Klaus Marhold

Measurement of Gravitomagnetic and Acceleration Fields around Rotating Superconductors

It is well known that a rotating superconductor produces a magnetic field proportional to its angular velocity. The authors conjectured earlier, that in addition to this so‐called London moment, also a large gravitomagnetic field should appear to explain an apparent mass increase of Niobium Cooper‐pairs. A similar field is predicted from Einstein’s general relativity theory and the presently observed amount of dark energy in the universe. An experimental facility was designed and built to measure small acceleration fields as well as gravitomagnetic fields in the vicinity of a fast rotating and accelerating superconductor in order to detect this so‐called gravitomagnetic London moment. This paper summarizes the efforts and results that have been obtained so far. Measurements with Niobium superconductors indeed show first signs which appear to be within a factor of 2 of our theoretical prediction. Possible error sources as well as the experimental difficulties are reviewed and discussed. If the gravitomagne...

Development and Test of a Miniature Hydrogen Peroxide Monopropellant Thruster

Analysis of present and future missions concluded that a miniaturised hydrogen peroxide monopropellant rocket engine is the optimum solution for the increasing demand for small and low cost propulsion systems for small satellites. The attractiveness of monopropellant thrusters is based on its operational and structural simplicity. Additionally, the utilization of hydrogen peroxide as propellant instead of hydrazine allows the reduction of the overall costs and would qualify such a system as a green propellant propulsion system. The present paper describes the development of a monopropellant thruster utilizing hydrogen peroxide and advanced catalyst beds. The utilization of a monolithic catalyst reduces the pressure loss across the catalyst bed significantly compared to formerly used pellet or gauze catalyst. This allows the use of relative lightweight tank and significantly minimizes the total weight. For Two different catalyst materials have been developed to achieve optimized decomposition. The present paper summarizes the experimental evaluation of the catalysts. Decomposition temperatures of up to 670°C and decomposition efficiencies up to 99% have been achieved. Up to 1.2 kg of hydrogen peroxide has been decomposed by a single catalyst, corresponding to about 1.25 hrs of operation. This is estimated to correspond in vacuum condition to a total delivered total impulse of 1600 Ns. A thrust balance was designed and built. Preliminary thrust measurements under atmospheric conditions have shown that the laboratory model can generate thrust in a range of at least 50 to 550 mN.

Indium FEEP Cluster Development

During the GOCE microthruster program and follow-up endurance tests, ARCS has collected more than 3800 operating hours at a mean thrust of 10 μN with one microthruster, and 18000 hours of cumulative operation with several thrusters. The lessons learned during this intensive test campaign allowed to greatly improve the performance of the indium FEEP emitters: higher mass efficiency, lower erosion, higher lifetime. These emitters have a maximum continuous thrust level of 10-12 μN. In order to fulfill the thrust requirements of missions like LISA Pathfinder (100 μN), it is necessary to cluster a certain number of emitters. This cluster must be operated with a single high voltage power supply, in order to reduce costs and system complexity. In this case, the ion emitters must fulfill stringent clustering requirements on mass efficiency, electrical impedance and threshold voltage. In this paper we report the experimental investigation on new emitter concepts suitable for clustering. Four emitters of the selected concept are now running in the first In-FEEP Cluster Endurance Test, which is the longest reported endurance test of a FEEP microthruster, with 3100 hours of continuous operation at maximum thrust (26-30 μN) collected till 4 of July; this corresponds to almost 40% of the LISA Pathfinder total impulse. We also report about the design of a 4x4 Indium FEEP Cluster Breadboard, which can operate at a maximum continuous thrust of 150 μN. This cluster includes a new focusing system, that reduces the ion beam divergence to less than 30°, within the LPF requirements.

Micronewton Thrust Balance for Indium FEEP Thrusters

Thrust measurements of electric propulsion devices are essential for validating, characterizing and qualifying their performance. For this purpose a direct thrust measurement system for use with In-FEEP thrusters has been designed at ARC Seibersdorf research (ARC -sr), based on a torsional balance design. A symmetric arm is able to rotate by means of two flexural pivots. The linear displacement of the arm (which is a function of the applied thrust) is measured with an optical displacement sensor. The system also allows upscaling to measure the thrust of a new generation of In -Feep Clusters that are currently developed at ARC- sr . An electrical damping system is used to reduce oscillations of the arm. Special attention has to be given to the cables supplying the heating and operating power of the In-Feep thruster. In this paper we present the design of the thrust stand as well as preliminary measurements.

Test of a Turbo-Pump Fed Miniature Rocket Engine

The increasing application of microsatellites (from 10 kg up to 100 kg) for a rising number of various missions requires the development of suitable propulsion systems. Microsatellites have special requirements for a propulsion system such as small mass, reduced volume, and very stringent electrical power constraints. Existing propulsion systems often can not satisfy these requirements. The present paper discusses the development and test of a bipropellant thruster complying with these requirements. The main development goal of this effort was the utilization of ethanol in combination with hydrogen peroxide (H2O2) as a non-toxic propellant combination. The Turbo-Pump Fed Miniature Rocket Engine (TPF-MRE) is a bipropellant thruster consisting of four subsystems: the propellant pumps, a decomposition chamber with a monolithic catalyst, a turbine, and the thruster itself. The turbine is driven by the decomposed hydrogen peroxide and magnetically coupled with a power generator. The power produced is then used to generate a pressure head in order to deliver the propellant into the combustion chamber. This system therefore constitutes a self-sustaining system and does not rely on the limited power supply of a micro-satellite. Previous test have shown that although the thruster can be operated with ethanol and oxygen, it was not possible to ignite the thruster when utilizing hydrogen peroxide in a 70% concentration by weight. A minor redesign of the thruster and the test facility was therefore initiated. This redesign together with the use of hydrogen peroxide in higher concentration was speculated to improve this behavior. However, even though the monolithic catalysts were able to decompose hydrogen peroxide in a concentration of 87.5 % with nearly 100 % efficiency, it was not possible to ignite or operate the thruster. Subsequently, a thorough investigation of the baseline design and operational conditions of the thruster was conduced. It was found that the failure of the thruster to ignite is due to a combination of reasons. The combustion chamber length is too short to facilitate sufficient mixing of the propellants, making an ignition impossible or very difficult at least. Additionally, the combustion chamber pressure which was chosen such that it accommodates the performance of commercially available mircopumps is considered too low. This further deteriorates the conditions for which an ignition is feasible.

Weight Measurements of High‐Temperature Superconductors during Phase Transition in Stationary, Non‐Stationary Condition and under ELF Radiation

There have been a number of claims in the literature about gravity shielding effects of superconductors and more recently on the weight reduction of superconductors passing through their critical temperature. We report several experiments to test the weight of superconductors under various conditions. First, we report tests on the weight of YBCO and BSCCO high temperature superconductors passing through their critical temperature. No anomaly was found within the equipment accuracy ruling out claimed anomalies by Rounds and Reiss. Our experiments extend the accuracy of previous measurements by two orders of magnitude. In addition, for the first time, the weight of a rotating YBCO superconductor was measured. Also in this case, no weight anomaly could be seen within the accuracy of the equipment used. In addition, also weight measurements of a BSCCO superconductor subjected to extremely‐low‐frequency (ELF) radiation have been done to test a claim of weight reduction under these conditions by De Aquino, and ...

Development of a Focus Electrode for an Indium FEEP Thruster

The geometry of the electrode array in a field emission electric propulsion (FEEP) thruster is extraordinarily important, not only for thrust-relevant parameters, but also to ensure long-term reliability. Ion beams require good focusing because stray ions and charged droplets cause damage to the device in multiple ways. The aim of this paper is to investigate the correlation of initial spray angle at the Taylor-cone to the emitter current for an indium Liquid Metal Ion Source (LMIS) and to design an improved focusing electrode which guides the ion beam in such a manner that even very divergent beams caused by large emitter currents are focused and expelled without contact to the extractor, the focus electrodes or the plume shield. To that goal, the electrode array of an Indium-based thruster being developed by the Austrian Research Center Seibersdorf (ARC-sr) is simulated in an ion-trajectory program and various geometries tested for their focusing qualities. Finally, a focus electrode is designed which shapes the ion beam in such a manner that the expelled ion beam conforms to the specifications imposed by the requirements for the LISA mission.

Experimental Study of the Machian Mass Fluctuation Effect Using a μN Thrust Balance

Already since 1990, James F. Woodward, professor of physics at the California State University, provided a set of equations showing that it should be possible, via Mach’s Principle, to change transiently the mass of a body. Several devices were developed, that suggest that the phenomenon is real. The main goal of the experimental campaign proposed here is to perform an independent test for the existence of machian mass fluctuations: we will study the behavior of a test device using a very sensitive thrust balance developed for field emission thrusters. The balance has a sub μN accuracy, which should prove the effect at least with a thrust‐to‐noise ratio of 100:1. This mass fluctuation effect, if proved to be genuine, would open the doors to a new kind of propellantless propulsion which could be directly applied to space exploration. Another aspect of our work is to explore also the possibility to achieve higher power efficiency and a more compact design, making then these devices attractive for practical ...

Electrostatic torque—a misinterpretation

In a work published by Khachatourian and Wistrom, it was shown that a special arrangement of three conducting spheres could expel a mechanic torque on these conductors [1]. They claimed to have experimental data available, which show the validity of their claim [2]. We will demonstrate from basic calculations that this effect does not exist, but is an artefact of truncating a series expansion.