Changes in Optical and Thermal Properties of the MISSE 2 Peace Polymers and Spacecraft Silicones

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This paper documents optical and thermal properties of polymers and silicones from the Materials International Space Station Experiment 2 (MISSE 2) Polymer Erosion and Contamination Experiment (PEACE) Polymers experiment and from the MISSE 4 Spacecraft Silicones experiment. PEACE included forty-one polymer samples that were exposed to the low Earth orbit (LEO) environment on the exterior of the International Space Station (ISS) for almost four years. The Spacecraft Silicones experiment is comprised of eight DC 93-500 silicone samples manufactured by Dow Corning, four of which were flown as part of MISSE 2, and four of which were flown as part of MISSE 4. MISSE 4 was exposed to the space environment on the exterior of ISS for 1 year. Both the PEACE Polymers and the Spacecraft Silicone experiments were exposed to atomic oxygen (AO) along with solar and charged particle radiation while in LEO. The majority of the PEACE samples are comprised of numerous thin film layers stacked together. Because many of the PEACE polymers are commonly used for spacecraft applications, their optical and thermal properties are very important. DC 93-500 silicone is a popular spacecraft optical adhesive, often used for photovoltaic applications, hence changes in optical properties, particularly transmittance, due to LEO exposure is very important. Changes in optical and thermal properties due to LEO environmental exposure have been analyzed for all of the materials that could be measured. Due to the long duration space exposure, several of the MISSE 2 samples were too degraded for their properties to be measured. Total and diffuse reflectance, and total and diffuse transmittance, were measured as a function of wavelength and compared with non-exposed control samples. Specular reflectance and specular transmittance were then computed. Thermal emittance data was also generated for numerous samples. For most samples, specular and diffuse reflectance characteristics changed greatly upon directed LEO atomic oxygen exposure. Typically, there is a decrease in specular reflectance with an increase in diffuse reflectance. These optical property changes are relevant to glare issues, Fresnel lens photovoltaic concentrator power loss issues and issues with spatial variations in the thermal load on a spacecraft. The wavelength dependant data also allows computation of the change in solar absorptance (αs) and thermal emittance, which is critical for predicting thermal control characteristics of a spacecraft. A summary of the MISSE 2 PEACE Polymers and Spacecraft Silicones experiments, the specific materials flown, optical and thermal property measurement procedures, and the optical and thermal property data are presented.

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Results of measuring neutron dose inside the Russian segment of the International Space Station using bubble detectors in experiment Matreshka-R

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Distribution of neutron equivalent dose both inside and outside the spherical phantom (experiment Matryeshka-R) was determined with the help of dedicated research equipment "Bubble-dosimeter". Equipment is built up from an automatic bubbles counter and 8 bubble detectors of neutrons with energy ranging from approximately 200 keV to 15 MeV. Measurements inside the ISS were made in several 7-day sessions in the period from April 2006 till October 2007 (ISS increments 13-15). According to the bubble detectors on the outside of the phantom, ambient neutron dose H*(10) was equal to 0.1 mSv/d or approximately 20% of the dose from charged particles inside the ISS. In the tissue-equivalent phantom, neutron dose was 1.2 +/- 0.2 times less as compared with the phantom surface which characterized the degree of dose attenuation in cosmonaut's body.

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http://www.ncbi.nlm.nih.gov/pubmed/21033392

Physics of colloids in space – Flight hardware operations on ISS

by on 9 June 2015in Physical Sciences No comment

The Physics of Colloids in Space (PCS) experiment was launched on Space Shuttle STS-100 in April 2001 and integrated into EXpedite the PRocess of Experiments to Space Station Rack 2 on the International Space Station (ISS). This microgravity fluid physics investigation is being conducted in the ISS U.S. Lab 'Destiny' Module over a period of approximately thirteen months during the ISS assembly period from flight 6A through flight 9A. PCS is gathering data on the basic physical properties of simple colloidal suspensions by studying the structures that form. A colloid is a micron or submicron particle, be it solid, liquid, or gas. A colloidal suspension consists of these fine particles suspended in another medium. Common colloidal suspensions include paints, milk, salad dressings, cosmetics, and aerosols. Though these products are routinely produced and used, we still have much to learn about their behavior as well as the underlying properties of colloids in general. The long-term goal of the PCS investigation is to learn how to steer the growth of colloidal structures to create new materials. This experiment is the first part of a two-stage investigation conceived by Professor David Weitz of Harvard University (the Principal Investigator) along with Professor Peter Pusey of the University of Edinburgh (the Co-Investigator). This paper describes the flight hardware, experiment operations, and initial science findings of the first fluid physics payload to be conducted on ISS: The Physics of Colloids in Space.

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http://dx.doi.org/10.2514/6.2002-762

Leak rate performance of three silicone elastomer compounds after ground-simulated and on-orbit environment exposures

by on 9 June 2015in Physical Sciences No comment

Three silicone elastomer compounds were evaluated to determine the effect of exposure to a spacecraft’s external environment and of exposure to atomic oxygen in terrestrial facilities. Air leak rate was used as the metric to quantify the degradation that occurred on S0383-70, S0899-50, and XELA-SA-401 elastomers formed into O-rings. Specimens were positioned external to the International Space Station (ISS) for 18 months aboard MISSE-6 where they were exposed to atomic oxygen, ultraviolet and particle radiation, vacuum pressure, and temperature fluctuations. The flight specimens were separated into two groups and positioned in ram-facing and in wake-facing directions, where the atomic oxygen fluence was 1.2×1022 and 6.0×1020 atoms/in2, respectively. Select specimens were pretreated with atomic oxygen generated by introducing air to radio frequency plasma. Yet another set of specimens was reserved as a control group to which the other were compared. The leak rates of the specimens were determined using a mass-point leak rate technique with uncertainty analysis and showed that the performances of the three elastomers degraded at different rates. The leak rate of XELA-SA-401 was eliminated from the study due to its poor relative flight performance. The ratio of the ram-facing to wake-facing leak rate was 1.2 and 2.9 for the S0383-70 and S0899-50 compounds, respectively, indicating the former compound was not appreciable affected by atomic oxygen while the later was. After receiving atomic oxygen fluency of 1.2×1022 atoms/in2 during flight, the leak rate of the S0899-50 was 5 times that of the S0383-70 specimens; however, the leak rate of the S0383-70.

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http://dx.doi.org/10.2514/6.2011-3823

SMOKE POINTS OF MICROGRAVITY AND NORMAL GRAVITY COFLOW DIFFUSION FLAMES

by on 9 June 2015in Physical Sciences No comment

Smoke points were measured in microgravity aboard the International Space Station (ISS) as part of the Smoke Points in Coflow Experiment (SPICE), and in normal gravity conditions. In microgravity conditions increasing the coflow velocity or decreasing the burner diameter increased the smoke point flame length. A simplified prediction of centerline jet velocity did not yield residence-time-based criticalities or data collapse. Simulation of non-reacting flows showed that the simplified centerline velocity prediction was able to predict velocity decay for only relatively weak coflows. An improved model may yield different results. In normal earth gravity coflow velocity exhibited mixed effects. For burner diameters of 0.41, 0.76, and 1.6 mm, smoke points increased with increases of coflow velocity. For an unconfined coflow burner with a burner diameter of 13.7 mm smoke point length decreased with increasing coflow velocity for ethylene and propylene, while increasing for propane flames.

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http://hdl.handle.net/1903/10005

Austrian dose measurements onboard space station MIR and the International Space Station – overview and comparison

by on 9 June 2015in Physical Sciences No comment

The Atominstitute of the Austrian Universities has conducted various space research missions in the last 12 years in cooperation with the Institute for Biomedical Problems in Moscow. They dealt with the exact determination of the radiation hazards for cosmonauts and the development of precise measurement devices. Special emphasis will be laid on the last experiment on space station MIR the goal of which was the determination of the depth distribution of absorbed dose and dose equivalent in a water filled Phantom. The first results from dose measurements onboard the International Space Station (ISS) will also be discussed. The spherical Phantom with a diameter of 35 cm was developed at the Institute for Biomedical Problems and had 4 channels where dosemeters can be exposed in different depths. The exposure period covered the timeframe from May 1997 to February 1999. Thermoluminescent dosemeters (TLDs) were exposed inside the Phantom, either parallel or perpendicular to the hull of the spacecraft. For the evaluation of the linear energy transfer (LET), the high temperature ratio (HTR) method was applied. Based on this method a mean quality factor and, subsequently, the dose equivalent is calculated according to the Q(LET∞) relationship proposed in ICRP 26. An increased contribution of neutrons could be detected inside the Phantom. However the total dose equivalent did not increase over the depth of the Phantom. As the first Austrian measurements on the ISS dosemeter packages were exposed for 248 days, starting in February 2001 at six different locations onboard the ISS. The Austrian dosemeter sets for this first exposure on the ISS contained five different kinds of passive thermoluminescent dosemeters. First results showed a position dependent absorbed dose rate at the ISS.

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http://www.sciencedirect.com/science/article/pii/S0273117704003278

Ground and Space-Based Measurement of Rocket Engine Burns in the Ionosphere

by on 9 June 2015in Physical Sciences No comment

On-orbit firings of both liquid and solid rocket motors provide localized disturbances to the plasma in the upper atmosphere. Large amounts of energy are deposited to ionosphere in the form of expanding exhaust vapors which change the composition and flow velocity. Charge exchange between the neutral exhaust molecules and the background ions (mainly O<sup>+</sup>) yields energetic ion beams. The rapidly moving pickup ions excite plasma instabilities and yield optical emissions after dissociative recombination with ambient electrons. Line-of-sight techniques for remote measurements rocket burn effects include direct observation of plume optical emissions with ground and satellite cameras, and plume scatter with UHF and higher frequency radars. Long range detection with HF radars is possible if the burns occur in the dense part of the ionosphere. The exhaust vapors initiate plasma turbulence in the ionosphere that can scatter HF radar waves launched from ground transmitters. Solid rocket motors provide particulates that become charged in the ionosphere and may excite dusty plasma instabilities. Hypersonic exhaust flow impacting the ionospheric plasma launches a low-frequency, electromagnetic pulse that is detectable using satellites with electric field booms. If the exhaust cloud itself passes over a satellite, in situ detectors measure increased ion-acoustic wave turbulence, enhanced neutral and plasma densities, elevated ion temperatures, and magnetic field perturbations. All of these techniques can be used for long range observations of plumes in the ionosphere. To demonstrate such long range measurements, several experiments were conducted by the Naval Research Laboratory including the Charged Aerosol Release Experiment, the Shuttle Ionospheric Modification with Pulsed Localized Exhaust experiments, and the Shuttle Exhaust Ionospheric Turbulence Experiments.

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

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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

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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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