Martin Tajmar

Earth’s residual atmosphere in the very low Earth orbit (VLEO) can be used as a fuel source for air-breathing electric propulsion (ABEP) systems, supplying satellites with a virtually unlimited amount of propellant so that mission lifetime becomes independent from fuel storage. Operating future satellites at such altitudes offers advantages, including low-latency communication, high-resolution Earth observation, the potential to reduce launch costs, and a rapidly self-cleaning orbit, thereby reducing the risk of long-term space debris. To characterize performance and reduce development time and costs for ABEP systems, the capability to conduct terrestrial tests of complete ABEP systems in vacuum facilities is crucial. Since 2021, a VLEO particle source has been under development at Institute of Aerospace Engineering (ILR) at TU Dresden for various applications, including material testing and ABEP system testing. This paper presents a concept for a suite of four combined diagnostics to determine the flux density and average velocity of the particle beam, which shall primarily consist of neutral atomic oxygen and molecular nitrogen, to precisely replicate the VLEO residual atmosphere. The selected diagnostics will be described, along with an explanation of how they work together to detect as many beam parameters as possible. The basic principles of the ABEP test facility are discussed, with binary conditions focusing on altitudes between 180 km to 250 km.

Modified Kaluza-Klein theories have recently claimed to explain variations in experiments to determine Newton's gravitational constant. Also, an experiment was published that shall demonstrate an anomalous force from a magnetically shielded solenoid on a non-magnetic pendulum in line with predictions. We recently performed a similar pendulum test in vacuum with no evidence for such a force. However, as the theory is claimed to depend on ambient matter density, we performed another experiment using a laboratory precision balance to test for anomalous weight or force changes from magnetic and non-magnetic samples originating from toroidal solenoids at ambient pressure and in a water environment. After eliminating thermal drifts and electromagnetic effects, no measurable mass change was found within the balance's resolution of 0.1 mg for DC with up to 3 A. Using predictions based on Mbelek's theory and coupling constant, our experiment lowers the limit of any anomalous coupling by at least 6-10 orders of magnitude, depending on the use of ferromagnetic or non-magnetic solenoids.

A fiber optic gyroscope (FOG) using the 3x3-configuration (3x3-FOG) with significantly improved angle random walk (ARW) and bias stability compared to previous designs is presented. The performance is intermediate gyroscope grade with further potential: this outperforms the currently best available MEMS gyroscopes in stability, with an Allan bias stability of 0.02 °/h and an 1σ-bias stability of 0.041 °/h. It is similar to performant minimum configuration FOGs in ARW with a value of 0.000912 °/√h. While the 3x3-FOG does not compete on size, mass, and high-end bias stability performance, it has advantages in price and complexity. With the use of commodity single mode fiber, it could be the most cost-efficient way to reach intermediate and inertial grade precision, and could be used for inertial navigation systems (INS). This article lays out the gyroscope setup and the results in detail, outlining the problems with different understandings of gyroscope precision. Present issues that impact 3x3-FOGs, like scale factor accuracy, are discussed, and design principles laid out. An outlook on the possible future of this written off technology and necessary research is presented.

Electrospray thrusters have garnered significant attention throughout the years as an exceptional propulsion technology for nano- and picosatellites due to their efficiency and precise thrust control. They operate on the principle of electrostatically accelerating charged particles (liquid droplets, pure ions or their mixtures) from ionic liquids and other low-volatility propellants, which are extracted from a Taylor-cone formation on top of porous emitter arrays. In this work we characterized the thrust performance of electrospray thrusters with the ionic liquid 1-ethyl-3-methylimidazoliumtetrafluoroborate (EMI-BF₄) as well as an attempt with an acetate-based ionic liquid. The arrays were operated at different polarities and at elevated temperatures of up to 43 °C which led to a decrease in viscosity and enhanced current emission for EMI-BF₄ with a factor of 1.43 at equal voltage levels. Temperature related effects resulted in a thrust difference of 3% between the maximum and minimum temperature throughout the tested current range. Thrust measurements for emission currents between 10 µA and 200 µA revealed a detectable and temperature independent difference between the positive and negative mode in favor of the negative polarity, indicating different ion-regimes compared to most data found in literature. The paper presents a novel thrust measurement setup for micro-propulsion systems based on a counterbalanced double pendulum thrust balance that achieves nanonewton resolution with the option to heat several thrusters. A comprehensive overview of the test setup and calculations of obtained electrospray parameters from experimental data is presented.

While traditional Hall-effect thrusters are known for their high specific impulse and efficiency, they require additional mechanical components to achieve the precise thrust vector control required for orbital maneuvers and attitude corrections. These additional components can impact the overall system performance by increasing weight, volume, complexity, and susceptibility to failure. To address these issues, the Technische Universität Dresden (TUD) has developed an innovative Hall-effect thruster with a segmented anode, the TUD-3D-1. This design allows thrust vector control in all three spatial directions solely by manipulating the ion beam, eliminating the need for additional mechanical components. The paper explains the underlying principles, as well as potential benefits of this advanced thruster technology and presents test results of the prototype.

Field emission cathodes are being developed as replacements for hollow cathodes, which are impractical for electrodynamic tether systems on small and microsatellites due to their size constraints. We have designed a novel radial electron emitter based on commercially available carbon nanotube fibres and yarns. To create a field emission array capable of delivering currents exceeding 10 mA over extended periods, we fabricated and tested miniaturised prototypes of varying sizes. This parameter study aimed to explore the complex interplay between the electric field, emitter design, and carbon nanotube degradation. Long-term testing of up to 350 hours for each configuration provided insights into the radial emitter’s performance and allowed for a reliable assessment of the long-term degradation of the carbon nanotube material. Using the best configuration, we achieved a power efficiency of 1.7 mA/W at 1.5 mA after 300 hours of operation. We have identified cathodes with a large emission surface and small electrode spacing as the best design for scaling to the application case. Additionally, we were able to successfully describe the degradation-induced voltage rise for the three very different cathodes in a mathematical model, which significantly simplifies the design of scaled versions.

In recent years, advanced nozzle concepts have attracted interest because of advancements in their technology readiness level and studies on applications to vertical take-off and landing reusable launch vehicles. This is ascribable to their intrinsic altitude compensation properties, which could mitigate the additional propellant cost resulting from the vertical landing manoeuvres based on retro-propulsion. Experimental and numerical campaigns at the Technical University of Dresden test the performance of annular-aerospike, dual-bell, and expansion-deflection nozzles compared with conventional bell-shaped nozzles in various subsonic counter-flow regimes and atmospheric conditions. The methods of investigation and a detailed description of the experimental and numerical results are reported. More specifically, the study offers a comparison between advanced and conventional nozzles, with a focus on nozzle performance through experiments and aerodynamic performance and retro-flow interaction through simulations. The flow topology that is established within the area of interaction between nozzle jets and counter-flows is detailed, with the advantages and limitations of each advanced nozzle in terms of adaptive performance. The numerical simulations confirm that advanced nozzles achieve altitude compensation in retro-flow configurations. Moreover, the distance obtained from the models for jet penetration into subsonic counter-flows is compatible with empirical formulations available in the literature.

This work presents a process for the creation of emitter structures for liquid metal ion sources based on suspensions of iron and nickel in gallium-based room temperature liquid metal alloys. The process does not require needle etching or vacuum wetting of the emitter. Tip radii of less than 3 μm have been achieved. In addition, first measurements and observations from single emitter emission experiments are presented, including current-voltage characteristics, vacuum stability, degradation mechanisms and first thruster characteristics for the use in field emission electric propulsion. The impedance of the magnetic liquid metal emitters was found to correlate with the mass fraction of particles suspended in the liquid metal. Total impedances up to 30 MΩ have been achieved, indicating the feasibility of emitter clustering. Thrust measurements were performed with a commercial of the shelf load cell and verified in a dedicated setup for field emission electric propulsion testing, featuring a sub micro newton counterbalanced double pendulum thrust balance.