Reduced Gravity Environment Research Articles

Commentaries on Viewpoint: Standardization of bed rest studies in the spaceflight contextCommentaries on Viewpoint: Standardization of bed rest studies in the spaceflight contextCommentaries on Viewpoint: Standardization of bed rest studies in the spaceflight contextCommentaries on Viewpoint: Standardization of bed rest studies in the spaceflight contextCommentaries on Viewpoint: Standardization of bed rest studies in the spaceflight context

to the editor: The work presented by Sundblad et al. ([5][1]) is important and is likely to improve present international efforts to develop countermeasures against, for example, cardiovascular deconditioning during spaceflight. However, one aspect that is not addressed to a sufficient extent is the

In situ observation of solidification patterns in diffusive conditions

We present a review of recent in situ experimentation studies of solidification front patterns and microstructures in alloys. Front-tracking diagnostics and real-time observation methods using high-resolution optical or X-ray imaging devices currently apply to model transparent systems as well as metallic alloys in thin and bulk samples. On a theoretical basis that spans the physics of nonequilibrium pattern formation and materials science, in combination with time-resolved numerical simulations, conclusive results of both fundamental- and applied-science interest have been obtained on major problems relative to multiscale microstructure selection, morphological transitions, and crystallographic effects during single- and multi-phase solidification. We will mainly focus on the dynamics of cellular, dendritic, and eutectic growth patterns in diffusive-growth conditions, that is, in the absence of convection in the liquid. This can be achieved in (semi-)thin samples, or, for bulk solidification, in the reduced-gravity environment of orbiting facilities. A selection of emerging work on, e.g., faceted growth and adaptive control of solidification patterns will furthermore be reported. We conclude by pointing out open questions and new perspectives for future research.

Dynamic single actuator robot climbing a chute

The planar mechanism analyzed in this paper, called DSAC for Dynamic, Single Actuated Climber, comprises only two links connected by a single oscillating actuator. This simple open loop motion propels the robot stably between two vertical walls. We explore the local orbital stability of the DSAC mechanism. Using the Poincare map, we reduce the analyzed dimension and find the stable regions while varying the control inputs and mechanism’s parameters. Moreover, in response to a continuous change of a parameter of the mechanism, the symmetric and steady stable gait of the mechanism gradually evolves through a regime of period doubling bifurcations. This investigation includes numerical approximation of the local stability, and basin of attraction. Finally, the paper reports experimental results of open-loop, stable climbing in a planar, reduced gravity environment undergoing bifurcations which correlate well to the numerical analysis.

Detection of spacecraft fire signatures and post-fire aerosols—Part I: Ground-based results

Preventing fires in spacecraft and other remote platforms is an important facet of avoiding fires that potentially compromise missions, hardware, and crew. If a fire occurs, the objective is to detect the associated fire signatures at the earliest possible time from inception, thus minimizing propagation and collateral damage while providing maximal margin for suppression. The goal is to provide detection sensitivity without introducing spurious false alarms that compromise operations and trigger responsive abatement and containment provisions. A related issue in sealed, self-contained environments is post-fire clean up, and sensors to evaluate the environmental suitability in crewed quarters. In both situations, knowledge of the particulate and/or gaseous fire signatures as they occur under the unique combination of a reduced-gravity environment and materials typical of spaceflight applications is essential for the design of spacecraft fire detectors and habitat sensors. This paper describes recent ground and spaced-based data on fire signatures, and the response of a novel multi-channel optical scattering sensor. This detector, known as the Multi-Parameter Aerosol Scattering Sensor (MPASS), determines multiple moments of the aerosol distributions. The methodology for designing a sensor with the desired response function is discussed, as well as test results that demonstrate the performance of prototype devices.

Gluteal muscle function and size in swimmers.

To compare the gluteus medius and minimus segments size and activity in swimmers versus non-swimmers. Case matched-control cross-sectional study. The three segments of gluteus medius (anterior, middle and posterior) and two segments of gluteus minimus (anterior and posterior) were evaluated using electromyography and magnetic resonance imaging in 15 swimmers (7 elite and 8 non-elite) and 15 gender- and aged-matched controls. For each muscle segment, values were obtained for peak amplitude, average amplitude, and time to peak from each phase of the gait cycle (0-20%, 20-60%, and total stance). The pattern of anterior gluteus minimus EMG activity in swimmers demonstrated additional activity early in the gait cycle when compared with controls. The segmental differences between anterior and posterior gluteus minimus during gait identified in the control group were not present in the swimmers. Overall, there were no significant differences in the gluteus medius EMG characteristics between groups and muscle size was not significantly different between groups for any of the hip abductor muscles. The preliminary evidence of non-segmental differences within the gluteus minimus of swimmers (as opposed to non-swimmers) might implicate reduced-gravity environments in contributing to subsequent changes in deep stabiliser muscles. Such changes might predispose the athlete to a greater risk of lower limb injury during weight bearing activities.

Influence of phase change on self-pressurization in cryogenic tanks under microgravity

Future operations of many fluid, thermal and power systems and their ability to store, transfer, and manage a variety of single or multiphase fluids in reduced gravity environment are of great importance. For many of these systems, cryogenic conditions will play an important role. Cryogenic vaporization, caused by heat leakage into the tank from the surrounding environment, is one of the main causes of mass loss and leads to self-pressurization of the storage tanks. Available publications on self-pressurization and stratification of cryogenic tanks mainly focus on the convection and surface evaporation influences. Because large superheats increase the likelihood of evaporation in the liquid, the evaporation and its effect on vapor pressure under microgravity is studied numerically in this paper. The effects of reduced gravity, contact angle of the vapor bubble, and surface tension are investigated. The computations are carried out by using the CFD software package, Ansys Fluent, and an in-house developed code to calculate the source term associated with the phase change. A coupled level set and the volume-of-fluid method (CLSVOF) are used to solve a single set of conservation equations for the whole domain and the interface between the two phases is tracked or captured. A heat and mass transfer model is implemented into the Fluent code for solving problems involving evaporation or condensation. Results show that small tiny vapor regions caused by the evaporation process change the pressure rise. Vortices are observed due to the vapor dynamics.

Radiation effect on temperature distribution and NO formation in a diffusion flame under reduced gravity conditions

Combustion of hydrocarbon fuel is accompanied with the formation of nitric oxide (NO) amongst other harmful emissions. In this work, a numerical investigation has been made for understanding the effect of radiative heat transfer on temperature distribution and formation of thermal NO in a methane–air diffusion flame under different reduced gravity environments. Conservation equations of overall mass, species concentration, momentum and energy for the reactive flows have been numerically solved with the use of finite difference scheme. In addition to that a semi-empirical soot model and an optically thin radiation model have been incorporated in the simulation. Gravity level is varied by the changed values of acceleration due to gravity. A thermal NO model incorporated accounts for the NO formation process which is decoupled from the hydrocarbon combustion. The relevant conservation equations have been solved as a post combustion reaction process. The flame height drops marginally with the reduction of gravity. Temperature becomes more uniformly distributed at lower gravity. NO formation boosts up with the fall of gravity below normal level when no radiation effect is considered. However, when radiation is considered, NO formation declines marginally with the reduction of gravity levels. Also in this case, concentration values of NO compare substantially lower with those without radiation. The upsurge of NO formation due to decline in gravity; and on the other hand, a shrinkage in concentration values of NO due to radiation effect can be attributed mainly to the rise and fall of temperature respectively in the computational zone.

On the determination of diffusion coefficients in two-component alloys and doped semiconductors. Several implications concerning the International Space Station

The accurate determination of mass diffusion coefficients is a technologically relevant problem that has implications on the modelling and control of material processes such as crystal growth and casting. It is also important in the validation of different theories of atomic diffusion. The experimental determination of these coefficients, when there is a liquid phase, is difficult due to the unavoidable presence of buoyancy driven convection currents that enhance mass transport and disturb diffusion measurements. To minimize as much as possible these problems, long capillaries are used in order to confine the fluid and reduce the intensity of the convective motions. These measurements have also been done in reduced gravity environments, but the residual gravity may still be able to induce buoyancy driven convection motions. The aim of our work is to analyze the impact of low solutal Rayleigh number environments on the accuracy of the interdiffusion coefficient measurements using long capillaries. In the present study we deal with two liquid systems; photovoltaic silicon and Al-based liquid binary alloys at high temperature. We have numerically simulated two different experimental techniques used to determine the diffusion coefficients; the shear cell and the long capillary techniques. We also consider the effect of rotating the cylindrical cell along their axis as a mechanism to reduce axial convective transport even in Earth laboratories. Finally, we use typical accelerometric signals from the International Space Station (ISS) in the quasi-steady range of frequencies. The signals concentrate on typical station reboosts because the accelerometric level of the rest of potentially dangerous disturbances – dockings, undockings and Extra Vehicular Activities, EVAs – is considerably lower.

Development and implementation of a coupled computational muscle force optimization bone shape adaptation modeling method.

Improved methods to analyze and compare the muscle-based influences that drive bone strength adaptation can aid in the understanding of the wide array of experimental observations about the effectiveness of various mechanical countermeasures to losses in bone strength that result from age, disuse, and reduced gravity environments. The coupling of gradient-based and gradientless numerical optimization routines with finite element methods in this work results in a modeling technique that determines the individual magnitudes of the muscle forces acting in a multisegment musculoskeletal system and predicts the improvement in the stress state uniformity and, therefore, strength, of a targeted bone through simulated local cortical material accretion and resorption. With a performance-based stopping criteria, no experimentally based or system-based parameters, and designed to include the direct and indirect effects of muscles attached to the targeted bone as well as to its neighbors, shape and strength alterations resulting from a wide range of boundary conditions can be consistently quantified. As demonstrated in a representative parametric study, the developed technique effectively provides a clearer foundation for the study of the relationships between muscle forces and the induced changes in bone strength. Its use can lead to the better control of such adaptive phenomena.

GeneChip expression profiling reveals the alterations of energy metabolism related genes in osteocytes under large gradient high magnetic fields.

The diamagnetic levitation as a novel ground-based model for simulating a reduced gravity environment has recently been applied in life science research. In this study a specially designed superconducting magnet with a large gradient high magnetic field (LG-HMF), which can provide three apparent gravity levels (μ-g, 1-g, and 2-g), was used to simulate a space-like gravity environment. Osteocyte, as the most important mechanosensor in bone, takes a pivotal position in mediating the mechano-induced bone remodeling. In this study, the effects of LG-HMF on gene expression profiling of osteocyte-like cell line MLO-Y4 were investigated by Affymetrix DNA microarray. LG-HMF affected osteocyte gene expression profiling. Differentially expressed genes (DEGs) and data mining were further analyzed by using bioinfomatic tools, such as DAVID, iReport. 12 energy metabolism related genes (PFKL, AK4, ALDOC, COX7A1, STC1, ADM, CA9, CA12, P4HA1, APLN, GPR35 and GPR84) were further confirmed by real-time PCR. An integrated gene interaction network of 12 DEGs was constructed. Bio-data mining showed that genes involved in glucose metabolic process and apoptosis changed notablly. Our results demostrated that LG-HMF affected the expression of energy metabolism related genes in osteocyte. The identification of sensitive genes to special environments may provide some potential targets for preventing and treating bone loss or osteoporosis.

The Onset of Normal Field Instability in a Ferrofluid in a Reduced Gravity Environment

A ferrofluid is a magnetic liquid comprised of nanoscale ferrous particles suspended in a low-viscosity carrier fluid. When subjected to a magnetic field, the surface of a ferrofluid deforms into peaks and valleys along the magnetic field lines. The onset of surface deformation is called the normal field instability. The theory describing the NFI identifies a critical magnetic field below which no magnetically driven surface deformations occur. The critical field depends on the gravitational acceleration and, according to the theory, should disappear as local gravitational acceleration approaches zero. While there have been previous demonstrations of the normal field instability in a reduced gravity environment, data has been inconclusive on the existence of a critical magnetic field in reduced gravity. For our work, we designed a sounding rocket payload for a suborbital rocket mission. Our experiment incorporates a ferrofluid sample and a uniform magnetic field which can be varied across a discrete range of values to observe surface deformations at different applied fields. During the microgravity portion of the rocket’s flight, we obtain video of the ferrofluid’s behavior and compare it to data taken in Earth’s gravity. A team of five undergraduate students designed and built the payload that will characterize the role of gravity in setting the critical magnetic field strength for the onset of the NFI. Data will be used to further understanding of ferrofluid behavior in a microgravity environment to advance its use in various space-based applications.

Retrofit Simulator to Train Cosmonauts for Working in Non-gravity and Reduced Gravity Environment

The paper describes implementation and operational features of the object transfer systems in the working space of simulators for training cosmonauts to fulfill extravehicular activity in non-gravity and reduced gravity environment. The control system design concepts of cosmonauts’ horizontal movements under non-gravity and reduced gravity environment simulation were studied. It was proved necessary to apply electromechanical systems for friction and inertial force compensation by additionally joined masses to the non-gravity object while implementing advanced simulators. The control system structure was developed; it contains feedbacks on current, speed and electric drive shaft accelerations, as well as on belt transmission force and power drive cable deflection angle from the perpendicular position. The paper presents the results of synthesizing the cosmonauts’ movement control system structure in the working space of simulators, as well as of correcting device parameters to provide damping of springy oscillations in machinery.

A Classification of Flammability of Thermoplastic Materials in Space - Challenges to Utilize ISO4589-2 to Estimate the Flammability Limit under Reduced Gravity Environments-

A Classification of Flammability of Thermoplastic Materials in Space - Challenges to Utilize ISO4589-2 to Estimate the Flammability Limit under Reduced Gravity Environments-

Reduced-gravity Environment Hardware Demonstrations of a Prototype Miniaturized Flow Cytometer and Companion Microfluidic Mixing Technology

Until recently, astronaut blood samples were collected in-flight, transported to earth on the Space Shuttle, and analyzed in terrestrial laboratories. If humans are to travel beyond low Earth orbit, a transition towards space-ready, point-of-care (POC) testing is required. Such testing needs to be comprehensive, easy to perform in a reduced-gravity environment, and unaffected by the stresses of launch and spaceflight. Countless POC devices have been developed to mimic laboratory scale counterparts, but most have narrow applications and few have demonstrable use in an in-flight, reduced-gravity environment. In fact, demonstrations of biomedical diagnostics in reduced gravity are limited altogether, making component choice and certain logistical challenges difficult to approach when seeking to test new technology. To help fill the void, we are presenting a modular method for the construction and operation of a prototype blood diagnostic device and its associated parabolic flight test rig that meet the standards for flight-testing onboard a parabolic flight, reduced-gravity aircraft. The method first focuses on rig assembly for in-flight, reduced-gravity testing of a flow cytometer and a companion microfluidic mixing chip. Components are adaptable to other designs and some custom components, such as a microvolume sample loader and the micromixer may be of particular interest. The method then shifts focus to flight preparation, by offering guidelines and suggestions to prepare for a successful flight test with regard to user training, development of a standard operating procedure (SOP), and other issues. Finally, in-flight experimental procedures specific to our demonstrations are described.

Reduced-gravity environment hardware demonstrations of a prototype miniaturized flow cytometer and companion microfluidic mixing technology.

Until recently, astronaut blood samples were collected in-flight, transported to earth on the Space Shuttle, and analyzed in terrestrial laboratories. If humans are to travel beyond low Earth orbit, a transition towards space-ready, point-of-care (POC) testing is required. Such testing needs to be comprehensive, easy to perform in a reduced-gravity environment, and unaffected by the stresses of launch and spaceflight. Countless POC devices have been developed to mimic laboratory scale counterparts, but most have narrow applications and few have demonstrable use in an in-flight, reduced-gravity environment. In fact, demonstrations of biomedical diagnostics in reduced gravity are limited altogether, making component choice and certain logistical challenges difficult to approach when seeking to test new technology. To help fill the void, we are presenting a modular method for the construction and operation of a prototype blood diagnostic device and its associated parabolic flight test rig that meet the standards for flight-testing onboard a parabolic flight, reduced-gravity aircraft. The method first focuses on rig assembly for in-flight, reduced-gravity testing of a flow cytometer and a companion microfluidic mixing chip. Components are adaptable to other designs and some custom components, such as a microvolume sample loader and the micromixer may be of particular interest. The method then shifts focus to flight preparation, by offering guidelines and suggestions to prepare for a successful flight test with regard to user training, development of a standard operating procedure (SOP), and other issues. Finally, in-flight experimental procedures specific to our demonstrations are described.

N-Butanol droplet combustion: Numerical modeling and reduced gravity experiments

Recent interest in alternative and bio-derived fuels has emphasized butanol over ethanol as a result of its higher energy density, lower vapor pressure and more favorable gasoline blending properties. Numerous efforts have examined the combustion of butanol from the perspective of low dimensional gas-phase transport configurations that facilitate modeling and validation of combustion kinetics. However, fewer studies have focused on multiphase butanol combustion, and none have appeared on isolated droplet combustion that couples experiments with robust modeling of the droplet burning process. This paper presents such an experimental/numerical modeling study of isolated droplet burning characteristics of n-butanol. The experiments are conducted in an environment that simplifies the transport process to one that is nearly one-dimensional as promoted by burning in a reduced gravity environment. Measurements of the evolution of droplet diameter (Do=0.56–0.57mm), flame standoff ratio (FSR≡Df/D) and burning rate (K) are made in the standard atmosphere under reduced gravity and the data are compared against numerical simulation. The detailed model is based on a comprehensive time-dependent, sphero-symmetric droplet combustion simulation that includes spectrally resolved radiative heat transfer, multi-component diffusive transport, full thermal property variations and detailed chemical kinetic. The simulations are carried out using both a large order kinetic mechanism (284 species, 1892 reactions) and a reduced order mechanism (44 species, 177 reactions). The results show that the predicted burning history and flame standoff ratios are in good agreement with the measurements for both the large and reduced order mechanisms. Additional simulations are conducted for varying oxygen concentration to determine the limiting oxygen index and to elucidate the kinetic processes that dictate the extinction of the flame at these low oxygen concentrations.

Cardiovascular models of simulated moon and mars gravities: head-up tilt vs. lower body unweighting.

In this study we compare two models [head-up tilt (HUT) vs. body unweighting using lower body positive pressure (LBPP)] to simulate Moon, Mars, and Earth gravities. A literature search did not reveal any comparisons of this type performed previously. We hypothesized that segmental fluid volume shifts (thorax, abdomen, upper and lower leg), cardiac output, and blood pressure (BP), heart rate (HR), and total peripheral resistance to standing would be similar in the LBPP and HUT models. There were 21 subjects who were studied while supine (simulation of spaceflight) and standing at 100% (Earth), 40% (Mars), and 20% (Moon) bodyweight produced by LBPP in Alter-G and while supine and tilted at 80 degrees, 20 degrees, and 10 degrees HUT (analogues of Earth, Mars, and Moon gravities, respectively). Compared to supine, fluid shifts from the chest to the abdomen, increases in HR, and decreases in stroke volume were greater at 100% bodyweight than at reduced weights in response to both LBPP and HUT. Differences between the two models were found for systolic BP, diastolic BP, mean arterial BP, stroke volume, total peripheral resistance, and thorax and abdomen impedances, while HR, cardiac output, and upper and lower leg impedances were similar. Bodyweight unloading via both LBPP and HUT resulted in cardiovascular changes similar to those anticipated in actual reduced gravity environments. The LBPP model/Alter-G has the advantage of providing an environment that allows dynamic activity at reduced bodyweight; however, the significant increase in blood pressures in the Alter-GC may favor the HUT model.

Neuronal Activity in the Subthalamic Cerebrovasodilator Area under Partial-Gravity Conditions in Rats.

The reduced-gravity environment in space is known to cause an upward shift in body fluids and thus require cardiovascular adaptations in astronauts. In this study, we recorded in rats the neuronal activity in the subthalamic cerebrovasodilator area (SVA), a key area that controls cerebral blood flow (CBF), in response to partial gravity. “Partial gravity” is the term that defines the reduced-gravity levels between 1 g (the unit gravity acceleration on Earth) and 0 g (complete weightlessness in space). Neuronal activity was recorded telemetrically through chronically implanted microelectrodes in freely moving rats. Graded levels of partial gravity from 0.4 g to 0.01 g were generated by customized parabolic-flight maneuvers. Electrophysiological signals in each partial-gravity phase were compared to those of the preceding 1 g level-flight. As a result, SVA neuronal activity was significantly inhibited by the partial-gravity levels of 0.15 g and lower, but not by 0.2 g and higher. Gravity levels between 0.2–0.15 g could represent a critical threshold for the inhibition of neurons in the rat SVA. The lunar gravity (0.16 g) might thus trigger neurogenic mechanisms of CBF control. This is the first study to examine brain electrophysiology with partial gravity as an experimental parameter.

EXPERIMENTAL STUDY OF BUBBLE DYNAMICS DURING NUCLEATE FLOW BOILING ON HORIZONTAL AND VERTICAL SURFACES

Knowledge of the physical mechanisms governing bubble dynamics and two-phase heat transfer is required to develop mechanistic models and to accurately predict and scale the performance of two-phase systems in reduced gravity environments. To better understand the effect of the magnitude of gravity on flow boiling, especially the dynamics of single bubbles under different levels of bulk liquid velocity, surface orientation at earth normal gravity and contact angle effects were studied in this work. A microfabricated nucleation site (10 mm in diameter) at the center of a flat heating surface was used to generate bubbles. Silicon and aluminum were used as substrate materials, with static contact angles of 56° and 19°, respectively, and water as the test liquid. Bulk liquid velocities ranged from 0 to 0.25 m/s, for horizontal and vertical surface orientations, in upflow conditions. Bulk liquid temperature was set close to saturation temperature, with bulk liquid subcooling less than 1°C, and wall superheat was maintained between 5.0°C and 6.0°C. The experimental results for bubble growth, departure diameter and time for departure, bubble sliding distance and velocity, bubble lift-off diameter and time for lift-off, and bubble base diameter are reported for vertical and horizontal orientations, as the system variables were varied parametrically. It is found that irrespective of orientation and contact angle, departure and lift-off diameters decrease with increase in bulk liquid velocity. At a given velocity, departure diameter decreases with increase in the component of gravity parallel to the heater surface. For a given bulk liquid velocity, increase in contact angle results in increase in bubble departure and lift-off diameters, for all orientations. For given conditions, bubble lift-off diameter increases with decrease in the component of gravity normal to the heater surface. The effect of gravity on lift-off diameter is reduced at high liquid bulk velocities. For given orientation and flow velocity, sliding distance decreases monotonically with decrease in contact angle. The bubble velocity at lift-off increases with increase in flow velocity and increase in the component of gravity parallel to heater surface.

Cardiovascular Regulation During Body Unweighting by Lower Body Positive Pressure

We hypothesized that human cardiovascular responses to standing in reduced gravity environments, as on the Moon or Mars, could be modeled using a lower body positive pressure (LBPP) chamber. Heart rate, blood pressure, body segment fluid shifts, ECG, indexes of sympathetic, parasympathetic balance, and baroreflex control of the heart and periphery plus echocardiographic measures of cardiac function were recorded from seven men and seven women supine and standing at 100% (Earth), 40% (-Mars), and 20% (-Moon) bodyweights (BW). The fluid shifted from the chest was greater when standing at 100% BW than at 20% and 40% BW, while fluid pooled in the abdomen was similar at all BWs. Compared to moving from supine to standing at 100% BW, moving to 20% and 40% BW resulted in smaller decreases in stroke volume and pulse pressure, smaller increases in heart rate and smaller decreases in parasympathetic control of heart rate, baroreflex slope, numbers of blood pressure ramps, and much reduced indexes of sympathetic drive to the heart and periphery. However, peripheral vascular resistance, systolic pressure, and baroreflex effectiveness were elevated during 20% and 40% BW, compared to supine and standing at 100% BW. Standing at reduced bodyweight suppressed indexes of sympathetic control of heart rate and peripheral vasomotion. Regulatory responses indicated a combination of arterial and cardiopulmonary baroreflex control: mean heart rate, vasomotion, and baroreflex sensitivity appeared to be more under cardiopulmonary control while baroreflex effectiveness appeared to be driven more by the arterial baroreflex.