The gravitational field and brain function.

The frontal cortex is recognized as the highest adaptive control center of the human brain. The principle of the "frontalization" of human brain function offers new possibilities for brain research in space. There is evolutionary and experimental evidence indicating the validity of the principle, including it's role in nervous response to gravitational stimulation. The gravitational field is considered here as one of the more constant and comprehensive factors acting on brain evolution, which has undergone some successive crucial steps: "encephalization", "corticalization", "lateralization" and "frontalization". The dominating effects of electrical responses from the frontal cortex have been discovered 1) in experiments under gravitational stimulus; and 2) in processes potentially relating to gravitational adaptation, such as memory and learning, sensory information processing, motor programing, and brain state control. A brain research experiment during space flight is suggested to test the role of the frontal cortex in space adaptation and it's potentiality in brain control.     

Understanding the organization of the amphibian egg cytoplasm: gravitational force as a probe.

A combination of hypergravity (centrifugation) and hypogravity (clinostat) studies have been carried out on amphibian (frog, Xenopus) eggs. The results reveal that the twinning caused by centrifugation exhibits substantial spawning to spawning variation. That variation can be attributed to the apparent viscosity of the egg's internal cytoplasm. Simulated hypogravity results in a relocation of the egg's third (horizontal) cleavage furrow, towards the equator. Substantial egg-to-egg variation is also observed in this "cleavage effect". For interpreting spaceflight data and for using G-forces as probes for understanding the egg's architecture the egg variation documented herein should be considered.     

Physiological, biochemical and molecular processes associated with gravitropism in roots of maize.

This research aims to characterize regulation of the principal cytosolic protein kinases in maize, cultivar 'Merit' root tips, since much evidence indicates that stimuli which modulate the gravitropic response in this system act through regulation of activity of these enzymes. To this end, we have cloned a maize protein kinase belonging to a group of plant protein kinases with a catalytic domain similar in primary structure to the second messenger-regulated protein kinases known in animal and fungal systems. However, both the unique structural features conserved among plant protein kinases in this group, and lack of evidence for cyclic nucleotide signalling in plants point to operation of a novel protein kinase regulatory mechanism in plants. In order to test effects of possible regulators on protein kinase activity, we developed a sensitive method for detecting regulation of autophosphoryl labelling of protein kinases in unfractionated maize protein extracts. Regulation of protein kinase autophosphorylation in these extracts was different from that known in animals and fungi, further suggesting operation of unique protein kinase regulatory mechanisms in plants. Previous research has shown that light, or factors modulated by light, regulate plant protein kinase activity. We found that protein kinase activity was co-immunoprecipitated with the plant photoreceptor phytochrome, and was associated with phytochrome by high-affinity chemical interactions. Far-red reversibility of red-light regulation of phytochrome phosphorylation by the associated protein kinase indicates that it may modulate or transduce the light signals which lead to gravitropic sensitivity in 'Merit' maize.     

Effect of current sheets on the power spectrum of the solar wind magnetic field using a cell model

A puzzling observation of solar wind MHD turbulence is the often seen Kolmogorov scaling of k^-5/3$k^{-5/3}$, even though the solar wind MHD turbulence is dominated by Alfvénic fluctuations. Recently Li et al. (2011) proposed that the presence of current sheets may be the cause of the Kolmogorov scaling. Here, using a cell model of the solar wind we examine the effect of current sheets on the power spectrum of the solar wind magnetic field. We model the solar wind as multiple cells separated by current sheets. We prescribe the spectra of turbulent magnetic field in individual cells as IK-like and examine the spectra along trajectories that cross multiple boundaries. We find that these spectra become softer and are consistent with the Kolmogorov-scaling. Our finding supports our recent proposal of Li et al. (2011).     

Solar-proton polar-cap intensity structures as a test of magnetic field models

The entry of energetic solar protons to the polar caps offers an interesting way to test models of the geomagnetic field. In this brief report, we present a comparison between SAMPEX observations of solar-particle intensity structure during a polar cap traversal with numerical trajectory calculations using the IGRF + T96 field model.     

Subcellular components of the amphibian egg: insights provided by gravitational studies.

Most cytoplasmic regions of fertilized amphibian eggs move with respect to the gravity vector in experimentally gravity oriented eggs. The pattern and extent of this movement varies among different batches of eggs. This variation in apparent cytoplasmic viscosity (or, conversely, cytoplasmic mobility) can be correlated with variations in subsequent morphogenesis of experimental, gravitationally manipulated eggs. Therefore, the proper interpretation of gravity experiments with amphibian eggs requires that one understand the subcellular basis for this variation on cytoplasmic mobility. Variation in the packing of the major cytoplasmic organelle, the yolk platelets, or the organization and amount of cytoskeletal components may explain the variation in cytoplasmic mobility. Evidence is presented that the variation in yolk volume density (fraction of total cytoplasmic volume occupied by yolk platelets) does not account for the variation in cytoplasmic mobility in Xenopus laevis eggs. Experimental evidence from cold-shocked inverted eggs indicates that microtubules may be involved in determining cytoplasmic mobility. However, quantitative evidence that the microtubule levels and state of the microtubules (polymerized vs. non-polymerized) in the whole Xenopus laevis egg does not correlate directly with cytoplasmic mobility is presented. The apparent conflict these data represent regarding the role of the cytoskeleton in determining cytoplasmic mobility is discussed.     

Transport phenomena and crystal growth of the GeSe-Xenon system for different gravitational conditions

Previous chemical vapor transport experiments of the GeSe-GeI₄ system performed under reduced gravity conditions /1/ yielded crystals of considerably improved surface and bulk morphology. In addition, the mass transport rates observed in microgravity environment were significantly greater than predicted. A quantitative thermodynamic analysis of the solid-gas phase reactions of the GeSe-GeI₄ system revealed the multi-component, multi-reaction nature of the vapor phase /2/. Continued transport studies on ground of the GeSe-GeI₄ system in the presence of inert gases provided experimental evidence for the existence of a boundary layer /2/ and its thickness dependence on GeI₄ pressure in closed tube systems. Systematic transport rate measurements for different orientations of the density gradient relative to the gravity vector demonstrated the effects of ampoule inclination on mass flux /3/. Based on a computational model for simultaneous chemical vapor transport, sublimation, and Stefan flow /3/, the excellent agreement of predicted with ground-based experimental mass transport rates over wide pressure ranges /3/ confirmed the validity of the model and the discrepancy between observed and expected transport rates of the GeSe-GeI₄ system in microgravity.     

On the parameterization of the biological effect in a mixed radiation field.

The exposure of astronauts and electronics to the cosmic radiation especially to the particle component pose a major risk to all space flights. Up to now it is not possible to quantify this risk within acceptable limits of accuracy. This uncertainty is not only caused by difficulties in the more or less exact prediction of the incidence of the cosmic radiation but depends also on the problem of the quantification of the radiation field and the correlation of the biological effect. Usually the biological action of a mixed radiation field is estimated as product of the measured dose with an average quality factor, the relative biological efficiency. Because of the large variation in energy and atomic number of the cosmic particles, average values of the quality factor are not precise for risk estimation. A more appropriate way to treat the biological effects of mixed radiation is the concept of particle fluence and action cross section.     

Crustaceans as a model for microgravity-induced muscle atrophy.

Atrophy of skeletal muscles is a serious problem in a microgravity environment. It is hypothesized that the unloading of postural muscles, which no longer must resist gravity force, causes an accelerated breakdown of contractile proteins, resulting in a reduction in muscle mass and strength. A crustacean model using the land crab, Gecarcinus lateralis, to assess the effects of spaceflight on protein metabolism is presented. The model is compared to a developmentally-regulated atrophy in which a premolt reduction in muscle mass allows the withdrawal of the large claws at molt. The biochemical mechanisms underlying protein breakdown involves both Ca(2+)-dependent and multicatalytic proteolytic enzymes. Crustacean claw muscle can be used to determine the interactions between shortening and unloading at the molecular level.     

Modeling the effects of pitch-angle scattering processes on the transport of solar energetic particles along the interplanetary magnetic field

We present a Monte-Carlo technique to study the time-dependent transport of energetic particles in the interplanetary medium. We use the guiding center approximation between discrete finite pitch-angle scatterings to quantify the competing effects of focusing and pitch-angle scattering on energetic particles propagating along a Parker spiral magnetic field. We consider that the pitch-angle scattering process is produced by small-scale magnetic field irregularities frozen in the expanding solar wind. We also include the effects of both solar wind convection and adiabatic deceleration. We use a joint probability distribution P(h, μ′) = p(h; μ′)q(μ′; μ) to describe both the distance traveled by the particle between two scattering processes and the change in the particle pitch-angle after a scattering process. Here, p(h; μ′) is the conditional probability that the particle travels a distance h along the field line before the next scattering if it had a pitch-angle cosine μ′ after the previous scattering, and q(μ′; μ) is the conditional probability for the pitch-angle cosine μ′ if the pitch-angle cosine was μ before the scattering. We consider several functional forms to describe the processes of pitch-angle scattering, such as an isotropic scattering without any memory of the initial particle’s pitch-angle or processes in which the scattering result depends upon the initial particle’s pitch-angle. The results of our simulations are pitch-angle distributions and time-intensity profiles that can be directly compared to spacecraft observations. Comparison of our simulations with near-relativistic (45–290 keV) electron events observed by the Electron, Proton and Alpha Monitor on board the Advanced Composition Explorer allows us to estimate both the time dependence of the injection of near-relativistic electrons into the interplanetary medium and the conditions for electron propagation along the interplanetary magnetic field.     

Use of coated silicon field emitters as neutralisers for fundamental physics space missions

Spacecraft neutralisers are required as part of the ion propulsion system for accurate station keeping in fundamental physics missions. This paper describes the use of thin layers of insulating materials as coatings for the gated silicon field emitter array structure used in a spacecraft neutraliser. These thin coatings are postulated to reduce power consumption and reduce overheating. The power consumption and lifetime of aluminium nitride and amorphous hydrogenated diamond-like carbon coatings have been tested by current–voltage and endurance tests. Diamond-like carbon coatings were promising, performing better in endurance tests than uncoated samples, but further work is required to characterise the coating’s physical properties and its effects on field emission. The thermal conductivity of the coating material had little effect on measured sample lifetimes. Aluminium nitride had reduced power consumption compared to diamond-like carbon coated and uncoated samples. A thin (∼5 nm) layer of aluminium nitride was found to be optimal, meeting European Space Agency specifications for the neutraliser engineering model.     

Arthropod model systems for studying complex biological processes in the space environment.

Three arthropod systems are discussed in relation to their complementary and potential use in Space Biology. In a next biosatellite flight, Drosophila melanogaster pre-adapted during several months to different g levels will be flown in an automatic device that separates parental from first and second generations. In the same flight, flies will be exposed to microgravity conditions in an automatic unit in which fly motility can be recorded. In the International Microgravity Laboratory-2, several groups of Drosophila embryos will be grown in Space and the motility of a male fly population will be video-recorded. In the Biopan, an ESA exobiology facility that can be flown attached to the exterior of a Russian biosatellite, Artemia dormant gastrulae will be exposed to the space environment in the exterior of the satellite under a normal atmosphere or in the void. Gastrulae will be separated in hit and non-hit populations. The developmental and aging response of these animals will be studied upon recovery. With these experiments we will be able to establish whether exposure to the space environment influences arthropod development and aging, and elaborate on some of the cellular mechanisms involved which should be tested in future experiments.     

Evaluation of experiments involving the study of plant orientation and growth under different gravitational conditions.

The manifestation of gravitropic reaction in plants has been considered from the phylogenetic point of view. A chart has been suggested according to which it is supposed that the first indications of the ability to identify the direction of the gravitational vector were inherent in the most ancient eukaryotes, which gave rise to green, brown, yellow-green, golden and diatomaceous algae as well as fungi. The experiments on the role of gravity in plant ontogenesis are being continued. The sum total of the data obtained in a number of experiments in space shows that under these conditions a structurally modified but normally functioning gravireceptive apparatus is formed. The data confirming the modification, under changed gravity, of the processes of integral and cellullar growth of the axial organs of seedlings as well as of the anatomo-morphological structure and developmental rates of plants during their prolonged growth in space are presented. It is assumed that this fact testifies to the presence of systems interacting with gravity during plant ontogenesis. At the same time the necessity for further experiments in order to differentiate an immediate biological effect of gravity from the ones conditioned by it indirectly due to the changes in the behavior of liquids and gases is pointed out. The methodological aspects of biological experiments in space as the main source of reliable information on the biological role of gravity are discussed.     

Use of lunar regolith as a substrate for plant growth.

Regenerative Life Support Systems (RLSS) will be required to regenerate air, water, and wastes, and to produce food for human consumption during long-duration missions to the Moon and Mars. It may be possible to supplement some of the materials needed for a lunar RLSS from resources on the Moon. Natural materials at the lunar surface may be used for a variety of lunar RLSS needs, including (i) soils or solid-support substrates for plant growth, (ii) sources for extraction of essential, plant-growth nutrients, (iii) substrates for microbial populations in the degradation of wastes, (iv) sources of O2 and H2, which may be used to manufacture water, (v) feed stock materials for the synthesis of useful minerals (e.g., molecular sieves), and (vi) shielding materials surrounding the outpost structure to protect humans, plants, and microorganisms from harmful radiation. Use of indigenous lunar regolith as a terrestrial-like soil for plant growth could offer a solid support substrate, buffering capacity, nutrient source/storage/retention capabilities, and should be relatively easy to maintain. The lunar regolith could, with a suitable microbial population, play a role in waste renovation; much like terrestrial waste application directly on soils. Issues associated with potentially toxic elements, pH, nutrient availability, air and fluid movement parameters, and cation exchange capacity of lunar regolith need to be addressed before lunar materials can be used effectively as soils for plant growth.     

Hierarchical Bayesian modeling of ionospheric TEC disturbances as non-stationary processes

We model regular and irregular variation of ionospheric total electron content as stationary and non-stationary processes, respectively. We apply the method developed to SCINDA GPS data set observed at Bahir Dar, Ethiopia $\left(11.6°\text{N,}37.4°\text{E}\right)$. We use hierarchical Bayesian inversion with Gaussian Markov random process priors, and we model the prior parameters in the hyperprior. We use Matérn priors via stochastic partial differential equations, and use scaled $\text{Inv}-{\chi }^2$ hyperpriors for the hyperparameters. For drawing posterior estimates, we use Markov Chain Monte Carlo methods: Gibbs sampling and Metropolis-within-Gibbs for parameter and hyperparameter estimations, respectively. This allows us to quantify model parameter estimation uncertainties as well. We demonstrate the applicability of the method proposed using a synthetic test case. Finally, we apply the method to real GPS data set, which we decompose to regular and irregular variation components. The result shows that the approach can be used as an accurate ionospheric disturbance characterization technique that quantifies the total electron content variability with corresponding error uncertainties.     

The determination for ideal release point of test masses in drag-free satellites for the detection of gravitational waves

Gravitational waves are ripples in space–time predicted by Albert Einstein's general relativity and provide a new way to understand the universe. Space-borne detectors of gravitational waves, extending to very large scales, can effectively detect the middle and low-frequency gravitational wave source with the frequency band of 0.1 mHz–1 Hz. The test masses are used to make an inertial reference point in the detection of gravitational waves. Currently, there are few studies concerning the ideal release position for the test masses in the detection of gravitational waves. In this study, we give a general solution for test mass release points to minimize the relative motion between the test mass and the satellite mass center. Moreover, we discuss the situation when the release point equation is not satisfied, and the ideal release point of the along-track. Finally, we report on simulations that verify the accuracy of the theoretical derivation.     

The Rhesus monkey as a model for testing the immunological effects of space flight.

The Rhesus monkey has been proposed as a model for the effects of space flight on immunity. In order to determine the feasibility of the use of the Rhesus monkey as a model, we studied the use of Rhesus monkey cells for immunological procedures that have been shown to be affected by space flight in both rodents and humans. We have shown that both lymph node cells and peripheral blood leukocytes can be stained with monoclonal antibodies to detect the following surface markers: CD4, CD-8, Ia and surface immunoglobulin. Also, the level of Ia antigen expression was increased by treatment of the cells with human interferon-gamma. In addition, cells were induced to produce interferons and interleukins. Isolated neutrophils also demonstrated increased oxidative burst. These data indicate that the Rhesus monkey will be a useful model for space flight studies of immunity.     

Necessary conditions for the optimality of singular arcs of spacecraft trajectories subject to multiple gravitational bodies

This document analyzes the optimality of intermediate thrust arcs (singular arcs) of spacecraft trajectories subject to multiple gravitational bodies. A series of necessary conditions for optimality are formally derived, including the generalized Legendre–Clebsch condition. As the order of singular optimality turns out to be two, an explicit formula for the singular optimal control is also presented. These analytical outcomes are validated by showing that they are identical to Lawden’s classical result if the equations of motion are reduced for a central gravity field. Practical utility is demonstrated by applying these analytical derivations to a candidate optimal trajectory near the Moon subject to solar and Earth perturbation. While the candidate optimal trajectory turns out to be bang-singular-bang, the intermediate thrust arc satisfies all the necessary conditions for optimality.     

Phosphorus as a potential guide in the search for extinct life on Mars.

In contrast to the search for extant organisms, the quest for fossil remains of life on Mars need not be guided by the presence of water and organic compounds on the present surface. An appropriate tracer might be the element phosphorus which is a common constituent of living systems. Utilizing terrestrial analogues, it should preferentially exist in the form of sedimentary calcium phosphate (phosphorites), which would have readily resisted changing conditions on Mars. Moreover, higher ratios of P/Th in phosphorites in comparison to calcium phosphates from magmatic rocks give us the possibility to distinguish them from inorganically formed phosphorus deposits at or close to the Martian surface. Identification of anomalous phosphorus enrichments by remote sensing or in situ analysis could be promising approaches for selecting areas preferentially composed of rocks with remains of extinct life.     

Adaptation of the macular vestibuloocular reflex to altered gravitational conditions in a fish (Oreochromis mossambicus).

Young fish (Oreochromis mossambicus) were exposed to microgravity (micro g) for 9 to 10 days, or to hypergravity (hg) for 9 days. For several weeks after termination of micro g and hg, the roll-induced static vestibuloocular reflex (rVOR) was recorded. In stage 11/12-fish, the rVOR amplitude (angle between the maximal up and down movement of an eye during a complete 360 degree lateral roll) of micro g-animals increased significantly by 25% compared to 1 g-controls during the first post-flight week but decreased to the control level during the second post-flight week. Microgravity had no effect in stage 14/16 fish on the rVOR amplitude. After 3 g-exposure, the rVOR amplitude was significantly reduced for both groups compared to their 1 g-controls. Readaptation to 1 g-condition was completed during the second post-3 g week. We postulate a critical period during which the development of the macular vestibuloocular reflex depends on gravitational input, and which is limited by the first appearance of the rVOR. At this period of early development, exposure to microgravity sensitizes the vestibular system while hypergravity desensitizes it.