Microgravity Level Research Articles

Experimental Study on the Effects of Discharge Chamber Length on 5 cm Radio-Frequency Ion Thruster

For keeping microgravity level of microgravity and space science satellites, a kind of electric thruster, the radio-frequency ion thruster (RIT) has been designed and applied. The RIT produces thrust through ionizing neutral particles in the discharge chamber and extracting ions by the ion optics system. The length of discharge chamber affects the ionization of neutral particles as well as the performance of RIT. In this paper, an experimental study has been carried out for analyzing the influence of discharge chamber length. In the experiment, the RIT-5 with various discharge chamber lengths, 27.6 mm, 30.0 mm, 31.9 mm, 35.5 mm, 40.0 mm, has different performances under the same condition. With the same radio frequency power and propellant flow rate, the RIT-5 has the optimal performance in beam current and efficiency when the discharge chamber length is 30.0 mm or 31.9 mm.

Acceleration control of a multi-rotor UAV towards achieving microgravity

In this paper, we present control and parameter estimation strategies with theoretical guarantees to turn a hex-rotor unmanned aerial vehicle (UAV) into a microgravity enabling platform. We make the UAV to maintain a constant acceleration equal to free-fall acceleration for it and any payload on-board to experience microgravity. Towards this, we derive a feedback linearisation-based acceleration control law exploiting the differential flatness property of our system. The proposed control law requires the estimates of the system parameters. Therefore, ancillary to this control law, we propose a parameter estimation scheme and prove that the proposed control law along with the parameter estimation scheme ensures convergence of acceleration to the desired value under certain conditions. We also characterize these conditions that guarantee convergence. The flight tests that we have performed employing the proposed control and parameter estimation schemes gave microgravity levels of the order of $$10^{-3}g$$ for 1.6 s. To our knowledge, our hex-rotor UAV is the first multi-rotor UAV to achieve microgravity, and the first UAV—fixed-wing or rotary—to attain and maintain such levels of microgravity.

Experimental study on liquid distribution in a vane type propellant tank

Propellant tank is used to store the propellant in propulsion system. Propellant management device (PMD) is the key component in propellant tank to manage the liquid propellant under zero gravity. A microgravity drop tower test system was established to investigate the performance of PMD. A kind of vane type propellant tank was used for the drop tower test. Single module was used for experiment tests, and the microgravity level wass between 10-2g0 and 10-3g0. The anhydrous ethanol is used as analogue liquid. Different volume fraction of liquid were used to study influence of the PMD on the management performance. Changes of gas-liquid interface during the test are studied. Velocities flow along the vane of different liquid volume fraction in the tank are different at the beginning (t<0.8s). The liquid reorientation time is 0.8s when the liquid volume fraction is larger than 10%. The liquid reorientation time is prolong when the liquid volume fraction is less than 10%. The liquid climbing height along vane under microgravity increases as the volume fraction of liquid reduces. Experimental results provide a favorable reference for further optimization design of vane type propellant tank.

Microgravity disturbance analysis on Chinese space laboratory

Many scientific experiments are conducted in space; therefore, it is critical to understand the microgravity environment of a space laboratory. The first Chinese cargo ship, Tianzhou-1 (TZ-1), entered space on 20 April, 2017 and later joined with the Tiangong-2 (TG-2) Chinese space laboratory. TZ-1 carried a high-precision electrostatic suspension accelerometer system (ES-ACC) for measuring the microgravity acceleration on the spacecraft and a microgravity-active vibration system (MAIS), which contained flexible quartz accelerometers (Q-ACC). The ES-ACC was able to provide a reduced-disturbance environment for the MAIS. The purpose of these two instruments was to validate novel technologies and as an opportunity to record the microgravity acceleration of TZ-1 and TG-2 in detail during spacecraft operation in different flight modes, with or without vibration isolation. The acceleration data were analyzed comprehensively in a time–frequency–amplitude spectrogram. Some periodical disturbances with orbital period and irregular signals related to certain in-orbit events were observed. After reducing those disturbances, the microgravity levels on TZ-1 and TG-2 could be resolved to better than 10−6 m/s2 in the root mean square in the frequency of 0.01–10 Hz. These accurate measurements aboard the Chinese space laboratory will provide valuable information to optimize working conditions for scientific experiments.

Regolith behavior under asteroid-level gravity conditions: low-velocity impact experiments

The dusty regolith covering the surfaces of asteroids and planetary satellites differs in size, shape, and composition from terrestrial soil particles and is subject to environmental conditions very different from those found on Earth. This regolith evolves in a low ambient pressure and low-gravity environment. Its response to low-velocity impacts, such as those that may accompany human and robotic exploration activities, may be completely different than what is encountered on Earth. Experimental studies of the response of planetary regolith in the relevant environmental conditions are thus necessary to facilitate future Solar System exploration activities.We combined the results and provided new data analysis elements for a series of impact experiments into simulated planetary regolith in low-gravity conditions using two experimental setups and a range of microgravity platforms. The Physics of Regolith Impacts in Microgravity Experiment (PRIME) flew on several parabolic aircraft flights, enabling the recording of impacts into granular materials at speeds of ∼ 4–230 cm/s. The COLLisions Into Dust Experiment (COLLIDE) is conceptually close to the PRIME setup. It flew on the Space Shuttle in 1998 and 2001 and more recently on the Blue Origin New Shepard rocket, recording impacts into simulated regolith at speeds between 1 and 120 cm/s.Results of these experimental campaigns found that there is a significant change in the regolith behavior with the gravity environment. In a 10 −2g environment (with g being the gravity acceleration at the surface of the Earth), only embedding of the impactor was observed and ejecta production was produced for most impacts at > 20 cm/s. Once at microgravity levels (<10−4g), the lowest impact energies also produced impactor rebound. In these microgravity conditions, ejecta started to be produced for impacts at > 10 cm/s. The measured ejecta speeds were somewhat lower than the ones measured at reduced-gravity levels, but the ejected masses were higher. In general, the mean ejecta velocity shows a power-law dependence on the impact energy with an index of ∼ 0.5. When projectile rebound occurred, we observed that its coefficients of restitution on the bed of regolith simulant decrease by a factor of 10 with increasing impact speeds from ∼ 5 up to 100 cm/s. We could also observe an increased cohesion between the JSC-1 grains compared to the quartz sand targets.

Characterization of the Accelerometric Environment of DCMIX2/3 Experiments

A comparative analysis of the vibratory environment of the DCMIX2/3 thermodiffusion experiments is presented here by using acceleration signals coming from different sensors placed in the Destiny, Columbus and Kibo modules. The es03 sensor nearest to the experimental device and located inside the Glovebox (Destiny module) has been defined as reference. Data were downloaded from the NASA PIMS website paying special attention to the runs coinciding with disturbances such as dockings or extravehicular activities (EVAs) as they could particularly affect the International Space Station (ISS) microgravity levels. The analyses have been made minute by minute for the three acceleration components by using the Frequency Factor Index (FFI), Spectral Entropy (SEN) and Root Mean Square (RMS) values evaluated over one-third-octave frequency bands. Spearman’s rank correlation coefficient and the coherence function have been used to investigate the degree of linear correlation between the reference signal and the other ones. SEN evolution showed different patterns compared to the reference. Also, RMS values surpassing the ISS microgravity limits were detected in all sensors, mainly at low frequency bands (< 10 Hz) and prevailing on zA direction. However the sensors located in the Destiny module better accomplished the ISS vibratory limits requirements. Finally, some degree of linear correlation at structural frequencies (< 3 Hz) has also been detected. Overall, the sensors placed in the Destiny, Columbus and Kibo modules presented different vibratory characteristics and, despite they offer valuable information of the whole environment, may not be sufficient to properly characterize DCMIX2/3 experiments.

The 2.5 s Microgravity Drop Tower at National Centre for Combustion Research and Development (NCCRD), Indian Institute of Technology Madras

Space missions involving humans require a better understanding of various phenomena happening in space environments. A number of experiments need to be conducted in microgravity for addressing various issues encompassing safety (primarily fire) and better understanding of fluid and material behaviour. Of the various methods used for obtaining microgravity conditions, drop towers offer ground based microgravity platform. They provide a cost effective platform for doing short duration, repeatable, high quality microgravity experiments. This paper describes key factors that influence the design of a drop tower. The salient features of 2.5 s microgravity tower set up at National Centre for Combustion Research and Development (NCCRD), IIT Madras (IITM) are discussed. Primary features of the three critical elements, namely the drop capsule, the release unit and the decelerator unit are described along with review of these elements in existing drop towers. The IITM drop tower operates in ambient atmospheric conditions to minimise the cost of operation. In order to achieve good quality microgravity levels, a dual capsule configuration is adopted. The shape of the outer capsule is arrived at by detailed transient computational fluid dynamic analysis of the drag shield under free fall condition over the drop height. A pneumatic mechanism is used for capsule release and brought to rest at the end of fall in a carefully designed decelerator unit. The decelerator unit consists of an airbag with controlled air outflow for smooth deceleration.

Heat transfer of micro-droplet during free fall in drop tube

To explore the heat transfer of micro-droplet during free fall in the drop tube, the falling velocity and microgravity level are calculated. The Newtonian heat transfer formulation is coupled with the classical heat conduction equation to predict the heat transfer process within micro-droplet. Based on the numerical solution by finite difference method with implicit Euler scheme, the temporal evolution of thermal information inside micro-droplet is obtained including the temperature distribution, cooling rate, temperature difference and gradient. To quantitatively reveal the mechanism how the various factors affect the heat transfer of micro-droplet, the effects of physical properties of liquid metal and cooling gas as well as the micro-droplet size are studied. As the important indicators of heat transfer process, the cooling rate and temperature difference are acquired to systematically investigate the relationship between thermophysical properties and heat transfer process of different metallic micro-droplets.

Effects of -12° head-down tilt with and without elevated levels of CO2 on cognitive performance: the SPACECOT study.

Microgravity and elevated levels of CO2 are two common environmental stressors in spaceflight that may affect cognitive performance of astronauts. In this randomized, double-blind, crossover trial (SPACECOT), 6 healthy males (mean ± SD age: 41 ± 5 yr) were exposed to 0.04% (ambient air) and 0.5% CO2 concentrations during 26.5-h periods of -12° head-down tilt (HDT) bed rest with a 1-wk washout period between exposures. Subjects performed the 10 tests of the Cognition Test Battery before and on average 0.1, 5.2, and 21.0 h after the initiation of HDT bed rest. HDT in ambient air induced a change in response strategy, with increased response speed (+0.19 SD; P = 0.0254) at the expense of accuracy (-0.19 SD; P = 0.2867), resulting in comparable cognitive efficiency. The observed effects were small and statistically significant for cognitive speed only. However, even small declines in accuracy can potentially cause errors during mission-critical tasks in spaceflight. Unexpectedly, exposure to 0.5% CO2 reversed the response strategy changes observed under HDT in ambient air. This was possibly related to hypercapnia-induced cerebrovascular reactivity that favors cortical regions in general and the frontal cortex in particular, or to the CNS arousing properties of mildly to moderately increased CO2 levels. There were no statistically significant time-in-CO2 effects for any cognitive outcome. The small sample size and the small effect sizes are major limitations of this study and its findings. The results should not be generalized beyond the group of investigated subjects until they are confirmed by adequately powered follow-up studies. NEW & NOTEWORTHY Simulating microgravity with exposure to 21 h of -12° head-down tilt bed rest caused a change in response strategy on a range of cognitive tests, with a statistically significant increase in response speed at the expense of accuracy. Cognitive efficiency was not affected. The observed speed-accuracy tradeoff was small but may nevertheless be important for mission-critical tasks in spaceflight. Importantly, the change in response strategy was reversed by increasing CO2 concentrations to 0.5%.

A Six-DOF Buoyancy Tank Microgravity Test Bed with Active Drag Compensation

Ground experiment under microgravity is very essential because it can verify the space enabling technologies before applied in space missions. In this paper, a novel ground experiment system that can provide long duration, large scale and high microgravity level for the six degree of freedom (DOF) spacecraft trajectory tracking is presented. In which, the most gravity of the test body is balanced by the buoyancy, and the small residual gravity is offset by the electromagnetic force. Because the electromagnetic force on the test body can be adjusted in the electromagnetic system, it can significantly simplify the balancing process using the proposed microgravity test bed compared to the neutral buoyance system. Besides, a novel compensation control system based on the active disturbance rejection control (ADRC) method is developed to estimate and compensate the water resistance online, in order to improve the fidelity of the ground experiment. A six-DOF trajectory tracking in the microgravity system is applied to testify the efficiency of the proposed compensation controller, and the experimental simulation results are compared to that obtained using the classic proportional-integral-derivative (PID) method. The simulation results demonstrated that, for the six-DOF motion ground experiment, the microgravity level can reach to 5 × 10−4 g. And, because the water resistance has been estimated and compensated, the performance of the presented controller is much better than the PID controller. The presented ground microgravity system can be applied in on-orbit service and other related technologies in future.

Human Pathophysiological Adaptations to the Space Environment.

Space is an extreme environment for the human body, where during long-term missions microgravity and high radiation levels represent major threats to crew health. Intriguingly, space flight (SF) imposes on the body of highly selected, well-trained, and healthy individuals (astronauts and cosmonauts) pathophysiological adaptive changes akin to an accelerated aging process and to some diseases. Such effects, becoming manifest over a time span of weeks (i.e., cardiovascular deconditioning) to months (i.e., loss of bone density and muscle atrophy) of exposure to weightlessness, can be reduced through proper countermeasures during SF and in due time are mostly reversible after landing. Based on these considerations, it is increasingly accepted that SF might provide a mechanistic insight into certain pathophysiological processes, a concept of interest to pre-nosological medicine. In this article, we will review the main stress factors encountered in space and their impact on the human body and will also discuss the possible lessons learned with space exploration in reference to human health on Earth. In fact, this is a productive, cross-fertilized, endeavor in which studies performed on Earth yield countermeasures for protection of space crew health, and space research is translated into health measures for Earth-bound population.

Microgravity Level Measurement of the Beijing Drop Tower Using a Sensitive Accelerometer.

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.

Microgravity elicits reproducible alterations in cytoskeletal and metabolic gene and protein expression in space-flown Caenorhabditis elegans.

Although muscle atrophy is a serious problem during spaceflight, little is known about the sequence of molecular events leading to atrophy in response to microgravity. We carried out a spaceflight experiment using Caenorhabditis elegans onboard the Japanese Experiment Module of the International Space Station. Worms were synchronously cultured in liquid media with bacterial food for 4 days under microgravity or on a 1-G centrifuge. Worms were visually observed for health and movement and then frozen. Upon return, we analyzed global gene and protein expression using DNA microarrays and mass spectrometry. Body length and fat accumulation were also analyzed. We found that in worms grown from the L1 larval stage to adulthood under microgravity, both gene and protein expression levels for muscular thick filaments, cytoskeletal elements, and mitochondrial metabolic enzymes decreased relative to parallel cultures on the 1-G centrifuge (95% confidence interval (P⩽0.05)). In addition, altered movement and decreased body length and fat accumulation were observed in the microgravity-cultured worms relative to the 1-G cultured worms. These results suggest protein expression changes that may account for the progressive muscular atrophy observed in astronauts.

Evaluation of Simulated Microgravity Environments Induced by Diamagnetic Levitation of Plant Cell Suspension Cultures

Ground-Based Facilities (GBF) are essetial tools to understand the physical and biological effects of the absence of gravity and they are necessary to prepare and complement space experiments. It has been shown previously that a real microgravity environment induces the dissociation of cell proliferation from cell growth in seedling root meristems, which are limited populations of proliferating cells. Plant cell cultures are large and homogeneous populations of proliferating cells, so that they are a convenient model to study the effects of altered gravity on cellular mechanisms regulating cell proliferation and associated cell growth. Cell suspension cultures of the Arabidopsis thaliana cell line MM2d were exposed to four altered gravity and magnetic field environments in a magnetic levitation facility for 3 hours, including two simulated microgravity and Mars-like gravity levels obtained with different magnetic field intensities. Samples were processed either by quick freezing, to be used in flow cytometry for cell cycle studies, or by chemical fixation for microscopy techniques to measure parameters of the nucleolus. Although the trend of the results was the same as those obtained in real microgravity on meristems (increased cell proliferation and decreased cell growth), we provide a technical discussion in the context of validation of proper conditions to achieve true cell levitation inside a levitating droplet. We conclude that the use of magnetic levitation as a simulated microgravity GBF for cell suspension cultures is not recommended.

부력의 영향을 최소화한 조건에서 대향류 확산화염의 화염 소화에 관한 실험적 연구

Experiments were conducted to clarify role of the outermost edge flame on low-strain-rate flame extinction in buoyancy-suppressed non-premixed methane flames diluted with He and <TEX>$N_2$</TEX>. The use of He curtain flow produced a microgravity level of <TEX>$10^{-2}-10^{-3}g$</TEX> in <TEX>$N_2$</TEX>- and He-diluted non-premixed counterflow flame experiments. The critical He and <TEX>$N_2$</TEX> mole fractions at extinction with a global strain rate were examined at various burner diameters (10, 20, and 25 mm). The results showed that the extinction curves differed appreciably with burner diameter. Before the turning point along the extinction curve, low-strain-rate flames were extinguished via shrinkage of the outermost edge flame with and without self-excitation. High-strain-rate flames were extinguished via a flame hole while the outermost edge flame was stationary. These characteristics could be identified by the behavior of the outermost edge flame. The results also showed that the outermost edge flame was not influenced by radiative heat loss but by convective heat addition and conductive heat losses to the ambient He curtain flow. The numerical results were discussed in detail. The self-excitation before the extinction of a low-strain-rate flame was well described by a dependency of the Strouhal number on global strain rate and normalized nozzle exit velocity.

Modeling of Ullage Collapse Within Rocket Propellant Tanks at Reduced Gravity

Orbital maneuvers of upper-stage rockets may generate propellant slosh waves and propellant breakup into droplets within the oxidizer and fuel tanks. When many droplets are created, increased propellant evaporation may occur and lead to a significant reduction in ullage gas temperature and pressure, known as ullage collapse. This work presents a new method that uses a numerical tool to predict the droplet distribution created during a maneuver, and subsequently uses an analytical model to calculate the droplet evaporation and consequent change in tank temperature and pressure. This new hybrid method uses less computational time than a detailed computational fluid dynamics model and is capable of providing mission planners with an improved tool to assess the impact of propellant evaporation on the requirements of additional helium mass for tank repressurization. The new method is applied to predict evaporation and the consequent ullage collapse in an upper-stage propellant tank undergoing simulated orbital maneuvers at microgravity levels.

Numerical simulation of InGaSb crystal growth by temperature gradient method under normal- and micro-gravity fields

InxGa1−xSb single crystals are to be grown by using a GaSb/InSb/GaSb-sandwich system onboard at the International Space Station (ISS). In order to have a better understanding for the transport phenomena occurring in the melt (solution) of this sandwich system, the dissolution and the growth processes were numerically simulated under a microgravity level of the ISS. Simulations were also performed under the gravitational field of Earth (1g) for comparison. The simulation domain includes the In–Ga–Sb solution (liquid phase) for fluid flow, and heat and mass transfer, and the crucible ampoule (solid phase) for heat transfer. Heat and mass balances were also used at the crystal–solution interfaces to examine the dissolution and growth processes globally. Simulation results showed that, at 1g, dissolution of the GaSb seed was enhanced due to the contribution of solutal natural convection, and the solution saturated faster compared with that under microgravity. Diffusion during growth was dominant at the both gravity levels. The GaSb concentration in the solution under microgravity was slightly affected by the temperature distribution in the ampoule.

Geophysical investigations of the Wairakei Field

Geophysical studies of the Wairakei sector of the Wairakei–Tauhara geothermal system started shortly after exploration drilling began in the early 1950s. These investigations have made a major contribution in defining the boundary of geothermal systems and understanding the changes that have occurred in the reservoir as a result of fluid production. The most successful tools have been electrical resistivity methods for delineating the field, while microgravity, heat loss and groundwater level monitoring surveys were useful to interpret production-induced changes. Seismic, gravity and magnetic surveys had only limited success.

Convection in Weld Pool under Microgravity and Terrestrial Conditions

Electron beam (EB) welding and tungsten inert gas (TIG) welding were performed under both microgravity and terrestrial conditions in order to investigate the effects of gravity and surface tension on the convection in a molten pool. The microgravity conditions were achieved using the drop-shaft at the Japan Microgravity Center (JAMIC). A small-sized EB or TIG welding system was loaded into the drop capsule, and then the capsule was dropped 710m below ground level. The system attains a microgravity level of 10-5 G for a duration of 10 seconds. Pure iron and an iron-tungsten alloy (SKD4) were used for the iron samples, while pure aluminum and an aluminum-copper alloy (A2219) were used for the aluminum samples. The cross sections of the specimens were analyzed by EPMA after the welding to investigate the distribution of the minor elements. During the EB welding, the surface tension and the buoyancy determine the convection. Under microgravity, only the surface tension causes the convection because the buoyancy is considered to be negligible. As a result, it was found that the convection due to the surface tension is dominant for the iron alloys, but it is very weak for the aluminum alloys.

Ground based ISS payload microgravity disturbance assessments

In order to verify that the International Space Station (ISS) payload facility racks do not disturb the microgravity environment of neighboring facility racks and that the facility science operations are not compromised, a testing and analytical verification process must be followed. Currently no facility racks have taken this process from start to finish. The authors are participants in implementing this process for the NASA Glenn Research Center (GRC) Fluids and Combustion Facility (FCF). To address the testing part of the verification process, the Microgravity Emissions Laboratory (MEL) was developed at GRC. The MEL is a 6 degree of freedom inertial measurement system capable of characterizing inertial response forces (emissions) of components, sub-rack payloads, or rack-level payloads down to 10 - 7 g 's. The inertial force output data, generated from the steady state or transient operations of the test articles, are utilized in analytical simulations to predict the on-orbit vibratory environment at specific science or rack interface locations. Once the facility payload rack and disturbers are properly modeled an assessment can be made as to whether required microgravity levels are achieved. The modeling is utilized to develop microgravity predictions which lead to the development of microgravity sensitive ISS experiment operations once on-orbit. The on-orbit measurements will be verified by use of the NASA GRC Space Acceleration Measurement System (SAMS). The major topics to be addressed in this paper are: (1) Microgravity Requirements, (2) Microgravity Disturbers, (3) MEL Testing, (4) Disturbance Control, (5) Microgravity Control Process, and (6) On-Orbit Predictions and Verification.