Free-fall Experiments Research Articles

微小重力環境移動ロボットの提案と着地実験

This paper proposes a new mobility system for exploration under microgravity by using springs and linear actuators. In a microgravity, it is difficult to obtain horizontal velocity because the friction force between the robot and the ground is very small. By pushing off the ground, however, the robot can not only hop, but also obtain horizontal velocity. The proposed hopping robot consists of three masses and can push off the ground using springs. The robot can hop from the stationary state by transforming the elastic energy to kinetic energy using the springs and linear actuators. The robot can land without bouncing by transforming kinetic energy back to elastic energy. Free fall experiments demonstrate the landing performance of the proposed system.

Influence of wet surfaces and fall height on pediatric injury risk in feet-first freefalls as predicted using a test dummy

Introduction: Falls are a major cause of morbidity and mortality in children, but are also reported falsely in child abuse. Therefore, it is of interest to understand those factors which may lead to a higher likelihood of injury in a feet-first freefall. Methods: We used laboratory freefall experiments and a 3-year-old Hybrid III anthropomorphic test dummy (ATD) to assess head and femur injury risk. Wet and dry linoleum impact surfaces were used from three fall heights: 22, 35 and 47 in. Results: For a given fall height, dry surfaces were associated with higher head injury criteria (HIC) values than wet surfaces. Changes in fall height 22–47 in. did not significantly affect HIC values for falls onto either surface. Generally, compressive and bending femur loading increased significantly for wet as compared to dry linoleum. Conclusions: In simulated feet first freefall experiments up to 47 in. using a 3-year-old test dummy, a low risk of contact type head injury and femur fracture was found. However, both fall height and surface conditions influenced femur loading and head injury measures. Future efforts should explore the risk of head injury associated with angular acceleration in freefalls.

Four-Wheeled Hopping Robot with Attitude Control

Because a hopping robot moves long distances at minimum energy and can observe its surrounding from high points when it jumps, it is expected to explore microgravity environments effectively. Despite the importance of attitude control in such exploratory robots, few attitude control mechanisms have been proposed. This paper proposes a four-wheeled hopping robot that hops horizontally and lands without bouncing. Its wheels are applied to attitude control in the air. A simulation study and free-fall experiments verified the feasibility of the proposed mobility and the applicability of the robot.

Testing the Weak Equivalence Principle with a free-fall experiment from a balloon

The paper describes a free-fall facility, called enhanced g-zero, to be dropped from a balloon at an altitude of 40–45 km for testing the Equivalence Principle. The free-fall duration is 30 s for a non-propelled capsule. Present estimates indicate that this facility provides an acceleration noise, away from the walls of the evacuated capsule, not to exceed 10 −12 g during the fall. The envisaged technique for testing the Equivalence Principle involves the measurement of differential accelerations between two test masses of different materials that are part of a high-sensitivity detector. The detector is housed inside an instrument package cooled at the temperature of liquid helium. This package is first spun about a horizontal axis at a frequency of typically 1 Hz, for providing gyroscopic stabilization and modulating the gravity signal, and then released inside the falling capsule. The estimated accuracy in testing the Equivalence Principle, with 95% confidence level, is 5 parts in 10 15 in a 30-s free fall.

One axis gravity gradiometer for the measurement of Newton's gravitational constant G

This Letter presents preliminary works concerning a new technique to measure the gravitational constant G, using a single axis gravity gradiometer designed to detect an off-line component of the gravity gradient tensor and able to reject the linear acceleration due to the vibrational noise (common mode rejection: CMR). The main part of such an instrument is a torsional mechanical oscillator which is forced at the frequency f r , by means of a gravitational torque produced with a system of two masses rotating at a frequency f r /2. The low frequency of the mechanical oscillator, together with a high sensitivity capacitive bridge measurement system, enables the detection of the gravitational signal with high accuracy, also in presence of quite high seismic noise. A precision of one part in 10 3 in the determination of the gravitational torque was achieved in our laboratory with an integration time of about 5 h and a factor 10 can be easily gained performing the measurement in a place with a lower differential seismic noise. The detection accuracy can be translated into experimental accuracy in the determination of G if the physical parameters of the whole system are measured with the same relative error. The experiment proposed in this Letter has strong similarities with the classic torsion balance [Rev. Sci. Instrum. 64 (1993) 283], but it has some peculiarities that make it particularly interesting as follows: the oscillating system is in indifferent equilibrium under the action of the Earth gravity field, so that it can have any orientation with respect to the local vertical; the instrument can also be used in the absence of gravity (free fall experiment); the capacitive bridge pick-up system has a high transducer factor for converting mechanical signals into electrical signals which are much greater than the pre-amplifier noise, even for very small displacements of the oscillator.

Numerical simulation of a free-falling liquid sodium droplet combustion

Droplet combustion is considered one of the combustion figurations in sodium-fire events; the detailed combustion mechanism by which it occurs is evaluated by a developed computational fluid dynamic (CFD) simulation code, called COMET, in which the extended MAC method is employed for calculating the reacting compressible flow coupled with the multi-component diffusion of chemical species. A single droplet combustion in steady-airflow was simulated using the COMET to analyze: (1) the spatial distributions of heat rate and temperature, and (2) the formation, decomposition, and transfer of combustion products. Next, a free-falling droplet combustion experiment was simulated for code validation, where the evaluated falling-velocity and burnt-mass showed good agreement with the experimental values.

Microgravity laser-photophoresis of high density microparticles in water

Abstract Laser-photophoresis is a new technique, which can be used to characterize and separate microparticles in liquids. The photophoretic migration of high density solid particles in water has been observed experimentally for the first time by experiments under microgravity conditions. The photophoretic velocity was measured under microgravity conditions, in order to minimize the effects of density difference and convection. Furthermore, by using an optical cylindrical cell, we could observe the precise photophoretic velocities without the wall-induced drag effect. The apparatus consisted of a cw Nd:YAG laser (532 nm), a microscope, a CCD system, and a remote controlled sample stage and was set in a capsule which was used for a free-fall experiment. All the experimental operations were made externally by using a personal computer. The photophoretic velocities for the particles of carbon, stainless steel, gold plated nickel, and polystyrene in water were determined under microgravity. It was found that the photophoretic efficiencies of the photo-absorbing carbon particles and the photo-reflecting metal particles were much larger than those of transparent particles. The order of magnitude of the observed photophoretic efficiency was carbon>stainless steel>gold plated nickel>polystyrene. The photophoretic efficiencies were compared with those calculated by a Mie scattering theory. It was proved that the Mie scattering theory was useful for the prediction of the photophoretic efficiency of various kinds of particles in water.

Influence of fall height and impact surface on biomechanics of feet-first free falls in children

Objective: The objectives of our study were to assess biomechanics associated with feet-first free falls in 3-year-old children and to investigate the influence of impact surface type and fall height on key biomechanical measures associated with injury risk. Methods: Repeatable feet-first free fall experiments were conducted in a laboratory mock-up environment using an instrumented Hybrid II 3-year-old test dummy. Impact surface type and fall height were varied to examine their influence on biomechanical measures. Results: Feet-first falls from short distances (27 in.) (0.69 m) were found to have a low risk of contact-type head injury, regardless of impact surface type. When comparing different types of impact surfaces in a 27 in. (0.69 m) fall, head acceleration associated with falls onto playground foam was significantly less than that associated with falls onto wood, linoleum or padded carpet. For falls onto playground foam, femoral compressive loads and bending moments were found to significantly increase as fall height increased. Conclusions: Impact surface type and fall height were found to influence biomechanics associated with injury risk in feet-first free falls as assessed through experimental mock-ups using an instrumented child test dummy. Feet-first falls from short distances (27 in.) (0.69 m) were associated with a low risk of contact-type head injury as assessed using HIC, irrespective of impact surface type.

Precise definition of the effective measurement height of free-fall absolute gravimeters

For up-to-date absolute gravimeters, the trajectory of the test mass during a free-fall experiment (drop) is about 20 cm along the vertical, and the corresponding gravity change is about 60×10−8 m s−2. The reference height of the derived free-fall acceleration g has to be defined with an accuracy of 1 mm to 2 mm within the dropping distance to preserve the accuracy of the measurement system (e.g. FG5: 1×10−8 m s−2 to 2×10−8 m s−2). The equation of motion comprises a vertical gravity gradient to take the height dependence of g into account. In general, a linear vertical gravity gradient γ is introduced that has been measured by relative gravimeters. In that case, the g-value refers to the origin of the coordinate system (z = 0), which is normally the starting position of the drop.In the case of an unknown or uncertain gradient we recommend an alternative approach. A simple parabolic equation (assumption γ = 0) can be used to evaluate the time/distance data pairs, and later these g-determinations have to be corrected for the vertical gravity gradient using the effective measurement height. The solution presented is not restricted to low initial velocities. It considers time/distance measurements equally spaced in distance. Also, in extreme cases, unknown non-linearities within the vertical gravity gradient do not significantly affect the result of the absolute gravity determination.

Effect of Earth's Rotation on Trajectories of Free-Fall Bodies in Equivalence Principle Experiment**The project supported in part by National Natural Science Foundation of China under Grant Nos. 19835040, 10175070, and 10047004 as well as by NKBRSF (G19990754)

Owing to Earth's rotation a free-fall body would move in an elliptical orbit rather than along a straight line forward to the center of the Earth. In this paper on the basis of the theory for spin-spin coupling between macroscopic rotating bodies we study violation of the equivalence principle from long-distance free-fall experiments by means of a rotating ball and a non-rotating shell. For the free-fall time of 40 s, the difference between the orbits of the two free-fall bodies is of the order of 10−9 cm which could be detected by an SQUID magnetometer because such a magnetometer can be used to measure displacements as small as 10−13 cm.

Interfacial polycondensation of nylon-6,6 in microgravity as studied by free-fall experiments

Nylon-6,6 vesicles are synthesized by the interfacial polycondensation of hexamethylenediamine and adipoyl chloride in microgravity, and their size and shape are compared with those formed in normal gravity. Two methods are applied for the nylon syntheses. First, a carbon tetrachloride solution of adipoyl chloride (AC) is sprayed into an aqueous solution of hexamethylenediamine (HD) in a reaction column from the nozzle at the bottom of the column, and inversely HD solution is sprayed into the AC solution column. Nylon vesicles containing the solvent inside are formed. In the second method, both of the reaction solutions are sprayed in an air column and the reaction proceeds by the collision of both mists. For both methods, the reaction is followed by the transmitted-light intensity of the reaction mixture. Furthermore, the products are analyzed by microscopic observation. The nylon vesicles were not completely spherical in most cases, even if formed in microgravity. However, the size and the aspect ratio of the vesicles in microgravity are always smaller than those in normal gravity.

Gravitation at a micron and mixing of quarks

Galilei Galileo would be somewhat surprised. When neutrons become ultra-cold, his famous fall experiment shows quantum aspects of the subtle gravity force in the sense that neutrons do not fall as larger objects do. In free-fall experiment they don't fall continuously. We find them on particular levels, when they come close to a reflecting mirror for neutrons. Of course, such bound states with discrete energy levels are expected when the gravitational potential is larger than the energy of the particle. Here, the quantum states have pico-eV energy, value that is smaller by many orders of magnitude compared with an electromagnetically bound electron in hydrogen atom, opening the way to a new technique for gravity experiments and measurements of fundamental properties. New motivations for gravity experiments come from frameworks where the fundamental Planck scale (the scale about 104s after the big bang where gravity becomes comparable in strength to the other interactions) is taken to the weak scale, the energy scale of the Standard Model at s after the big bang. Considering this very early stage of our universe, we have the strong feeling, that a Standard Model description is incomplete, and many new observables pointing to physics beyond the Srandard Model emerge from superstring theory, supersymmetry or other Grand Unified Theories GUT). For example, in theories with submillimeter dimensions, gauge fields can mediate repulsive gravity-like forces -1 O'O times stronger than gravity in submillimeter distances. Furthermore, the quark-mixing CabibboKobayashi-Maskawa (CKM) matrix remains unexplained in the Standard Model as well as CP-violation, which might explain the baryon-antibaryon asymmetry of the universe. Some observables of these theories require neutron physics, for others the neutron provides one of several possible ingredients.

New criterion for splashing in flattening of thermal sprayed particles onto flat substrate surface

In the collision of a liquid droplet onto a flat solid surface, the splashing parameter K=We 0.5Re 0.25 (which is composed of both in-flight information and the physical properties of the droplet) has been used to evaluate the break-up phenomenon of the droplet. However, the transition phenomenon in the flattening morphology of a thermal sprayed particle from splash-shaped to disk-shaped with increasing substrate temperature cannot be explained by K. In order to evaluate the transition phenomenon, the splashing parameter on flattening K f=0.5 a 1.25Re −0.3 K (which includes the influence of both the in-flight information of the particle and the substrate temperature change) was proposed in this study as a general evaluation criteria for splashing in the flattening of thermal sprayed particles. A critical value of K f, K f c, corresponds to the critical condition for splashing. In the present study, the relations between K and T t for Ni, Cu and Fe particles were examined to observe the transition phenomenon of the splat morphology. A strong linearity between K and T t for each material was recognized. Consequently, by introducing the measurement results in a free-falling experiment as a simulation of thermal spraying, K f c was estimated to be approximately 7. This value was almost constant, regardless of the splat material and the collision conditions. It is expected that the disk-splat is formed at K f< K f c and the splash-splat at K f> K f c.

Effect of Interface Wetting on Flattening of Freely Fallen Metal Droplet onto Flat Substrate Surface

A free-falling experiment was conducted as a simulation of a thermal spray process. The flattening behavior of the freely fallen metal droplet impinged onto a flat substrate surface was investigated in a fundamental way. The substrates were kept at various temperatures, and the substrates were coated with gold by physical vapor deposition (PVD) and were prepared in order to investigate the effect of wetting at the splat-substrate interface on the flattening behavior of the droplet. A falling atmosphere was created with atmospheric pressure of nitrogen to prevent the oxidation of the melted droplet. Experiments under low-pressure conditions also were conducted. The different types of splat morphology were recognized in experiments conducted under a nitrogen atmosphere with atmospheric pressure. The splat morphology on a substrate at room temperature was of the splash type, whereas that on a substrate at high temperature was of the disk type. The microstructure observed on a cross-section of the splat obtained on the substrate at room temperature was an isotropic coarse grain, whereas that on the substrate at high temperature was a fine columnar grain. The grain size changed transitionally with increasing substrate temperature. The temperature of the transition on the gold-coated substrate was higher than that on the naked substrate. The microstructure of the cross-section of the splat obtained under low pressure was finely columnar even on the substrate at room temperature. The results indicate that the metal droplet wets better under the low-pressure condition than under the atmospheric pressure nitrogen condition and that wetting has a significant role in the flattening of the droplet.

Casting Manipulation. 3rd Report. Analysis on Viscoelasticity of Flexible String and Mid-Air Trajectory Control of Gripper by Impulsive Force.

We have been developing a casting manipulator which includes a flexible string in the link mechanism to enlarge the work space of a manipulator. In this paper we deal with the mid-air trajectory control of the gripper after throwing it. First, we examine dynamic characteristics of a flexible string against impulse. A flexible string is modeled as a viscoelastic model. We estimate model parameters of a flexible string through free fall experiments. Then we propose the utilization of impulsive force applied to the gripper in the air through the string by restricting the motion of the string. Investigating the generation of the impulsive force through experiments, we confirm the effectiveness of the method, which is evaluated by comparing the results of numerical simulations with those of the experiments using our experimental casting manipulator hardware.

A newexperimental baseline for testing the weak equivalenceprinciple at the Bremen drop tower

Free-fall experiments to test the weak equivalence principle are inprogress at the drop tower in Bremen. The differential acceleration of twotest masses made from different materials is being measured by means ofa superconducting-quantum-interference-device- (SQUID-) based sensingtechnique. These pseudo-Galilean tests are aimed at determining theEötvös ratio to an accuracy of better than 10-12. The free-fallheight of the experimental capsules is 110 m, translating into anexperimental time of about 4.5 s. The SQUID-based sensing systemguarantees a high measuring resolution of 10-12 m Hz-1/2 forthe relative positions of the test masses.

Rotational diffusion of tungstic acid colloids in microgravity studied by free-fall experiments. Effects of sodium chloride and ethyl alcohol

Rotational relaxation times (τ) of anisotropic tungstic acid colloids in aqueous suspension containing sodium chloride or ethyl alcohol are studied in microgravity achieved by free-fall experiments. Experimental errors at 0 G, in many cases, are small compared with those at 1 G, which is ascribed to the lack of the convection of suspension in microgravity. Much more reliable data of the diffusion coefficients are obtained in microgravity. The limiting slopes of the relaxation curves in the plots of the transmitted-light intensity against time at 1 G depend on the flow direction of the suspension in the flow cell, whereas those at 0 G are close to zero irrespective of the flow direction. Sodium chloride decreases τ, whereas ethanol addition increases this time. These effects are ascribed to the thinning of the electrical double layers and to the increase in the suspension viscosity.

F-1531 放出回収機能を備えた小型親子衛星用ドッキング機構の研究(S56-3 大学小型衛星の研究開発)(S56 大学小型衛星システム)

This paper describes study and development of docking mechanism to release and retract a micro satellite. The docking mechanism which was designed this time is aimed at applying to small mothership-daughtership satellite for formation flying. The docking strategy using this docking mechanism divides two phases. The first is a phase of approaching and grasping a daughtership. The second is a retracting phase. The mechanism is required to release a daughtership stably and to retract it into the desired point on a mothership. The size of docking space is 350mm-diameter (daughtership size is 200mm-diameter) enough to permit position/attitude control error of daughtership. Furthermore it is necessary to secure enough size of docking space but to make a mechanism as small as possible. In addition, a recharging system is developed and equipped this mechanism. We report the result of design and introduce plans of ground experiment using air-floating test beds and a free-fall Microgravity experiment using free-fall tower.

1201 粗面基材状の溶滴の扁平過程(G.S.11 材料工学)

This paper presents a mechanism for impinging deformation of molten droplets after they impinge onto the substrates by simulating plasma-sprayed coatings. The free fall experiments of molten droplets are done on the substrates with different roughness. The flattening process is evaluated by the unevenness and flattening ratio, which are analyzed by a high-speed video camera and image analysis. It was concluded that the surface roughness influences on both the flattening and unevenness ratio and that its influencing degree depends on the droplet properties.

Developments of the general relativity accuracy test (GReAT): aground-based experiment to test the weak equivalence principle

Some future tests of the weak equivalence principle(WEP) with laboratory-sizeproof masses are likely to be conducted in freefall conditions inorder toimprove the test accuracy substantially. Some years ago the authorsof this paperproposed to test the WEP in avertical freefall inside a capsule released from a high-altitudeballoon.The estimated accuracy in testing the WEP, with a 95% confidencelevel,is a few parts in 1015 in a 30 s freefall.When compared with other proposed orbital freefall experiments andground-based tests, the verticalfreefall retains some key advantages of the former without some ofthedisadvantages of the latter. Moreover, a two orders of magnitudeincreasein the accuracy of testing the WEP could be achieved with anaffordableexperiment that allows us to recover the detector and repeat thelaunches at short time intervals.