Potential effects of optical solar sail degredation on trajectory design

The optical properties of the thin metalized polymer films that are projected for solar sails are assumed to be affected by the erosive effects of the space environment. Their degradation behavior in the real space environment, however, is to a considerable degree indefinite, because initial ground test results are controversial and relevant inspace tests have not been made so far. The standard optical solar sail models that are currently used for trajectory design do not take optical degradation into account, hence its potential effects on trajectory design have not been investigated so far. Nevertheless, optical degradation is important for high-fidelity solar sail mission design, because it decreases both the magnitude of the solar radiation pressure force acting on the sail and also the sail control authority. Therefore, we propose a simple parametric optical solar sail degradation model that describes the variation of the sail film's optical coefficients with time, depending on the sail film's environmental history, i.e., the radiation dose. The primary intention of our model is not to describe the exact behavior of specific film-coating combinations in the real space environment, but to provide a more general parametric framework for describing the general optical degradation behavior of solar sails. Using our model, the effects of different optical degradation behaviors on trajectory design are investigated for various exemplary missions

Unique Flexibility in Energy Metabolism Allows Mycobacteria to Combat Starvation and Hypoxia

Mycobacteria are a group of obligate aerobes that require oxygen for growth, but paradoxically have the ability to survive and metabolize under hypoxia. The mechanisms responsible for this metabolic plasticity are unknown. Here, we report on the adaptation of Mycobacterium smegmatis to slow growth rate and hypoxia using carbon-limited continuous culture. When M. smegmatis is switched from a 4.6 h to a 69 h doubling time at a constant oxygen saturation of 50%, the cells respond through the down regulation of respiratory chain components and the F1Fo-ATP synthase, consistent with the cells lower demand for energy at a reduced growth rate. This was paralleled by an up regulation of molecular machinery that allowed more efficient energy generation (i.e. Complex I) and the use of alternative electron donors (e.g. hydrogenases and primary dehydrogenases) to maintain the flow of reducing equivalents to the electron transport chain during conditions of severe energy limitation. A hydrogenase mutant showed a 40% reduction in growth yield highlighting the importance of this enzyme in adaptation to low energy supply. Slow growing cells at 50% oxygen saturation subjected to hypoxia (0.6% oxygen saturation) responded by switching on oxygen scavenging cytochrome bd, proton-translocating cytochrome bc1-aa3 supercomplex, another putative hydrogenase, and by substituting NAD+-dependent enzymes with ferredoxin-dependent enzymes thus highlighting a new pattern of mycobacterial adaptation to hypoxia. The expression of ferredoxins and a hydrogenase provides a potential conduit for disposing of and transferring electrons in the absence of exogenous electron acceptors. The use of ferredoxin-dependent enzymes would allow the cell to maintain a high carbon flux through its central carbon metabolism independent of the NAD+/NADH ratio. These data demonstrate the remarkable metabolic plasticity of the mycobacterial cell and provide a new framework for understanding their ability to survive under low energy conditions and hypoxia

A de novo transcriptome of the Asian tiger mosquito, Aedes albopictus, to identify candidate transcripts for diapause preparation

<p>Abstract</p> <p>Background</p> <p>Many temperate insects survive the harsh conditions of winter by undergoing photoperiodic diapause, a pre-programmed developmental arrest initiated by short day lengths. Despite the well-established ecological significance of photoperiodic diapause, the molecular basis of this crucial adaptation remains largely unresolved. The Asian tiger mosquito, <it>Aedes albopictus </it>(Skuse), represents an outstanding emerging model to investigate the molecular basis of photoperiodic diapause in a well-defined ecological and evolutionary context. <it>Ae. albopictus </it>is a medically significant vector and is currently considered the most invasive mosquito in the world. Traits related to diapause appear to be important factors contributing to the rapid spread of this mosquito. To generate novel sequence information for this species, as well as to discover transcripts involved in diapause preparation, we sequenced the transcriptome of <it>Ae. albopictus </it>oocytes destined to become diapausing or non-diapausing pharate larvae.</p> <p>Results</p> <p>454 GS-FLX transcriptome sequencing yielded >1.1 million quality-filtered reads, which we assembled into 69,474 contigs (N50 = 1,009 bp). Our contig filtering approach, where we took advantage of strong sequence similarity to the fully sequenced genome of <it>Aedes aegypti</it>, as well as other reference organisms, resulted in 11,561 high-quality, conservative ESTs. Differential expression estimates based on normalized read counts revealed 57 genes with higher expression, and 257 with lower expression under diapause-inducing conditions. Analysis of expression by qPCR for 47 of these genes indicated a high correlation of expression levels between 454 sequence data and qPCR, but congruence of statistically significant differential expression was low. Seven genes identified as differentially expressed based on qPCR have putative functions that are consistent with the insect diapause syndrome; three genes have unknown function and represent novel candidates for the transcriptional basis of diapause.</p> <p>Conclusions</p> <p>Our transcriptome database provides a rich resource for the comparative genomics and functional genetics of <it>Ae. albopictus</it>, an invasive and medically important mosquito. Additionally, the identification of differentially expressed transcripts related to diapause enriches the limited knowledge base for the molecular basis of insect diapause, in particular for the preparatory stage. Finally, our analysis illustrates a useful approach that draws from a closely related reference genome to generate high-confidence ESTs in a non-model organism.</p

Places Only Sails Can Go

Solar sails are a near term, low thrust, propellantless propulsion technology suitable for orbital maneuvering, station keeping, and attitude control applications for small payloads. Furthermore, these functions can be highly integrated, reducing mass, cost and complexity. The solar sail concept is based on momentum exchange with solar flux reflected from a large, deployed thin membrane. Thrust performance increases as the square of the distance to the sun. In comparison to conventional chemical systems, there are missions where solar sails are vastly more and less economical. The less attractive applications involve large payloads, outer solar system transfers, and short trip times. However, for inclination changes and station keeping at locations requiring constant thrust, the solar sail is the only economical option for missions of more than a few weeks duration. We compare the location and energies required for these applications between solar sails, advanced electric propulsion, and conventional rockets. We address the effect on mass fraction to understand solar sail mission cost and capability. Finally, the benefit of potential applications to near term science missions is reported

Obstructive Lung Disease and Exposure to Burning Biomass Fuel in the Indoor Environment

It is estimated that up to half of the world's population burns biomass fuel (wood, crop residues, animal dung and coal) for indoor uses such as cooking, lighting and heating. As a result, a large proportion of women and children are exposed to high levels of household air pollution (HAP). The short and long term effects of these exposures on the respiratory health of this population are not clearly understood. On May 9-11, 2011 NIH held an international workshop on the "Health Burden of Indoor Air Pollution on Women and Children," in Arlington, VA. To gather information on the knowledge base on this topic and identify research gaps, ahead of the meeting we conducted a literature search using PubMed to identify publications that related to HAP, asthma, and chronic obstructive pulmonary disease (COPD). Abstracts were all analyzed and we report on those considered by the respiratory sub study group at the meeting to be most relevant to the field. Many of the studies published are symptom-based studies (as opposed to objective measures of lung function or clinical examination etc.) and measurement of HAP was not done. Many found some association between indoor exposures to biomass smoke as assessed by stove type (e.g., open fire vs. liquid propane gas) and respiratory symptoms such as wheeze and cough. Among the studies that examined objective measures (e.g. spirometry) as a health outcome, the data supporting an association between biomass smoke exposure and COPD in adult women are fairly robust, but the findings for asthma are mixed. If an association was observed between the exposures and lung function, most data seemed to demonstrate mild to moderate reductions in lung function, the pathophysiological mechanisms of which need to be investigated. In the end, the group identified a series of scientific gaps and opportunities for research that need to be addressed to better understand the respiratory effects of exposure to indoor burning of the different forms of biomass fuels