This thesis investigates low-energy xenon-molybdenum (Xe+-Mo) sputtering yields for ion energies of 100 eV and less. Sputtering yield data at these energies are important for ion thruster design and lifetime prediction. The basic principles of sputtering phenomena are discussed. An overview of various popular types of experimental sputtering yield methods is presented with an emphasis on the techniques that have been used to find Xe+-Mo sputtering yields in the past. Sputtering yields in this study are found through both models and experiments. Sputtering yields are calculated using the Sigmund, Bohdansky, Yamamura, and Wilhelm formulas. The computed sputtering yields for these models varied widely at low-energy. TRIM (The TRansport of Ions in Matter), a Monte-Carlo simulation program, was adapted to study sputtering yields, and energy and angular distributions of sputtered atoms. Simulations were run at various combinations of ion energy and ion incidence angle. TRIM did not prove to be an adequate model for low-energy sputtering. Experimental measurements of sputtering were made using both Rutherford backscattering spectrometry (RBS) and mass-loss methods. Sputtering was performed in a small vacuum facility using an ion gun. For the RBS technique, sputtered material was collected on aluminum foil substrates. The area density of the deposited Mo film on the substrates was measured using RBS. These measurements enabled calculation of differential sputtering yields, which were integrated to find the total sputtering yield. Sputtering yield was found by the mass-loss technique by simply comparing the mass of the sample both before and after sputtering using a microbalance. Sputtering yields at 100 eV, 90 eV, 80 eV, 70 eV, and 60 eV were found using the RBS technique. The mass-loss technique was only successful in the 80 eV experiment. The experimental results were unexpected. The measured sputtering yields were significantly higher than those reported by other researchers. Also, sputtering yields were found to increase with decreasing ion energy from 90 eV down to 60 eV. / Master of Science

This paper has investigated if utilising Ion-Propulsion on a solar sunshade would lead to a reduction in total mass. The mechanism leading to this effect is that by using IP, the sunshade could be positioned closer to Earth. Positioning the sunshade closer to Earth would in turn allow for a smaller absolute size in the sunshade (whilst remaining a fixed angular size), and thus a decrease in total mass. This would lead to a decrease in launch costs and manufacturing costs.  The results indicate that fitting satellites with Ion-Propulsion would lead to a reduction in the total mass for the sunshade. More specifically they showcase the extent of which using IP has an effect on total mass, for example certain minimum ISP values that are needed to be reached in order for significant reductions of mass to arise. In a similar manner, the duration of which the satellites can remain in orbit also heavily impacts the total mass of the sunshade. If Ion-Propulsion where to be utilised it is quintessential to understand how the technology impacts the total lifetime of the satellites. Additional investigation may also be made in investigating if Ion-Propulsion could be used in such a way where the satellites do not remain stationary in respect to the distance between Earth and the Sun, perhaps this could lead to additional reductions of mass.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Recent years have seen a decline in the rate of space exploration due to the inefficiency of chemical rockets. Therefore alternative fuel efficient propulsion methods are being sought to enable cost effective deep space exploration. The high fuel efficiency of electric thrusters enable a spacecraft to travel further, faster and cheaper than any other propulsion technology available. Thus electric propulsion has become the propulsion of choice for scientists and engineers. A typically electric thruster contains some sort of electrode to ionise the propellant. Although this is feasible for short space missions, it becomes impractical for more ambitious space missions as electrodes erode over time. The alternative is to ionise the propellant using electromagnetic fields, which eliminates lifespan issues associated with electrode based thrusters. In order to examine methods of improving the lifespan and performance of electric thrusters, this thesis aimed to study the method of microwave discharge ionisation for an electric thruster. This includes the design of an RF Ion Thruster with extraction and acceleration grids to generate thrust. A 600 W 2.45 GHz magnetron (obtained from a conventional microwave oven), coupled to circular TM010 resonant cavity, was used to ionise neutral argon gas. The process of electron cyclotron resonance (ECR) was used to ensure the efficient ionisation of a high density plasma. The thrust was achieved with a three-grid system biased at high voltages to accelerate positively charged argon ions to high exhaust velocities. Results yielded the success of the designed electromagnetic based thruster, measuring approximatively 1.78 mN of thrust with a specific impulse of Isp = 3786 seconds. The ECR process produced a high plasma density with a plasma absorption rate of approximately 77% of the total input microwave power. The final results obtained were found to match the predicted results extremely well and resembled results found in literature. This demonstrates the efficiency of the RF ion thruster that was designed in this project and the future use in space exploration activities. However, future research needs to be undertaken on a controlled feedback system that will ensure optimal operating conditions for maximum performance. In addition, the method of grid-less acceleration needs to be studied to achieve maximum thrust and specific impulse. / AFRIKAANSE OPSOMMING: In onlangse jare het ’n afname in die tempo van die verkenning van die ruimte dit te danke aan die ondoeltreffendheid van chemiese vuurpyle. Derhalwe moet alternatiewe brandstof aandrywing metodes ondersoek word, om koste-effektiewe diep ruimte-eksplorasie moontlik te maak. Die hoë brandstof-doeltreffendheid van elektriese ontbranders stel ’n ruimtetuig in staat om verder, vinniger en goedkoper te reis as enige ander aandrywing tegnologie wat tans beskikbaar is. Dus het elektriese aandrywing metodes die aandrywings keuse vir wetenskaplikes en ingenieurs geword. ’n Tipies elektriese vuurpyl/aandrywer bevat ’n vorm van elektrode om die brandstof (argon gas) te ioniseer. Alhoewel hierdie elektrode proses van ionisasie effektief is vir kort ruimte missies, word dit onprakties vir meer ambisieuse ruimte missies as gevolg van verweering van elektrodes met verloop van tyd. ’n Alternatief is om die dryfmiddel/brandstof te ioniseer deur gebruik te maak van elektromagnetiese velde. Die elekromagnetiese velde sal die lewensduur van die vuurpyl vermeerder deur die verweering van elektrodes, wat geassosieer word met tipiese elektrieses vuurpyle, te elimineer. Hierdie tesis se doelwit is om die metode van mikrogolf ontslag ionisasie vir ’n elektriese vuurpyl/aandrywer te bestudeer om ten einde die lewensduur en doeltreffendheid van elektriese vuurpyl/aandrywer te ondersoek. Dit sluit in die ontwerp van ’n radio frekewensie ioon vuurpyl/aandrywer met ’n ontginning en versnelling matriks/rooster om stukrag te genereer. ’n 2,45 GHz magnetron (verkry vanaf ’n konvensionele mikrogolfoond), gekoppel aan ’n TM010 resonante holte, was gebruik om neutrale argon gas te ioniseer. Die proses van elektron siklotron resonansie (ESR) was gebruik om die doeltreffende ionisasie van ’n hoë digtheid plasma te verseker. Die aandrywing/stukrag was behaal met ’n drie-matriks-stelsel, bevoordeel deur hoë spannings om die positief-gelaaide argon ione te versnel. Resultate opgelewer, het die sukses van die ontwerp van ’n elektromagnetiese gebaseerde vuurpyl/aandrywer met ’n benaderde meting van ongeveer 1.78 mN van stukrag/aandrywing met ’n spesifieke impuls van Isp = 3786 sekondes bewys. Die ECR proses het ’n hoë plasma digtheid geproduseer met ’n plasma opname persentasie van ongeveer 77% van die totale inset mikrogolf energie. Die finale uitslae wat verkry was, het bevind dat die voorspelde resultate baie goed inpas met resultate in beskikbare literatuur. Dit dui op die doeltreffendheid van die RF ioon vuurpyl/aandrywer wat ontwerp is in hierdie projek vir die toekomstige gebruik in ruimte eksplorasie-aktiwiteite. Toekomstige navorsing moet op ’n beheerde terugvoer sisteem onderneem word, wat optimale werktoestande verseker vir maksimum prestasie. Daarbenewens moet die metode van matriks-lose versnelling bestudeer word, om maksimum versnelling/stukrag en spesifieke impuls te verseker.

Beyond Atlas is a Swedish private company with the goal of exploring the solar system with cheap and reliable spacecraft. Part of their maiden mission, Hugin, aims to demonstrate navigation, propulsion, and communication technology on a 3U CubeSat. This thesis aims to investigate the feasibility of using the Enpulsion NANO electric propulsion (EP) system for deep-space applications and how to best demonstrate its capabilities in low-Earth orbit. Literature reviews of scientific papers and software simulations were conducted to gain an understanding of the underlying processes involved in EP in-orbit operations. Analyses were made on orbital maneuvers, momentum unloading, power and thermal restrictions. The results suggest that the EP system's capabilities is mainly limited by the saturation time of the reaction wheels restricting longer duration orbital maneuvers. Orbital maneuvers for demonstrating the capabilities are proposed based on the limitations imposed on the EP system by the rest of the spacecraft. On the basis of the results of this research, it can be concluded that the Enpulsion NANO thruster's operational range can be utilized both as a low thrust efficient main drive and as a high thrust maneuvering thruster for deep-space applications but is limited by the high power consumption and low thrust-to-power ratio.

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