Bremen Drop Tower Research Articles

Zero-g wind tunnel experiments on planetesimal erosion

ABSTRACT Wind erosion thresholds for planetesimals in protoplanetary discs depend on particle size, cohesion, ambient gas pressure, and gravity. In the experiments reported here, we used a low pressure shear wind tunnel for the first time under real zero gravity. That is, we carried out the experiments in the drop tower in Bremen at $10^{-5} \text{g}$. In concert with earlier work, we confirm the applicability of a single semi-empirical equation to describe the threshold shear stress for wind erosion. It can be applied to calculations of unstable orbits of planetesimals and the dissolution of planetesimals passing through evolving planetary atmospheres.

Magnetically-Induced Buoyancy for Efficient Electrochemical Oxygen Production in Microgravity

The realization of long-term space travels and the establishment of a lunar research platform are challenged by the lack of technological device architectures for efficient, stable and continuous oxygen production. One obstacle is that the near-absence of buoyancy in microgravity results in hindered gas bubble desorption at the electrode-electrolyte interface, causing lower efficiencies for electrolyser systems when operating in space.1,2 The significantly reduced buoyancy force also has severe complications for phase separation, which is a crucial process for a variety of space technologies also including heat transfer, fuel production and removal of carbon dioxide from cabin air. Multiple approaches have been studied in the past to induce phase separation such as creating centrifugal force fields. These approaches lack however efficiency, stability and robustness.3,4 In our recent work, we demonstrate the use of magnetic polarisation to artificially induce buoyancy in the electrolytic oxygen evolution half-cell reaction and thus significantly increasing the overall half-cell efficiency. This was carried out in a series of experiments at the Bremen Drop Tower, Center of Space Technology and Microgravity (ZARM, Germany), where short-term microgravity conditions of 9.2 s were achieved.5,6. Chronoamperometric and cyclic voltammetry measurements on high-activity RuOx electrocatalyst structures on a Ti substrate were undertaken with and without a magnet in close proximity to the electrode to closely monitor the electrochemical performance in a three-electrode potentiostatic arrangement and to demonstrate the magnetic effect on gas bubble desorption during free fall. It was observed that current densities for the electrodes at a potential of +1.49 V vs RHE were significantly higher in the presence of a magnet. We conclude that magnetic phase separation can be utilised in electrolytic systems in reduced gravitational environments to efficiently detach oxygen bubbles from the electrode surface and operate the devices at higher efficiencies, providing a key advancement for future oxygen production in space missions.2,3,5 References Cheng, W.-H.; Richter, M. H.; May, M. M.; Ohlmann, J.; Lackner, D.; Dimroth, F.; Hannappel, T.; Atwater, H. A.; Lewerenz, H.-J. (2018). Monolithic Photoelectrochemical Device for Direct Water Splitting with 19% Efficiency. ACS Energy Lett., 3, 1795−1800.Saravanabavan, S.; Coulthard, C. T.; Kaur, M.; Brinkert, K. (2022). Catalysis in Space Environments. doi.org/10.1002/9783527830909.ch7 In: Hessel V., Stoudemire J., H. Miyamoto & I. D. Fisk (Eds.). In Space Manufacturing and Resources.Wiley-VCH. ISBN: 978-3-527-83091-6Romero-Calvo, Á.; Akay, Ö.; Schaub, H.; Brinkert, K. (2022). Magnetic phase separation in microgravity. npj Microgravity 8 (32). doi.org/10.1038/s41526-022-00212-9.Harvey, A.; Ramshaw, C.; Reay, D. A. Process Intensification: Engineering for Efficiency. Sustainability and Flexibility. 2nd edition. Butterworth- Heinemann; 201Brinkert, K.; Richter, M. H.; Akay, Ö.; Liedtke, J.; Giersig, M.; Fountaine, K. T.; Lewerenz, H. J. (2018). Efficient solar hydrogen production in microgravity environment. Commun. 9(2527). doi: 10.1038/s41467-018-04844-yhttps://www.zarm.uni-bremen.de/fileadmin/user_upload/drop_tower/Users_Manual_0412.pdf

Synergistic Microfluidic and Optical Performance Enhancements of Photoelectrodes for Space Applications

The realisation of long-term space missions as well as lunar habitats require reliable and efficient oxygen and chemical producing devices e.g., for life support, fuel generation and in-situ resource utilisation (ISRU). We have recently demonstrated that integrated semiconductor-electrocatalyst systems can be operated in microgravity environments generated for 9.2 s at the Bremen Drop Tower (Center of Applied Space Technology and Microgravity, ZARM) at terrestrial efficiencies, thus opening the possibility of utilising these photoelectrochemical (PEC) devices for chemical synthesis in space. 1,2 , 3 Our findings reveal that by altering the electrocatalyst surface morphology through nanostructuring, we can introduce catalytic hot-spots on the photoelectrode which - through their hydrophilic nature - can also enhance gas bubble detachment in microgravity and thus circumvent the near-absence of buoyancy.1,3 We have found that the surface hydrophilicity and electrocatalyst loading require however careful balancing as the most effective nanostructures for gas bubble desorption can also result in less catalyst material on the photoelectrode surface, which in turn leads to a non-optimal PEC device performance.Here, we present a combined theoretical and experimental microfluidic, optical and photoelectrocatalytic performance analysis of photoelectrodes with integrated, nanostructured electrocatalysts, aiming at providing a guideline for an optimal design for microgravity applications. Focusing on the hydrogen evolution reaction (HER) and a well-investigated photoabsorber for this reaction, p-type InP, we firstly built an optoelectronic model in COMSOL Multiphysics in pursuit of quantifying the optical performance enhancements of Rh and Pt electrocatalyst nanostructures such as nanopyramids, nanowires and sub-wavelength aperture holes.4 We then developed a microfluidic model using the same nanostructure geometries to predict the hydrophilicity of the device surface and subsequently, the gas bubble contact angle. The best-performing nanostructured photoelectrodes predicted in our models where then manufactured, photoelectrochemically tested and fully optically and spectroscopically characterised. Predicted local electric field enhancements through catalytic hotspot formation were moreover experimentally validated using scanning electrochemical cell microscopy (SECCM). Our findings indicate that our developed optoelectronic and microfluidic models can be utilised to design a theoretical framework for identifying ideal electrocatalyst nanostructures for microgravity applications.References Brinkert K, et al. Efficient solar hydrogen generation in microgravity environment. Nature Communications 9, (2018). Brinkert K, Mandin P. Fundamentals and future applications of electrochemical energy conversion in space. npj Microgravity 8, (2022). Akay Ö, et al. Releasing the Bubbles: Nanotopographical Electrocatalyst Design for Efficient Photoelectrochemical Hydrogen Production in Microgravity Environment. Advanced Science 9, 2105380 (2022). Tembhurne S, Haussener S. Integrated Photo-Electrochemical Solar Fuel Generators under Concentrated Irradiation. Journal of The Electrochemical Society 163, H988 (2016). Pan Y, Huang S, Li F, Zhao X, Wang W. Coexistence of superhydrophilicity and superoleophobicity: theory, experiments and applications in oil/water separation. Journal of Materials Chemistry A 6, 15057-15063 (2018).

Hydrogen Gas Bubble Evolution on Electrocatalytic Nanostructures in Microgravity Environment

Photoelectrochemical (PEC) monolithic devices for oxygen and chemical production are attractive for space applications due to predominant weight and volume constraints as well as a high system tunability. Here, advanced semiconductor-electrocatalyst systems integrate the processes of light absorption, charge separation and catalysis in one device - processes, which are usually carried out e.g., on the International Space Station (ISS) by an electrolyser coupled to external PV cells. Due to the near absence of buoyancy and buoyancy-induced convection in micro gravity, all (photo)electrolyser systems in space naturally have lower efficiencies, as gas bubble desorption and phase separation are severely hindered. We report on a new approach to design the electrocatalyst morphology on a nanoscale in order to modify the physicochemical properties of the photoelectrode and thus allow for continuous gas bubbles desorption and efficient operation of the PEC device in microgravity. Using a rhodium-coated p-InP model photoelectrochemical system, we discuss different Rh electrocatalyst nanotopographies fabricated by shadow nanosphere lithography and report on their characterisation as well as performance in photoelectrochemical measurements realised during 9.2 s of free fall at the Bremen Drop Tower, Center of Applied Space Technology and Microgravity (ZARM). In particular, we elucidate on how the electrocatalyst nanostructures affect the gas bubble size during growth and at detachment from the electrode and conclude on an efficient (photo-)electrode design for hydrogen evolution in microgravity.

(Keynote) Releasing the Bubbles: Efficient Phase Separation in (Photo-)Electrochemical Devices in Microgravity Environment

One of the major challenges human space exploration faces is the absence of buoyancy forces in orbit. Consequently, phase separation is severely hindered which impacts a large variety of space technologies including propellant management devices, heat transfer and life support systems e.g., during the production of oxygen and the recycling of carbon dioxide. Of particular interest are hereby (photo-)electrochemical (PEC) devices as they can produce essential chemicals such as oxygen and hydrogen in two set-ups: either, by coupling the electrochemical cell to external photovoltaic cells as currently utilized on the International Space Station or by direct utilization of sunlight in a monolithic device, where integrated semiconductor-electrocatalyst systems carry out the processes of light absorption, charge separation and catalysis in analogy to natural photosynthesis in one system. The latter device is particularly interesting for space applications due to present mass and volume constraints. Here, we discuss two combined approaches to overcome phase separation challenges in (photo-)electrolyzer systems in reduced gravitational environments: using the hydrogen evolution reaction (HER) as a model reaction, we combine nanostructured, hydrophilic electrocatalyst surfaces for efficient gas bubble desorption with magnetically-induced buoyancy to direct the produced hydrogen gas bubbles on specific trajectories away from the (photo-)electrode surface. (Photo-)current-voltage (J-V) profiles obtained in microgravity environments generated for 9.2 s at the Bremen Drop Tower show that our systems can operate with our two-fold approach near terrestrial efficiencies. Simulations of gas bubble trajectories accompany our experimental observations, allowing us to attribute the achieved phase separation in the PEC cells to the increased electrode wettability as well as the systematic use of diamagnetic and Lorentz forces.

Experimental Investigation of Liquid Interface Stability During the Filling of a Tank in Microgravity

The storage of propellants in space as well as the transfer and filling of spacecraft tanks is a prerequisite for future long-term space exploration missions. In this work, the vented filling of a partially filled tank, which is envisioned as a spacecraft tank, was investigated experimentally under compensated gravity in the Bremen Drop Tower. Experiments were performed with a partially filled tank and a test liquid HFE-7500. The drop tower provides 9 s of compensated gravity. The shape of the free liquid surface inside a right circular cylinder changes from the normal gravity configuration to a free fall configuration during the test. The filling was initiated after 3.5 s and continued until the end at 9 s. The interaction of the incoming liquid jet with the liquid interface was studied for different volumetric flow rates. A stable, but not steady liquid interface was characterized by a deformation due to the incoming liquid jet and the formation of a geyser. The growth of the geyser and the following disintegration into liquid droplets indicated an unstable liquid interface. Subcritical, critical and supercritical regimes of the volumetric flow rates were identified to classify stable and unstable liquid interfaces. The critical Weber number was found to be 1.04, which corresponds to a critical volumetric flow rate of 1.30 mL s-1. This critical Weber number was compared with the existing literature. Additionally, the behaviour of the liquid interface during the reorientation of the liquid inside the tank was observed.

Human neural network activity reacts to gravity changes in vitro.

During spaceflight, humans experience a variety of physiological changes due to deviations from familiar earth conditions. Specifically, the lack of gravity is responsible for many effects observed in returning astronauts. These impairments can include structural as well as functional changes of the brain and a decline in cognitive performance. However, the underlying physiological mechanisms remain elusive. Alterations in neuronal activity play a central role in mental disorders and altered neuronal transmission may also lead to diminished human performance in space. Thus, understanding the influence of altered gravity at the cellular and network level is of high importance. Previous electrophysiological experiments using patch clamp techniques and calcium indicators have shown that neuronal activity is influenced by altered gravity. By using multi-electrode array (MEA) technology, we advanced the electrophysiological investigation covering single-cell to network level responses during exposure to decreased (micro-) or increased (hyper-) gravity conditions. We continuously recorded in real-time the spontaneous activity of human induced pluripotent stem cell (hiPSC)-derived neural networks in vitro. The MEA device was integrated into a custom-built environmental chamber to expose the system with neuronal cultures to up to 6 g of hypergravity on the Short-Arm Human Centrifuge at the DLR Cologne, Germany. The flexibility of the experimental hardware set-up facilitated additional MEA electrophysiology experiments under 4.7 s of high-quality microgravity (10-6 to 10-5 g) in the Bremen drop tower, Germany. Hypergravity led to significant changes in activity. During the microgravity phase, the mean action potential frequency across the neural networks was significantly enhanced, whereas different subgroups of neurons showed distinct behaviors, such as increased or decreased firing activity. Our data clearly demonstrate that gravity as an environmental stimulus triggers changes in neuronal activity. Neuronal networks especially reacted to acute changes in mechanical loading (hypergravity) or de-loading (microgravity). The current study clearly shows the gravity-dependent response of neuronal networks endorsing the importance of further investigations of neuronal activity and its adaptive responses to micro- and hypergravity. Our approach provided the basis for the identification of responsible mechanisms and the development of countermeasures with potential implications on manned space missions.

Experiments on rebounding slow impacts under asteroid conditions

We present a newly developed experiment for the examination of low-speed impacts under asteroid conditions. More specifically, our experimental setup enables us to simulate a very clean milligravity environment under vacuum, in which projectiles are shot at a granular bed at several cm/s. This granular bed consists of irregularly formed basalt particles with different size distributions. The experiment is carried out in the Bremen drop tower in its catapult mode, granting more than 9 s microgravity. Here, we discuss the setup and assess its performance.

Premixed methane-air flame under alternate gravity

The study is devoted to the flames instabilities that occur during the transition from the normal gravity to zero one. The experiments were carried out at the Bremen Drop tower. A stoichiometric methane-air flame was investigated during the first second after the capsule release. High amplitude oscillations with periodic flame flashback inside the burner and detaching of the hot spots during the transition period were found. The similarity of oscillation spectra for stoichiometric flames with different flow rates was observed. The coincidence of the first and second fundamental harmonics of the oscillations frequencies for all the studied flows indicates instability mechanism independence from the Reynolds number for the investigated range of Re: 600–2000 (laminar and weak turbulent regimes). It was found that the oscillations logarithmic decrements for all flow Reynolds numbers under investigation have a similar value. Based on a linear approximation, the hydrodynamic instability of a flame was considered and it was shown that the transition from conditions of normal terrestrial gravity to microgravity leads to the flame instability region extension which was confirmed experimentally. A following instability occurrence model was proposed. The buoyant motion of Kelvin-Helmholtz vortices arising at the air/combustion products interface slows down due to gravity decrease. Therefore the vortices deform not only the flame front tip but side part as well, leading to flame front deformations and constrictions, forming separating hot spots.

Evaporative cooling from an optical dipole trap in microgravity

In recent years, cold atoms could prove their scientific impact not only on ground but in microgravity environments such as the drop tower in Bremen, sounding rockets and parabolic flights. We investigate the preparation of cold atoms in an optical dipole trap, with an emphasis on evaporative cooling under microgravity. Up to $ 1\times10^{6} $ rubidium-87 atoms were optically trapped from a temporarily dark magneto optical trap during free fall in the droptower in Bremen. The efficiency of evaporation is determined to be equal with and without the effect of gravity. This is confirmed using numerical simulations that prove the dimension of evaporation to be three-dimensional in both cases due to the anharmonicity of optical potentials. These findings pave the way towards various experiments on ultra-cold atoms under microgravity and support other existing experiments based on atom chips but with plans for additional optical dipole traps such as the upcoming follow-up missions to current and past spaceborne experiments.

Experimental Methods for Efficient Solar Hydrogen Production in Microgravity Environment.

Long-term space flights and cis-lunar research platforms require a sustainable and light life-support hardware which can be reliably employed outside the Earth's atmosphere. So-called 'solar fuel' devices, currently developed for terrestrial applications in the quest for realizing a sustainable energy economy on Earth, provide promising alternative systems to existing air-revitalization units employed on the International Space Station (ISS) through photoelectrochemical water-splitting and hydrogen production. One obstacle for water (photo-) electrolysis in reduced gravity environments is the absence of buoyancy and the consequential, hindered gas bubble release from the electrode surface. This causes the formation of gas bubble froth layers in proximity to the electrode surface, leading to an increase in ohmic resistance and cell-efficiency loss due to reduced mass transfer of substrates and products to and from the electrode. Recently, we have demonstrated efficient solar hydrogen production in microgravity environment, using an integrated semiconductor-electrocatalyst system with p-type indium phosphide as the light-absorber and a rhodium electrocatalyst. By nanostructuring the electrocatalyst using shadow nanosphere lithography and thereby creating catalytic 'hot spots' on the photoelectrode surface, we could overcome gas bubble coalescence and mass transfer limitations and demonstrated efficient hydrogen production at high current densities in reduced gravitation. Here, the experimental details are described for the preparations of these nanostructured devices and further on, the procedure for their testing in microgravity environment, realized at the Bremen Drop Tower during 9.3 s of free fall.

Compact and robust diode laser system technology for dual-species ultracold atom experiments with rubidium and potassium in microgravity.

We present a compact and robust distributed-feedback diode laser system architecture for ultracold atom experiments with K41 and Rb87 in a mobile setup operating at the ZARM drop tower in Bremen. Our system withstands DC accelerations of up to 43 g in operation with only minor adjustments over several drop campaigns. Micro-integrated master-oscillator-power-amplifier modules in conjunction with miniaturized, free-space opto-mechanics are integrated on a platform with a volume of 43 L. With compact control and driver electronics, this laser system features output power and spectral characteristics suitable for 2D+ and 3D magneto-optical trapping operation, atomic state preparation, Bragg-diffraction-based atom interferometry, and detection.

Liquid hydrogen sloshing in superheated vessels under microgravity

We consider the influence of superheated walls on the axial sloshing motion of liquid hydrogen in an upright circular cylinder. The sloshing motion is induced by the capillary driven reorientation of the free surface after a step reduction of gravity. The step reduction is achieved in a drop tower facility which provides 4.7 s of compensated gravity conditions (Drop Tower Bremen). We conducted 15 experiments with two vessel radii of 26.2 mm and 20.15 mm, and various wall temperature gradients from isothermal up to 101.4 K/m. The vessels were filled with hydrogen only (single species system), and operated at a pressure of approximately 100 kPa. The saturation temperature of hydrogen at this pressure is 20.7 K. Right after the step reduction of gravity, the perfectly wetting liquid rises at the superheated wall and overshoots the steady state position of the new equilibrium, thus causing an axial sloshing motion which persists throughout the whole experiments time. It is shown that the wall superheat reduces the initial rise velocity and decreases the period of oscillation. A single sided model is presented which computes the transient temperature distribution in the wall. This model allows us to compute the heat flux into the liquid film at the wall, and therefor to determine the evaporated mass. We present a relation between the evaporated mass and the sloshing half-periods. The results contribute to the understanding of the behavior of cryogenic liquids, such as hydrogen, oxygen, and methane, in launchers, spacecrafts and future orbital propellant depots.

Effect of Gravity on Premixed Methane–Air Flames

Premixed flames under different levels of gravity were studied experimentally and numerically. The experiments were carried out in the Bremen Drop tower. The object of investigation were conical premixed rich, lean, and stoichiometric CH4–air flames with wide range of flow regimes, at Reynolds numbers of 600–2000, which were generated on specially designed cone nozzle and premixed cylinder chamber with grids and beads. Planar laser-induced fluorescence OH radicals and high-speed video recording was performed under microgravity, terrestrial conditions, and inverted gravity. All the experiments were performed at atmospheric pressure. Our experiments confirm that gravity has a complex influence on laminar and weakly turbulent premixed flames. Gravity causes flame flickering, while under reduced gravity flames are stable and almost not flicker. Based on the experimental data and numerical simulation, a correlation of flickering frequency with different mixture equivalence ratio and gravity is formed.

Low-velocity collision behaviour of clusters composed of sub-millimetre sized dust aggregates

The experiments presented aim to measure the outcome of collisions between sub-mm sized protoplanetary dust aggregate analogues. We also observed the clusters formed from these aggregates and their collision behaviour. The experiments were performed at the drop tower in Bremen. The protoplanetary dust analogue materials were micrometre-sized monodisperse and polydisperse SiO$_2$ particles prepared into aggregates with sizes between 120~$\mu$m and 250~$\mu$m. One of the dust samples contained aggregates that were previously compacted through repeated bouncing. During three flights of 9~s of microgravity each, individual collisions between aggregates and the formation of clusters of up to a few millimetres in size were observed. In addition, the collisions of clusters with the experiment cell walls leading to compaction or fragmentation were recorded. We observed collisions amongst dust aggregates and collisions between dust clusters and the cell aluminium walls at speeds ranging from about 0.1 cm/s to 20 cm/s. The velocities at which sticking occurred ranged from 0.18 to 5.0 cm/s for aggregates composed of monodisperse dust, with an average value of 2.1 cm/s for reduced masses ranging from 1.2x10-6 to 1.8x10-3 g with an average value of 2.2x10-4 g. From the restructuring and fragmentation of clusters composed of dust aggregates colliding with the aluminium cell walls, we derived a collision recipe for dust aggregates ($\sim$100 $\mu$m) following the model of Dominik \& Thielens (1997) developed for microscopic particles. We measured a critical rolling energy of 1.8x10-13 J and a critical breaking energy of 3.5x10-13 J for 100 $\mu$m-sized non-compacted aggregates.

Microgravity spreading of water spheres on hydrophobic capillary plates

We create nearly perfect centimetric spheres of water by splitting a cavity consisting of two metal hemispheres coated with a hydrophobic paint and under-filled with liquid, while releasing the apparatus in free-fall. A high-speed camera captures how water spread on hydrophobic aluminum and polycarbonate plates perforated with cylindrical capillaries. We compare observations at the ZARM drop tower in Bremen with Lattice-Boltzmann numerical simulations of Frank, Perre and Li for the inertial phase of imbibition.

Miniaturized Lab System for Future Cold Atom Experiments in Microgravity

We present the technical realization of a compact system for performing experiments with cold $^{87}{\text{Rb}}$ and $^{39}{\text{K}}$ atoms in microgravity in the future. The whole system fits into a capsule to be used in the drop tower Bremen. One of the advantages of a microgravity environment is long time evolution of atomic clouds which yields higher sensitivities in atom interferometer measurements. We give a full description of the system containing an experimental chamber with ultra-high vacuum conditions, miniaturized laser systems, a high-power thulium-doped fiber laser, the electronics and the power management. In a two-stage magneto-optical trap atoms should be cooled to the low $\mu$K regime. The thulium-doped fiber laser will create an optical dipole trap which will allow further cooling to sub-$\mu$K temperatures. The presented system fulfills the demanding requirements on size and power management for cold atom experiments on a microgravity platform, especially with respect to the use of an optical dipole trap. A first test in microgravity, including the creation of a cold Rb ensemble, shows the functionality of the system.

Electrostatic Positioning System for a free fall test at drop tower Bremen and an overview of tests for the Weak Equivalence Principle in past, present and future

The Weak Equivalence Principle (WEP) is at the basis of General Relativity – the best theory for gravitation today. It has been and still is tested with different methods and accuracies. In this paper an overview of tests of the Weak Equivalence Principle done in the past, developed in the present and planned for the future is given. The best result up to now is derived from the data of torsion balance experiments by Schlamminger et al. (2008). An intuitive test of the WEP consists of the comparison of the accelerations of two free falling test masses of different composition. This has been carried through by Kuroda & Mio (1989, 1990) with the up to date most precise result for this setup. There is still more potential in this method, especially with a longer free fall time and sensors with a higher resolution. Providing a free fall time of 4.74s (9.3s using the catapult) the drop tower of the Center of Applied Space Technology and Microgravity (ZARM) at the University of Bremen is a perfect facility for further improvements. In 2001 a free fall experiment with high sensitive SQUID (Superconductive QUantum Interference Device) sensors tested the WEP with an accuracy of 10-7 (Nietzsche, 2001). For optimal conditions one could reach an accuracy of 10-13 with this setup (Vodel et al., 2001). A description of this experiment and its results is given in the next part of this paper. For the free fall of macroscopic test masses it is important to start with precisely defined starting conditions concerning the positions and velocities of the test masses. An Electrostatic Positioning System (EPS) has been developed to this purpose. It is described in the last part of this paper.

The “Daphnia” Lynx Mark I Suborbital Flight Experiment: Hardware Qualification at the Drop Tower Bremen

The Drop Tower Bremen, a ground-based facility enabling research under real microgravity conditions, is an excellent platform for testing new types of experimental hardware to ensure full performance when deployed in costly and rare flight opportunities such as suborbital flights. Here we describe the “Daphnia” experiment which will fly on XCOR Aerospace Lynx Mark I and our experience from the hardware tests with the catapult system at the drop tower. The aim of the “Daphnia” experiment is to obtain data on the biological performance of daphnids and predator-prey interactions in microgravity, which are important for the development of aquatic bioregenerative life support systems (BLSS). The experiment consists of two subunits: The first unit is dedicated to predator-prey interactions, where behavioural analysis should reveal if microgravity interfere with prey (Daphnia) detection or feeding and therefore may interrupt the trophic cascade. The functioning of such an artificial food web is indispensable for a long-lasting BLSS suitable for long-duration manned space missions or Earth-based explorations to extreme habitats. The second unit is designed to investigate the impact of microgravity on gene expression and the cytoskeleton in Daphnia. Next to data collection, the real microgravity conditions at the drop tower have helped to identify the weak points of the “Daphnia” experimental hardware and lead to further improvement. Hence, the drop tower is ideal for testing new experimental hardware which is indispensable before the implementation in suborbital flights.

Drop Tower Physics

The drop towers of yesteryear were used to make lead shot for muskets, as described in The Physics Teacher1 in April 2012. However, modern drop towers are essentially elevators designed so that the cable can “break” on demand, creating an environment with microgravity for a short period of time, currently up to nine seconds at the drop tower in Bremen, Germany. Using these drop towers, one can briefly investigate various physical systems operating in this near zero-g environment. The resulting “Drop Tower Physics” is a new and exciting way to challenge students with a physical example that requires solid knowledge of many basic physics principles, and it forces them to practice the scientific method. The question is, “How would a simple toy, like a pendulum, behave when it is suddenly exposed to a zero-g environment?” The student must then postulate a particular behavior, test the hypothesis against physical principles, and if the hypothesis conforms to these chosen physical laws, the student can formulate a final conclusion. At that point having access to a drop tower is very convenient, in that the student can then experimentally test his or her conclusion. The purpose of this discussion is to explain the response of these physical systems (“toys”) when the transition is made to a zero-g environment and to provide video demonstrations of this behavior to support in-class discussions of Drop Tower Physics.