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A critical issue in future long-term space exploration missions is the storage and management of cryogenic propellants. Storage tanks are exposed to extreme temperatures and radiation, which can generate hot spots on the tank internal walls even with an efficient temperature insulation. Counteract the effects of the sources of heat on the propellant is a necessity as vapor bubbles may be created, which can become dangerous for some engine components apart from decreasing the amount of available propellant. We present an experimental study carried out in terrestrial gravity and in microgravity conditions on the effects of acoustic actuation in the heat transfer between a two-dimensional heating element and a liquid in a nucleate boiling regime. Two configurations of the heater orientation with respect to the direction of propagation of the acoustic wave and several acoustic frequencies were considered. Heater surface temperature and heat flux were measured in all the performed tests. Acoustic actuation in microgravity increased the heat flux from the heater to the liquid an 8.6% in comparison with the gravity scenario without actuation, and an 8.4% in comparison with a microgravity scenario without actuation. The heat transfer enhancement is larger at frequencies providing higher acoustic amplitudes, which are the frequencies close to the nominal frequency of the piezoelectric acoustic actuator. The influence of the material of the heater substrate on the acoustic field plays a role in the behavior of temperature and heat flux. The results of this work show that acoustic actuation is a feasible approach for the thermal management of boil-off in cryogenic propellants. This research was funded by the Agencia Estatal de Investigacion (Spain)projects ESP2015-72277-EXP and ESP2016-79196-P (AEI/FEDER, UE). We thank the European Space Agency for funding the drops at the ZARM drop tower, and 350 ZARM for technical support and assistance.

This work describes large strain quasi-static and impact tests of a new class of low-cost, uniaxially thermoformed, transverse isotropic auxetic foams with compression ratio ranging from 20% to 80%. A custom drop tower rig with high-speed cameras suitable for these soft porous foam materials is designed and used to perform impact tests with energy ranging from 0.38J to 1.90J, corresponding to strain rates from 64/s to 143/s. The thermoformed foams only show auxeticity when loaded along the transverse direction to the uniaxial thermoforming compression, with Poisson’s ratio ν_21 reaching as low as -1.5 at 20% strain and then close to 0 at large strains. The samples deform with large shear band deformations, also due to the auxeticity. The negative Poisson’s ratio foams along that transverse direction also show enhanced impact energy absorption performance, with normalized peak force reduction as high as ~40% against the pristine foam; the reduction is however 20% along the thermoforming direction. A constitutive model based on Nagy’s approach is applied to describe the enhancement of dynamic stress during the impact tests compared with the quasi-static one, due to strain rate effects.

Propellant management devices (PMDs) are a key component used to manage liquid propellant in a propellant tank under zero gravity conditions. A microgravity drop tower test system was established to investigate the performance of a PMD. A single module was used for the experiments, and the microgravity level was less than 3 × 10 − 3 g . Anhydrous ethanol was used as the simulate liquid. Different volume fractions of liquid were used to study the influence of the PMD on performance management. Experiments were conducted with the position of the container oriented in different directions. Changes in the gas-liquid interface were studied during the test. This kind of vane transports liquid through the rectangular area between the vane and the wall. The velocity flows along the vane of different liquid volume fractions in the tank were different at the beginning ( t < 0.8 s ) compared with the end of the test. The liquid relocation time was less than 0.8 s while the liquid volume fraction was larger than 25%. The liquid relocation time was prolonged when the liquid volume fraction was less than 25%. The liquid climbing height along the vane under microgravity increased as the volume fraction of liquid reduced. The climbing velocity of the liquid is half reduction when the liquid volume fraction is small. The time for the liquid transferred from the top of the tank to the liquid outlet can be obtained by climbing velocity. It shows that the maneuverability of the satellite decreases at the end of its life. The above results are applicable to all propellant tank with vertical vanes. These results provide a favorable reference for further optimized design of vertical vane-type propellant tanks.

Propellant tank is used to store the propellant in propulsion system of satellite. Propellant management device (PMD) is the key component in propellant tank to manage the liquid propellant under zero gravity. In this paper, a microgravity drop tower test system was established to investigate the performance of vanes and refillable reservoir separately. Single module is used for experiment tests, and the microgravity level is between 10 − 2 g 0 and 10 − 3 g 0 . Vane is fixed in a plexiglas container which provide a visual windows for the inner flow distribution. The anhydrous ethanol is used as analogue liquid. Different kinds of vanes were used to study influence of the geometry on the transport performance. Experiment tests of refillable reservoir were performed with different direction of gravity. Changes of liquid-gas interface during the test are studied. The width of the vane is related to the velocity of the liquid flow along the vane. The liquid climbing height along vane under microgravity is proportional to the time t 1 / 2 . Experiment results show that the direction of microgravity has great effect on the expulsion efficiency of a vane type tank. Experimental results provide a favorable reference for further optimization design of vanes and refillable reservoir.

A new experimental setup for the generation of homogeneous, monodisperse bubble suspensions in turbulent duct flows in microgravity has been designed and tested in drop tower experiments. The setup provides independent control of bubble size, void fraction and degree of turbulence. The device combines several slug-flow injectors that produce monodisperse bubble jets, with a turbulent co-flow that ensures homogeneous spatial spreading. Bubble separation in the scale of the most energetic eddies of the flow, and bubble size sufficiently smaller, ensure that turbulence is most efficient as a mechanism for spatial spreading of bubbles while preventing coalescence, thus optimizing the homogeneous and monodisperse character of the suspension. The setup works in a regime for which bubbles are spherical, but sufficiently large compared to the turbulent dissipative scales to allow for two-way coupling between bubbles and carrying flow. The volume fraction is kept relatively small to facilitate particle tracking techniques. To illustrate the potential uses of the method we characterize the statistics of bubble velocity fluctuations in steady regimes and we characterize the transient relaxation of the buoyancy-driven pseudo-turbulence when gravity is switched-off. We acknowledge the support from ESA for the funding of the drop tower experiments that provided the raw data analyzed and the ZARM crew, in particular to Dieter Bischoff, for their valuable support all along the experiments and their hospitality. We acknowledges financial support from Ministerio de Economia y Competividad (Spain) under projects FIS2013-41144-P, FIS2016-78507-C2-2-P (J.C.), FIS2015-66503-C3-2-P (L.R.-P., also financed by FEDER, European Union), ESP2014-53603-P (X.R.), and Generalitat de Catalunya under projects 2014-SGR-878 (J.C.), 2014-SGR-365 (X.R.). P.B. acknowledges Ministerio de Ciencia y Tecnología (Spain) for a pre-doctoral fellowship

Through the striving of humanity into space, new production processes and technologies for the use under microgravity will be essential in the future. Production of objects in space demands for new processes, like additive manufacturing. This paper presents the concept and the realization for a new machine to investigate microgravity production processes on earth. The machine is based on linear long stator drives and a vacuum chamber carrying up to 1000 kg. For the first time high repetition rate and associated low experimental costs can provide basic research. The paper also introduces the substrate-free additive manufacturing as a future research topic and one of our primary application.

Experiments with granular gases do not only provide statistical information on multi-particle systems undergoing random dissipative interactions, they may also help to test predictions of numerical simulations and to gain understanding of the self-organization of dilute granular matter to clusters and stable assemblies. We shortly review an experiment under zero gravity conditions on different platforms. Implementations on a sounding rocket flight, parabolic flights and drop tower shots are analyzed. We evaluate general experimental requirements, judge the appropriateness of the different platforms, and present quantitative results.

This paper describes about the development of microgravity condition on Earth using drop tower method. Microgravity is an environment or a condition in which weight of a system is very small as compared to its actual weight which is experienced due to Earth's gravity. Drop tower method is an important ground based facility for microgravity science experiment. Although the duration of microgravity is relatively short, the drop tower/well facility has many advantages, such as excellent microgravity level, low cost per experiment, many drops per day, ability to use precise equipment etc. All these advantages make it an important facility for performing microgravity experiments.

In this paper design, implementation, laboratory and microgravity tests of a space tether length and length rate measurer are discussed. The instrument presented was part of an experimental setup consisting in a new concept of space tether deployer with retrieval capability, which was designed and built in the framework of the Drop Your Thesis! 2016 educational programme, held by the European Space Agency Education Office. The instrument working principle is based on optical sensors and is inspired to similar instruments used on SEDS and YES2 space missions. The entire setup was first tested in laboratory on a low friction rail, then in microgravity conditions at the ZARM Drop Tower. The results of the test campaign proved the functionality of the measurement instrument which allowed the experiment to meet the prefixed goals.

The MICROSCOPE mission is fully dedicated to the in-orbit test of the Universality of free fall, the so-called Weak Equivalence Principle (WEP), with an expected accuracy better than 10 −15 . The test principle consists in comparing the accelerations of two proof masses of different composition in the Earth gravitational field. The payload embarks two pairs of test-masses made of Platinum Rhodium and Titanium alloys at the core of two dedicated coaxial electrostatic accelerometers. These instruments are under qualification for a launch in 2016. Their operations are only possible in microgravity environment which makes its validation on ground a real issue. In Europe, only the drop tower of the ZARM Institute provides a facility for experiments under conditions of weightlessness and offers the experimental conditions to verify the correct functioning of the MICROSCOPE payload. The height of the tower limits the “free fall” experiment period to 4.72 s. Under this strong constraint, the demonstration of the capability to control the test masses of the two coaxial electrostatic accelerometers is challenging. This paper describes the complete experimental set up and in which condition the test has been performed, then an analysis of a drop result is given with its interpretations.

The propellant acquisition vane (PAV) is a key part of a vane type surface tension propellant management device (PMD), which can manage the propellant effectively. In the present paper, the fluid transportation behaviors for five PAVs with different sections were investigated by using microgravity drop tower test. Further, numerical simulation for the propellant flow in a PMD under microgravity condition was also carried out based on VOF model, and showed the similar flow pattern for PAVs to the experiment. It is noted that the section geometry of PAVs is one of the main factors affecting the fluid transportation behavior of PMD. PAVs with bottom length ratio of 5/6 and 1/2 have larger propellant transportation velocity. Based on the experiments, there were two stages during the process of propellant transportation under microgravity environment: liquid relocation and steady transportation stage. It is also recognized that there is a linear correlation between liquid transportation velocity and relative time`s square root. Those results can not only provide a guideline for optimization of new vane type PMDs, but also are helpful for fluid control applications in space environment.

The computational and experimental studies have been performed to investigate the hydrodynamic process of liquid propellant reorientation for the launch vehicle series fuel tanks in microgravity environment. The VOF method was used to simulate the free surface flow of gas-liquid. The process of the liquid propellant reorientation started from initially curved interface at low Bond number. The propellant reorientation flow procedure at high Bond number was obtained from numerical simulation and scale model experiment in drop tower. The numerical results agreed well with the experiments. The results can be used to adjust the engineering reorientation parameters.

Satellites store and manage propellant by surface tension. A surface tension propellant management device (PMD) consists of a propellant refillable reservoir (PRR) for propellant storage and propellant acquisition vanes (PAVs) for propellant transportation. PRR is a key part of vane type surface tension tank (STT), and its storage performance determines the fluid management of vane type STT. In the present paper, a model test system was established and microgravity drop tower tests conducted based on experimental study of fluid storage and transportation behavior of PRR. Laws of fluid storage and transportation of PRR in microgravity environment were obtained. The test results show that two types of PRR both have good liquid storage capacity, and the double cone PRR exhibits good liquid storage capacity in lateral acceleration. A rational design of PRR can effectively store liquid and control liquid transportation velocity. The test results offer a guideline for optimization of new-style vane type PMD, and also provide a new method for fluid control in space environment.

Aiming at vented orbital refueling, the microgravity experiment research on orbital refueling process (ORP) is carried out in the paper. By using the microgravity test system of orbital refueling and proper experiment means, the microgravity drop tower (DT) test of all the ORP is accomplished triumphantly, then the transformation process of fuel surface and flow characteristic are obtained, and the extrusion efficiency of the refueling tank is gotten, and the on-orbit propellant resupply performance of VTT is validated. The results indicate that, the orbital refueling in the vane type tank is absolutely feasible, and the performance of propellant management device (PMD) in the tank is good.

Drop tower is the most common ground-based facility to provide microgravity environment and widely used in many science experiments. A differential space accelerometer has been proposed to test the spin-gravity interaction between rotating extended bodies onboard a drag-free satellite. In order to assist design and test of this inertial sensor in a series of ground- based pre-flight experiments, it is very important to know accurately the residual acceleration of drop towers. In this report, a sensitive instrument for this purpose was built with a high-performance servo quartz accelerometer and the dedicated interface electronics design providing small full-scale range and high sensitivity, up to 136.8 V/g0. The residual acceleration at the Beijing drop tower was measured using two different drop capsules. The experimental result shows that the microgravity level of the free-falling double capsule is better than 2 × 10−4g0 (Earth’s gravity). The measured data in this report provides critical microgravity information for design of the following ground experiments.

The European Space Research and Technology Center ESTEC, ESA’s premises in Noordwijk, The Netherlands, has a long lasting cooperation with the ZARM-FAB (Centre of Applied Space Technology and Microgravity—Drop Tower Operation and Service Company) in Bremen on the utilization of the Drop Tower for ground-based microgravity research and space hardware development studies. During the period January 2000 to December 2011 ESA will have procured in total some 840 drops addressing a variety of scientific and technological disciplines. The experiments are usually carried out in campaigns of 15 to 20 drops each, with an annual average of about 5 campaigns. The cooperation agreement between ESA and the ZARM-FAB includes experiment preparation advice by ZARM’s experts, the integration of the hardware into the drop capsule, dedicated safety reviews, the execution of the drop or catapult experiments, the post-flight payload de-integration as well as the handover of acquired data to the experimenters. The experiment hardware itself is provided by the scientists or has to be procured from sources outside of ESA’s drop tower utilization contract. ESA appreciates the cooperation of the ZARM-FAB in Bremen whose drop- and catapult facility provides excellent microgravity quality, is operated by a highly competent, flexible and extremely supportive expert team, allows campaign integration at relatively short notice throughout the entire year, offers real-time experiment operations and immediately after each drop delivers experiment results and provides on-site hardware modification possibilities.

"Fly Your Thesis!—An Astronaut Experience" is an educational programme launched by the ESA Education Office that aims to offer to European students the unique opportunity to design, build, and eventually fly, a scientific experiment as part of their Master or Ph.D. thesis. Selected teams accompany their experiments onboard the Zero-G aircraft for a series of three flights, each consisting of 30 parabolas, with each parabola providing about 20 s of microgravity. ESA Education Office financially supports the flights and part of the hardware development, as well as travel and accommodation for participants. For the first edition of this programme, four student teams were selected to participate in the 51st ESA Microgravity Research Campaign in November 2009. The 2010 edition of the programme was launched in April 2009 and the final selection was announced in January 2010. In parallel, ESA Education Office is setting up two new hands-on activities to provide European university students with access to drop tower (up to 9.3 s of microgravity) and centrifuge (from 1 to 20 times Earth’s gravity) facilities. Through ELGRA, the selected student teams are working in close contact with renowned European scientists working in gravity-related research. This paper will introduce the three new educational programmes and present the selected experiments, as well as give information to students interested in the future editions.

Blast mitigation seats have been employed in armored vehicles to protect occupants from injuries caused by improvised explosive devices (IEDs). Currently, there exist no standard experimental evaluation methods that can be used to fully assess the protection capability of a particular seat design. For historical reasons, drop-towers have been used extensively for such purpose, as a repeatable laboratory method with some limitations. In this paper, the authors developed analytical models to study the difference between results obtained from a drop tower test and those from actual blast events. It was found that the selection of the test method had a significant effect on the results. In particular, it was found that the drop-tower methodology can often overestimate the performance of blast mitigation seats, which can result in the fielding of sub-optimal solutions for the protection of occupants.

Although inception of the measurement of astronaut body mass measurement was as old as Skylab era, progress in the field has not been as expected. There are fundamental physical difficulties as well as program management issues. New mass measurement systems with the current sensor technologies should be prepared, and the new sensor system could be expanded for “Drop Tower” in space.

The Bremen drop tower at the Center of Applied Space Technology and Microgravity (ZARM) provides high quality micro-g condition needed for many high precision tests. This is even more improved by the development of a free flyer technology. This new technology is used for a free fall test of the MICROSCOPE differential accelerometers which only can work with a residual acceleration disturbance level below 25 nano-g in the high resolution mode. The French MICROSCOPE space mission for testing the Weak Equivalence Principle is scheduled for 2012/2013. The free fall accelerometer test campaign at ZARM is an important part of the pre-mission test program. In this article the new free flyer technology, its performance as well as the accelerometer tests are described.

Velocities of primary (P) and shear (S) waves in granular materials are highly dependent on confining stress. These wave velocities are related to mechanical properties of the materials such as stiffness, density, and stress history. Measurements of the wave velocities using piezoelectric sensors provide scientists and engineers a technique for nonintrusive characterization of those mechanical properties. For aerospace engineering, measuring the wave velocities under microgravity, which simulates low loading and stress conditions, has a number of potential applications. It can help the understanding of the soil mechanics and the development of appropriate materials handling technologies in extraterrestrial environments, which will be crucial to meeting NASA’s future space exploration goals. This paper presents the technique and results of experiments conducted at NASA Glenn Research Center using the 2.2 s drop tower. Velocities of P and S waves in three sizes of glass beads and one size of alumina beads w...

Experiments on the Drop Tower Bremen aim at a proof of the Weak Equivalence Principle and the determination of the Eotvos factor with an accuracy of less than 10 −12 . The Drop Tower Bremen offers the unique possibility for this pseudo-Galilean test by dropping two cylindrical bodies of different composition and observing their relative movement. To measure the extremely small displacements, a SQUID-based position detector with an ultra-high resolution has been developed. The low-temperature SQUIDs are unaffected by repeated thermal cycling and have an extremely low-noise-limited resolution of 2 × 10 −12 m/√Hz. The experiments serve not only to prove the Weak Equivalence Principle with an accuracy not attained before, but also to test and develop components for future space missions aimed at carrying out precise gravitation experiments and geodetic measurements. This report focuses on recent experimental results concerning the position control and measurement.

Up to now an experimental proof of a violation of the Weak Principle of Equivalence (WEP) has been missing. Experiments carried out differ mainly in the applied measurement technique and can be classified into groups: (1) torsion balance experiments and (2) Galilean (free fall) experiments. With torsion balance experiments, the WEP is proven on the 10 −12 level. We discuss the possibility to carry out experiments to test the universality of free fall, the WEP, on Drop Tower Bremen with higher accuracy and report on experimental results.

The design of a Galilean-type free-fall experiment to test Einstein's equivalence principle at an improved level of sensitivity is described. Two test bodies of different material fall down from a height of 109 m inside of an evacuated drop tube (Drop Tower Facility Bremen, Germany). Their possible relative displacement is measured using LTS DC SQUID based position sensors. Experiences and results of this experiment meet directly the current STEP project of NASA/ESA to test the Equivalence Principle in space at a level of one part in 10/sup 18/. Several issues of the developed measuring system are discussed, above all, the performance of two types of SQUID position sensors. Furthermore some recent results of free fall tests of components of the measuring system at the Bremen Drop Tower are presented.

The mechanism of secondary bubble creation induced by bubble coalescence, observed during drop tower experiments, is studied. To carry out detailed investigations of the creation phenomena, 2-dimensional numerical simulations are performed. The simulation results agree fairly well with the experimental ones and indicate that the size ratio A and the non-dimensional surface tension St play the most important role in the phenomena. Considering energy distributions of the phenomena, it is found that the criteria of the creation can be well described by two simple equations.

Investigation of instrumented drop tower impact of Resin Transfer Molded Composite plates indicates that the initial reaction to dynamic out-of-plane loading is well behaved until decoupling commences between local and global plate reactions. Self consistent expressions are developed for local and global plate reactions of quasi-isotropic polymer matrix composites and are combined into a coupled lumped parameter dynamic model. Predicted energy partitioning into pools of stored, dissipated, and damage propagation related energies are shown to correlate well with experimental observations. The absence of relaxed stiffness based formulations to accommodate penetration induced damage does not appear to diminish the utility of the model over a wide-range of dynamic response for the specific type of composite investigated.

This paper utilizes the scenario approach of risk assessment to identify modeling needs and, in turn, experiments that would aid in the development of models that would meet these needs. Due to the closed environment of a spacecraft and the lack of egress, fire on-board may pose a severe problem. There are many differences between a fire on-board the spacecraft and one in a terrestrial facility and they must be accounted for in the assessment of risk. Both the risk assessment methodology and the phenomena-based models must be modified. This paper discusses some of the methodology modifications, as well as special experimental results. Multiple experiments have been conducted in terrestrial and microgravity environments in order to construct and validate models required for the assessment and management of risk on-board spacecraft. A logic diagram analyzing the ways in which the crew may be injured and/or the spacecraft may be damaged, as well as operating experience, have identified wire overheating events as being potentially significant accident initiators. As a result, the experiments have concentrated on quantifying the pyrolysis event of a wire being overheated with excessive current. A preliminary set of experiments at the 2·2-second NASA Lewis Drop Tower has led to several observations. The event is violent due to the high heating rates. At these high heating rates, a jet of hot gases and smoke was observed. Frequently the conductor would melt down, sometimes ejecting molten pieces of the copper conductor. The event poses a threat to targets in the near vicinity and further away. Also, the smoke particle size distribution is shifted towards larger sizes in a microgravity environment. This may prove very important in designing a smoke detector. While significant results were obtained from these tests, longer durations of microgravity are required for further quantification to be possible.

The application of modern laser diagnostical measurement techniques for combustion research in earth-based laboratories has brought essential experimental progress. In this paper the development of an UV-laser system is described, which for the first time will allow the application of two dimensional laser spectroscopic measurement techniques for experiments at the drop tower “Bremen”. The laser system will be integrated at the top of the tower, the laser beam follows the falling drop capsule and enters it from above. The drift between capsule and laser beam has to be compensated with an accuracy in the sub-mm range. Described are the laser-, control-, detection- and data acquisition systems, first results of the experimental properties and planned applications for experiments at the drop tower, “Bremen”.

In our experiments a magnetic fluid is enclosed in a hollow-cylindrical container heated from the center and cooled at the outer surface. It is under the influence of an azimuthal magnetic field with radial gradient. The flow profile has been investigated by small thermistors placed at the inner surface of the outer wall of the container. The experiments were carried out with sounding rockets and at the drop tower “Bremen” (ZARM, University of Bremen). The flow profile of the convective flow, and the critical magnetic Rayleigh number obtained in these experiments agree well with theoretical predictions.

Summary This paper examines the plastic deformation and failure behaviour of mild steel bolts subjected to tensile loads exerted at strain rates ranging from about 10 −5 to 10 2 s −1 . Three experimental techniques were used to generate different strain rates; these being tensile testing (for a strain rate of 2.5 × 10 −5 s −1 ), drop tower impact testing (~ 1–10 s −1 ), and underwater explosion shock testing (~ 10 2 s −1 ). Measurements of the tensile failure strengths of the shank and threads of the bolt revealed that the threads fail at loads which are significantly lower than the breaking strength of the shank. The threads were damaged under loading in a two-stage process: firstly their tips were sheared off, and then the remaining thread was severely plastically deformed. These findings are important considerations when determining the load-bearing capacity of bolted joints and structures under impact conditions.

This paper describes two student competition programs that allow student teams to conceive a science or engineering experiment for a microgravity environment. Selected teams design and build their experimental hardware, conduct baseline tests, and ship their experiment to NASA where it is operated in the 2.2 Second Drop Tower. The hardware and acquired data is provided to the teams after the tests are conducted so that the teams can prepare their final reports about their findings.

This chapter deals first with the main characteristics of the space environment, outside and inside a spacecraft. Then the space and space-related (ground-based) infrastructures are described. The most important infrastructure is the International Space Station, which holds many European facilities (for instance the European Columbus Laboratory). Some of them, such as the Columbus External Payload Facility, are located outside the ISS to benefit from external space conditions. There is only one other example of orbital platforms, the Russian Foton/Bion Recoverable Orbital Capsule. In contrast, non-orbital weightless research platforms, although limited in experimental time, are more numerous: sounding rockets, parabolic flight aircraft, drop towers and high-altitude balloons. In addition to these facilities, there are a number of ground-based facilities and space simulators, for both life sciences (for instance: bed rest, clinostats) and physical sciences (for instance: magnetic compensation of gravity). Hypergravity can also be provided by human and non-human centrifuges.

In the next future Small satellites can be used as experimental platforms improving their capabilities. It has been demonstrated that nanosatellites or picosatellites using the technology of CubeSats are being developed by different universities around the world. Which missions are possible to execute or which payloads can be installed in a such a satellite platform? Small satellites are conceived as dedicated systems to execute experiments or tests in space. We can compare a small satellite platform with others systems. A Drop Tower will be used to create some seconds (aprox. 10s) of microgravity. With S ounding Rockets the generated microgravity will take some minutes (max 14 min). With a small satellite platform the microgravity condition will result in months or longer! From this point of view small satellites have obviouslly much advantage than a drop tower or a sounding rocket by executing experiments in microgravity. For sure the others systems have also advantages like an intact experimental pay load (Drop Tower), or the recovery of the payload and recorded data in short time just after the flight (S ounding Rocket) but for a small satellite this system functionality can also be developed, so that the payload can be also recovered intact or the data provided to ground as quick as possible. Peruvian engineers are working on a next generation of subsyste ms and payloads to be implemented in such experimental platforms. They are modelling and improving the capabilities of some, used in sounding rocket systems, importants instruments which can be carried in the proposed small satellite Platform. The instruments must be simplified, reduced in size, adapted and designed to properly perform their functions in the designed platform. All the subsystems will continually be designed for making them more efficient in order to use best possible the limited resources available in the satellite. Depending of the mission a next generation of pico satellites can emerge.

During evolution, life on earth had adapted to the gravity of 1 g . Due to space flight, in the last decades the question arose what happens to the brain under microgravity on the molecular level. Ion channels among others are the molecular basis of brain function. Therefore, the investigation of ion channel function under microgravity seems to be a promising approach to gather knowledge on brain function during space flight. In a first step, the ion channel forming peptide Alamethicin was used as a model channel in an artificial membrane. It is well suitable for this kind of investigation, since its properties are well described under standard gravity [1] . For that reason, changes due to microgravity can be detected easily. All experiments were performed in the German drop tower at ZARM-FAB, Bremen. A special set-up was constructed based on the bilayer technique introduced by Mueller and Rudin [2] . All functions of this set-up can be observed and controlled remotely. In the first set of experiments, a dramatic change of electrical properties of Alamethicin under microgravity could be observed. Mainly, the pore frequency is significantly reduced.

An intensified array camera has been used to image weakly luminous flames spreading over thermally thin paper samples in a low-gravity environment aboard the NASA-Lewis Learjet. The aircraft offers 10 to 20 sec of reduced gravity during execution of a Keplerian trajectory and allows the use of instrumentation that is delicate or requires higher electrical power than is available in drop towers. The intensified array camera is a charge intensified device type that responds to light between 400 and 900 nm and has a minimum sensitivity of 10(exp 6) footcandles. The paper sample, either ashless filter paper or a lab wiper, burns inside a sealed chamber which is filled with 21, 18, or 15 pct. oxygen in nitrogen at one atmosphere. The camera views the edge of the paper and its output is recorded on videotape. Flame positions are measured every 0.1 sec to calculate flame spread rates. Comparisons with drop tower data indicate that the flame shapes and spread rates are affected by the residual g level in the aircraft.

The Universidad Politecnica de Madrid participates in the MINISAT 01 program as the experiment CPLM responsible. This experiment aims at the study of the fluid behaviour in reduced gravity conditions. The interest of this study is and has been widely recognised by the scientific community and has potential applications in the pharmaceutical and microelectronic technologies (crystal growth), among others. The scientific team which has developed the CPLM experiment has a wide experience in this field and had participate in the performance of a large number of experiments on the fluid behaviour in reduced gravity conditions in flight (Spacelab missions, TEXUS sounding rockets, KC-135 and Caravelle aeroplanes, drop towers, as well as on earth labs (neutral buoyancy and small scale simulations). The experimental equipment used in CPLM is a version of the payload developed for experimentation on drop towers and on board microsatellites as the UPM-Sat 1, adapted to fly on board MINISAT 01.

A UV-laser based non-intrusive, highly specially and temporally resolving diagnostics for experiments under microgravity condition has been accomplished at (he drop tower Bremen recently. By means of an UV-excimer laser beam, that is guided from the top of the tower into the falling drop bus, two dimensional measurements of the concentration field of selected species can be conducted with a framing rate of up to 250 pictures/ sec. The data are beeing acquired by a digital high speed camera, that is equipped with a two staged, gated intensifier. The complete picture sequence of 1500 frames (256 x 256 pixel, 8 bit resolution) is stored real time aboard the capsule in a 96MByte RAM image storage unit. For the first time, in situ data of transient combustion phenomena preceding under conditions without thermal bouancy can be obtained by laser-inducedfluorescence LIF and laser-induced-predissociationfluorescence LIPF. In the current project, the gas phase reaction of burning droplets using different hydrocarbon fuels are beeing investigated by OH-LIPF. The structure of the flame has been identified and the limitations of the technique are discussed.

The drop tower Bremen was inaugurated on September 28, 1990. Then, it was not clear that such a facility, with 5 s free fall time of highly compensated gravity would turn out to be a great leap forward for research under space conditions. Today, 20 years later, drop tower facilities all over the world play an important role. They serve all disciplines where gravity dependent phenomena play a role, in two ways: to prepare experiments with longer microgravity time on suborbital flights, retrievable capsules, the space shuttle and the international space station, or in many cases to provide sufficient data for comparison with theory and numerical simulations. This topical issue on drop tower related research, on the occasion of the 20th anniversary of the drop tower Bremen presents actual results from different research

This paper describes the Low Temperature Research Facility program now under development at the Jet Propulsion Laboratory. This program will develop the experiments and cryogenic facility to fly experiments requiring temperatures in the liquid helium range, from the superfluid range (1.6 K) to the critical point (5.2 K). A shuttle facility is planned for 1998. It will be flown about every two years after that time. A free flyer is also being evaluated for the end of the decade or early in the next century. A brief discussion of the quality of micro-gravity available in various carriers is also given.

The effect of pressure on the propane diffusion flames burning in quiescent air under both normal-gravity and microgravity conditions (in the NASA's 2.2-Second Drop Tower at the Lewis Research Center) were studied at pressures of 0.5, 1.0, and 1.5 atm, with three fuel mass-flow rates for each pressure. Compared to normal-gravity flames, the microgravity tests showed enhanced sooting, tip-opening, and soot escape, accompanied with changes in color, size, and luminosity of the flames. At low pressures, less-efficient burning and a broader flame zone was found to exist due to the kinetics effects, while at high pressures, where was more soot and longer soot-burning zones. Results show that there exist a particular intermediate pressure at which both the microgravity and normal-gravity flame heights are minimized.

This paper presents recent results from a continuing study on the burning characteristics of pure, single component fuel droplets in a microgravity environment. A new, economical, microprocessor‐based, computer imaging and data analysis method for determining the diameter and the position of the burning droplet from photographic records is described and demonstrated using experimental data previously obtained on the combustion of n‐decane droplets in air. Initial observations on the combustion of methanol droplets in air are also reported.

A containerless electromagnetic levitator has been now constructed for precise measurement of the thermophysical properties of molten silicon in the 10 s Japan Microgravity Center (JAMIC) drop shaft. Precise control of the levitated sample position from normal gravity to microgravity was aimed and a compact electromagnetic levitator for demonstrating the control technology at the gravity transition point was tested at the 1.3 s HNIRI (Hokkaido National Industrial Research Institute) drop tower. The oscillation generated at the transition was completely eliminated with current control of electromagnetic coil.

The paper presents the results of experiments on the burning of individual 1-2 mm decane droplets in air at room temperature and atmospheric pressure. The NASA Lewis 2.2 s drop tower was used as well as a newly designed droplet-combustion apparatus that promotes nearly spherically symmetrical combustion. Unanticipated disruptions related to sooting behavior were encountered.

Fracture-toughness properties should be measured in the laboratory at loading rates and temperatures similar to those expected in the application of interest. This is not usually the case because of the experimental difficulties involved. This report describes a method being used to obtainJIc, J-R curves, andJ at cleavage for three-point-bend tests conducted at drop tower rates through the ductile to brittle transition regime of the ferritic A106 steel being tested. The major conclusion is that these tests can now be accomplished, though a high degree of expertise and considerable practical experience is necessary to obtain good test results. The steel tested here is quite rate dependent as shown both by tensile tests and fracture-toughness tests. A load elevation of 30 to 50 percent results in the drop tower 100 in./s (2.5 m/s) tests on this material in comparison with static tests when both tests are conducted on the ductile upper shelf. Nonetheless, for this materialJIc andJ-R curves are not elevated by the loading rate. Looking at the elastic and plastic components ofJ one sees that theJEL increases with increased loading rate but also thatJPL decreases with loading rate. It is also demonstrated that for the high rate tests more crack extension is present at a given bend angle for the rapid tests than with the static tests.

Hydrostatic stability and damping characteristics of perforated plates and screens for passive propellant control schemes from drop tower tests

An engineering model built for droplet combustion drop tower tests is described. The model was built using a design with mechanical and electrical assemblies of the same level of complexity as they will have in flight. The model was tested for functional operation and integrated into a 5-sec drop tower. Test data obtained to date are presented together with model and test cell diagrams.

Full-scale propellant reorientation flow dynamics for the Centaur D-1T fuel tank were analyzed. A computer code using the simplified marker and cell technique was modified to include the capability for a variable-grid mesh configuration. Use of smaller cells near the boundary, near baffles, and in corners provides improved flow resolution. Two drop tower model cases were simulated to verify program validity: one case without baffles, the other with baffles and geometry identical to Centaur D-1T. Flow phenomena using the new code successfully modeled drop tower data. Baffles are a positive factor in the settling flow. Two full-scale Centaur D-1T cases were simulated using parameters based on the Titan/Centaur proof flight. These flow simulations indicated the time to clear the vent area and an indication of time to orient and collect the propellant. The results further indicated the complexity of the reorientation flow and the long time period required for settling.