules. The PSAC is typically used in full module evaluation and systems integration/optimization processes which allows for quick translation of thruster prototypes into operationally ready systems for ground testing in preparation for space qualification.
Scaled plasma space environment simulator (PSEC)
The PSEC has dimensions of 65 cm x 40 cm x 100 cm and has a vacuum pumping suite which comprises of six high capacity pumps working in tandem (dry vacuum pump, turbomolecular and cryo vacuum pumps). It is able to achieve a base pressure lower than 10-5 Pa when the whole pumping system is operating (all pumps are in use). Pressure and propellant flows are monitored in real-time through integrated mass flow readout boxes and pressure gauges. The PSEC is primarily employed in endurance testing of thrusters. Thrusters are fired for extended periods of time to evaluate effects of plasma damage on discharge channels and on its lifetime. Additionally, as shown in Figure 2,&#160;a complex gas flow controller network in this facility enables quick connection of other feedstock propellants to the cathode and anodes to test compatibility of thrusters with novel propellants and effects of the latter on thruster performance. This is of increased interest to research groups working on &#34;air-breathing&#34; electric thrusters utilizing novel propellants during operation.
Integrated diagnostic facilities (multi-modal diagnostics)
Different integrated diagnostic facilities, equipped with automated integrated robotic systems (AIRS-&#181;S)19,23, have been developed for the two systems in PSEC and PSAC to cater for diagnostics at different scales and purposes.
Integrated diagnostics in PSEC
The diagnostic tools in PSEC essentially hinge on real-time monitoring of discharge through extended operations. The quality management system monitors residual gas in the facility for contaminant species that arise from sputtering of material during a discharge. These trace amounts are quantitatively monitored over time to evaluate erosion rates of the discharge channel and electrodes of the thruster to estimate the thruster&#39;s lifetime. The optical emissions spectrometer (OES) complements this procedure by monitoring spectral lines corresponding to electronic transitions of contaminant species due to erosion, such as copper from the electronics. OES also enables non-invasive plasma diagnostics and active monitoring of plume profile which qualitatively evaluates performance of the thruster. Finally, a robotic Faraday probe which can be controlled remotely, or set to fully autonomous mode, is used to derive quick sweeps of the plume profile to optimize collimation of beam through parametrically varying discharge conditions (Figure 3).
Integrated diagnostics in PSAC 
The luxury of physical space in the PSAC enables installation of multiple thruster systems at various locations due to its modular design, allowing for plug-and-play-like installation for various diagnostics simultaneously. Figure 4 shows the internal cross-section of the PSAC in various configurations, with the fully suspended quadfilar thrust measurement platform being its most notable and permanent fixture. Turret systems, controlled autonomously or wirelessly via Android apps using microcontrollers and Bluetooth modules, can then be mounted in a modular manner facing the thruster to obtain characteristics of the plume through the installation of various probes such as Faraday, Langmuir and Retarding Potential Analyzer (RPA). Also shown in Figure 4 is the ability of the PSAC to allow for configurable mounting of thruster systems for rapid simultaneous diagnostics of various plasma parameters. The thrusters can be mounted vertically in a single column and tested rapidly, one after another to avoid interactions between the different thruster systems. It has been verified that efficient evaluation of up to 3 different modules at a single instance is possible, thus significantly reducing the downtime during evacuation and purging processes required otherwise when testing systems individually. On the other hand, this system is a valuable opportunity for testing the thruster assemblies that should operate in a bunch, on the same satellite. The thrusters can be mounted vertically in a single column and tested rapidly, one after another to avoid interactions between the different thruster systems. It has been tested to be effective in the evaluation of up to 3 different modules at a single instance, significantly reducing downtime during evacuation and purging processes required otherwise when testing systems individually.
It is vital to determine the thrust in micropropulsion systems accurately so that parameters such as efficiency, &#951;eff&#160;and the specific impulse Isp, are accurate, thus, giving a reliable representation of the dependence of thruster performance on various input parameters such as the propellant flow, and power supplied to the different terminals of the thrusters as shown in Equations 1 and 2. Explicitly, performance evaluation of micropropulsion systems typically revolves around the measurement of thrust generated from the system at various operating parameters. Therefore, performance evaluation systems need to be calibrated according to a set of standards before being installed into the space environment for use in diagnostics and testing to ensure their reliability and accuracy19.
<img alt="Equation 1" src="/files/ftp_upload/58466/58466eq1.jpg" />
<img alt="Equation 2" src="/files/ftp_upload/58466/58466eq2.jpg" />
Typical systems employ force calibration externally before thrust measurement units are installed into the test environment38. However, such systems do not account for the space environments affecting the material properties of the calibration standards, and for electrical, vacuum and thermal influences on the degradation of the calibrated standards over the dynamic course of performance evaluation of the thrusters. The automated wireless calibration unit shown in Figure 5, on the other hand, allows for in situ calibration of the system in the simulated environment before the thruster is operational. This accounts for the dynamic effects of the test environment on the measurement stage, and allows for rapid re-calibration of the system prior to firing of thrusters. The system also features a symmetric modular null thrust verification unit which verifies the thrust independently. It is operated while the thruster is operational for in situ analysis of the derived thrusts from given discharge conditions. The entire process is done via MATLAB apps, allowing users to focus on optimization of hardware and design of propulsion systems, and expedites testing of such systems. Details of this method would be elaborated in the following subsection.

<table><tbody><tr><td>Arduino Microcontroller</td><td>Arduino</td><td>Arduino Uno Rev 3</td><td></td></tr><tr><td>Bluetooth communication device</td><td>SG Botic</td><td>WIR-02471</td><td></td></tr><tr><td>Cryogenic Pump</td><td>ULVAC</td><td>CRYO-U12HLE&amp;nbsp;</td><td></td></tr><tr><td>Digital Oscilloscope</td><td>Yokogawa</td><td>DLM 2054</td><td></td></tr><tr><td>Dry Pump</td><td>Agilent</td><td>Triscroll-600</td><td></td></tr><tr><td>High resolution laser displacement sensor</td><td>Micro-Epsilon</td><td>optoNCDT ILD-1420-50</td><td></td></tr><tr><td>Mass Flow Controller</td><td>MKS</td><td>MKS M100B</td><td></td></tr><tr><td>Optical Emission Spectrometer</td><td>Avantes</td><td>AvaSpec-ULS2048XL-EVO</td><td></td></tr><tr><td>Servo Motor</td><td>Tower Pro</td><td>Servo Motor SG90</td><td></td></tr><tr><td>Stepper Motor</td><td>Oriental Motor</td><td>PKP213D05A</td><td></td></tr><tr><td>Turbomolecular Pump</td><td>Pfeiffer</td><td>ATH-500M</td><td></td></tr></tbody></table>

optimization, test and diagnostics of miniaturized hall thrusters

Miniaturized spacecraft and satellites require smart, highly efficient and durable low-thrust thrusters, capable of extended, reliable operation without attendance and adjustment. Thermochemical thrusters which utilize thermodynamic properties of gases as a means of acceleration have physical limitations on their exhaust gas velocity, resulting in low efficiency. Moreover, these engines demonstrate extremely low efficiency at small thrusts and may be unsuitable for continuously operating systems which provide real-time adaptive control of the spacecraft orientation, velocity and position. In contrast, electric propulsion systems which use electromagnetic fields to accelerate ionized gases (i.e., plasmas) do not have any physical limitation in terms of exhaust velocity, allowing virtually any mass efficiency and specific impulse. Low-thrust Hall thrusters have a lifetime of several thousand hours. Their discharge voltage ranges between 100 and 300 V, operating at a nominal power of &lt;1 kW. They vary from 20 to 100 mm in size. Large Hall thrusters can provide fractions of millinewton of thrust. Over the past few decades, there has been an increasing interest in small mass, low power, and high efficiency propulsion systems to drive satellites of 50-200 kg. In this work, we will demonstrate how to build, test, and optimize a small (30 mm) Hall thruster capable of propelling a small satellite weighing about 50 kg. We will show the thruster operating in a large space environment simulator, and describe how thrust is measured and electric parameters, including plasma characteristics, are collected and processed to assess key thruster parameters. We will also demonstrate how the thruster is optimized to make it one of the most efficient small thrusters ever built. We will also address challenges and opportunities presented by new thruster materials.

Thrust calibration procedure and thrust performance evaluation
Evaluation of thrust values from the quadfilar thrust measurement stage comes in two phases. The first phase is through obtaining calibration factors from the automated wireless calibration unit shown to the right of Figure 5. In this calibration process, fine weights are lowered across a smooth polytetrafluoroethylene b...

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Optimization, Test and Diagnostics of Miniaturized Hall Thrusters

Here, we present a protocol to test and optimize space propulsion systems based on miniaturized Hall-type thrusters.

Miniaturized spacecraft and satellites require smart, highly efficient and durable low-thrust thrusters, capable of extended, reliable operation without ...

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8.9K Views.  Nanyang Technological University. Here, we present a protocol to test and optimize space propulsion systems based on miniaturized Hall-type thrusters. 

Video: Optimization, Test and Diagnostics of Miniaturized Hall Thrusters

Fabrication And Characterization Of Photonic Crystal Slow Light Waveguides And Cavities

Slow light has been one of the hot topics in the photonics community in the past decade, generating great interest both from a fundamental point of view and for its considerable potential for practical applications. Slow light photonic crystal waveguides, in particular, have played a major part and have been successfully employed for delaying optical signals1-4 and the enhancement of both linear5-7 and nonlinear devices.8-11
Photonic crystal cavities achieve similar effects to that of slow light waveguides, but over a reduced band-width. These cavities offer high Q-factor/volume ratio, for the realization of optically12 and electrically13 pumped ultra-low threshold lasers and the enhancement of nonlinear effects.14-16 Furthermore, passive filters17 and modulators18-19 have been demonstrated, exhibiting ultra-narrow line-width, high free-spectral range and record values of low energy consumption.
To attain these exciting results, a robust repeatable fabrication protocol must be developed. In this paper we take an in-depth look at our fabrication protocol which employs electron-beam lithography for the definition of photonic crystal patterns and uses wet and dry etching techniques. Our optimised fabrication recipe results in photonic crystals that do not suffer from vertical asymmetry and exhibit very good edge-wall roughness. We discuss the results of varying the etching parameters and the detrimental effects that they can have on a device, leading to a diagnostic route that can be taken to identify and eliminate similar issues.
The key to evaluating slow light waveguides is the passive characterization of transmission and group index spectra. Various methods have been reported, most notably resolving the Fabry-Perot fringes of the transmission spectrum20-21 and interferometric techniques.22-25 Here, we describe a direct, broadband measurement technique combining spectral interferometry with Fourier transform analysis.26 Our method stands out for its simplicity and power, as we can characterise a bare photonic crystal with access waveguides, without need for on-chip interference components, and the setup only consists of a Mach-Zehnder interferometer, with no need for moving parts and delay scans.
When characterising photonic crystal cavities, techniques involving internal sources21 or external waveguides directly coupled to the cavity27 impact on the performance of the cavity itself, thereby distorting the measurement. Here, we describe a novel and non-intrusive technique that makes use of a cross-polarised probe beam and is known as resonant scattering (RS), where the probe is coupled out-of plane into the cavity through an objective. The technique was first demonstrated by McCutcheon et al.28 and further developed by Galli et al.29

Use of photonic crystal slow light waveguides and cavities has been widely adopted by the photonics community in many differing applications. Therefore fabrication and characterization of these devices are of great interest. This paper outlines our fabrication technique and two optical characterization methods, namely: interferometric (waveguides) and resonant scattering (cavities).

Slow light has been one of the hot topics in the photonics community in the past decade, generating great interest both from a fundamental point of view ...

A 100 KW Class Applied-field Magnetoplasmadynamic Thruster

Applied-field magnetoplasmadynamic thrusters (AF-MPD thrusters) are hybrid accelerators in which electromagnetic and gas dynamic processes accelerate plasma to high speed; they have considerable potential for future space applications with the significant advantages of high specific impulse and thrust density. In this paper, we present a series of protocols for designing and manufacturing a 100 kW class of AF-MPD thruster with water-cooling structures, a 130 V maximum discharge voltage, a 800 A maximum discharge current, and a 0.25 T maximum strength of magnetic field. A hollow tantalum tungsten cathode acts as the only propellant inlet to inhibit the radial discharge, and it is positioned axially at the rear of the anode in order to relieve anode starvation. A cylindrical divergent copper anode is employed to decrease anode power deposition, where the length has been reduced to decrease the wall-plasma connecting area. Experiments utilized a vacuum system that can achieve a working vacuum of 0.01 Pa for a total propellant mass flow rate lower than 40 mg/s and a target thrust stand. The thruster tests were carried out to measure the effects of the working parameters such as propellant flow rates, the discharge current, and the strength of applied magnetic field on the performance and to allow appropriate analysis. The thruster could be operated continuously for significant periods of time with little erosion on the hollow cathode surface. The maximum power of the thruster is 100 kW, and the performance of this water-cooled configuration is comparable with that of thrusters reported in the literature.

The goal of this protocol is to introduce the design of a 100 kW class applied-field magnetoplasmadynamic thruster and relevant experimental methods.

Applied-field magnetoplasmadynamic thrusters (AF-MPD thrusters) are hybrid accelerators in which electromagnetic and gas dynamic processes accelerate ...

Fabrication and Testing of Miniature Automatic Photophoretic Trapping Rigs

This paper presents an automated, rapid-fab-compatible, photophoretic trap test rig to enable the democratization and crowdsourcing of volumetric display research. The rig can be constructed within 2 h using a laser cutter, 3-dimensional (3D) printer, and common hand tools. In its current form, the rig can be used to test the following critical parameters: particle type, trap type, numerical aperture, and airflow at a rate of approximately 250 samples per hour. With minor modification, the rig can be made to test an even larger set of parameters, such as laser power and laser wavelength, depending on the user's needs. The rig can use machine vision for automated data capture and analysis. The operation and construction of the test rig are described with concise, easy-to-follow steps. Results from a four-unit test rig 'farm' covering the power and particle type parameters are reported. This platform will broaden the scope and composition of optical trap display parameters and researchers through accessibility and democratization.

This work describes and characterizes the fabrication of miniature automatic photophoretic trapping rigs.

This paper presents an automated, rapid-fab-compatible, photophoretic trap test rig to enable the democratization and crowdsourcing of volumetric display ...

The Traceable Calibration of Thrust Stand by Electrostatic Force

Micro thrusters have important applications in low-frequency gravitational wave detection, satellite formation, and inter-satellite laser communication, so it is necessary to accurately measure the thrust of micro thrusters with traceability. A thrust stand is a widely used micro thrust measuring device with the advantages of high resolution and large load. Traceability calibration of mechanical characteristics of thrust stand is an essential prerequisite to ensure traceability measurement of thrust. In this study, a parallel plate capacitor was used to calibrate the thrust stand by generating a micronewton electrostatic force, which could be traced to the International System of Units (SI). The constant capacitance gradient range was obtained through simulation and theoretical calculation. Moreover, the electrostatic force could be changed by standard voltage with the advantages of simple principle, instantaneous trigger, and traceability. The device could be used for traceability calibration of micro newton thrust stand due to simple assembly and short traceability path.

Traceability calibration of mechanical characteristics of thrust stand is an essential prerequisite to ensure traceability measurement of thrust. Here, we describe how to calibrate the thrust stand by the electrostatic force generated by the parallel plate capacitor.

Micro thrusters have important applications in low-frequency gravitational wave detection, satellite formation, and inter-satellite laser communication, ...

Modeling and Experimental Analysis of the Single-Shaft Coaxial Motor-Pump Assembly in Electrohydrostatic Actuators

An electrohydrostatic actuator (EHA) can be the most promising alternative compared with the traditional hydraulic servo actuators for its high power density, ease of maintenance, and reliability. As the core power unit that determines the performance and service life of the EHA, the motor-pump assembly should simultaneously possess a wide speed/pressure range and a high dynamic response.
This paper presents a method to test the performance of the motor-pump assembly through simulation and experimentation. The flow output characteristics were defined through simulation and analysis of the assembly at the beginning of the experiment, leading to the conclusion of whether the pump could meet the requirements of the EHA. A series of performance tests were conducted on the motor-pump assembly via a pump test bench in the speed range of 1,450-9,000 rpm and the pressure range of 1-30 MPa.
We tested the overall efficiency of the motor-pump assembly under various working conditions after confirming the consistency between the test results of the flow output characteristics with the simulation results. The results showed that the assembly has higher overall efficiency when working at 4,500-7,000 rpm under the pressure of 10-25 MPa and at 2,000-2,500 rpm under 5-15 MPa. Overall, this method can be utilized for determining in advance whether the motor-pump assembly meets the requirements of EHA. Moreover, this paper proposes a rapid test method of the motor-pump assembly in various working conditions, which could assist in predicting EHA performance.

We built a simulation model to evaluate pump flow characteristics and performance of the single-shaft coaxial motor-pump assembly in electrohydrostatic actuators and investigate the overall efficiency in a wide set of working conditions of the motor-pump assembly experimentally.

An electrohydrostatic actuator (EHA) can be the most promising alternative compared with the traditional hydraulic servo actuators for its high power ...

A Modeling and Simulation Method for Preliminary Design of an Electro-Variable Displacement Pump

Electro-hydrostatic actuators (EHAs) have been considerably researched in academia, and their applications in various industrial fields are expanding. The variable-speed EHA has now taken priority over the variable-displacement EHA, but its driving motor and associated electronics encounter issues when applied in high-power applications: low-dynamics, high thermal dissipation, high price, etc. Therefore, a variable-displacement EHA equipped with an electro-variable displacement pump (EVDP) has been considered. The EVDP itself is a mechatronic system that integrates a piston pump, a ball screw, a gearbox, and a permanent magnet synchronous motor (PMSM). Consequently, the EVDP needs to be investigated to ensure its system-level performance when applied in an EHA. In addition to the previous research on the technical parameters of the EVDP, a dedicated design method is necessary for further reducing the cost of using the EVDP and exploring its performance potential. Here, a simulation based EVDP preliminary design method is selected for designing a 37 kW EVDP. Firstly, a previously proposed multidisciplinary model of the EVDP is extended by improving the parameter generation, including the EVDP life, reliability, control models, etc. Secondly, the proposed model is partially verified using a downsized prototype. Thirdly, the EVDP is simulated at a system level, supported by the proposed model. The EVDP performance is evaluated according to the specified design requirements. The temperature, bandwidth and accuracy, reliability and lifetime, etc., are all predicted for the EVDP. The simulation results demonstrate the EVDP's applicability in variable-displacement EHA. The proposed modeling and simulation method can be used to evaluate diverse EVDP performance and respond to general design requirements. The method can also support the resolution of the preliminary design challenges in terms of limited information and robustness. Therefore, the proposed method is appropriate for the realization of the simulation-based EVDP preliminary design method.

A simulation model specifically supporting the preliminary design of an electro-variable displacement pump (EVDP) is developed and partially verified by experiments. The control performance, life, reliability, etc., can all be evaluated using the proposed model, which covers the main performance requirements under the EVDP preliminary design task.

Electro-hydrostatic actuators (EHAs) have been considerably researched in academia, and their applications in various industrial fields are expanding. The ...

Reduced-gravity Environment Hardware Demonstrations of a Prototype Miniaturized Flow Cytometer and Companion Microfluidic Mixing Technology

Until recently, astronaut blood samples were collected in-flight, transported to earth on the Space Shuttle, and analyzed in terrestrial laboratories. If humans are to travel beyond low Earth orbit, a transition towards space-ready, point-of-care (POC) testing is required. Such testing needs to be comprehensive, easy to perform in a reduced-gravity environment, and unaffected by the stresses of launch and spaceflight. Countless POC devices have been developed to mimic laboratory scale counterparts, but most have narrow applications and few have demonstrable use in an in-flight, reduced-gravity environment. In fact, demonstrations of biomedical diagnostics in reduced gravity are limited altogether, making component choice and certain logistical challenges difficult to approach when seeking to test new technology. To help fill the void, we are presenting a modular method for the construction and operation of a prototype blood diagnostic device and its associated parabolic flight test rig that meet the standards for flight-testing onboard a parabolic flight, reduced-gravity aircraft. The method first focuses on rig assembly for in-flight, reduced-gravity testing of a flow cytometer and a companion microfluidic mixing chip. Components are adaptable to other designs and some custom components, such as a microvolume sample loader and the micromixer may be of particular interest. The method then shifts focus to flight preparation, by offering guidelines and suggestions to prepare for a successful flight test with regard to user training, development of a standard operating procedure (SOP), and other issues. Finally, in-flight experimental procedures specific to our demonstrations are described.

Spaceflight blood diagnostics need innovation. Few demonstrations have been published illustrating in-flight, reduced-gravity health diagnostic technology. Here we present a method for construction and operation of a parabolic flight test rig for a prototype point-of-care flow-cytometry design, with components and preparation strategies adaptable to other setups.

Until recently, astronaut blood samples were collected in-flight, transported to earth on the Space Shuttle, and analyzed in terrestrial laboratories. If ...

Biology

Propeller Characterization: Variations in Pitch, Diameter, and Blade Number on Performance

Source: Shreyas Narsipur, Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC
A propeller is a twisted airfoil, where the angle of the chord changes with respect to the location, along the radial station, as shown in Figure 1. Propellers are widely used in aircraft and watercraft propulsion systems thereby necessitating detailed characterizations of propellers to design high performance vehicles.
<img src="/files/ftp_upload/10460/10460fig1.jpg" />
Figure 1. Chord, thickness, and pitch at a radial station.
One of the defining characteristics of a propeller is the pitch/twist. The pitch of the propeller, generally given in units of length, is the theoretical distance the propeller will travel through the air in one single revolution. However, due to the drag force on the aircraft and the propeller, the propeller never travels its theoretical distance. The actual distance travelled is referred to as the effective pitch of the propeller, and the difference between the theoretical or geometric pitch and the effective pitch is referred to as propeller slip, as illustrated in Figure 2.
<img src="/files/ftp_upload/10460/10460fig2.jpg" />
Figure 2. Representation of pitch and slip.
In this demonstration, seven propellers are characterized using a propeller test rig in a subsonic wind tunnel. This is followed by a detailed parametric study to analyze the effects of variations in pitch, diameter, and number of blades on propeller performance.

Propeller Characterization: Pitch, Diameter and Blade Number

Source: Shreyas Narsipur, Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC
A propeller is a twisted airfoil, where the ...

JoVE Science Education

Aeronautical Engineering

Propulsion and Thrust

Source: Alexander S Rattner; Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA
Aircraft, rockets, and ships produce propulsion by accelerating surrounding fluid or high temperature combustion products to high velocity. Because of the principle of conservation of momentum, the increased fluid velocity results in an effective thrust force on the vehicle. The thrust capabilities of propulsion systems are often measured with static thrust tests. In these tests, propulsion systems are mounted and operated on fixed, instrumented platforms, and the holding force on the mounts is measured as the thrust
In this experiment, a small-scale static thrust measurement facility will be constructed and modeled. The thrust curves for two model aircraft motors and propeller systems and a computer cooling fan will be measured. Thrust efficiencies will also be evaluated (thrust force / electrical power input). Measured thrust values will be compared with theoretical predictions based on measured air velocities.

Aircraft/Rocket/Ship Propulsion; Static Thrust Measurement

Source: Alexander S Rattner; Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA
Aircraft, rockets, ...

Mechanical Engineering

Multicopter Aerodynamics: Characterizing Thrust on a Hexacopter

Source: Prashin Sharma and Ella M. Atkins, Department of Aerospace Engineering, University of Michigan, Ann Arbor, MI
Multicopters are becoming popular for a variety of hobby and commercial applications. They are commonly available as quadcopter (four thrusters), hexacopter (six thrusters), and octocopter (eight thrusters) configurations. Here, we describe an experimental process to characterize the multicopter performance. A modular small hexacopter platform providing propulsion unit redundancy is tested. The individual static motor thrust is determined using a dynamometer and varying propeller and input commands. This static thrust is then represented as a function of motor RPM, where the RPM is determined from motor power and control input. The hexacopter is then mounted on a load cell test stand in a 5&#8217; x 7&#8217; low-speed recirculating wind tunnel, and its aerodynamic lift and drag force components were characterized during flight at varying motor signals, free-stream flow speed, and angle of attack.

A hexacopter was selected for this study because of its resilience to motor (propulsion unit) failure, as reported in Clothier1. Along with redundancy in the propulsion system, the selection of high-reliability components is also required for safe flight, particularly for missions over-populated regions. In Ampatis2, the authors discuss the optimal selection of multicopter parts, such as motors, blades, batteries, and electronic speed controllers. Similar research has also been reported in Bershadsky3, which focuses on the proper selection of a propeller system to satisfy mission requirements. Along with redundancy and reliability of components, understanding vehicle performance is also essential to assure flight envelope limits are respected and to select the most efficient design.

Characterizing Thrust on Hexacopter: Dynamometer Experiment

Source: Prashin Sharma and Ella M. Atkins, Department of Aerospace Engineering, University of Michigan, Ann Arbor, MI
Multicopters are becoming popular ...