The present work aims to study mechanical nonlinearities detected in the accelerometric records during a thermodiffusion experiment performed at the International Space Station, ISS. In that experiment the test cell was subjected to harmonic vibrations of different frequencies and amplitudes. Accelerometric data associated to the runs were downloaded from NASA PIMS website. Second order spectral analysis shows that the shaker modifies the normality of the data and introduces nonlinearities in the distribution of energy. High Order Spectral Analysis, HOSA, based on the bispectrum, bicoherence, trispectrum and tricoherence functions enabled us to study the kind of these nonlinearities. Additionally, a new method using the biphase and triphase histograms helps us to assess if quadratic and/or cubic phase coupling mechanisms are responsible for the anomalous nonlinear energy transfer detected. Finally, the RMS acceleration values are investigated to check if the vibratory limit requirements of the ISS are exceeded. This methodology is important not only in generic research of aerospace engineering but also in space sciences in order to help space researchers to characterize more globally their experiments. It is mentioned finally that HOSA techniques are not new, but never have been used in the analysis of accelerometric data coming from the ISS.
Research Containing: Space Flight
Two accelerometric records coming from the SAMSes es08 sensor in the Columbus module, the so-called Runs 14 and 33 in terms of the IVIDIL experiment, has been studied here using standard digital signal analysis techniques. The principal difference between both records is the vibrational state of the IVIDIL experiment, that is to say, during Run 14 the shaking motor of the experiment is active while that in Run 33 this motor is stopped. Identical procedures have been applied to a third record coming from the SAMSII 121f03 sensor located in the Destiny module during an IVIDIL quiescent period. All records have been downloaded from the corresponding public binary accelerometric files from the NASA Principal Investigator Microgravity Services, PIMS website and, in order to be properly compared, have the same number of data. Results detect clear differences in the accelerometric behavior, with or without shaking, despite the care of the designers to ensure the achievement of the ISS μg-vibrational requirements all along the experiments.
Pore-size expansion of hexagonal-structured nanocrystalline titania/CTAB Nanoskeleton using cosolvent organic molecules
Pore-size expansion of hexagonal-structured assembly of nanocrystalline titania (anatase) combined with cetyltrimethyammonium bromide (CH3(CH2)15N+(CH3)3Br−, CTAB) (named as Hex-ncTiO2/CTAB Nanoskeleton) was achieved with the aid of cosolvent organic molecules (COMs). The pore-size expanded Hex-ncTiO2/CTAB Nanoskeleton was prepared through the sol–gel reaction of titanium oxysulfate sulfuric acid hydrate (TiOSO4·xH2SO4·xH2O, TiOSAH) in an aqueous solution initiated by CTAB swollen micelles pre-prepared with the addition of COMs into aqueous CTAB micellar solutions at 60 °C (the product was named as Hex-ncTiO2/CTAB/COM Nanoskeleton). Long-chain alcohol (1-hexadecanol, C16OH), normal alkane (n-decane, C10) and benzene derivatives (benzene, Bz; 1,3,5-trimethylbenzene, TMB; 1,3,5-triethylbenzene, TEB; 1,3,5-triisopropylbenzene, TiPB) were used as COMs to evaluate the effects of COM solubilization site in CTAB micelles and COM molecular size on the pore-size expansion of the Hex-ncTiO2/CTAB/COM Nanoskeleton. We found that 1,3,5-trimethylbenzene (TMB) and 1,3,5-triethylbenzene (TEB) act as effective COMs for pore-size expansion of the Hex-ncTiO2/CTAB/COM Nanoskeleton in aqueous media. Pore sizes (average diameters) of the Hex-ncTiO2/CTAB/TMB Nanoskeleton and Hex-ncTiO2/CTAB/TEB Nanoskeleton were enlarged up to 4.2 nm and 4.3 nm, respectively, while pore size (average diameter) of the Hex-ncTiO2/CTAB Nanoskeleton prepared in the absence of any COMs was 2.9 nm. We also revealed that thermal stability of the Hex-ncTiO2/CTAB/TMB Nanoskeleton became higher than that of Hex-ncTiO2/CTAB Nanoskeleton. The hexagonally pore-structure of the Hex-ncTiO2/CTAB/TMB Nanoskeleton was retained up to 400 °C, while the hexagonally pore-structure of the Hex-ncTiO2/CTAB Nanoskeleton was kept up to 300 °C.
Study of radiation conditions onboard the International space station by means of the Liulin-5 dosimeter
For estimating radiation risk in space flights it is necessary to determine radiation dose obtained by critical organs of a human body. For this purpose the experiments with human body models are carried out onboard spacecraft. These models represent phantoms equipped with passive and active radiation detectors which measure dose distributions at places of location of critical organs. The dosimetric Liulin-5 telescope is manufactured with using three silicon detectors for studying radiation conditions in the spherical tissue-equivalent phantom on the Russian segment of the International space station (ISS). The purpose of the experiment with Liulin-5 instrument is to study dynamics of the dose rate and particle flux in the phantom, as well as variations of radiation conditions on the ISS over long time intervals depending on a phase of the solar activity cycle, orbital parameters, and presence of solar energetic particles. The Liulin-5 dosimeter measures simultaneously the dose rate and fluxes of charged particles at three depths in the radial channel of the phantom, as well as the linear energy transfer. The paper presents the results of measurements of dose rate and particle fluxes caused by various radiation field components on the ISS during the period from June 2007 till December 2009.
Astronaut's organ doses inferred from measurements in a human phantom outside the international space station
Space radiation hazards are recognized as a key concern for human space flight. For long-term interplanetary missions, they constitute a potentially limiting factor since current protection limits for low-Earth orbit missions may be approached or even exceeded. In such a situation, an accurate risk assessment requires knowledge of equivalent doses in critical radiosensitive organs rather than only skin doses or ambient doses from area monitoring. To achieve this, the MATROSHKA experiment uses a human phantom torso equipped with dedicated detector systems. We measured for the first time the doses from the diverse components of ionizing space radiation at the surface and at different locations inside the phantom positioned outside the International Space Station, thereby simulating an extravehicular activity of an astronaut. The relationships between the skin and organ absorbed doses obtained in such an exposure show a steep gradient between the doses in the uppermost layer of the skin and the deep organs with a ratio close to 20. This decrease due to the body self-shielding and a concomitant increase of the radiation quality factor by 1.7 highlight the complexities of an adequate dosimetry of space radiation. The depth-dose distributions established by MATROSHKA serve as benchmarks for space radiation models and radiation transport calculations that are needed for mission planning.
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.
Colloidal silica gels are shown to stiffen with time, as demonstrated by both dynamic light scattering and bulk rheological measurements. Their elastic moduli increase as a power law with time, independent of particle volume fraction; however, static light scattering indicates that there are no large-scale structural changes. We propose that increases in local elasticity arising from bonding between neighboring colloidal particles can account for the strengthening of the network, while preserving network structure.
Interim Results from the Capillary Flow Experiment Aboard ISS: The Moving Contact Line Boundary Condition
This paper highlight the in-flight operations of the Capillary Flow Experiment Contact Line experiments (2 each) performed aboard the International Space Station (ISS) during the period between Increment 9 ad 13 (8/2004-9/2006). The CFE-CL vessels are simple fluid interface experiments that probe the uncertain impact of the boundary condition at the contact line – the region where liquid, gas, and solid meet. This region controls perhaps the most significant static and dynamic characteristics of the large length scale capillary phenomena critical to most multiphase fluid management systems aboard spacecraft. Difference in fluid behavior of nearly identical statics interfaces to nearly identical disturbances are attributed to differences in fluid physics in the vicinity of the contact line. The CFE-CL experiments are conducted on five occasions by ISS Astronauts M. Fincke, W. McArthur, and J. Williams. The number of tests performed including additional science experiments is made possible by various centrifuge techniques employed by the astronauts permitting the re-use of the once-wetted container. Several of these ‘extra science’ experiments are briefly described herein. Intermittent real-time video and audio downlink, continuous communication with the ground crews at NASA JSC, MSGFC and GRC, and the clear and entreating commentary of the crew made the conduct of the tests on ISS an enjoyable, laboratory-like experience for the science on the ground. The flight tapes from the onboard cameras have been results to Earth (name flight) and are expected to be digitized, reduced and made publically available in the near future. A concurrent blind numerical analysis is underway to predict the experiments result using a generally accepted CFD-tool with specific contact line boundary conditions.
This paper serves as a first presentation of quantitative data reduced from the Capillary Flow Contact Line Experiments recently completed aboard the International Space Station during Expeditions 9-16, 8/2004-11/2007. The simple fluid interface experiments probe the uncertain impact of the boundary condition at the contact line—the region where liquid, gas, and solid meet. This region controls perhaps the most significant static and dynamic characteristics of the large length scale capillary phenomena critical to most multiphase fluids management systems aboard spacecraft. Differences in fluid behavior of nearly identical static interfaces to nearly identical perturbations are attributed primarily to differences in fluid physics in the vicinity of the contact line. Free and pinned contact lines, large and small contact angles, and linear and nonlinear perturbations are tested for a variety of perturba- tion types (i.e. axial, slosh, and other modes) to right circular cylinders. The video and digi- tized datasets are to be made publicly available for model benchmarking. In parallel with the experimental effort, blind numerical predictions of the dynamic interface response to the experimentally applied input perturbations are offered as a demonstration of current capa- bilities to predict such phenomena. The agreement and lack of agreement between the experiments and numerics is our best guide to improve and/or verify current analytical methods to predict such phenomena critical to spacecraft fluid systems design.
Everybody is familiar with the action of gravity on a fluid where density gradients are present due to heating or compositional difference. Due to buoyancy, the denser portions sink to the bottom of the container, pushing away the lighter ones. As a result, convection sets in, transporting heat and mass. In weightlessness conditions, this driving force is absent but inertia exists as the tendency of a body to resist acceleration. When a container filled with liquid is subjected to high frequency vibrations, the fluid is not able to react due to inertia and this may create a flow. If the density is uniform, then the fluid moves as a solid body. However, when density gradient is present, also inertia will not be uniform, resulting in convective motion. Obviously, there is analogy between gravity-induced and inertia-driven convection, as a result of the Einstein equivalence principle, although the second one is almost unknown. What would be the impact of vibration on dispersion by molecular diffusion and heat transfer without buoyancy?