Periods Of Microgravity Research Articles

Atrial distension in humans during microgravity induced by parabolic flights

The hypothesis was tested that human cardiac filling pressures increase and the left atrium is distended during 20-s periods of microgravity (microG) created by parabolic flights, compared with values of the 1-G supine position. Left atrial diameter (n = 8, echocardiography) increased significantly during microG from 26.8 +/- 1.2 to 30.4 +/- 0.7 mm (P < 0.05). Simultaneously, central venous pressure (CVP; n = 6, transducer-tipped catheter) decreased from 5.8 +/- 1.5 to 4.5 +/- 1.1 mmHg (P < 0.05), and esophageal pressure (EP; n = 6) decreased from 1.5 +/- 1.6 to -4.1 +/- 1.7 mmHg (P < 0.05). Thus transmural CVP (TCVP = CVP - EP; n = 4) increased during microG from 6.1 +/- 3. 2 to 10.4 +/- 2.7 mmHg (P < 0.05). It is concluded that short periods of microG during parabolic flights induce an increase in TCVP and left atrial diameter in humans, compared with the results obtained in the 1-G horizontal supine position, despite a decrease in CVP.

Single-bubble sonoluminescence in microgravity

A recent experiment involving single-bubble sonoluminescence aboard NASA’s parabolic research aircraft will be described. Measurements of the intensity of the light emission were performed during periods of microgravity (near 0 g) and hypergravity (near 2 g). Gravitational effects on the luminescence and extinction pressure thresholds were examined. In addition, the light emission was monitored under constant drive conditions as the gravitational acceleration varied during the parabolas. Measurements show some variability in the sonoluminescence intensity for both thresholds. However, during otherwise constant conditions in which the drive pressure amplitude did not change, the intensity from stable single-bubble sonoluminescence was observed to increase during periods of microgravity. There was an initial increase in intensity that occurred simultaneous with the decrease in the gravitational acceleration, followed by a slow increase in intensity that appeared to level off near the end of the microgravity period. The longer time scales over which the intensity changed during the microgravity period may be indicative of gas diffusion occurring as the bubble attains a new equilibrium condition. [Research supported by NSF and NASA.]

Structural and functional adaptations of skeletal muscle to weightlessness.

This brief review examines the effects of weightlessness on the structure and function of human and rat skeletal muscle. Data collected from spaceflights or Earth-based models suggest that a rapid atrophy (5-8 days) occurs in lower limb muscles associated with impairments in muscle strength, physical work capacity and locomotor coordination. The reduction in muscle cross-sectional area cannot entirely explain the loss of strength in postural muscles suggesting a reduced neural drive. Muscle atrophy is accompanied by a general shift in the contractile and enzymatic profiles of a slow-twitch oxidative muscle toward that of a fast twitch glycolytic muscle. In humans, limited structural and functional data collected in astronauts after short periods of microgravity are qualitatively similar to those observed in rats after real or simulated microgravity suggesting that animal models are relevant to muscle research in space. A preventive prescription i.e. exercise or pharmacological treatment, cannot be proposed until future research has better defined the basic mechanisms of muscle plasticity during long duration spaceflights.

Transition of oscillatory floating half zone convection from Earth's gravity to microgravity

Oscillatory features of floating half zone convection were experimentally studied by using the drop shaft facility of Japan Microgravity Center which supported microgravity period of 10 s. Coordinated measurements including free surface deformation and oscillation, temperature and flow pattern in both 1g and micro-g environment were obtained. The oscillatory frequency and amplitude in micro-g condition were lower and larger than the ones in 1-g condition, respectively. The results gave, at first time, the oscillatory features such as free surface wave in micro-g, coordinated measurements of more than two physical quantities in the micro-g, and transition of thermocapillary oscillatory convection from 1-g to micro-g.

On the kinetics of carbide precipitation during reaction between graphite and Fe-Ti liquids under microgravity

Experiments on the reaction between graphite and liquid Fe-Ti alloys were performed with a mirror furnace on board an airplane during parabolic flights. Small Fe-Ti alloy samples were melted in contact with graphite and held for some seconds at a temperature of 1550 °C. The samples were melted and solidified during a microgravity period. Carbon and titanium atoms reacted in the melt and titanium carbides were formed. In the experiments, a precipitation zone with faceted titanium carbide crystals dispersed in high carbon Fe-C-Ti alloy matrix was obtained near the graphite/alloy interface. The thicknesses of the carbide precipitation zones were measured and effects of alloy composition on the growth rates of the carbide zones were revealed by experiments and calculations. It was shown that the process was controlled by the diffusion of titanium in the liquid at low titanium concentrations and by diffusion of carbon through the precipitation layer at high titanium concentrations in the melt. Supersaturation of the carbide in front of the reaction interface was predicted from the calculations. The analysis showed that homogeneous nucleation of titanium carbide can readily occur in the alloys. Carbide morphologies were analyzed, and the mechanisms which lead to their formation are discussed.

Preliminary experimental observations of the effects of buoyancy on single-bubble sonoluminescence in microgravity and hypergravity

The buoyancy force [given by the product of the density of the liquid, the gravitational constant, and the volume, ρgV(t)] may play an important role in the stability of small bubbles undergoing highly nonlinear radial pulsations. In particular, during a single acoustic cycle, a sonoluminescence bubble undergoes volume changes on the order of 1000, and thus the buoyancy force changes by this same factor. Since the equilibrium position of such a bubble in a standing wave is balanced by the Bjerknes and buoyancy forces, the bubble may be subjected to large translational velocities and accelerations during each acoustic cycle [S. M. Cordry, Ph.D. thesis, U. M. (1995) and J. Acoust. Soc. Am. 97, 3375 (1995)]. The buoyancy-force stability issue was examined in a series of experiments aboard a NASA KC-135A, which performs parabolic maneuvers to generate limited periods of microgravity. Effects were examined in both microgravity and hypergravity (≊ 0 and 2 g, respectively). Results of this study, performed in November 1995 in the Netherlands, under the auspices of the European Space Agency, will be presented. [Work supported by NSF, CPAC, NASA, and ESA.]

Regeneration of plant cell protoplasts under microgravity: Investigation of protein patterns by SDS-PAGE and immunoblotting

As part of the D-2 Spacelab mission, tobacco (Nicotiana tabacum L.) protoplasts were cultured for 10 days in microgravity and successfully regenerated into microcalli, which, after further cultivation on the ground, gave rise to intact plants. Protein analysis was performed on samples taken during the initial microgravity period and compared to ground controls. Total protein content and protein patterns were monitored, as well as the cytoskeletal proteins tubulin and actin, a key enzyme of secondary metabolism, phenylalanine ammonia lyase, and the pathogenesis-related protein osmotin. None of the investigated proteins showed a gravity-dependent effect. Since relative changes due to culture age were detectable in the immunoblots as well as in the total protein pattern, an adaptation of the cells to microgravity without major modifications of their protein complement may be assumed.

Central venous pressure in humans during microgravity

Based on the results of head-down simulation studies and the results of parabolic flights, the hypothesis was tested that central venous pressure (CVP) in humans increases during microgravity (weightlessness) compared with during the ground-based supine position. CVP was recorded with an intravascular pressure transducer in seven healthy humans during short (20-s) periods of microgravity created by parabolic-flight maneuvers and in one astronaut before, during, and up to 3 h after launch of the Spacelab D-2 mission (Space Transport System-55). When the subjects were supine during the parabolic maneuver, CVP decreased during microgravity from 6.5 +/- 1.3 to 5.0 +/- 1.4 mmHg (P < 0.05). during the Spacelab D-2 mission, CVP was 6.2 mmHg during the initial minutes of microgravity, which was very similar to the value of 6.5 mmHg in the supine position 3.5 h before launch of the space shuttle. During the subsequent 3 h of weightlessness, CVP during rest varied between 2.0 and 6.2 mmHg. We conclude that CVP during short (20-s) and longer (3-h) periods of microgravity is close to or below that of the supine position on the ground.

Effect of spaceflight on human stem cell hematopoiesis: suppression of erythropoiesis and myelopoiesis

Humans subjected to periods of microgravity develop anemia, thrombocytopenia, and abnormalities in red blood cell structure. The causes of these abnormalities are complex and unclear. The in vitro effects of spaceflight on hematopoietic cell proliferation and differentiation were investigated during the space shuttle missions STS-63 (Discovery) and STS-69 (Endeavour). CD34+ bone marrow progenitor cells were cultured in liquid suspension culture and on hematopoietic supportive stromal cells using hollow-fiber culture modules. One set of cultures was maintained at microgravity (flight cultures) for the last 8-10 days of culture and a second control was at full gravity (ground control). Over the 11- to 13-test-day period, ground control culture total cell number increased 41.0- to 65.5-fold but flight culture total cell number increased only 10.1- to 17.6-fold (57-84% decrease). Comparing ground control cultures and microgravity cultures, respectively, for progenitor cell content, myeloid progenitor cell numbers expanded 2.6- to 17.5-fold compared with 0.9- to 7.0-fold and erythroid progenitor cell numbers expanded 2.0- to 4.1-fold in ground control cultures but actually declined at microgravity (>83% reduction). Moreover, microgravity cultures demonstrated accelerated maturation/differentiation toward the macrophage lineage. These data indicate that spaceflight has a direct effect on hematopoietic progenitor cell proliferation and differentiation and that specific aspects of in vitro hematopoiesis, particularly erythropoiesis, involve gravity-sensitive components.

On the reaction between Fe-Ti and Fe-C liquids under microgravity

Reaction between liquid Fe-Ti and Fe-C alloys has been studied under microgravity on board an aeroplane during parabolic flights. The two alloys were melted in contact with each other and held for some seconds at a temperature of 1450 °. The samples were melted and solidified during the microgravity period. During the contact of the two liquid alloys, carbon and titanium atoms reacted in the melt and titanium carbides were formed. A carbide containing layer was formed at the interface region between the two liquids on the Fe-Ti side. The thicknesses of the carbide layers were meas-ured. Theoretical calculation of the precipitation kinetics was attempted, and good agreement between the calculated and experimental results was obtained. The effect of alloy composition on the growth rates of the carbide zones was revealed by both experiments and calculations. Supersaturation of the carbide in front of the reaction interface was calculated. Homogeneous nucleation of titanium carbide can readily occur according to the present calculations.

Small-scale smoldering combustion experiments in microgravity

Results from small-scale experiments of the smolder characteristics of a porous combustible material (flexible polyurethane foam) in microgravity and normal gravity are presented. The microgravity experiments were conducted in the Spacelab Glovebox on the USML-1 mission of the Space Shuttle Columbia, June/July 1992, and represent the first smolder experiments ever conducted under extended periods of microgravity. The use of the Glovebox limited the size of the fuel sample that could be tested and the power available for ignition but provided the opportunity to conduct such experiments in space. Four tests were conducted, varying the igniter geometry (axial and plate) and the convective environment (quiescent and forced). A series of comparative tests was also conducted in normal gravity. Measurements conducted included temperature histories at several locations along the fuel sample, video recording of the progress of the smolder, and postcombustion char and gas composition analyses. The results of the tests showed that smolder did not propagate without the assistance of the igniter, primarily because of heat losses from the reaction to the surrounding environment. In microgravity, the reduced heat losses caused by the absence of natural convection resulted in only slightly higher temperatures in the quiescent microgravity test than in normal gravity but a dramatically larger production of combustion products in all microgravity tests. Particularly significant is the proportionately larger amount of carbon monoxide and light organic compounds produced in microgravity, despite comparable temperatures and similar char patterns. This excessive production of fuel-rich combustion products may be a generic characteristic of smoldering polyurethane in microgravity, with an associated increase in the toxic hazard of smolder in spacecraft.

Transient effects of microgravity on early embryos of Xenopus laevis

In order to study the role of gravity on the early development of the clawed toad Xenopus laevis, we performed an experiment on the Maser-6 sounding rocket launched from Kiruna (Sweden) on 4 Nov 1993. The aim was to find out whether a short period of microgravity (μg) during fertilization and the first few minutes of development does indeed result in abnormal axis formation as was suggested by a pilot experiment on the Maser 3 in 1989. On the Maser 6 we used two new technical additions in the Fokker CIS unit, viz. a 1-g control centrifuge and a video recording unit which both worked successfully. The 1-g control centrifuge was used to discriminate between the influences of flight perturbations and μg. After fertilization shortly before launch, one of the first indications of successful egg activation, the cortical contraction, was registered in μg and on earth. Analysis of the video tapes revealed that the cortical contraction in μg starts earlier than at 1 g on earth. After recovery of the eggs fertilized in μg and culture of the embryos on earth, the morphology of the blastocoel has some consistent differences from blastulae from eggs fertilized in the 1-g centrifuge of the rocket. However from the gastrula stage onward, the μg embryos apparently recover and resume normal development: the XBra gene is normally expressed, and histological examination shows normal axis formation.

The effects of spaceflight on open-loop and closed-loop postural control mechanisms: human neurovestibular studies on SLS-2.

Stabilogram-diffusion analysis was used to examine how prolonged periods in microgravity affect the open-loop and closed-loop postural control mechanisms. It was hypothesized that following spaceflight: (1) the effective stochastic activity of the open-loop postural control schemes in astronauts is increased; (2) the effective stochastic activity and uncorrelated behavior, respectively, of the closed-loop postural control mechanisms in astronauts are increased; and (3) astronauts utilized open-loop postural controls schemes for shorter time intervals and smaller displacements. Four crew members and two alternates from the 14-day Spacelab Life Sciences 2 Mission were included in the study. Each subject was tested under eyes-open, quiet-standing conditions on multiple preflight and postflight days. The subjects' center-of-pressure trajectories were measured with a force platform and analyzed according to stabilogram-diffusion analysis. It was found that the effective stochastic activity of the open-loop postural control schemes in three of the four crew members was increased following spaceflight. This result is interpreted as an indication that there may be in-flight adaptations to higher-level descending postural control pathways, e.g., a postflight increase in the tonic activation of postural muscles. This change may also be the consequence of a compensatory (e.g., "stiffening") postural control strategy that is adopted by astronauts to account for general feeling of postflight unsteadiness. The crew members, as a group, did not exhibit any consistent preflight/postflight differences in the steady-state behavior of their closed-loop postural control mechanisms or in the functional interaction of their open-loop and closed-loop postural control mechanisms. These results are interpreted as indications that although there may be in-flight adaptations to the vestibular system and/or proprioceptive system, input from the visual system can compensate for such changes during undisturbed stance.

Boiling heat transfer in the quenching of a hot tube under microgravity

Quenching of a hot tube by injection of a subcooled liquid was investigated under microgravity conditions. Liquid Freon (R-113) was injected at mass fluxes between 160-850 kg/ms into an initially hot, thin-walled stainless steel tube, 11.3 mm i.d. and 914 mm long. Data collected in microgravity aboard NASA's KC-135 aircraft were compared with quenching tests in a horizontal tube under normal gravity. The re wetting temperatures were found to be 15°-25°C lower in microgravity than those obtained under 1 g, and the film boiling heat transfer coefficients in microgravity were only 20-50% of the values obtained in 1 g. This resulted in much longer precursory cooling periods in microgravity, and hence, the time to totally quench the initially hot tube in microgravity was greatly extended. However, once the tube was cooled sufficiently to allow axial propagation of the quench front, the re wetting velocity was found to be slightly greater in microgravity. The boiling curves showed that the nucleate and transition boiling curves in microgravity were shifted to lower wall superheats as compared to 1 g as a result of the lower re wetting temperature. The heat flux profiles were otherwise quite similar, indicating that these boiling regimes are little affected by reduction in gravity.

Behavioral reactions of the bat Carollia perspicillata to abrupt changes in gravity.

As part of an ongoing survey of the behavioral responses of vertebrates to abrupt changes in gravity, we report here on the reactions of bats (Carollia perspicillata) exposed to altered gravity during parabolic aircraft flight. In microgravity, mammals typically behave as if they were upside-down and exhibit repetitive righting reflexes, which often lead to long axis rolling. Since bats, however, normally rest upside-down, we hypothesized that they would not roll in microgravity. Only one of three specimens attempted to fly during microgravity. None rolled or performed any righting maneuvers. During periods of microgravity the bats partially extended their forearms but kept their wings folded and parallel to the body. Between parabolas and occasionally during microgravity the bats groomed themselves. Both the extended limbs and autogrooming may be stress responses to the novel stimulus of altered gravity. This is the first behavioral record of Chiroptera in microgravity.

Mechanical design and simulation of a microgravity isolation mount for Columbus

A microgravity isolation mount (MGIM) designed to provide active vibration isolation for microgravity payloads is described. The required microgravity level is achieved by adopting a noncontact strategy, whereby the payload floats inside its enclosure and its position is controlled by magnetic actuators. The design concentrates on the requirements of materials science payloads and provides a detailed description of the locking mechanisms used to release and capture the payload during microgravity periods. A nonlinear model used to simulate payload release shows that a successful release depends on the severity of the input vibration level.

Motion sickness in amphibians

We explored the question of whether amphibians get motion sickness by exposing anurans (frogs) and urodeles (salamanders) to the provocative stimulus of parabolic aircraft flight. Animals were fed before flight, and the presence of vomitus in their containers after flight was used to indicate motion-induced emesis. None of the species that we studied vomited during the 8 to 10 parabolas of each flight. However, at least one specimen from each of the anuran species Rana rugosa, Rana nigromaculata, Hyla japonica, and Rhacophorus schlegelii vomited in a period of 0.5 to 42 h after flight. Some specimens of R. nigromaculata, H. japonica, and R. schlegelii were also observed retching without emesis either during or shortly after exposure to parabolic flight. We were unable to induce either emesis or retching behavior in the aquatic from Xenopus laevis. Among the urodeles studied we saw no signs of motion sickness in either adult or larval Cynops pyrrhogaster, but at least one larval Hynobius nebulosus vomited shortly after parabolic flight. The amphibian species that exhibited the most motion sickness were the same ones that showed the greatest amount of tumbling during the microgravity phases of their parabolic flights. The most distinctive difference between motion sickness in amphibians and mammals that vomit, including man, is the long delay between a provocative stimulus and emesis proper in the amphibians. The retching behavior we induced in the frogs was identical to that described previously for frogs treated with emetic drugs. H. japonica, exposed to extended periods of microgravity on the MIR Space Station, flattened their bellies against the substrate and dorsiflexed their heads in a manner reminiscent of drug-induced nausea. In light of our current observations of retching behavior in motion sick H. japonica, we suggest that the previously observed behavior of three frogs on the MIR Space Station was a manifestation of motion sickness.

Microgravity annealing system for thin-film superconductors

A mirror furnace system for annealing of superconducting thin films, which is adapted for the world’s longest dropshaft completed at Kamisunagawa, Japan, is described. The system must be designed for completing both melting and solidification processes during a short 10-s microgravity period, and also for withstanding the deceleration of a drop capsule in which the furnace system is contained. All moving components must be operated so as not to disturb the microgravity environment. A random vibration test for the entire system was carried out before the microgravity experiment, and structural compatibility was verified. The furnace system worked well, and the accumulated number of free falls was 19. Results of annealing of the superconducting material at one gravity and microgravity were compared using scanning electron microscopy and x-ray microanalysis.

Platelet shape change and protein phosphorylation induced by ADP and thrombin are not sensitive to short periods of microgravity

Recent experiments have shown that the stimulation of animal cells in vitro by direct protein kinase C (PKC) activators is significantly reduced under microgravity (micro g). Platelets undergo protein phosphorylation and morphological changes a few seconds after stimulation by agonists such as phorbol esters which activate PKC. Therefore, taking advantage of parabolic plane flight to obtain short periods of microgravity, we studied phosphorylation of myosin light chain (20K), specific PKC-dependent phosphorylation of a 40,000 M(r) protein, pleckstrin (40K) and platelet shape change. SDS-PAGE analysis and electron microscopy were performed on platelets subjected to 20 seconds microgravity as compared to normal gravity (1 g) conditions. These investigations showed that neither Ca(2+)-calmodulin-mediated activation nor the PKC-dependent pathways are inhibited during short periods of microgravity.

EMATS, a robot-based equipment manipulation and transportation system for the columbus free flying laboratory

This paper describes the concept for a robot-based Equipment Manipulation and Transportation System (EMATS) for the Columbus Free Flying Laboratory developed under ESA contract by a study team headed by Dornier. EMATS could not only automatically provide the greater part of the payload facility handling and logistics functions during the unmanned microgravity periods, but also perform unmanned servicing operations in conjunction with various logistics vehicles concepts and assist the crew during manned servicing from the Space Station Freedom and from Hermes. To that end, a variety of telerobotics features are foreseen such as teleoperation and supervised automatic operation from ground or from a small control station aboard the Free Flyer, Hermes, or the Space Station Freedom. The paper summarizes the overall EMATS architecture and illustrates the flexibility of the concept by results from computer graphics simulations.