Space Microgravity Research Articles

特集： ＳＬ‐Ｊ／ＦＭＰＴライフサイエンス実験の体験記録 無重力を利用した酵素の結晶成長

特集： ＳＬ‐Ｊ／ＦＭＰＴライフサイエンス実験の体験記録 無重力を利用した酵素の結晶成長

Effects of caudal elevation on testicular function in rats. Separation of effects on spermatogenesis and steroidogenesis.

A variety of biologic processes are perturbed when exposed to microgravity (space flight) for more than 7 days, including testicular function. Suspension of rats in a special harness (caudal elevation) to induce thoracic pooling of blood fluids and remove the support function of the hind limbs is used to mimic, on earth, the effects of microgravity encountered during space flight. Typically, this induces cryptorchidism in male rats. Three experiments were conducted to differentiate the effects of caudal elevation (30 degrees angle) and anatomic location of testes on spermatogenesis and steroidogenesis. Rats were subjected to caudal elevation for 7 days using either a tail harness (experiments 1 and 2) or a whole-body harness (experiment 3). Testes of rats fell into the abdominal cavity when a tail harness was used, but ligation of the inguinal canal prevented this repositioning. For rats with abdominal testes, testicular weight was reduced (P less than 0.05) and histology of testes was abnormal; the number of spermatids per gram parenchyma was lower (P less than 0.05) in tail-suspended rats compared with control rats. In contrast, spermatogenesis was not affected by caudal elevation in most rats in which the inguinal canal was ligated or in rats elevated by whole-body harness. Concentrations of testosterone in serum and testicular interstitial fluid were lower (P less than 0.05) in suspended rats, regardless of the method used for caudal elevation or anatomic location of testes. Concentrations of luteinizing hormone in serum were elevated (P less than 0.05) in rats with intra-abdominal testes.(ABSTRACT TRUNCATED AT 250 WORDS)

Thermoregulatory responses of Rhesus monkeys during spaceflight

This study examines the activity, axillary temperature ( T ax), and ankle skin temperature ( T ak) of two male Rhesus monkeys exposed to microgravity in space. The animals were flown on a Soviet biosatellite mission (COSMOS 1514). Measurements on the flight animals, as well as synchronous flight controls, were performed in the Soviet Union. Additional control studies were performed in the United States to examine the possible role of metabolic heat production in the T ax response observed during the spaceflight. All monkeys were exposed to a 24-h light-dark cycle (LD 16:8) throughout these studies. During weightlessness, T ax in both flight animals was lower than on earth. The largest difference (0.75°C) occurred during the night. There was a reduction in mean heart rate and T ak during flight. This suggests a reduction in both heat loss and metabolic rate during spaceflight. Although the circadian rhythms in all variables were present during flight, some differences were noted. For example, the amplitude of the rhythms in T ak and activity were attenuated. Furthermore, the T ax and activity rhythms did not have precise 24.0 hour periods and may have been externally desynchronized from the 24-h LD cycle. These data suggest a weakening of the coupling between the internal circadian pacemaker and the external LD synchronizer.

Lymphocytes on sounding rockets.

The effect of gravity on human lymphocytes in-vitro has been extensively studied by our team in true microgravity in space /1-3/, in simulated lowgravity in the clinostat /4,5/ and in hypergravity in the centrifuge /5-7/. Lymphocytes are easily purified from peripheral blood and can be ictivated either chemically or by exposure to mitogens in culture. Thereby, cells start to proliferate, T—lymphocytes secrete lymphokines (IL-2, IL-3, IL—4 as well as interferon). The mechanism of the in-vitro activation is analogous to that occurring in—vivo when the immune system is challenged by antigens.

Control issues of microgravity vibration isolation

Active vibration isolation systems contemplated for microgravity space experiments may be designed to reach given performance requirements in a variety of ways. An analogy to passive isolation systems proves to be illustrative but lacks the flexibility as a design tool of a control systems approach and may lead to poor designs. For example, it is shown that a focus on equivalent stiffness in isolation system design leads to a controller that sacrifices robustness for performance. Control theory as applied to vibration isolation is reviewed and passive analogies are discussed. The loop shaping trade-off is introduced and used to design a single degree of freedom feedback controller. An algebraic control design methodology is contrasted to loop shaping and critiqued. Multi-axis vibration isolation and the problems of decoupled single loop control are introduced through a two degree of freedom example problem. It is shown that center of mass uncertainty may result in instability when decoupled single loop control is used. This results from the ill conditioned nature of the feedback control design. The use of the Linear Quadratic Regulator synthesis procedure for vibration isolation controller design is discussed.

Limits on the isolation of stochastic vibration for microgravity space experiments

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Can Plants Normally Produce Seeds under Microgravity in Space?

Growth analysis was performed on a barley (Hordeum vulgare L.) mutant line showing an abnormal gravity response, and also on the original normal line. The reproductive structures of mutant plants were quite different from the original normal plants. Analysis by stratified clip method revealed difference in distribution of leaves, stems, and heads, as well as leaf area index (LAI) in the mutant line caused by diagravitropic or plagiogravitropic growth. Mutant plants showed an abnormal gravity response even in the seedling stage. In mutant but not normal plants, the direction of first-leaf growth depended on the position of the embryo. Seed production of mutant plants was about 60% compared with normal plants, even though net assimilation rate (NAR) and relative growth rate (RGR) were not decreased. Seed fertility of mutant plants was correlated with the angle between heads and ground level. However, when plants were turned upside down, all heads, both mutants and normal, were nearly vertical, and seed fertility recovered to a level that not significantly different from normal plants. From these results, it was predicted that barley plants may not produce seeds normally under microgravity.

Containerless processing at high temperatures using acoustic levitation

Containerless processing of a specimen while it is heated to high temperatures can be accomplished using acoustic levitation. This involves the creation of sufficiently strong and suitably shaped acoustic fields and it is more easily achieved in the microgravity of space. This technique permits the heating, melting, reacting, cooling, and solidification of a substance without contamination or heterogenous nucleation caused by contact with the container. It further enables the processing of materials for which there is no acceptable crucible material. These acoustic containment techniques have been demonstrated in space at temperatures to 1800K in early sounding rocket and space shuttle experiments. Newly developed approaches can improve the processing capabilities at higher temperatures and provide more contamination-free environments. Advanced techniques are described which facilitate the development of inert or reducing atmospheres in excess of 2000K. Recent testing, in the laboratory and aboard the NASA KC-135 aircraft, of a high temperature acoustic positioner has demonstrated the effectiveness of a specimen motion damping system and the control of specimen spin. These new techniques can produce the extremely quiescent states which help enable the study of deep undercooling processes. The high degree of specimen stability also permits more accurate measurement of high temperature material properties.

Development of a vibration isolation prototype system for microgravity space experiments

Growing concern about the microgravity environment on the Space Shuttle orbiter has generated interest in vibration isolation systems for microgravity science experiments. The presence of small levels of low frequency accelerations on the orbiter has degraded this “microgravity” environment for the science community. This interest in systems capable of isolating against the acceleration environment on orbital carriers has directed most research, in these isolation systems, to active methods of compensation. In this paper the development of a magnetically suspended six degree-of-freedom (DOF) active vibration isolation prototype system capable of performing the needed compensation to the orbital environment is presented. A design for the magnetic actuators is described. Relative and inertial sensors are used in providing an inertial reference for isolating the payload. The control law for the prototype system is also described giving a non-intrusive inertial isolation response to the system.

A new approach to controller design for microgravity isolation systems

A new method has been developed to design an active vibration isolation system for microgravity space experiments. This method yields the required controller transfer functions for a specified transmissibility. Hence, it is a straightforward task to guarantee that the desired vibration isolation performance is achieved at each frequency. The theory for such a controller design has been presented by considering a single degree of freedom system. The magnitude of the control force required by the new method has been found to be less than that used by a standard phase lead/lag compensator.

Limitations on vibration isolation for microgravity space experiments

The vibration-isolation limitations of spaceborne microgravity experiments are largely due to isolation-system volume restrictions. In the present one-degree-of-freedom representation of an experimental aircraft, assuming an ideal vibration actuator, wall motion is characterized as sinusoidal at a single frequency. The result is a kinematic representation which poses the problem of the minimum acceleration trajectory within a pair of moving walls; analysis then yields a simple condition under which a closed-form solution is available. The results obtained demonstrate that isolation from low-frequency vibration requires more interior space than is available for vibration isolation on manned orbiters.

Actin filaments responsible for the location of the nucleus in the lentil statocyte are sensitive to gravity

The location of the nucleus in statocytes of lentil roots grown: I), at 1 g on the ground, 2), on a 1 g centrifuge in space, 3), in simulated microgravity on a slowly rotating clinostat (0.9 rmp) 4), in microgravity in space was investigated and statistically evaluated. In cells differentiated at 1 g on the ground, the nuclear membrane was almost in contact with the plasmalemma lining the proximal cell wall, whereas in statocytes of roots grown on the clinostat there was a distance of 0.47 μm horizontal clinorotation) and of 0.76 μm vertical clinorotation) between these membranes. However, in microgravity the nucleus was the most displaced, 0.87 μm from the proximal cell wall. Centrifugation of vertically grown roots in the root-tip direction showed that the threshold of centrifugal force to detach all nuclei from the proximal cell wall was about 40 g. In statocytes developed in the presence of cytochalasin B at 1 g the nuclei were sedimented on the amyloplasts at the distal cell pole, demonstrating that the location of the nucleus depends on actin filaments. The results obtained are in agreement with the hypothesis that gravity causes a tension of actin filaments and that this part of the cytoskeleton undergoes a relaxation in microgravity.

Control of Water and Nutrients Using a Porous Tube: A Method for Growing Plants in Space

A plant nutrient delivery system that uses a microporous, hydrophilic tube was developed with potential application for crop production in the microgravity of space. The tube contains a nutrient solution and delivers it to the roots. Pumps attached to the tubing create a very small suction that holds the solution within the tube. This system was used to grow wheat (Triticum aestivum cv. Yecora Rojo) for 107 days in a controlled environment at suctions of 0.40, 1.48, or 2.58 kPa. The water absorbed through the pores of the tube by baby diaper sections decreased as suction increased. Correspondingly, final plant biomass, seed number, and spikelet number also tended to decrease as suction increased. The reduced yield at higher suction suggests that the plants experienced water stress, although all suctions were below those typical of soils at field capacity.

Theoretical and Experimental Study on In-Orbit Capture Operation With Satellite Mounted Manipulator

This paper treats both theoretical and experimental study on a control problem of a space free-flying space manipulator. The authors' main target is to develop a new control method for trajectory tracking or target capturing, considering the dynamical interaction between the manipulator arm and the base vehicle in space micro-gravity environment. In the theoretical study, the Generalized Jacobian Matrix (GJM) concept is introduced. By means of this new matrix, the conventional control methods for ground-fixed manipulators is directly applicable for space manipulators. In the experimental study, a laboratory model of robot satellite supported on air bearings is developed in order to simulate the flee-flying behavior of mechanical links in micro-gravity environment. The model comprises a base satellite and a two-link manipulator arm. An on-line Resolved Motion Rate Control scheme with vision feedback is developed for experimenting capture operations, utilizing the GJM. The manipulator can properly chase and capture both a standing target and a moving target in spite of complex satellite/manipulator dynamical interaction. The experimental results confirm the validity of the GJM concept and the proposed control method.

自由浮遊する宇宙用テレロボット・モデルによる対象物の捕捉制御実験

This paper presents an experimental study on a control problem of a space manipulator installed on a free-flying telerobot. The authors' main goal is to develop a control method for dexterous operation of telerobot, with considering the dynamical interaction between the manipulator arm and the base satellite in space micro-gravity environment. In order to control space free-flying manipulators, the generalized Jacobian matrix is introduced. By substituting the conventional Jacobian for this matrix, conventional control methods for ground-fixed manipulators is directly applicable for space manipulators. In order to simulate the free-flying behavior of mechanical links in micro-gravity environment, a laboratory model of space telerobot supported on air bearings is developed. An on-line resolved motion-rate control scheme with vision feedback is proposed for experimenting target capture operation, by means of the generalized Jacobian matrix. The telerobot model can properly chase and capture both a standing target and a moving target in spite of complex satellite/manipulator dynamical interaction. The experimental results confirm the validity of the generalized Jacobian concept and proposed control method.

Acoustic levitation technique for containerless processing at high temperatures in space

High temperature processing of a small specimen without a container has been demonstrated in a set of experiments using an acoustic levitation furnace in the microgravity of space. This processing technique includes the positioning, heating, melting, cooling, and solidification of a material supported without physical contact with a container or other surface. The specimen is supported in a potential energy well, created by an acoustic field, which is sufficiently strong to position the specimen in the microgravity environment of space. This containerless processing apparatus has been successfully tested on the Space Shuttle during the STS-61A mission. In that experiment, three samples were successfully levitated and processed at temperatures from 600 ‡C to 1500 ‡C. Experiment data and results are presented.

Non-contaminating method to reduce Marangoni convection in microgravity float zones

A non-contaminating method is proposed for reduction of Marangoni (thermal capillary) convection in float-zone processing of corrosive materials in space microgravity. A ground-based experiment was constructed and used to demonstrate that the basic principle of the method is valid, and it produces significant reduction in Marangoni convection, in spite of three inherent difficulties caused by 1- g. A drop of silicone oil 1.5 mm high was enclosed in a transparent box with one vertical wall removed to permit a vertical free surface for the oil. A constant temperature difference Δ T was imposed between top and bottom surfaces, with higher temperature at the top. the small size of the drop effectively suppressed the 1- g thermal-buoyant convection. A vertical jet of air (an inert gas would be used for corrosive materials) was blown tangentially over the free surface, producing a viscous shear drag which opposed the Marangoni (surface-tension) shear at the surface. An average reduction of 66% in Marangoni velocities was obtained in the lowest one-third portion of the drop, corresponding to the resolidification surface in a float-zone melt. An experiment is now in design phase for a potential Space Shuttle flight to determine how much more reduction will be obtained in microgravity. Estimates are given for required velocities of argon and xenon if this method would be applied to a large silicon FZ in the Space Station.

Acoustic levitation at high temperatures in the microgravity of space

Acoustic levitation of a small specimen is obtained in the energy well produced by a single axis arrangement consisting of a sound source and a small acoustic reflector. At high temperatures, the acoustic forces are generally insufficient to levitate a specimen except in the microgravity environment available in space. A single axis acoustic levitator (SAAL) has been built to levitate a specimen inside a high-temperature furnace where it may be heated, melted, cooled, and solidified while being positioned without physical contact. The acoustic field configuration in such a containerless processing device has been analyzed and the expected levitation or positioning forces are calculated for the specific case of the NASA-SAAL experimental hardware as flown on the Space Shuttle on the STS-61A mission. This experiment successfully levitated and processed three samples at temperatures from 600 °C to 1550 °C. Experimental data are presented and the results compared with those predicted. [Work supported by NASA.]

The influence of gravity on the formation of amyloplasts in columella cells of Zea mays L.

Columella (i.e., putative graviperceptive) cells of Zea mays seedlings grown in the microgravity of outer space allocate significantly less volume to putative statoliths (amyloplasts) than do columella cells of Earth-grown seedlings. Amyloplasts of flight-grown seedlings are significantly smaller than those of ground controls, as is the average volume of individual starch grains. Similarly, the relative volume of starch in amyloplasts in columella cells of flight-grown seedlings is significantly less than that of Earth-grown seedlings. Microgravity does not significantly alter the volume of columella cells, the average number of amyloplasts per columella cell, or the number of starch grains per amyloplast. These results are discussed relative to the influence of gravity on cellular and organellar structure.

Space technology today

Technologies developed in support of our civil space program have progressed considerably over the 25‐year life of the National Aeronautics and Space Administration. Many of these advances are the result of a continuing increase in knowledge relative to the environment of space and the utilization of these previously designated hostile elements to gain design application advantages. Much more significant utilization of the environmental elements is forecast as space research and commercial goals and objectives begin to gain momentum. Challenges in the design of our Shuttle System and the next major goal, the Space Station, are significant and will result in greater utilization of the microgravity and vacuum of space as a benefit to research and operational goals.