STS-95 Mission Research Articles

Measurement of a Linear Energy Transfer Distribution with Antioxidant Doped CR-39 Correcting for the Dip Angle Dependence of Track Formation Sensitivity

Antioxidant doped CR-39 detectors were loaded onto the STS-95 space shuttle mission (altitude: 574 km; inclination: 28.45°; flight duration: 8.9 days) for measuring the linear energy transfer (LET) distribution above 10 keV/µm for space radiation dosimetry. It is known that the track formation sensitivity of antioxidant doped CR-39 detectors depends on the dip angle of the incident particle. We investigated this dip angle dependence for a wide range of LET values and dip angles. The track formation sensitivities at lower dip angles were obviously decreased in the LET region below 100 keV/µm. We introduced minimum-cutoff dip angles in order to correct for such dip-angle dependence. The LET distribution of the STS-95 mission was obtained from the measurements of etch pits having dip angles larger than the minimum-cutoff dip angles. This new correction method increased the absorbed dose and dose equivalent above 10 keV/µm by 54 and 28%, respectively.

Cell wall changes involved in the automorphic curvature of rice coleoptiles under microgravity conditions in space

Seedlings of rice (Oryza sativa L. cv. Koshihikari and cv. Tan-ginbozu) were cultivated on board the Space Shuttle STS-95 mission and changes in the morphology and the cell wall properties of coleoptiles were analyzed. In space, rice coleoptiles showed a spontaneous (automorphic) curvature toward the caryopsis in the elongating region. The angle of automorphic curvature was larger in Koshihikari than in a gibberellin-deficient dwarf cultivar, Tan-ginbozu, and the angle gradually decreased during the growth of coleoptiles in both cultivars. The more quickly expanding convex side of the bending region of the rice coleoptiles showed a greater extensibility of the cell wall than the opposite side. There was a significant correlation between the angle of curvature and the difference in the cell wall extensibility between the convex and the concave sides. Both the levels of the cell wall polysaccharides per unit length of coleoptile and the ratio of high-molecular-mass polysaccharides in the hemicellulose fraction were lower in the convex side than the concave one. Also, the activity of (1-->3),(1-->4)-beta-glucanases in the cell wall was higher in the convex side than the concave one. These results suggest that the uneven modifications of cell wall metabolism bring about the difference in the levels and the molecular size of the cell wall polysaccharides, thereby causing the difference in capacity of the cell wall to expand between the dorsal and the ventral sides, leading to the automorphic curvature of rice coleoptiles in space. The data also suggest the involvement of gibberellins in inducing the automorphic curvature under microgravity conditions.

Dewetted growth of CdTe in microgravity (STS‐95)

AbstractTwo CdTe crystals had been grown in microgravity during the STS‐95 mission. The growth configuration was dedicated to obtain dewetting of the crystals and to achieve high quality material. Background for the performed experiments was based on the theory of the dewetting and previous experience. The after flight characterization of the crystals has demonstrated existance of the dewetting areas of the crystals and their improved quality regarding the earth grown reference sample. The samples had been characterized by EDAX, Synchrotron X‐ray topography, Photoluminescence and Optical and IR microscopy. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth and cell wall changes in rice roots during spaceflight.

We analyzed the changes in growth and cell wall properties of roots of rice (Oryza sativa L. cv. Koshihikari) grown for 68.5, 91.5, and 136 h during the Space Shuttle STS-95 mission. In space, most of rice roots elongated in a direction forming a constant mean angle of about 55 degrees with the perpendicular base line away from the caryopsis in the early phase of growth, but later the roots grew in various directions, including away from the agar medium. In space, elongation growth of roots was stimulated. On the other hand, some of elasticity moduli and viscosity coefficients were higher in roots grown in space than on the ground, suggesting that the cell wall of space-grown roots has a lower capacity to expand than the controls. The levels of both cellulose and the matrix polysaccharides per unit length of roots decreased greatly, whereas the ratio of the high molecular mass polysaccharides in the hemicellulose fraction increased in space-grown roots. The prominent thinning of the cell wall could overwhelm the disadvantageous changes in the cell wall mechanical properties, leading to the stimulation of elongation growth in rice roots in space. Thus, growth and the cell wall properties of rice roots were strongly modified under microgravity conditions during spaceflight.

Stimulation of Elongation Growth and Cell Wall Loosening in Rice Coleoptiles under Microgravity Conditions in Space

We analyzed the growth rate and the cell wall properties of coleoptiles of rice seedlings grown at 23.6 degrees C for 68.5, 91.5 and 136 h during the Space Shuttle STS-95 mission. In space, elongation growth of coleoptiles was stimulated and the cell wall extensibility increased. Also, the levels of the cell wall polysaccharides per unit length of coleoptiles and the relative content of the high molecular mass matrix polysaccharides decreased in space. These differences in the cell wall polysaccharides could be involved in increasing the cell wall extensibility, leading to growth stimulation of rice coleoptiles in space.

Effect of Space Flight on the Frequency of Micronuclei and Expression of Stress-responsive Proteins in Cultured Mammalian Cells

Results of past space experiments suggest that the biological effect of space radiation could be enhanced under microgravity in some cases, especially in insects. To examine if such a synergistic effect of radiation and microgravity also exists in human cells, frequencies of chromosome instability and cellular levels of several stress-responsive proteins were analyzed in cultured human and rodent cells after space flight. Human (MCF7 and AT2KY), mouse (m5S) and hamster (SHE) cell lines were loaded on the Space Shuttle Discovery (STS-95 mission) and grown during a 9-day mission. After landing, the micronuclei resulting from abnormal nuclear division and accumulation of stress-responsive proteins such as p53 and mitogen-activated protein kinases (MAPKs), which are involved in radiation-induced signal transduction cascades, were analyzed. The frequencies of micronuclei in all the four mammalian cell strains tested were not significantly different between flight and ground control samples. Also, the cellular amounts of p53, p21 (WAF1/SDI1/CIP1) and activated (phosphorylated) forms of three distinct MAPKs in MCF7 and m5S cells of flight samples were similar to those of ground control samples. These results indicated that any effect of space radiation, microgravity, or combination of both were not detectable, at least under the present experimental conditions.

Comparative study of the Columnar-Equiaxed Transition in microgravity and on ground during directional solidification of a refined Al - 3.5 wt% Ni alloy

A comparative analysis of directional solidification experiments performed on a refined Al - 3.5 wt% Ni alloy in microgravity (facility AGHF, STS95 mission, Nov. 98; facility TITUS, MIR-PERSEUS mission, May-June 99) and on ground is presented here. The objective is to separate the respective influence of growth rate and natural convection on the formation of dendritic microstructures in the columnar/equiaxed transition range. Local segregations observed both in tag and on ground in transient regions along the solidification direction are discussed. Ground reference experiments, which were performed vertically upwards i.e. in a solutally stabilizing configuration, show increasing radial macrosegregation at decreasing low growth rates, resulting from a local thermosolutal flow pattern, which is characteristic of this configuration. In microgravity, equiaxed microstructures are observed at all the investigated rates, a specific dendritic morphology being obtained at the lowest rate where the equiaxed grain size is the largest. By contrast, the ground experiments present transitions from purely columnar to mixed columnar-equiaxed and purely equiaxed structures for increasing rates.

Video observation of protein crystal growth in the advanced protein crystallization facility aboard the space shuttle mission STS-95

Crystals of polypeptide with sequence (Pro-Pro-Gly) 10 were grown in the Advanced Protein Crystallization Facility during the US Space Shuttle STS-95 Mission. Well diffracting crystals were obtained by dialysis; they provided the highest resolution X-ray data so far collected for a collagen-like triple helical structure (Berisio et al., Acta Crystallogr. D 56 (2000) 55). During the Mission the crystal growth was monitored by a CCD video camera. The image analysis provided information on spatial distribution of crystals, their movements and their growth. The spatial distribution was non-uniform inside the reactors. Limited motions were observed. The linear growth rate indicates that, in some cases, the growth did not cease in the microgravity environment.

Nucleation and growth of thaumatin crystals within a gel under microgravity on STS-95 mission vs. under Earth's gravity

In the frame of a study of the effects of microgravity on protein crystallization, tetragonal thaumatin crystals were, for the first time, prepared in agarose gel within the Advanced Protein Crystallization facility (APCF) on Space Shuttle mission STS-95 (October 1998). We have reported elsewhere that these crystals are of superior crystallographic quality, with regard to their diffraction intensity and limit as well as mosaic spread, when compared to control crystals grown on Earth [Lorber et al ., Acta Crystallogr. (1999) D55, 1491]. The analysis of images taken during the growth of these crystals under microgravity indicates that their nucleation was more synchronous than that of control crystals which were prepared simultaneously on Earth under otherwise identical conditions. Nucleation occurred essentially in the bulk of the medium and crystal growth proceeded up to 2 times faster. Crystals prepared under microgravity had better optical properties than control crystals. Experimental results give evidence of the existence of zones depleted in protein located around growing crystals. Also, they are in favor of a correlation between the better diffraction properties of these crystals and the more favorable crystallization parameters in Space. The content of individual crystals was analyzed and the results of purity analyses are presented. The advantages of crystallization in a gel under microgravity and importance of image documentation for asserting growth cessation are discussed.

Effects of microgravity on the crystal quality of a collagen-like polypeptide.

(Pro-Pro-Gly)(10) is one of the most widely studied collagen polypeptide models. Microgravity crystal growth of (Pro-Pro-Gly)(10) was carried out in the Advanced Protein Crystallization Facility aboard the Space Shuttle Discovery during the STS-95 mission. Crystals were successfully grown in all experiments, using both dialysis and free-interface diffusion methods. The quality of the microgravity-grown crystals and of ground-grown counterparts was assessed by X-ray synchrotron diffraction. Microgravity-grown crystals exhibited a significant improvement in terms of dimensions and resolution limit. As previously reported, crystals were orthorhombic, space group P2(1)2(1)2(1). However, the diffraction pattern showed weak reflections, never previously measured, that were consistent with new unit-cell parameters a = 26.9, b = 26.4, c = 182.5 A. This allowed the derivation of a new model for the arrangement of the triple-helical molecules in the crystals.

The cosmic dust aggregation experiment CODAG

For the simulation of the first stage of preplanetary dust aggregation, we developed the cosmic dust aggregation experiment (CODAG). With CODAG, we intend to study the aggregational behaviour of a cloud of micron-sized dust particles due to Brownian motion of the grains. For a realistic simulation of the processes in the young solar system, the dust grains have to be dispersed in a rarefied gas so that mutual collisions are ballistic. Fast sedimentation of the grains in the Earth's gravitational field leads to unrealistic collision velocities and to a rapid loss of particles to the container walls. Therefore, CODAG was designed to work in a microgravity environment. In this paper, we present an overview of the experimental design of CODAG which was recently flown in a Get Away Special container during the STS-95 mission.

VFEU water quality control in STS-95 mission.

In STS-95 Space Shuttle mission, an aquatic animal research facility, Vestibular Function Experiment Unit (VFEU), was flown to perform neurobiological experiment with marine fish, oyster toadfish. For this purpose, we have developed a sea water purification system using highly active nitrifying bacteria at low temperature. With this system, the water quality in the VFEU was maintained in sufficient condition to keep the toadfish in healthy state for 9 days of the mission. This report summarizes the efficiency of the filter system based on the results from pre-flight bacterial preparation, water analysis of samples taken during flight, and the post-flight analysis of the bacterial filter.

STS-95 Space Experiments (plants and cell biology).

We report the outline of Space Experiments conducted on Space Shuttle (STS-95) launched in autumn of 1998. In this STS-95 mission, Japanese astronaut Dr. Chiaki Mukai achieved her 2nd space flight and conducted a part of 82 space experiments including Japanese experiments. US astronaut Senator John Glenn also achieved his second space flight, 36 years after his first space flight. Senator Glenn was a leader of the original (the first) 7 US astronauts and very famous in US because he succeeded US first orbital space flight around the earth. NASDA had started the project of space experiment using STS-95 at the summer of 1997, therefore we had only one year for the all preparation Yamashita, et al. Biological Sciences in Space, Vol.12 No.3(1998). Scientific results will be reported by investigators, therefore we report here how we had been developing the space experiment plan, on board operation procedure and ground operations including ground control experiments about four plant experiments and one cell biology experiment.