ARTICLES

Ammonia fuelled space electric propulsion systems using C12A7:e- electride as electron emitter

J. F. Plaza, J. Toledo, A. Post.
Advanced Thermal Devices (ATD), C/Villaconejos 4, 28925-Alcorcon, Madrid, Spain

Abstract.

Given the significant changes taking place in the geopolitical global situation, and the derived supply chain issues for some traditional electric propulsion propellants like xenon, alternative propellants issue is perceived as a strategic topic to tackle, and ammonia (NH3) is becoming one serious candidate. Ammonia is increasingly being investigated to extend green hydrogen use by overcoming the storage and transportation issues of hydrogen. Ammonia characteristics like its superior energy density and low temperature and/or pressure needs for storage (10 bar at 20ºC for liquid ammonia), make it very valuable for simplified unexpensive energy storage and transportation, and these characteristics makes it also especially suitable for on-board spacecrafts electric propulsion purposes. Based on our research activities on ammonia generation and dissociation processes with C12A7:e- electride as catalyst, this work will describe the most relevant characteristics and properties associated to the advantages of using the cheap and abundant ammonia, and will also present and discuss the results of the first successful tests performed with ammonia as fuel for a C12A7:e- electride based neutralizer, including relevant endurance tests in operation conditions. Additionally, the dual application as propellant and on-board energy generation system of ammonia will also be discussed.

Measurement of the C12A7:e- thermionic emission enhancement due to photon exposure

J. Toledo, A. Post, J. F. Plaza.
Advanced Thermal Devices (ATD), C/Villaconejos 4, 28925-Alcorcon, Madrid, Spain

Abstract.

In this work, a test set-up device is designed, developed and manufactured to perform a direct measurement of the current emission enhancement that the photon absorption can bring to the thermionic emission in a Photon-Enhanced Thermionic Emission Device (PETED) where the C12A7:e- electride is used as the semiconductor due to its low work function value of 2.4 eV. Even though the measured thermionic emission starts at low operational temperatures, obtaining for example a current density emission of 5 mA/cm2 at 500 ºC, there is barely an increase of 1% in the current emission when the device is exposed to a source of photons. This effect is mainly due to the presence of a dielectric layer at the material surface, which acts as a barrier, reduces the current enhancement effect from photon excitation, and drives to a limited efficiency of 27 μA/cm2/W.

Identifying different electronic transport mechanisms in nanoporous inorganic electrides – a combined study using Hall measurements and electron paramagnetic resonance spectroscopy

Julius K. Dinter, Jurek Lange, Detlev M. Hofmann, J. Fabiàn Plaza Fernández, Angel Post, Sangam Chatterjee, Matthias T. Elm and Peter J. Klar

Abstract.

Mayenite [Ca24Al28O64]4+(2O2-) is a nanoporous compound, whose properties are strongly determined by its degree of reduction. It consists of a positively charged, subnanometer sized cage structure [Ca24Al28O64]4+ and two additional oxygen ions O2-, which ensure charge neutrality. The O2- ions occupy 1/6th of the cages and can move almost freely between them. A transition from insulating behavior to metallic behavior occurs when replacing the O2- ions in the cages by electrons, finally generating the electride [Ca24Al28O64]4+(4e). This wide tunability together with its mechanical stability and chemical stability make the [Ca24Al28O64]4+(2O2-)(1-x)(4e)x system highly attractive for various electronic device applications. However, a complete understanding of the charge transport mechanisms of the [Ca24Al28O64]4+(2O2-)(1-x)(4e)x system and their variation with the degree of reduction x is far from complete. Here, we present the characterization of a series of polycrystalline [Ca24Al28O64]4+(2O2-)(1-x)(4e)x with different x using Hall-measurements and electron paramagnetic resonance (EPR) spectroscopy in the full temperature range between 10 K and 300 K.

The study of temperature dependence of the effective carrier concentrations, the effective mobility, and the spin relaxation processes provides detailed insight into the electronic properties of the material. Three different transport mechanisms are identified which dominate at different temperatures. The crossover-temperature between these mechanisms is observed in both types of experiments and depends on x, which determines the effective charge carrier concentration. In addition, the interplay of the three transport mechanisms explains discrepancies which occur when solely the EPR signal intensity is used as a measure of the partially reduced effective carrier concentrations [Ca24Al28O64]4+(2O2-)(1-x)(4e)x.

Key design and operation factors for high performance of C12A7:e- based cathodes

A. Post1, J. F. Plaza1, J. Toledo1, D. Zschätzsch2, M. Reitemeyer2, L. Chen2, A. Gurciullo3, A. Siegel4, , P. J. Klar2, P. Lascombes3, and B. Seifert4.

1 Advanced Thermal Devices, C/Villaconejos 4, 28925-Alcorcon, Madrid, Spain

2 Institute of Experimental Physics I, Justus-Liebig-University, Hessen, 35392 Giessen, Germany

3 Exotrail, 3 Rue Galvani, 91300 Massy, France4 FOTEC, Viktor Kaplan-Straße 2, 2700 Wiener Neustadt, Austria

4 FOTEC, Viktor Kaplan-Straße 2, 2700 Wiener Neustadt, Austria

Abstract.

This work, based on an EU-funded project (NEMESIS), is summarising some of the results from the project activities on the research and development on electride-based cathode technology compatible with all kinds of electric propulsion (EP) systems requiring neutralization or electron emission. Further information describing in detail the performed tests and captured measurements can be found in the referenced documents of each section. Different cathode architectures and several emitter configurations with traditional and with alternative propellants are being developed and tested within the project, all of them using C12A7:e- electride material as thermionic electron source. Findings and conclusions derived from these multiple designs are allowing to figure out some of the key factors that determine the best performance of C12A7:e- electride based cathodes. In this work, a discussion of some of these key design and operation factors will be presented based both on the material characterization parameters, and on the performance tests carried out for the different cathode designs.

Full article.

Journal: Material Science and Engineering. At 2022 IOP Conf. Ser.: Mater. Sci. Eng. 1226 012092

https://iopscience.iop.org/article/10.1088/1757-899X/1226/1/012092

Performance comparison of LaB6 and C12A7:e- emitters for space electric propulsion cathodes

A. Post1, J. F. Plaza1, J. Toledo1, D. Zschätzsch2, M. Reitemeyer2, L. Chen2, A. Gurciullo3, A. Siegel4, P. J. Klar2, P. Lascombes3, and B. Seifert4.

1 Advanced Thermal Devices, C/Villaconejos 4, 28925-Alcorcon, Madrid, Spain

2 Institute of Experimental Physics I, Justus-Liebig-University, Hessen, 35392 Giessen, Germany

3 Exotrail, 3 Rue Galvani, 91300 Massy, France

4 FOTEC, Viktor Kaplan-Straße 2, 2700 Wiener Neustadt, Austria

Abstract.

This work, based on an EU-funded project (NEMESIS), is summarising some of the results from the project activities on the research and development on electride-based cathode technology compatible with all kinds of electric propulsion (EP) systems requiring neutralization or electron emission. Further information describing in detail the performed tests and captured measurements can be found in the referenced documents of each section. Different cathode architectures and several emitter configurations with traditional and with alternative propellants are being developed and tested within the project, all of them using C12A7:e- electride material as thermionic electron source. Findings and conclusions derived from these multiple designs are allowing to figure out some of the key factors that determine the best performance of C12A7:eelectride based cathodes. In this work, a discussion of some of these key design and operation factors will be presented based both on the material characterization parameters, and on the performance tests carried out for the different cathode designs.

Full article.

Journal: Material Science and Engineering. At 2022 IOP Conf. Ser.: Mater. Sci. Eng. 1226 012093

https://iopscience.iop.org/article/10.1088/1757-899X/1226/1/012093

Ion thrusters for electric propulsion – scientific issues developing a niche technology into a game changer

K.Holste,1, a) P.Dietz,1 S.Scharmann,1 K.Keil,1 T.Henning,1 D.Zschätzsch,1 M.Reitemeyer,1 B.Nauschütt,1 F.Kiefer,1 F.Kunze,1 J.Zorn,1 C.Heiliger,2 N.Joshi,2 U.Probst,3 R.Thüringer,3 C.Volkmar,3 D.Packan,4 S.Peterschmitt,4 K.-T.Brinkmann,5 H.-G.Zaunick,5 M.H.Thoma,1 M.Kretschmer,1 H.J.Leiter,1 S.Schippers,1 K.Hannemann,1, 6 and P.J.Klar1

1) Institute of Experimental Physics I, Justus Liebig University, Heinrich-Buff-Ring 16, 35392 Giessen, Germany

2) Institute of Theoretical Physics, Justus Liebig University, Heinrich-Buff-Ring 16, 35392 Giessen, Germany

3) Department of Electrical Engineering, University of Applied Sciences, Wiesenstr. 14, 35390 Giessen, Germany

4) ONERA, Palaiseau 91120, France

5) Institute of Experimental Physics II, Justus Liebig University, Heinrich-Buff-Ring 16, 35392 Giessen, Germany

6) German Aerospace Center, Institute of Aerodynamics and Flow Technology, Spacecraft Department, Bunsenstrasse 10, 37073 Goettingen, Germany

Abstract:
The transition from OLD SPACE to NEW SPACE along with increasing commercialization has a major impact on space flight in general and on electric propulsion by ion thrusters in particular. Ion thrusters are nowadays used as primary propulsion systems in space. The article describes how these changes related to NEW SPACE affect various aspects that are important for the development of electric propulsion systems. Starting with a historical overview of the development of space flight and of the technology of electric propulsion systems, a number of important missions with EP and the underlying technologies are presented. The focus of our discussion is the technology of the radio frequency ion thruster as a prominent member of the gridded ion engine family. Based on this discussion, we give an overview of important research topics such as the search for alternative propellants, the development of reliable neutralizer concepts based on novel insert materials as well as promising neutralizer-free propulsion concepts. In addition, aspects of thruster modeling and requirements for test facilities are discussed. Furthermore, we address aspects of space electronics with regard to the development of highly efficient electronic components as well as aspects of electromagnetic compatibility and radiation hardness. The article concludes with a resentation of the interaction of electric propulsion systems with the spacecraft.