With the advent of smaller satellites, along with the need for less than 0.1 μN precision attitude control for interferometry and imaging missions, finer micro- to sub-micro- thrusters have become an area of high interest. As thrusters are developed and ground-tested, it is necessary to evaluate their thrust performance on-orbit. On-orbit measurements offer actual thrust performance in mission conditions, free from ground facility vibrations and miniaturization restraints, and allow a thruster system to achieve a NASA Technology Readiness Level (TRL) of 7-8. A review is conducted of existing and proposed ground and on-orbit thrust measurement techniques. Experimental gaps and complementary methods are examined along with the current thrust resolution limits. A novel fusion technique combining attitude determination, torsional balance, and filtering techniques is proposed to increase resolution beyond current on-orbit minimums, 4μN, via a dedicated sub-μN on-orbit thrust measurement mission. A simulated case study in the application of this measurement technique to a theoretical Casimir-thruster-equipped, 10-7-10-13 N, smallsat mission is explored. A detailed error analysis is conducted, and the technique is found to be analytically viable for greater than or equal to 10-7 N on a 1U nanosat equipped with sun sensor and three-axis gyroscope, as well as physically viable at a TRL 7-9 level. Recommended next steps are modification of the post-processing technique to decrease gyroscope noise and mass restrictions or exploration of suggested alternate methods, including orbit estimation, direct force sensing, and formation flying.

Vacuum arc thrusters offer a relatively simple and cheap form of satellite propulsion, especially suitable for nanosatellites such as CubeSats or even smaller. This thesis focuses on vacuum arc thruster design considering the thruster’s manufacturing, assembly and integration into the spacecraft, and proposes a new anode geometry easing thruster production. Vacuum arc thruster research is traditionally experimental in nature due to a lack of accurate models. This work follows this approach, and studies experimentally the effect of several geometric design parameters on thruster performance. The outcome confrms findings from several papers, and suggests specifc improvements towards existing models for predicting the effect of the thruster’s geometry on its thrust. The chosen experimental approach raised the need for a micro-thrust measurement stand. Two distinct measurement stands have been designed, realized and used to test various thruster prototypes. One test stand is more accurate. However, the other setup allows for considerably faster testing.

Existing thrust measurement systems (TMSs) at NASA Stennis Space Center use strain gauges and flux plates to measure forces produced by a test article. Alignment and calibration can take two weeks or more every time a piece of hardware or test article is changed. Cross axis loading is also problematic because it is impossible to perfectly align the flex plates and strain gauges in the thrust direction. In response to these problems, a magnetically levitated thrust measurement system has been proposed and a 300lb capacity demonstrator has been designed and built. In this design, the magnetic bearings work concurrently as support bearings and force measurement devices. The demonstrator consists of a floating frame that is completely levitated within a fixed frame by four support bearings carrying loads in the x- and y-direction and seven thrust bearings carrying loads in the z- or thrust direction. Joe Imlach of Imlach Consulting Engineering designed the demonstrator and magnetic bearing components, while Virginia Tech's role has been the application of the multipoint calibration technique including code development, the implementation of a 128-channel data acquisition system, and the overall test verification of the TMS demonstrator.A turnbuckle assembly and magnetostrictive actuator are used in series with a conventional load cell for static and dynamic testing, respectively. Both current based and flux based force equations were used to measure the reaction forces at the bearings. The static results using the current based equations including the current based fringing equations resulted in accuracies of 93% of full load, while the static results using the flux based equations including the flux based fringing equations resulted in accuracies of 99.5% of full load. These accuracies can be compared to accuracies of 83-90% seen in previous work using magnetic bearings to measure forces by monitoring currents and to accuracies of about 99% in previous work using magnetic bearings to measure forces by monitoring fluxes. All of the improved accuracies were made possible through the implementation of a calibration technique known as the multipoint method and the implementation of a gap dependent fringing correction factor developed by Joe Imlach. The demonstrator was not outfitted with accelerometers so the inertia of the floating frame could not be accounted for, limiting the scope of dynamic testing. However, the tests confirmed the ability of the demonstrator to measure dynamic loads in general. / Master of Science

No description available.

Good estimation of aerodynamic coefficients is of fundamental importance in the design and development process of an aircraft. Generally, these parameters are obtained using analytical, numerical and experimental methods, which are sometimes either inaccurate or very expensive. The use of subscale aircraft is becoming increasingly common in the study and evaluation of new aircraft concepts. Flight testing results in an efficient solution for obtaining parameters that can define drag characteristics. This project presents a solution for achieving the drag aerodynamic model from the design and manufacturing of a micro engine thrust measuring system integrated on subscale aircraft. Strain gauge technology permits to identify the stresses that the engine forces cause to the aircraft internal structure by analysing the strain of several strategic zones of the engine mounting created for this purpose. Different structural support geometries have been presented and stress-analysed together with the design of the appropriate strain gauge model conguration in order to select and manufacture a system that represents a good compromise between all the requirements while ensuring the quality and accuracy of the data acquired. After calibration, installation and set-up, the system is ready for real in-flight measurements.

The VEM Drive (Variable-Electro-Magnetic Drive) is an invention by Space Warp Dynamics LLC that claims to distort space-time and thus creating an attractive force upon a target using frequencies in the VHF band. The experimental setup was replicated and tested at the Institute of Aerospacee Engineering at TU Dresden. We conclude that no anomalous force was present within our tested power levels and balance resolution some 6 orders of magnitude below the reported claim. The interaction of the high frequency with the power supply that was controlling a voice-coil actuator for teh balance was found to be responsible for a faciity side-effect that can mimic such an effect. This is important to consider foro future measurements.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2009. / This thesis describes the development of a vacuum arc thruster (VAT) to be used as a potential low mass (< 500 g), low power (< 5–10W) propulsion system for nanosatellites. The thruster uses a high voltage capacitive circuit to initiate and power the arc process with a 400 ns high current (150–800A) pulse. A one-dimensional steady state analyticalmodel describing the cathode region of the vacuum arc was developed. The model made use of mass and energy balances at the sheath region and cathode surface respectively to predict key quantities such as thrust, ion velocity, ion-to-arc current ratio and erosion rate. Predicted results were shown to be within the limits of reported literature (∼63 μN/A, 26.12 km/s, 0.077 and 110 μg/C respectively). A sensitivity analysis of the analytical model found that a high electric field in the cathode region impedes and decelerates ion flow, which is used for thrust. This was confirmed experimentally for thrust values at arc voltages greater than 2000 V. Both direct and indirect means of measuring thrust were achieved by using a deflecting cantilever beam and an ion collector system, respectively. The transient response of the cantilever beam to impulsive thrust was analytically modeled, whilst the ion current was found by measuring the current induced on a plate subject to ion bombardment. Knowledge of the ion current density distribution was successfully used to approximate the effective normal thrust vector. Direct and indirect thrust levels were roughly 140 and 82 μN/A of average arc current, respectively. Measured thrust was found to be higher than predicted thrust due to thrust contributions fromthe ablation of Teflon insulation. The discrepancy is also due to the uncertainty in quantifying free parameters in the analytical model such as the fraction of generated ions flowing away from the cathode region. The thrust-topower ratio, specific impulse and efficiency of the vacuum arc thruster at an average arc current of 200 A was measured to be 0.6 μN/W, 160 s and 0.05 %, respectively. A thruster performance analysis and specification showed that the VAT is capable of achieving specific orbital and slew manoeuvres within a constant 5–10 W average power. It was concluded that thruster performance could be improved by using a two-stage arc circuit consisting of a high voltage, low current, short pulse trigger and a low voltage, high current, long pulse driver.

It is well known that the layout of a large wind turbine cluster aects the energyoutput of the wind farm. The individual placement and distances betweenturbines will in uence the wake spreading and the wind velocity decit. Manyanalytical models and simulations have been made trying to calculate this, butstill there is a lack of experimental data to conrm the models. This thesis isdescribing the preparations and the execution of an experiment that has beenconducted using about 250 small rotating turbine models in a wind tunnel. Theturbine models were developed before the experiment and the characteristicswere investigated. The main focus was laid on special eects occurring in largewind turbine clusters, which were named Global Turbine Array Eects.It was shown that the upstream wind was little aected by a large windfarm downstream, even though there existed a small dierence in wind speedbetween the undisturbed free stream and the wind that arrived to the rstturbines in the wind farm. The dierence in wind speed was shown to beunder 1% of the undisturbed free stream. It was also shown that the densityof the wind farm was related to the reduced wind velocity, with a more densefarm the reduction could get up to 2.5% of the undisturbed free stream at theupstream center turbine. Less velocity decit was observed at the upstreamcorner turbines in the wind farm.When using small rotating turbine models some scaling requirements hadto be considered to make the experiment adaptable to reality. It was concludedthat the thrust coecient of the turbine models was the most important parameterwhen analysing the eects. One problem discussed was the low Reynoldsnumber, an eect always present in wind tunnel studies on small wind turbinemodels.A preliminary investigation of a photo measuring technique was also performed,but the technique was not fully developed. The idea was to take oneor a few photos instantaneously and then calculate the individual rotationalspeed of all the turbine models. It was dicult to apply the technique becauseof uctuations in rotational speed during the experiment, therefore thecalculated values could not represent the mean value over a longer time period.