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PubMed2004

The measurement of solute diffusion coefficients in dilute liquid alloys: the influence of unit gravity and g-jitter on buoyancy convection.

Liquid diffusion experiments conducted on the MIR space station using the Canadian Space Agency QUELD II processing facility and the microgravity isolation mount (MIM) showed that g-jitter significantly increased the measured solute diffusion coefficients. In some experiments, milli-g forced vibration was superimposed on the sample when isolated from the ambient g-jitter; this resulted in markedly increased solute transport. To further explore the effects arising in these long capillary diffusion couples from the absence of unit-gravity and the presence of the forced g-jitter, the effects of a 1 milli-g forcing vibration on the mass transport in a 1.5 mm diameter long capillary diffusion couple have been simulated. In addition, to increase understanding of the role of unit gravity in determining the extent to which gravity can influence measured diffusion coefficient values, comparative experiments involving gold, silver, and antimony diffusing in liquid lead have been carried out using a similar QUELD II facility to that employed in the QUELD II/MIM/MIR campaign but under terrestrial conditions. It was found that buoyancy-driven convection may still persist in the liquid even when conditions are arranged for a continuously decreasing density gradient up the axis of a vertical long capillary diffusion couple due to the presence of small radial temperature gradients.

Acceleration↗
PubMed1965

The NASA Biosatellite Program.

The United States Biosatellite Program includes critical and sophisticated experiments to study the effects of weightlessness and decreased gravity at the cellular, tissue, organ, and organism levels during orbital periods of 3 to 30 days. The experiments involve a wide variety of plants and animals from single-celled organisms to primates. The effects of weightlessness combined with a known source of radiation will be studied to determine if there are any antagonistic or synergistic genetic or somatic effects on various organisms. Experiments are included to study the effect of removal from the Earth's rotation in relation to biological rhythms of organisms. The experimental test organisms have been exposed to the simulated dynamic forces of launch and flight profiles.

Adaptation, Physiological↗
PubMed2003

Weightlessness induced apoptosis in normal thyroid cells and papillary thyroid carcinoma cells via extrinsic and intrinsic pathways.

Apoptosis plays a pivotal role in development, tissue homeostasis, cancer, immune defense, and response to weightlessness. It can be initiated by external signals via death receptors, but may also emerge from mitochondria. We exposed mitochondria-rich thyroid carcinoma cells (ONCO-DG1 cell line) and normal thyroid cells (HTU-5) to conditions of simulated microgravity. After 24 h, 10% of the cancer cells had entered a Fas-dependent apoptotic pathway, but destruction and redistribution of mitochondria, microtubuli disruption, and caspase-3 activation were also detected, demonstrating the activation of extrinsic as well as intrinsic pathways. Furthermore, ONCO-DG1 cells grown on the clinostat showed elevated amounts of Bax, but reduced quantities of bcl-2. In addition, signs of apoptosis became detectable, as assessed by terminal deoxynucleotidyl transferase-mediated dUTP digoxigenin nick end labeling, 4',6-diamidino-2-phenylindole staining, and 85-kDa apoptosis-related cleavage fragments. These fragments resulted from enhanced 116-kDa poly(ADP-ribose)polymerase activity and apoptosis. Apoptosis was also detected in normal HTU-5 cells, as demonstrated by electron microscopy, activation of caspase-3, increases in Fas and Bax, and elevation of 85-kDa apoptosis-related cleavage fragments resulting from enhanced poly(ADP-ribose) polymerase activity. Gravitational unloading affects the mitochondria and thereby may trigger apoptosis in thyroid cells subjected to weightlessness by clinorotation.

Apoptosis↗
PubMed1990

Acute and intermediate cardiovascular responses to zero gravity and to fractional gravity levels induced by head-down or head-up tilt.

Determination of early cardiovascular responses to simulated gravity levels between 0 and 1 G will add knowledge of cardiovascular responses to space flight. Cardiovascular responses to 6 hours in a -5 degrees head-down bedrest model of weightlessness (0 G) were compared to those in head-up tilts of +10 degrees, +20 degrees, and +42 degrees (1/6, 1/3, and 2/3 G, respectively). Six healthy young adult males experienced the four angles on separate days. Impedance cardiography was used to measure thoracic fluid index, cardiac output, stroke volume, and peak flow. Although much intersubject variation occurred, the mean thoracic fluid content at -5 degrees decreased during the first hour and remained decreased; 6-hour values were similar to +10 degrees and +20 degrees. Heart rate decreased the first 2 hours for all angles, then increased, converging at 3-4 hours, and reached control by hour 6. Stroke volume decreased for the first 3 hours at -5 degrees, +10 degrees, +20 degrees; values at all four angles converged at hour 3 and increased in unison thereafter. Cardiac output and peak aortic flow reflected the angle at start of tilt; values at all angles converged by the second hour, decreased through the third hour, and increased thereafter. Pulse pressure decreased for the first 3 hours for angles -5 degrees, +10 degrees, and +20 degrees, converged at the fourth hour, and returned to control. Peak flow at +42 degrees was constant for the first 3 hours and increased thereafter. Blood pressure decreased for the first 2 hours, although the greatest decrease occurred at -5 degrees and +42 degrees; thereafter, values at all angles increased in unison and converged at the fourth hour. Total peripheral resistance increased during the first hour at -5 degrees and +20 degrees and decreased from hour 3 to hours 5-6 at the +42 degrees angle. Cardiovascular values were related to tilt angle for the first 2 hours of tilt, but after hour 3 values at all four angles began to converge, suggesting that cardiovascular homeostatic mechanisms seek a common adapted state regardless of effective gravity level (tilt angle) up to 2/3 G.

Bed Rest↗
PubMed2004

An ultrasonic methodology for muscle cross section measurement to support space flight.

The number one priority for any manned space mission is the health and safety of its crew. The study of the short and long term physiological effects on humans is paramount to ensuring crew health and mission success. One of the challenges associated in studying the physiological effects of space flight on humans, such as loss of bone and muscle mass, has been that of readily attaining the data needed to characterize the changes. The small sampling size of astronauts, together with the fact that most physiological data collection tends to be rather tedious, continues to hinder elucidation of the underlying mechanisms responsible for the observed changes that occur in space. Better characterization of the muscle loss experienced by astronauts requires that new technologies be implemented. To this end, we have begun to validate a 360 degree ultrasonic scanning methodology for muscle measurements and have performed empirical sampling of a limb surrogate for comparison. Ultrasonic wave propagation was simulated using 144 stations of rotated arm and calf MRI images. These simulations were intended to provide a preliminary check of the scanning methodology and data analysis before its implementation with hardware. Pulse-echo waveforms were processed for each rotation station to characterize fat, muscle, bone, and limb boundary interfaces. The percentage error between MRI reference values and calculated muscle areas, as determined from reflection points for calf and arm cross sections, was -2.179% and +2.129%, respectively. These successful simulations suggest that ultrasound pulse scanning can be used to effectively determine limb cross-sectional areas. Cross-sectional images of a limb surrogate were then used to simulate signal measurements at several rotation angles, with ultrasonic pulse-echo sampling performed experimentally at the same stations on the actual limb surrogate to corroborate the results. The objective of the surrogate sampling was to compare the signal output of the simulation tool used as a methodology validation for actual tissue signals. The disturbance patterns of the simulated and sampled waveforms were consistent. Although only discussed as a small part of the work presented, the sampling portion also helped identify important considerations such as tissue compression and transducer positioning for future work involving tissue scanning with this methodology.

Animals↗
PubMed1995

Extravehicular activity training and hardware design consideration.

Preparing astronauts to perform the many complex extravehicular activity (EVA) tasks required to assemble and maintain Space Station will be accomplished through training simulations in a variety of facilities. The adequacy of this training is dependent on a thorough understanding of the task to be performed, the environment in which the task will be performed, high-fidelity training hardware and an awareness of the limitations of each particular training facility. Designing hardware that can be successfully operated, or assembled, by EVA astronauts in an efficient manner, requires an acute understanding of human factors and the capabilities and limitations of the space-suited astronaut. Additionally, the significant effect the microgravity environment has on the crew members' capabilities has to be carefully considered not only for each particular task, but also for all the overhead related to the task and the general overhead associated with EVA. This paper will describe various training methods and facilities that will be used to train EVA astronauts for Space Station assembly and maintenance. User-friendly EVA hardware design considerations and recent EVA flight experience will also be presented.

Astronauts↗
PubMed1995

Human posture in microgravity: an experiment on EUROMIR '95 to verify and improve a simulation tool.

An anthropometric mannequin implemented in robotic modelling software has proved very useful in the simulation of static and semi-dynamic reachability envelopes. Its prediction of working postures has been verified to some extent during neutral buoyancy trials. While a robotic solution is useful for static analyses or rough estimates of simple movements, more realistic movement strategies need to be identified directly measuring astronauts' in-orbit behaviour. A set of experiments is to be performed as part of the EUROMIR '95 mission to the MIR orbiting station in which dynamic posture (i.e. posture and movement) measurements will be taken using the ELITE system. The data and analyses of the data will be used to animate the Alenia anthropometric mannequin and to develop movement algorithms more similar to those of a person in microgravity than the robotic solutions currently employed. This paper presents the experiments to be performed and the changes to Alenia's mannequin that will allow the model to effect movements according to the experimental results. It is aimed at expanding the dialog between the biomechanical and human factors disciplines started in this experiment to other potential end-users of the experimental results.

Adaptation, Physiological↗
PubMed1993

European astronaut training in Houston.

Three European astronauts are currently training as Space Shuttle Mission Specialists at NASA's Johnson Space Center in Houston. Two of the astronauts, Maurizio Cheli and Jean-Francois Clervoy, recently became members of NASA's 'astronaut pool' and have entered the Advanced Training phase. The third one, Claude Nicollier, is now preparing for the mission to service the Hubble Space Telescope in December.

Astronauts↗
PubMed2001

[Numerical study of the effects (correction of efects) of size of inlets and outlets of ventilation system in experimental space station cabin].

OBJECTIVE: To make the status of flow and heat transfer fit the requirement of comfortable condition in the experimental cabin and ventilation and cooling in the apparatus cabin of the space station. METHOD: In present numerical simulation, a model approximate the practice at condition of the ventilation pipeline and influence of inlet and outlet was used, so that there is no need of supposing the distribution of outlets. In microgravity condition, the influence of the size of inlets and outlets on the flow field in the experimental space station cabin was studied. According to different function zones in the experimental space station cabin, the region at evenness parameter was put forward. RESULT: The taper inlet and crescent outlet had the best integrated performance. CONCLUSION: The use of variational section was recommended in designing and building of ventilation project in space station cabin.

Air Conditioning↗
PubMed2003

Enzyme catalysis in microgravity: steady-state kinetic analysis of the isocitrate lyase reaction.

Two decades of research in microgravity have shown that certain biochemical processes can be altered by weightlessness. Approximately 10 years ago, our team, supported by the European Space Agency (ESA) and the Agenzia Spaziale Italiana, started the Effect of Microgravity on Enzyme Catalysis project to test the possibility that the microgravity effect observed at cellular level could be mediated by enzyme reactions. An experiment to study the cleavage reaction catalyzed by isocitrate lyase was flown on the sounding rocket MASER 7, and we found that the kinetic parameters were not altered by microgravity. During the 28th ESA parabolic flight campaign, we had the opportunity to replicate the MASER 7 experiment and to perform a complete steady-state analysis of the isocitrate lyase reaction. This study showed that both in microgravity and in standard g controls the enzyme reaction obeyed the same kinetic mechanism and none of the kinetic parameters, nor the equilibrium constant of the overall reaction were altered. Our results contrast with those of a similar experiment, which was performed during the same parabolic flight campaign, and showed that microgravity increased the affinity of lipoxygenase-1 for linoleic acid. The hypotheses suggested to explain this change effect of the latter were here tested by computer simulation, and appeared to be inconsistent with the experimental outcome.

Catalysis↗
PubMed2004

Limits to gelation in colloidal aggregation.

We show that the dynamics of large fractal colloid aggregates are well described by a combination of translational and rotational diffusion and internal elastic fluctuations, allowing both the aggregate size and internal elasticity to be determined by dynamic light scattering. The comparison of results obtained in microgravity and on Earth demonstrates that cluster growth is limited by gravity-induced restructuring. In the absence of gravity, thermal fluctuations ultimately inhibit fractal growth and set the fundamental limitation to the lowest volume fraction which will gel.

Colloids↗
PubMed2002

Physical aspects of protein crystal growth investigated with the Advanced Protein Crystallization Facility in reduced-gravity environments.

The physicochemical aspects of protein crystallization in reduced-gravity environments ( micro g) have been investigated with the Advanced Protein Crystallization Facility during six space missions. This review summarizes the results, dealing with the mechanisms of nucleation and crystal growth and with the quality of the crystals that were obtained under reduced gravity as well as under normal gravity on earth. Statistical analyses of the experimental data strongly support the fact that micro g has a positive effect on crystallization and on crystal quality. A comparison of experiments and theories of protein crystallization in reduced-gravity environments is presented. Recommendations for improving the performance of protein crystallization experiments in micro g and on earth are discussed.

Animals↗
PubMed1993

Simulation of the fluid retention effects of a vasopressin analog using the Guyton model of circulation.

Fluid-loading (FL) consisting of water and salt tablets equivalent of 32 oz of isotonic saline is a countermeasure currently in use by NASA to improve the orthostatic tolerance of astronauts during Shuttle reentry. However, the effectiveness of this countermeasure has been observed to decrease with the duration of space flight. Possible ways to improve fluid retention and thus the effectiveness of FL include use of analogs of vasopressin such as lypressin (LVP). This study used a computer simulation approach to analyze the potential benefits on fluid retention with LVP administered before FL.

Blood Volume↗