06 Fakultät Luft- und Raumfahrttechnik und Geodäsie
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/7
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Item Open Access A coaxial pulsed plasma thruster model with efficient flyback converter approaches for small satellites(2023) O’Reilly, Dillon; Herdrich, Georg; Schäfer, Felix; Montag, Christoph; Worden, Simon P.; Meaney, Peter; Kavanagh, Darren F.Pulsed plasma thrusters (PPT) have demonstrated enormous potential since the 1960s. One major shortcoming is their low thrust efficiency, typically <30%. Most of these losses are due to joule heating, while some can be attributed to poor efficiency of the power processing units (PPUs). We model PPTs to improve their efficiency, by exploring the use of power electronic topologies to enhance the power conversion efficiency from the DC source to the thruster head. Different control approaches are considered, starting off with the basic approach of a fixed frequency flyback converter. Then, the more advanced critical conduction mode (CrCM) flyback, as well as other optimized solutions using commercial off-the-shelf (COTS) components, are presented. Variations of these flyback converters are studied under different control regimes, such as zero voltage switching (ZVS), valley voltage switching (VVS), and hard switched, to enhance the performance and efficiency of the PPU. We compare the max voltage, charge time, and the overall power conversion efficiency for different operating regimes. Our analytical results show that a more dynamic control regime can result in fewer losses and enhanced performance, offering an improved power conversion efficiency for PPUs used with PPTs. An efficiency of 86% was achieved using the variable frequency approach. This work has narrowed the possible PPU options through analytical analysis and has therefore identified a strategic approach for future investigations. In addition, a new low-power coaxial micro-thruster model using equivalent circuit model elements is developed.This is referred to as the Carlow-Stuttgart model and has been validated against experimental data from vacuum chamber tests in Stuttgart’s Pulsed Plasma Laboratory. This work serves as a valuable precursor towards the implementation of highly optimized PPU designs for efficient PPT thrusters for the next PETRUS (pulsed electrothermal thruster for the University of Stuttgart) missions.Item Open Access Development of a ferrofluid-based attitude control actuator for verification on the ISS(2024) Zajonz, Sebastian; Korn, Christian; Großmann, Steffen; Dietrich, Janoah; Kob, Maximilian; Philipp, Daniel; Turco, Fabrizio; Steinert, Michael; O’Donohue, Michael; Heinz, Nicolas; Gutierrez, Elizabeth; Wagner, Alexander; Bölke, Daniel; Sütterlin, Saskia; Schneider, Maximilian; Remane, Yolantha; Kreul, Phil; Wank, Bianca; Buchfink, Manuel; Acker, Denis; Hofmann, Sonja; Karahan, Bahar; Ruffner, Silas; Ehresmann, Manfred; Schäfer, Felix; Herdrich, GeorgFerrofluid-based systems provide an opportunity for increasing the durability and reliability of systems, where mechanical parts are prone to wear and tear. Conventional reaction control systems are based on mechanically mounted rotating disks. Due to inherent friction, they suffer from degradation, which may eventually lead to failure. This problem is further intensified due to the limited possibility for repair and maintenance. Ferrofluid-based systems aim to replace mechanical components by exploiting ferrofluidic suspended motion. Ferrofluids consist of magnetic nanoparticles suspended in a carrier fluid and can be manipulated by external magnetic fields. This paper describes the working principle, design, and integration of a working prototype of a ferrofluid-based attitude control system (ACS), called Ferrowheel. It is based on a stator of a brushless DC motor in combination with a rotor on a ferrofluidic bearing. The prototype will be verified in a microgravity environment on the International Space Station, as part of the Überflieger 2 student competition of the German Aerospace Center. First ground tests deliver positive results and confirm the practicability of such a system.Item Open Access Ferrofluid reaction wheel development and in-orbit verification(2025) Ehresmann, Manfred; Zajonz, Sebastian; Korn, Christian; Großmann, Steffen; Dietrich, Janoah; Kob, Maximilian; Philipp, Daniel; Turco, Fabrizio; Steinert, Michael; O’Donohue, Michael; Heinz, Nicolas; Gutierrez, Elizabeth; Wagner, Alexander; Bölke, Daniel; Sütterlin, Saskia; Schneider, Maximilian; Remane, Yolantha; Kreul, Phil; Wank, Bianca; Buchfink, Manuel; Acker, Denis; Hofmann, Sonja; Karahan, Bahar; Ruffner, Silas; Schäfer, Felix; Herdrich, GeorgIn contemporary satellite systems, the Attitude and Orbit Control System (AOCS) manages internal torque generation primarily through Reaction Wheels (RW) and Control Moment Gyros (CMG), which use mechanically mounted rotating disks to control orientation without expelling mass. Unlike magnetorquers, which interact with Earth’s magnetic field, or thruster-based Reaction Control Systems (RCS), which generate external forces by expelling propellant, RW and CMG systems rely solely on momentum exchange within the spacecraft. While state-of-the-art RWs are highly reliable and have demonstrated exceptional performance over decades of operation, their design still presents inherent challenges, such as wear, nonlinear friction effects, and tribological degradation of contact surfaces. These challenges are critical in space, where repairs are impractical and/or resource-intense. Consequently, engineers have devoted significant effort to developing robust and reliable mechanical reaction wheels. This paper explores an innovative proof-of-concept design based on a fluid-magnetic system utilizing ferrofluids and permanent magnets. This study aims to address limitations of traditional RWs by eliminating mechanical interfaces susceptible to wear and tear and replacing them with a low friction ferrofluidic bearing. Ferrofluid-based system concepts can offer a longer life due to reduced wear and tear, lower production costs by requiring less exotic materials and tolerances, self-center within the provided magnetic potential field and can therefore exhibit reduced vibration behavior. The Ferrowheel experiment, flown as part of the FARGO mission ( Überflieger 2 competition of the space agency within DLR) in March and April 2023, demonstrated the feasibility of ferrofluidic bearings for attitude control in ISS microgravity. These results contribute to exploration of innovative reaction wheel technologies, highlighting the potential of fluid-based systems for applications requiring enhanced robustness and reduced mechanical wear.Item Open Access Fargo : validation of space-relevant ferrofluid applications on the ISS(2024) Sütterlin, Saskia; Bölke, Daniel; Ehresmann, Manfred; Heinz, Nicolas; Dietrich, Janoah; Karahan, Bahar; Kob, Maximilian; O’Donohue, Michael; Korn, Christian; Grossmann, Steffen; Philipp, Daniel; Steinert, Michael; Acker, Denis; Remane, Yolantha; Kreul, Phil; Schneider, Maximilian; Zajonz, Sebastian; Wank, Bianca; Turco, Fabrizio; Buchfink, Manuel; Gutierrez, Elizabeth; Hofmann, Sonja; Ruffner, Silas; Wagner, Alexander; Breitenbücher, Laura; Schäfer, Felix; Herdrich, Georg; Fasoulas, StefanosThe Ferrofluid Application Research Goes Orbital (FARGO) project desires to harness the potential of ferrofluids for advanced space system applications. Thereby, the student-led research project aims to develop, evaluate and subsequently validate three different ferrofluid-based applications on board the International Space Station (ISS): a novel attitude control system called Ferrowheel as well as a Thermal and an Electrical Switch. The project is part of the Überflieger2 competition of the German Aerospace Center (DLR) in cooperation with the Luxembourg Space Agency (LSA). Central to this study is the role of ferrofluids in ensuring the functional principles to minimize the number of moving components ultimately. Therefore, the proposed systems have the potential to mitigate wear, reduce friction, and consequently improve the longevity and reliability of space systems. In the Ferrowheel, a disc is supported on ferrofluid cushions instead of conventional ball-bearing-mounted rotors. This innovative approach, facilitated by the magnetic pressure positioning of the ferrofluid, eliminates the need for solid-to-solid contact. Circularly arranged coils function as the stator, propelling the disc with a 3-phase control, resulting in a spinning magnetic field. In addition to determining the generated torque, the objective is to validate experiments on system operations in which various acceleration and deceleration manoeuvres, as well as the stored angular momentum, are evaluated. The Electrical Switch leverages a self-manufactured magnetorheological fluid (MRF) developed by augmenting a liquid-metal base with iron powder. As a result, the fluid, akin to ferrofluid, has a magnetic field-responsive movement. Since a liquid metal is used as the base, the ferrofluid-like fluid acts as both the magnetically actuatable and the current conducting fluid. To enable a current flow, the fluid is brought between the two electrical contacts utilizing electropermanent magnets (EPMs). These magnets combine the high magnetic field strengths of permanent magnets with the adaptive switching capability of electromagnets. Compared to all other demand-controlled magnetic field sources, this results in the great advantage that no energy is consumed as long as they are in one state. Only the switching process of the EPMs itself requires a high amount of energy, but only for a relatively short period. The switching behaviour under different loads will be investigated, evaluated, and compared to reference data recorded on Earth. The design of the Thermal Switch is characterized by the fact that it can be actively switched. Active thermal switching is still a relatively new field, so there is little comparative data from industrial solutions. Particularly for spacecraft, thermal design is crucial because the harsh environment of space must be taken into account. In addition to the challenge that heat can only be transferred to the environment via thermal radiation, severe conditions in space are characterized by extreme temperature differences. While extreme heat develops on the satellite surface on the side facing the sun, the opposite is valid on the shaded side. The resulting heat flow, which is irregular in time, location, and direction, leads to temperature peaks and gradients that can affect the system’s performance, functionality, and reliability. Active switching provides selective control over heat transfer, allowing more flexible temperature regulation in critical areas and implementing a dynamic system response. Different design ideas are tested and evaluated for the applications in various experiments. The most suitable design is finally selected, further modified, and tailored for experimentation on the ISS and presented in this study. The most significant challenge is the time-critical factor of only a 1-year development phase. A total of 21 students from six different courses of study and two supervising PhD students from the Institute of Space Systems are involved in the FARGO project, all members of the small satellite student society at the University of Stuttgart, KSat e.V.