Quantensensoren auf Basis ultra-kalter Atome sind gegenwärtig auf dem Weg ihre klassischen Pendants als Messintrumente sowohl in Präzision als auch in Genauigkeit zu überholen, obwohl ihr Potential noch immer nicht vollständig ausgeschöpft ist. Die Anwendung von Quantensensortechnologie wie Materiewelleninterferometern im Weltraum wird ihre Sensitivität weiter steigen lassen, sodass sie potentiell die genauesten erdbasierten Systeme um mehrere Grössenordnungen übertreffen könnten. Mikrogravitationsplattformen wie Falltürme, Parabelflugzeuge und Höhenforschungsraketen stellen exzellente Testumgebungen für zukünftge atominterferometrische Experimente im Weltraum dar. Andererseits erfordert ihre Nutzung die Entwicklung von Schlüsseltechnologien, die hohe Standards in Bezug auf mechanische und thermische Robustheit, Autonomie, Miniaturisierung und Redundanz erfüllen müssen. In der vorliegenden Arbeit wurden erste Interferometrieexperimente mit degenerieten Quantengasen in Schwerelosigkeit im Rahmen des QUANTUS Projektes durchgeführt. In mehr als 250 Freifall-Experimenten am Bremer Fallturm konnte die Präparation, freie Entwicklung und Phasenkohärenz eines Rubidium Bose- Einstein Kondensates (BEC) auf makroskopischen Zeitskalen von bis zu 2 s untersucht werden. Dazu wurde ein BEC-Interferometer mittels Bragg-Strahlteilern in einen Atomchip-basierten Aufbau implementiert. In Kombination mit dem Verfahren der Delta-Kick Kühlung (DKC) konnte die Expansionsrate der Kondensate weiter reduziert werden, was zur Beobachtung von effektiven Temperaturen im Bereich von 1 nK führte. In einem Interferometer mit asymetrischer Mach-Zehnder Geometrie konnten Interferenzstreifen mit hohem Kontrast bis zu einer Verweildauer von 2T = 677 ms untersucht werden. / State-of-the-art cold atomic quantum sensors are currently about to outpace their classical counterparts in precision and accuracy, but are still not exploiting their full potential. Utilizing quantum-enhanced sensor technology such as matter wave interferometers in the unique environment of microgravity will tremendously increase their sensitivity, ultimately outperforming the most accurate groundbased systems by several orders of magnitude. Microgravity platforms such as drop towers, zero-g airplanes and sounding rockets are excellent testbeds for advanced interferometry experiments with quantum gases in space. In return, they impose demanding requirements on the payload key technologies in terms of mechanical and thermal robustness, remote control, miniaturization and redundancy. In this work, first interferometry experiments with degenerate quantum gases in zero-g environment have been performed within the QUANTUS project. In more than 250 free fall experiments operated at the drop tower in Bremen, preparation, free evolution and phase coherence of a rubidium Bose-Einstein condensate (BEC) on macroscopic timescales of up to 2 s have been explored. To this end, a BEC interferometer using first-order Bragg diffraction was implemented in an atomchip based setup. Combined with delta-kick cooling (DKC) techniques to further slow down the expansion of the atomic cloud, effective temperatures of about 1 nK have been reached. With an asymmetrical Mach-Zehnder geometry, high-contrast interferometric fringes were observed up to a total time in the interferometer of 2T = 677 ms.

This thesis presents a research project in the field of oxygen system fire safety relating to the heterogeneous burning of iron in normal gravity and reduced gravity. Fires involving metallic components in oxygen systems often occur, with devastating and costly results, motivating continued research to improve the safety of these devices through a better understanding of the burning phenomena. Metallic materials typically burn in the liquid phase, referred to as heterogeneous burning. A review of the literature indicates that there is a need to improve the overall understanding of heterogeneous burning and better understand the factors that influence metal flammability in normal gravity and reduced gravity. Melting rates for metals burning in reduced gravity have been shown to be higher than those observed under similar conditions in normal gravity, indicating that there is a need for further insight into heterogeneous burning, especially in regard to the rate-limiting mechanism. The objective of the current research is to determine the cause of the higher melting rates observed for metals burning in reduced gravity to (a) identify the rate-limiting mechanism during heterogeneous burning and thus contribute to an improved fundamental understanding of the system, and (b) contribute to improved oxygen system fire safety for both ground-based and space-based applications. In support of the work, a 2-s duration ground-based drop tower reduced-gravity facility was commissioned and a reduced-gravity metals combustion test system was designed, constructed, commissioned and utilised. These experimental systems were used to conduct tests involving burning 3.2-mm diameter cylindrical iron rods in high-pressure oxygen in normal gravity and reduced gravity. Experimental results demonstrate that at the onset of reduced gravity, the burning liquid droplet rapidly attains a spherical shape and engulfs the solid rod, and that this is associated with a rapid increase in the observed melting rate. This link between the geometry of the solid/liquid interface and melting rate during heterogeneous burning is of particular interest in the current research. Heat transfer analysis was performed and shows that a proportional relationship exists between the surface area of the solid/liquid interface and the observed melting rate. This is confirmed through detailed microanalysis of quenched samples that shows excellent agreement between the proportional change in interfacial surface area and the observed melting rate. Thus, it is concluded that the increased melting rates observed for metals burning in reduced gravity are due to altered interfacial geometry, which increases the contact area for heat transfer between the liquid and solid phases. This leads to the conclusion that heat transfer across the solid/liquid interface is the rate-limiting mechanism for melting and burning, limited by the interfacial surface area. This is a fundamental result that applies in normal gravity and reduced gravity and clarifies that oxygen availability, as postulated in the literature, is not rate limiting. It is also established that, except for geometric changes at the solid/liquid interface, the heterogeneous burning phenomenon is the same at each gravity level. A conceptual framework for understanding and discussing the many factors that influence heterogeneous burning is proposed, which is relevant to the study of burning metals and to oxygen system fire safety in both normal-gravity and reduced-gravity applications.