Earth–Moon libration point orbit stationkeeping: Theory,modeling, and operations

Collinear Earth–Moon libration points have emerged as locations with immediate applications. These libration point orbits are inherently unstable and must be maintained regularly which constrains operations and maneuver locations. Stationkeeping is challenging due to relatively short time scales for divergence, effects of large orbital eccentricity of the secondary body, and third-body perturbations. Using the Acceleration Reconnection and Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) mission orbit as a platform, the fundamental behavior of the trajectories is explored using Poincaré maps in the circular restricted three-body problem. Operational stationkeeping results obtained using the Optimal Continuation Strategy are presented and compared to orbit stability information generated from mode analysis based in dynamical systems theory.     

Dual-Task Interference in Spatial Reorientation: Linguistic and Nonlinguistic Factors

Abstract

Language has been proposed as a medium that serves to promote spatial orientation through integrating geometric and featural information (Spelke, 2003 Spelke, E. S. 2003. “What makes us smart? Core knowledge and natural language”. In Language in mind: Advances in the study of language and thought, Edited by: Gentner, D. and Goldin-Meadow, S. 277–312. Cambridge, MA: MIT Press..  [Google Scholar]). This proposal has been explored in dual-task experiments where linguistic resources are blocked by verbal shadowing. Although some studies report disruption in using environmental cues for spatial reorientation, findings have not been consistently replicated, and the source of disruption to reorientation by verbal shadowing remains unclear. We examined conditions under which verbal shadowing affects reorientation. Shadowing of meaningful language disrupted healthy adults' use of geometric and featural information to reorient only when task instructions were unclear and when extraneous visual information provided a source of nonlinguistic interference. Reorientation was examined during the shadowing of meaningful prose or nonword syllables and was similar under both concurrent task conditions. These results indicate that language is not necessary for spatial cue integration.     

Categorical Bias in Line Angle Judgments: Sex Differences and the Use of Multiple Categories

According to the Category Adjustment (CA) model, spatial estimates (e.g., of location) involve Bayesian combination across multiple, hierarchical pieces information, each weighted by its relative certainty. Recent work, though, has shown that men and women differ in terms of their certainty regarding fine-grained and categorical information in location memory. Here we demonstrate that this reflects a more general sex difference in visuospatial processing by examining bias patterns in a line angle judgment task (JLAP-15). In addition, the data suggest that multiple, hierarchical levels of categorical information influenced spatial judgments. These results imply that the hierarchical combination outlined by the CA model extends beyond two levels, and that men and women apply differential weighting to these representations.     

Structural health management technologies for inflatable/deployable structures: Integrating sensing and self-healing

Inflatable/deployable structures are under consideration as habitats for future Lunar surface science operations. The use of non-traditional structural materials combined with the need to maintain a safe working environment for extended periods in a harsh environment has led to the consideration of an integrated structural health management system for future habitats, to ensure their integrity. This article describes recent efforts to develop prototype sensing technologies and new self-healing materials that address the unique requirements of habitats comprised mainly of soft goods. A new approach to detecting impact damage is discussed, using addressable flexible capacitive sensing elements and thin film electronics in a matrixed array. Also, the use of passive wireless sensor tags for distributed sensing is discussed, wherein the need for on-board power through batteries or hardwired interconnects is eliminated. Finally, the development of a novel, microencapuslated self-healing elastomer with applications for inflatable/deployable habitats is reviewed.     

Order out of Randomness: Self-Organization Processes in Astrophysics

Self-organization is a property of dissipative nonlinear processes that are governed by a global driving force and a local positive feedback mechanism, which creates regular geometric and/or temporal patterns, and decreases the entropy locally, in contrast to random processes. Here we investigate for the first time a comprehensive number of (17) self-organization processes that operate in planetary physics, solar physics, stellar physics, galactic physics, and cosmology. Self-organizing systems create spontaneous “order out of randomness”, during the evolution from an initially disordered system to an ordered quasi-stationary system, mostly by quasi-periodic limit-cycle dynamics, but also by harmonic (mechanical or gyromagnetic) resonances. The global driving force can be due to gravity, electromagnetic forces, mechanical forces (e.g., rotation or differential rotation), thermal pressure, or acceleration of nonthermal particles, while the positive feedback mechanism is often an instability, such as the magneto-rotational (Balbus-Hawley) instability, the convective (Rayleigh-Bénard) instability, turbulence, vortex attraction, magnetic reconnection, plasma condensation, or a loss-cone instability. Physical models of astrophysical self-organization processes require hydrodynamic, magneto-hydrodynamic (MHD), plasma, or N-body simulations. Analytical formulations of self-organizing systems generally involve coupled differential equations with limit-cycle solutions of the Lotka-Volterra or Hopf-bifurcation type.     

Thick galactic cosmic radiation shielding using atmospheric data

NASA is concerned with protecting astronauts from the effects of galactic cosmic radiation and has expended substantial effort in the development of computer models to predict the shielding obtained from various materials. However, these models were only developed for shields up to about 120 g/cm² in mass thickness and have predicted that shields of this mass thickness are insufficient to provide adequate protection for extended deep space flights. Consequently, effort is underway to extend the range of these models to thicker shields and experimental data is required to help confirm the resulting code. In this paper empirically obtained effective dose measurements from aircraft flights in the atmosphere are used to obtain the radiation shielding function of the Earth's atmosphere, a very thick, i.e. high mass, shield. Obtaining this result required solving an inverse problem and the method for solving it is presented. The results are shown to be in agreement with current code in the ranges where they overlap. These results are then checked and used to predict the radiation dosage under thick shields such as planetary regolith and the atmosphere of Venus.     

On the conditions for fluidisation in cometary mantles

In our current understanding, active cometary nuclei comprise a volatile-depleted outer crust covering a mixture of dust and ices. During each perihelion passage the thermal wave penetrates the crust and sublimates a portion of these ices, which then escape the nucleus, dragging with them dust particles that replenish the coma and dust tail. The flux of released gases is likely to vary as a complex function of solar distance, nucleus structure, spin rate, etc. It has been previously hypothesised that at some point a fluidised state could occur, in which the gas drag is approximately equal to the weight of overlying dust and ice grains. This state is well understood and used in industrial processes where extensive mixing of the gas and solid components is desired. The literature on fluidisation under reduced gravity and pressure conditions is here reviewed and published relations used to predict the conditions under which fluidisation could occur in the near-surface of a cometary nucleus.     

Stable Isotope Ratios as a Biomarker on Mars

As both Earth and Mars have had similar environmental conditions at least for some extended time early in their history (Jakosky and Phillips in Nature 412:237–244, 2001), the intriguing question arises whether life originated and evolved on Mars as it did on Earth (McKay and Stoker in Rev. Geophys. 27:189–214, 1989). Conceivably, early autotrophic life on Mars, like early life on Earth, used irreversible enzymatically enhanced metabolic processes that would have fractionated stable isotopes of the elements C, N, S, and Fe. Several important assumptions are made when such isotope fractionations are used as a biomarker. The purpose of this article is two-fold: (1) to discuss these assumptions for the case of carbon and to summarize new insights in abiologic reactions, and (2) to discuss the use of other stable isotope systems as a potential biomarker. It is concluded that isotopic biomarker studies on Mars will encounter several important obstacles. In the case of carbon isotopes, the most important obstacle is the absence of a contemporary abiologic carbon reservoir (such as carbonate deposits on Earth) to act as isotopic standard. The presence of a contemporary abiologic sulfate reservoir (evaporite deposits) suggests that sulfur isotopes can be used as a potential biomarker for sulfate-reducing bacteria. The best approach for tracing ancient life on Mars will be to combine several biomarker approaches; to search for complexity, and to combine small-scale isotopic variations with chemical, mineralogical, and morphological observations. An example of such a study can be a layer-specific correlation between δ ¹³C and δ ³⁴S within an ancient Martian evaporite, which morphologically resembles the typical setting of a shallow marine microbial mat.     

Plasmaspheric Density Structures and Dynamics: Properties Observed by the CLUSTER and IMAGE Missions

Plasmaspheric density structures have been studied since the discovery of the plasmasphere in the late 1950s. But the advent of the Cluster and Image missions in 2000 has added substantially to our knowledge of density structures, thanks to the new capabilities of those missions: global imaging with Image and four-point in situ measurements with Cluster. The study of plasma sources and losses has given new results on refilling rates and erosion processes. Two-dimensional density images of the plasmasphere have been obtained. The spatial gradient of plasmaspheric density has been computed. The ratios between H⁺, He⁺ and O⁺ have been deduced from different ion measurements. Plasmaspheric plumes have been studied in detail with new tools, which provide information on their morphology, dynamics and occurrence. Density structures at smaller scales have been revealed with those missions, structures that could not be clearly distinguished before the global images from Image and the four-point measurements by Cluster became available. New terms have been given to these structures, like “shoulders”, “channels”, “fingers” and “crenulations”. This paper reviews the most relevant new results about the plasmaspheric plasma obtained since the start of the Cluster and Image missions.