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NASA NTRS1999

Utilizing Advanced Vibration Isolation Technology to Enable Microgravity Science Operations

Microgravity scientific research is performed in space to determine the effects of gravity upon experiments. Until recently, experiments had to accept the environment aboard various carriers: reduced-gravity aircraft, sub-orbital payloads, Space Shuttle, and Mir. If the environment is unacceptable, then most scientists would rather not expend the resources without the assurance of true microgravity conditions. This is currently the case on the International Space Station, because the ambient acceleration environment will exceed desirable levels. For this reason, the g-LIMIT (Glovebox Integrated Microgravity Isolation Technology) system is currently being developed to provide a quiescent acceleration environment for scientific operations. This sub-rack isolation system will provide a generic interface for a variety of experiments for the Microgravity Science Glovebox. This paper describes the motivation for developing of the g-LIMIT system, presents the design concept and details some of the advanced technologies utilized in the g-LIMIT flight design.

Alhorn, Dean Carl↗

NASA NTRS1997

The Development of Vestibular Connections in Rat Embryos in Microgravity

Existing experimental embryological data suggests that the vestibular system initially develops in a very rigid and genetically controlled manner. Nevertheless, gravity appears to be a critical factor in the normal development of the vestibular system that monitors position with respect to gravity (saccule and utricle). In fact several studies have shown that prenatal exposure to microgravity causes temporary deficits in gravity-dependent righting behaviors, and prolonged exposure to hypergravity from conception to weaning causes permanent deficits in gravity-dependent righting behaviors. Data on hypergravity and microgravity exposure suggest some changes in the otolith formation during development, in particular the size although these changes may actually vary with the species involved. In adults exposed to microgravity there is a change in the synaptic density in the otic sensory epithelia suggesting that some adaptation may occur there. However, effects have also been reported in the brainstem. Several studies have shown synaptic changes in the lateral vestibular nucleus and in the nodulus of the cerebellum after neonatal exposure to hypergravity. We report here that synaptogenesis in the medial vestibular nucleus is retarded in developing rat embryos that were exposed to microgravity from gestation days 9 to 19.

Bruce, Laura L.↗

NASA NTRS1999

Diffusion Flame Tip Instabilities of a Wide Sample in Microgravity

This work is a study of diffusion flame tip instabilities of a wide thermally thin sample in a microgravity environment. The purpose of this work is to determine the thermodiffusive and hydrodynamic instability mechanisms which cause a spreading diffusion flame to become corrugated and later fragment into smaller separate flames that we call flamelets. These thermodiffusive and hydrodynamic mechanisms are prominent forces in the near limit because buoyancy is quashed in the microgravity environment. A fundamental knowledge of the underlying mechanisms controlling the extinction limit of a diffusion flame can be applied to any real world device involving a spreading diffusion flame as well as fire safety applications on earth and in space. Our work, which combines microgravity experiments, theoretical models, and numerical computation, is a joint effort between NASA and Michigan State University. Experiments in the 2.2 second drop tower at NASA Lewis Research Center in the Microgravity Combustion Branch have been a preliminary step in locating a region where these instabilities are prevalent. These positive results will be discussed as well as the second phase of our project and future plans and recommendations.

Oravecz, Lisa↗

NASA NTRS1999

Microgravity Two-Phase Flow Transition

Two-phase flows under microgravity condition find a large number of important applications in fluid handling and storage, and spacecraft thermal management. Specifically, under microgravity condition heat transfer between heat exchanger surfaces and fluids depend critically on the distribution and interaction between different fluid phases which are often qualitatively different from the gravity-based systems. Heat transfer and flow analysis in two-phase flows under these conditions require a clear understanding of the flow pattern transition and development of appropriate dimensionless scales for its modeling and prediction. The physics of this flow is however very complex and remains poorly understood. This has led to various inadequacies in flow and heat transfer modeling and has made prediction of flow transition difficult in engineering design of efficient thermal and flow systems. In the present study the available published data for flow transition under microgravity condition are considered for mapping. The transition from slug to annular flow and from bubbly to slug flow are mapped using dimensionless variable combination developed in a previous study by the authors. The result indicate that the new maps describe the flow transitions reasonably well over the range of the data available. The transition maps are examined and the results are discussed in relation to the presumed balance of forces and flow dynamics. It is suggested that further evaluation of the proposed flow and transition mapping will require a wider range of microgravity data expected to be made available in future studies.

Parang, M.↗

NASA NTRS1999

Potential Mechanism Leading to Impaired Thermoregulation Following Microgravity Exposure

Prolonged exposure to microgravity or its analogues impairs thermoregulation in humans evidenced by higher internal temperatures following the exposure during a thermal challenge. Although the mechanism leading to this response has not been clearly delineated, we identified that prolonged head-down tilt (HDT) markedly impairs thermoregulatory reflex control of skin blood flow, as demonstrated by an increased internal temperature threshold for cutaneous vasodilation, and by a reduced slope of the relationship between the elevation in skin blood flow relative to the elevation in internal temperature. Recently, Fortney et al. identified similar responses in two individuals following 115 days of microgravity exposure. One possible mechanism leading to altered cutaneous vasodilation during a thermal challenge following actual or simulated microgravity exposure may be associated with baroreflex-mediated attenuation in the elevation of skin blood flow. During a heat stress the elevation in skin blood flow is accomplished through a combination of increased cutaneous vascular conductance and cardiac output, both of which result in central venous pressure (CVP) decreasing 2-6 mmHg. Reductions in CVP of this magnitude in normothermia decrease muscle blood flow and skin blood flow presumably through unloading the cardiopulmonary baroreceptors. It is unclear whether the reduction in CVP, and accompanying cardiopulmonary baroreceptor unloading, during passive heating buffers the elevation in skin blood flow. That is, would the elevation in skin blood flow be greater if CVP did not decrease, or decreased to a lesser extent during the heat stress? Conversely, if CVP decreased to a greater extend during a thermal challenge following a perturbation such as prolonged HDT, would the elevation in skin blood flow be attenuated during that thermal challenge? Given that prolonged HDT decreases plasma volume and central venous pressure, such a finding would provide a plausible hypothesis to explain why skin blood flow does not increase to the same extent during a heat stress following simulated or actual microgravity exposure. Thus, the purpose of this project was to identify whether cardiopulmonary baroreceptor unloading coincident with heat stress buffers the elevation in skin blood flow.

Crandall, C. G.↗

NASA NTRS1999

Bone Blood Flow During Simulated Microgravity: Physiological and Molecular Mechanisms

Blood flow to bone has been shown to affect bone mass and presumably bone strength. Preliminary data indicate that blood flow to the rat femur decreases after 14 days of simulated microgravity, using hindlimb suspension (HLS). If adult rats subjected to HLS are given dobutamine, a synthetic catecholamine which can cause peripheral vasodilation and increased blood flow, the loss of cortical bone area usually observed is prevented. Further, mechanisms exist at the molecular level to link changes in bone blood flow to changes in bone cell activity, particularly for vasoactive agents like nitric oxide (NO). The decreases in fluid shear stress created by fluid flow associated with the shifts of plasma volume during microgravity may result in alterations in expression of vasoactive agents such as NO, producing important functional effects on bone cells. The primary aim of this project is to characterize changes in 1) bone blood flow, 2) indices of bone mass, geometry, and strength, and 3) changes in gene expression for modulators of nitric oxide activity (e.g., nitric oxide synthase) and other candidate genes involved in signal transduction of mechanical loading after 3, 7, 14, 21, and 28 days of HLS in the adult rat. Using a rat of at least 5 months of age avoids inadvertently studying effects of simulated microgravity on growing, rather than adult, bone. Utilizing the results of these studies, we will then define how altered blood flow contributes to changes in bone with simulated microgravity by administering a vasodilatory agent (which increases blood flow to tissues) during hindlimb suspension. In all studies, responses in the unloaded hindlimb bones (tibial shaft, femoral neck) will be compared with those in the weightbearing humeral shaft and the non-weightbearing calvarium (skull) from the same animal. Bone volumetric mineral density and geometry will be quantified by peripheral quantitative CT; structural and material properties of the long bones will be determined by 3-point bending (tibia, humerus) or compression (femoral neck) testing to failure. A unique aspect of these studies will be defining the time course of changes in gene expression in bone cell populations with unloading, accomplished with Northern blots, in situ hybridization, and immunohistochemistry. These studies have high relevance for concurrent protocols being proposed by investigators on NSBRI Cardiovascular and Muscle teams, with blood flow data available on a number of tissues other than bone. Further, dobutamine and other Beta-agonists have been tested as countermeasures for altered muscle and cardiovascular function. Results of the intervention tested in our studies have potential relevance for a number of systemic changes seen with prolonged spaceflight.

Bloomfield, Susan A.↗

NASA NTRS1999

Microgravity Vibration Output Testing of Space Station Rotary Joints

The mission of the International Space Station is to provide a working laboratory in orbit for research in engineering, life sciences, and microgravity. Ensuring that the mechanical equipment on Space Station does not unduly disturb the microgravity environment is of paramount importance in meeting the Station's mission. The large inertia being moved by the Space Station's solar array and thermal radiator rotary joints make them one of the largest potential disturbance sources. The present paper describes the mechanical and control system design of these joints, their disturbance producing characteristics, and analytical predictions of some key performance indicators. The component and system functional tests performed to measure the actual vibration output of the joints are detailed and the test results discussed. Results of the rotary joint test program presented here show that the joints do meet the Space Station microgravity requirements, ensuring that this unique laboratory for microgravity research will be unaffected by the operation of the largest moving machinery on board.

Boucher, Robert L.↗

NASA NTRS2000

Microgravity Vibration Isolation for the International Space Station

The International Space Station (ISS) is being envisioned as a laboratory for experiments in numerous microgravity (micrograms) science disciplines. Predictions of the ISS acceleration environment indicate that the ambient acceleration levels ill exceed levels that can be tolerated by the science experiments. Hence, microgravity vibration isolation systems are being developed to attenuate the accelerations to acceptable levels. While passive isolation systems are beneficial in certain applications, active isolation systems are required to provide attenuation at low frequencies and to mitigate directly induced payload disturbances. To date, three active isolation systems have been successfully tested in the orbital environment. A fourth system called g-LIMIT is currently being developed for the Microgravity Science Glovebox and is manifested for launch on the UF-1 mission. This paper presents an overview of microgravity vibration isolation technology and the g-LIMIT system in particular.

Whorton, Mark S.↗

NASA NTRS2000

Macromolecule Crystal Quality Improvement in Microgravity: The Role of Impurities

While macromolecule impurities may affect crystal size and morphology the over-riding question is; "How do macromolecule impurities effect crystal X-ray quality and diffraction resolution?" In the case of chicken egg white lysozyme, crystals can be grown in the presence of a number of impurities without affecting diffraction resolution. One impurity however, the lysozyme dimer, does negatively impact the X-ray crystal properties. Crystal quality improvement as a result of better partitioning of this impurity during crystallization in microgravity has been reported'. In our recent experimental work dimer partitioning was found to be not significantly different between the two environments. Mosaicity analysis of pure crystals showed a reduced mosaicity and increased signal to noise for the microgravity grown crystals. Dimer incorporation however, did greatly reduce the resolution limit in both ground and microgravity grown crystals. These results indicate that impurity effects in microgravity are complex and may rely on the conditions or techniques employed.

Judge, Russell A.↗

NASA NTRS1999

Modeled Microgravity Inhibits Apoptosis in Peripheral Blood Lymphocytes

Impairment of the immunity in astronauts and cosmonauts even in short term flights is a recognized risk. Long term orbital space missions and anticipated interplanetary flights increase the concern for more pronounced effects on the immune system with potential clinical consequences. Impairment of the immunity in space may be due tonumerous physiological changes caused by space-related factors, which in turn affect the immune system, or alternatively, it may be due to direct effects of different factors encountered in space on lymphoid cells and their interactions. Indeed, in modeled microgravity (MMG) experiments on Earth we and others showed that microgravity directly affects multiple lymphocyte functions. It interferes with expression of cell surface molecules, causes inhibition of lymphocyte locomotion, suppresses polyclopal and antigen-specific lymphocyte activation, selectively inhibits protein kinase C (PKC) isoforms. Some of these effects were also confirmed in cell culture experiments in real space conditions during Spacelab, Biokosmos and Shuttle Missions. The results of these studies, taken together, strongly indicated that microgravity interferes with fundamental biological processes associated with functional and structural changes in cell surface membranes, cell surface molecules and in their interaction. Based on the data and on their interpretation, we hypothesized that microgravity in addition to observed functional changes affects programmed cell death (PCD) in lymphocyte populations and that this mechanism could contribute to the impairment of the immunity.

Risin, Diana↗

NASA NTRS1999

Suppression of Antigen-Specific Lymphocyte Activation in Simulated Microgravity

Various parameters of immune suppression are observed in astronauts during and after spaceflight, and in isolated immune cells in true and simulated microgravity. Specifically, polyclonal activation of T cells is severely suppressed in true and simulated microgravity. These recent findings with various polyclonal activators suggests a suppression of oligoclonal lymphocyte activation in microgravity. We utilized rotating wall vessel (RWV) bioreactors that simulate aspects of microgravity for cell cultures to analyze three models of antigen-specific activation. A mixed-lymphocyte reaction (MLR), as a model for a primary immune response; a tetanus toxoid (TT) response and a B. burgdorferi (Bb) response, as models of a secondary immune response, were all suppressed in the RWV bioreactor. Our findings confirm that the suppression of activation observed with polyclonal models also encompasses oligoclonal antigen-specific activation.

Cooper, David↗

NASA NTRS1999

PKC Isoform Expression in Modeled Microgravity

Our previous studies showed that modeled (MMG) and true (USA Space Shuttle Missions STS-54 and STS-56) microgravity (MG) inhibit human lymphocyte locomotion, Modeled MG also suppressed polyclonal and antigen-specific lymphocyte activation. Activation of PKC by phorbol myristate acetate (PMA) restored the microgravity-inhibited lymphocyte locomotion as well as activation by phytohaemagglutinin (PHA), whereas calcium ionophore (ionomycin) was unable to restore these functions. Based on these results we hypothesized that MG-induced changes in lymphocyte functions are caused by a fundamental defect in signal transduction mechanism. This defect may be localized either at the PKC level or upstream of PKC, most likely, at the cell membrane level. In this study we examined the expression of PKC isoforms alpha, epsilon and delta in PBMC cultured in rotating wall vessel bioreactor, developed at NASA JSC, which models microgravity by sustaining cells in continuous free fall. The assessment of the isoforms was performed by FACS analysis following cell permeabilization. A decrease in the expression of isoforms epsilon and delta, but not isoform a, was observed in PBMC cultured in microgravity conditions. These data suggest that MMG might selectively affect the expression of Ca2+ independent isoforms of PKC Molecular analysis confirm selective suppression of Ca2+ independent isoforms of PKC.

Risin, Diana↗

NASA NTRS1999

Lymphocyte Functions in Microgravity

To understand the mechanism of immunity impairment in space it is important to analyze the direct effects of space-related conditions on different lymphocytes functions. Since 1992, we are investigating the effect of modeled and true microgravity (MG) on numerous lymphocyte functions. We had shown that modeled (MMG) and true microgravity inhibit lymphocyte locomotion through type I collagen. Modeled microgravity also suppresses polyclonal and antigen-specific lymphocyte activation. Polyclonal activation of lymphocytes prior to exposure to MMG abrogates the MG-induced inhibition of lymphocyte locomotion. The relationship between activation deficits and the loss of locomotion in MG was investigated using PKC activation by phorbol ester (PMA) and calcium ionophore (ionomycin). Direct activation of PKC by PMA substantially restored the MMG-inhibited lymphocyte locomotion and PHA-induced lymphocyte activation lonomycin by itself did not restore either locomotion or activation of the lymphocytes, indicating that these changes are not related to the impairment in the calcium flux in MMG. Treatment of lymphocytes with PMA before exposure to MMG prevented the loss of locomotion. It was observed that DNA synthesis is not necessary for restoration of locomotion since mitomicin C treated and untreated cells recovered their locomotion to the same level after PKC activation. Our recent data indicate that microgravity may selectively effect the expression of novel Ca2+ independent isoforms of PKC, in particularly PKC sigma and delta. This provides a new insight in understanding of the mechanisms of MG-sensitive cellular functions.

Pellis, Neal R.↗

NASA NTRS1999

Suppression of Antigen-Specific Lymphocyte Activation in Simulated Microgravity

Pellis, Neal R.↗

NASA NTRS1999

Proceedings of the Fourth Microgravity Fluid Physics and Transport Phenomena Conference

This conference presents information to the scientific community on research results, future directions, and research opportunities in microgravity fluid physics and transport phenomena within NASA's microgravity research program. The conference theme is "The International Space Station." Plenary sessions provide an overview of the Microgravity Fluid Physics Program, the International Space Station and the opportunities ISS presents to fluid physics and transport phenomena researchers, and the process by which researchers may become involved in NASA's program, including information about the NASA Research Announcement in this area. Two plenary lectures present promising areas of research in electrohydrodynamics/electrokinetics in the movement of particles and in micro- and meso-scale effects on macroscopic fluid dynamics. Featured speakers in plenary sessions present results of recent flight experiments not heretofore presented. The conference publication consists of this book of abstracts and the full Proceedings of the 4th Microgravity Fluid Physics and Transport Phenomena Conference on CD-ROM, containing full papers presented at the conference (NASA/CP-1999-208526/SUPPL1).

Singh, Bhim S.↗

NASA NTRS2000

Testing the BUNDLE Experiment for Microgravity Disturbance Characterization

A primary objective of the International Space Station is to provide a premier facility for microgravity research. There are many disturbances on board the Station that can disturb the quality of the microgravity environment, including disturbances caused by both system and payload hardware. Disturbances within experiments themselves can also affect the quality of their own environment. The primary functions of the Bridgman Unidirectional Dendrites in Liquids Experiment (BUNDLE) are to melt, directionally solidify, and perform in-situ quench of metallic alloys, providing data to aid in understanding the effects of the microgravity environment on the characteristics of these processed metals. Quenching of the samples in the BUNDLE furnace is accomplished by rapidly introducing high pressure helium into the furnace chamber. This type of quench will induce sample vibrations which may be large enough to adversely affect sample quality. The primary objective of the test described in this presentation was to determine the acceleration imparted on the BUNDLE sample during helium quench. From this information, the science community can better assess whether this method of quench will allow them to obtain the data they need. Utilizing breadboard hardware, the sample quench sequence was conducted. Data was collected from accelerometers located on the breadboard hardware and inside the sample cartridge. The test data indicated that the maximum acceleration achieved by the sample was 0.325 g, which is much higher than the desired microgravity (10(exp -6) g) environment. However, this acceleration level occurred over a time period of less than 0.1 second. Because this time period is so short, there should be no detrimental effects to dendrite growth. This result was consistent with the observations of the experiment scientists, who are satisfied with the results of previous dendrite growth in this breadboard unit.

Gattis, Christy↗

NASA NTRS2001

Toward Understanding Pore Formation and Mobility During Controlled Directional Solidification in a Microgravity Environment Investigation (PFMI)

Porosity in the form of "bubbles and pipes" can occur during controlled directional solidification processing of metal alloys. It is detrimental to material properties and precludes obtaining meaningful scientific results. On Earth, density differences allow an initiated bubble can rise through the liquid and "pop" at the surface resulting in a sound casting. This is not likely to occur in a microgravity environment and, unfortunately, a number of experiments conducted in microgravity have suffered from porosity effects. The current investigation is a systematic effort towards understanding porosity formation and mobility during controlled directional solidification in a microgravity environment. This will be investigated by utilizing a transparent material, succinonitrile (SCN), in conjunction with a translating temperature gradient stage so that direct observation and recording of pore generation and mobility can be made. The talk will cover the porosity problem, the details of the proposed experiments and the experimental hardware, and the expectations from the microgravity experiments.

Grugel, R. N.↗

NASA NTRS2001

Low Stretch PMMA Burning in Microgravity: Status of the Ground-Based Program and New ISS Glovebox Experiment SALSA

The objective of this ground-based program is to study low stretch diffusion flames burning PMMA as the solid fuel to determine the relationship between buoyant low stretch burning in normal gravity and forced flow low stretch burning in microgravity. The low stretch is generated in normal gravity by using the buoyant convection induced by burning the bottom of a large radius of curvature sample. Low stretch is also generated using the Combustion Tunnel drop tower rig (2.2 and 5.2 second facilities), which provides a forced convective low velocity flow past smaller radius of curvature samples. Lastly, an ISS glovebox investigation is being developed to study low stretch burning of PMMA spheres to obtain long duration testing needed to accurately assess the flammability and burning characteristics of the material in microgravity. A comparison of microgravity experiment results with normal gravity test results allows us to establish a direct link between a material's burning characteristics in normal gravity (easily measured) with its burning characteristics in extraterrestrial environments, including microgravity forced convective environments. Theoretical predictions and recent experimental results indicate that it should be possible to understand a material's burning characteristics in the low stretch environment of spacecraft (non-buoyant air movement induced by fans and crew disturbances) by understanding its burning characteristics in an equivalent Earth-based low stretch environment (induced by normal gravity buoyancy). Similarly, Earth-based stretch environments can be made equivalent to those in Lunar- and Martian-surface stretch environments (which would induce partial-gravity buoyancy).

Olson, S. L.↗