The “SCORPION” experiment onboard the International Space Station. Preliminary results

by on 9 June 2015in Physical Sciences No comment

The “SCORPION” program onboard the Russian Segment (RS) of the International Space Station (ISS) is designed to carry out complex research of the effects of the nar-Earth space parameters on the conditions under which various experiments and operations are being conducted. Special attention in this program was paid to the biological objects onboard the orbital station, e.g. it w as found that variation in the number of colony forming units (micromicets and bacteria) correlates with the solar activity and the absorbed dose. The “SCORPION” experiment onboard the RS ISS started in January 2002. It was designed to measure the following parameters inside the space absorbed doses in different places inside the RS ISS, the fluxes of energetic charged particles, neutrons and gamma-quanta; the vectors of the magnetic field and low-frequency electromagnetic waves. At the same time the growth of micromicets on the samples of various materials was studied. The description of the “SCORPION” experiment and the preliminary results obtained onboard the RS ISS in 2002 are presented.

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http://www.sciencedirect.com/science/article/pii/S0273117703905680

Free surfaces in open capillary channels—Parallel plates

by on 9 June 2015in Physical Sciences No comment

This paper is concerned with forced flow through partially open capillary channels under microgravity conditions. The investigated channel consists of two parallel plates and is bounded by free liquid surfaces along the open sides. The curvature of the channel’s gas-liquid interface, which is exposed to the ambient pressure, adjusts to the pressure difference across the interface in accordance with the Young-Laplace equation. Flow within the channel becomes unstable when the free surface collapses and gas ingestion into the flow path occurs—a process that is also referred to as the “choking” phenomenon. During stable flow, the behavior of the free surface is influenced by flow conditions, geometric properties of the channel, and the pre-defined system pressure. In this work, a previously published stability theory is verified for a wide range of model parameters. A detailed study is provided for stable flow in capillary channels, including static and dynamic solutions. The results of the Capillary Channel Flow (CCF) experiment are evaluated and are found to agree well with numerical predictions. A clear limit is determined between stable and unstable flows. It is shown that the model can predict the shape of the free surface under various flow conditions. A numerical tool is employed to exploit the mathematical model, and the general behavior of free surfaces in said capillary channels is studied. Studies are conducted in both viscous and convective flow regimes and in the transition area between the two. The validity of the model is confirmed for a wide range of geometrical configurations and parameters.

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http://scitation.aip.org/content/aip/journal/pof2/27/1/10.1063/1.4906154

Self-assembled Gels of Amphiphilic Sequential Peptide in Water and Organic Solvents

by on 9 June 2015in Physical Sciences No comment

An amphiphilic peptide designed with serine as a polar residue showed gelation in both water and organic solvents. This sequential peptide has a strong tendency to adopt β-sheet conformation in these solvents. Such gels of β-sheet peptide based on hierarchical self-assembly consist of nanofiber construction because of the β-sheet structure, and because of crosslinking attributable to hydrogen bonding among hydroxy groups of the serine side chain.

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Atomic Oxygen Erosion Yield Prediction for Spacecraft Polymers in Low Earth Orbit

by on 9 June 2015in Physical Sciences No comment

The ability to predict the atomic oxygen erosion yield of polymers based on their chemistry and physical properties has been only partially successful because of a lack of reliable low Earth orbit (LEO) erosion yield data. Unfortunately, many of the early experiments did not utilize dehydrated mass loss measurements for erosion yield determination, and the resulting mass loss due to atomic oxygen exposure may have been compromised because samples were often not in consistent states of dehydration during the pre-flight and post-flight mass measurements. This is a particular problem for short duration mission exposures or low erosion yield materials. However, as a result of the retrieval of the Polymer Erosion and Contamination Experiment (PEACE) flown as part of the Materials International Space Station Experiment 2 (MISSE 2), the erosion yields of 38 polymers and pyrolytic graphite were accurately measured. The experiment was exposed to the LEO environment for 3.95 years from August 16, 2001 to July 30, 2005 and was successfully retrieved during a space walk on July 30, 2005 during Discovery’s STS-114 Return to Flight mission. The 40 different materials tested (including Kapton H fluence witness samples) were selected specifically to represent a variety of polymers used in space as well as a wide variety of polymer chemical structures. The MISSE 2 PEACE Polymers experiment used carefully dehydrated mass measurements, as well as accurate density measurements to obtain accurate erosion yield data for high-fluence (8.43× 10 21 atoms/cm2). The resulting data was used to develop an erosion yield predictive tool with a correlation coefficient of 0.895 and uncertainty of ±6.3 × 10 –25 cm3/atom. The predictive tool utilizes the chemical structures and physical properties of polymers to predict in-space atomic oxygen erosion yields. A predictive tool concept (September 2009 version) is presented which represents an improvement over an earlier (December 2008) version.

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MISSE Scattered Atomic Oxygen Characterization Experiment.

by on 9 June 2015in Physical Sciences No comment

An experiment designed to measure the atomic oxygen (AO) erosion profile of scattered AO was exposed to Low Earth Orbital (LEO) AO for almost four years as part of the Materials International Space Station Experiment 1 and 2 (MISSE 1 and 2). The experiment was flown in MISSE Passive Experiment Carrier 2 (PEC 2), Tray 1, attached to the exterior of the International Space Station (ISS) Quest Airlock. The experiment consisted of an aperture disk lid of Kapton H (DuPont) polyimide coated on the space exposed surface with a thin AO durable silicon dioxide film. The aperture lid had a small hole in its center to allow AO to enter into a chamber and impact a base disk of aluminum. The AO that scattered from the aluminum base could react with the under side of the aperture lid which was coated sporadically with microscopic sodium chloride particles. Scattered AO erosion can occur to materials within a spacecraft that are protected from direct AO attack but because of apertures in the spacecraft the AO can attack the interior materials after scattering. The erosion of the underside of the Kapton lid was sufficient to be able to use profilometry to measure the height of the buttes that remained after washing off the salt particles. The erosion pattern indicated that peak flux of scattered AO occurred at and angle of approximately 45 from the incoming normal incidence on the aluminum base unlike the erosion pattern predicted for scattering based on Monte Carlo computational predictions for AO scattering from Kapton H polyimide. The effective erosion yield for the scattered AO was found to be a factor of 0.214 of that for direct impingement on Kapton H polyimide.

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by on 9 June 2015in Physical Sciences No comment

There have been five Materials International Space Station Experiment (MISSE) passive experiment carriers (PECs) (MISSE 1-5) to date that have been launched, exposed in space on the exterior of International Space Station (ISS) and then returned to Earth for analysis. An additional four MISSE PECs (MISSE 6A, 6B, 7A, and 7B) are in various stages of completion. The PECs are two-sided suitcase to size sample carriers that are intended to provide information on the effects of the low Earth orbital environment on a wide variety of materials and components. As a result of post retrieval analyses of the retrieved MISSE 2 experiments and numerous prior space experiments, there have been valuable lessons learned and needs identified that are worthy of being documented so that planning, design, and analysis of future space environment experiments can benefit from the experience in order to maximize the knowledge gained. Some of the lessons learned involve the techniques, concepts, and issues associated with measuring atomic oxygen erosion yields. These are presented along with several issues to be considered when designing experiments, such as the uncertainty in mission duration, scattering and contamination effects on results, and the accuracy of measuring atomic oxygen erosion.

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The Constrained Vapor Bubble (CVB) Experiment in the Microgravity Environment of the International Space Station

by on 9 June 2015in Physical Sciences No comment

The Constrained Vapor Bubble (CVB) experiment was run in the microgravity environment of the International Space Station as part of the Increment 23-24 which ended in September 2010. Here we present preliminary results which indicate significant differences in the operation of the CVB heat pipe in the micro-gravity environment as compared to the Earth's gravity. The temperature profile data along the heat pipe indicate that the heat pipe behavior is affected favorably by increased capillary flow and adversely by the absence of convective heat transfer as a heat loss mechanism. Image data of the liquid profile in the grooves of the heat pipe indicate that the curvature gradient is considerably different from that on Earth. An initial discussion of the data collected is presented.

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Materials International Space Station Experiment-6 (MISSE-6) Atomic Oxygen Fluence Monitor Experiment

by on 9 June 2015in Physical Sciences No comment

An atomic oxygen fluence monitor was flown as part of the Materials International Space Station Experiment-6 (MISSE-6). The monitor was designed to measure the accumulation of atomic oxygen fluence with time as it impinged upon the ram surface of the MISSE 6B Passive Experiment Container (PEC). This was an active experiment for which data was to be stored on a battery-powered data logger for post-flight retrieval and analysis. The atomic oxygen fluence measurement was accomplished by allowing atomic oxygen to erode two opposing wedges of pyrolytic graphite that partially covered a photodiode. As the wedges of pyrolytic graphite erode, the area of the photodiode that is illuminated by the Sun increases. The short circuit current, which is proportional to the area of illumination, was to be measured and recorded as a function of time. The short circuit current from a different photodiode, which was oriented in the same direction and had an unobstructed view of the Sun, was also to be recorded as a reference current. The ratio of the two separate recorded currents should bear a linear relationship with the accumulated atomic oxygen fluence and be independent of the intensity of solar illumination. Ground hyperthermal atomic oxygen exposure facilities were used to evaluate the linearity of the ratio of short circuit current to the atomic oxygen fluence. In flight, the current measurement circuitry failed to operate properly, thus the overall atomic oxygen mission fluence could only be estimated based on the physical erosion of the pyrolytic graphite wedges. The atomic oxygen fluence was calculated based on the knowledge of the space atomic oxygen erosion yield of pyrolytic graphite measured from samples on the MISSE 2. The atomic oxygen fluence monitor, the expected result and comparison of mission atomic oxygen fluence based on the erosion of the pyrolytic graphite and Kapton H atomic oxygen fluence witness samples are presented in this paper.

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 Undercutting Studies of Protected Kapton H Exposed to In-Space and Ground-Based Atomic Oxygen

by on 9 June 2015in Physical Sciences No comment

This study is part of a Materials International Space Station Experiment (MISSE) sequence to characterize the performance of prospective spacecraft materials when subjected to the synergistic effects of the space environment. Atomic oxygen (AO) is the most prevalent species in low earth orbit (LEO). In this environment AO is mainly responsible for the erosion of hydrocarbons and halocarbon polymers. The AO erosion rates of Kapton (DuPont) H are known and well documented. Hence, it is customary to compare the AO erosion yields of candidate materials to the commonly accepted standard of this polyimide. The purpose of this study was to provide characterization of AO degradation of SiO(x) protected Kapton H film, which was subject during MISSE 2 to undercutting erosion beneath microscopic defects in the protective film, and compare the degradation resulting from hyperthermal ram (approx.4.5 eV) LEO AO to the degradation resulting from exposure to thermal ground-based (approx.0.04 eV) AO.

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Radiation measurements on the International Space Station

by on 9 June 2015in Physical Sciences No comment

The International Space Station (ISS) is becoming a reality with the docking of the Russian Service module (Zarya) with the Unity module (Zaveda). ISS will be in a nominal 51.65-degree inclination by 400 km orbit. This paper reviews the currently planned radiation measurements, which are in many instances, based on experiments previously flown on the Space Shuttle. Results to be expected based on Shuttle measurements are presented.

Related URLs:
http://www.ncbi.nlm.nih.gov/pubmed/11780621