Group force mobility model and its obstacle avoidance capability

Many mobility models attempt to provide realistic simulation to many real world scenarios. However, existing mobility models, such as RPGM [X. Hong, M. Gerla, G. Pei, C. Chiang, A group mobility model for ad hoc wireless networks, in: Proceedings of ACM/IEEE MSWiM’99, Seattle, WA, August 1999, pp. 53–60] and others, fail to address many aspects. These limitations range from mobile node (MN) collision avoidance, obstacle avoidance, and the interaction of MNs within a group. Our research, the group force mobility model (GFMM) [S.A. Williams, D. Huang, A group force mobility model, Appeared at 9th Communications and Networking Simulation Symposium, April 2006], proposes a novel idea which introduces the concept of attraction and repulsion forces to address many of these limitations. Williams and Huang [A group force mobility model, Appeared at 9th Communications and Networking Simulation Symposium, April 2006] described some of the limitations and drawbacks that many models neglect. This model effectively simulates the interaction of MNs within a group, the interaction of groups to one another, the coherency of a group, and the avoidance of collision with groups, nodes, and obstacles. This paper provides an overview of GFMM and particularly illustrates the GFMM's ability to avoid collision with obstacles, which is a vital property to posses in order to provide a realistic simulaition. We compare our model with the commonly used RPGM model and provide statistical assessments based on connectivity metrics such as link changed, link duration, and relative speed. All will be detailed and explained in this paper.     

The NASA Astrobiology Roadmap

The NASA Astrobiology Roadmap provides guidance for research and technology development across the NASA enterprises that encompass the space, Earth, and biological sciences. The ongoing development of astrobiology roadmaps embodies the contributions of diverse scientists and technologists from government, universities, and private institutions. The Roadmap addresses three basic questions: how does life begin and evolve, does life exist elsewhere in the universe, and what is the future of life on Earth and beyond? Seven Science Goals outline the following key domains of investigation: understanding the nature and distribution of habitable environments in the universe, exploring for habitable environments and life in our own Solar System, understanding the emergence of life, determining how early life on Earth interacted and evolved with its changing environment, understanding the evolutionary mechanisms and environmental limits of life, determining the principles that will shape life in the future, and recognizing signatures of life on other worlds and on early Earth. For each of these goals, Science Objectives outline more specific high priority efforts for the next three to five years. These eighteen objectives are being integrated with NASA strategic planning.     

Improving magnetosphere in situ observations using solar sails

Past and current magnetosphere missions employ conventional spacecraft formations for in situ observations of the geomagnetic tail. Conventional spacecraft flying in inertially fixed Keplerian orbits are only aligned with the geomagnetic tail once per year, since the geomagnetic tail is always aligned with the Earth-Sun line, and therefore, rotates annually. Solar sails are able to artificially create sun-synchronous orbits such that the orbit apse line remains aligned with the geomagnetic tail line throughout the entire year. This continuous presence in the geomagnetic tail can significantly increase the science phase for magnetosphere missions. In this paper, the problem of solar sail formation design is explored using nonlinear programming to design optimal two-craft, triangle, and tetrahedron solar sail formations, in terms of formation quality and formation stability. The designed formations are directly compared to the formations used in NASA’s Magnetospheric Multi-Scale mission.     

The challenges in long-term altimetry calibration for addressing the problem of global sea level change

Long-term change of the global sea level resulting from climate change has become an issue of great societal interest. The advent of the technology of satellite altimetry has modernized the study of sea level on both global and regional scales. In combination with in situ observations of the ocean density and space observations of Earth’s gravity variations, satellite altimetry has become an essential component of a global observing system for monitoring and understanding sea level change. The challenge of making sea level measurements with sufficient accuracy to discern long-term trends and allow the patterns of natural variability to be distinguished from those linked to anthropogenic forcing rests largely on the long-term efforts of altimeter calibration and validation. The issues of long-term calibration for the various components of the altimeter measurement system are reviewed in the paper. The topics include radar altimetry, the effects of tropospheric water vapor, orbit determination, gravity field, tide gauges, and the terrestrial reference frame. The necessity for maintaining a complete calibration effort and the challenges of sustaining it into the future are discussed.     

Iris recognition technology

IriScan Inc. has been developing an identification/verification system capable of positively identifying and verifying the identity of individuals without physical contact or human intervention. A new technology, using the unique patterns of the human iris, shows promise of overcoming previous shortcomings and providing positive identification of an individual without contact or invasion, at extremely high confidence levels. The video-based system locates the eye and iris; evaluates the degree of occlusion by eyelid and spectral reflection; determines the quality of image focus; and determines the center and boundary of the pupil and the limbus (outer edge of the iris) for processing. The iris is zoned, and the features therein measured and encoded into a 256-byte (2048 bit) IrisCode for enrollment or identification. The presented biometric is compared to an extensive database for identification, or to a referenced IrisCode for verification. Computations and decisions are accomplished at extremely high rates of speed, resulting in processing times of less than two seconds. The process is based on the unique nature and extreme richness of the human iris. The multiple features produce a non-duplicable organ with more than 400 degrees of freedom, or measurable variables. The IriScan process typically uses about 200 of these to create a code which can be compared to an entire database in milliseconds, producing a positive identification with “imposter odds” as high as 1 in 10³⁴     

The O/OREOS mission: first science data from the Space Environment Survivability of Living Organisms (SESLO) payload

We report the first telemetered spaceflight science results from the orbiting Space Environment Survivability of Living Organisms (SESLO) experiment, executed by one of the two 10?cm cube-format payloads aboard the 5.5?kg Organism/Organic Exposure to Orbital Stresses (O/OREOS) free-flying nanosatellite. The O/OREOS spacecraft was launched successfully to a 72° inclination, 650?km Earth orbit on 19 November 2010. This satellite provides access to the radiation environment of space in relatively weak regions of Earth's protective magnetosphere as it passes close to the north and south magnetic poles; the total dose rate is about 15 times that in the orbit of the International Space Station. The SESLO experiment measures the long-term survival, germination, and growth responses, including metabolic activity, of Bacillus subtilis spores exposed to the microgravity, ionizing radiation, and heavy-ion bombardment of its high-inclination orbit. Six microwells containing wild-type (168) and six more containing radiation-sensitive mutant (WN1087) strains of dried B. subtilis spores were rehydrated with nutrient medium after 14 days in space to allow the spores to germinate and grow. Similarly, the same distribution of organisms in a different set of microwells was rehydrated with nutrient medium after 97 days in space. The nutrient medium included the redox dye Alamar blue, which changes color in response to cellular metabolic activity. Three-color transmitted intensity measurements of all microwells were telemetered to Earth within days of each of the 48?h growth experiments. We report here on the evaluation and interpretation of these spaceflight data in comparison to delayed-synchronous laboratory ground control experiments.     

Interplanetary Origin of Intense,Superintense and Extreme Geomagnetic Storms

We present a review on the interplanetary causes of intense geomagnetic storms (Dst≤−100 nT), that occurred during solar cycle 23 (1997–2005). It was reported that the most common interplanetary structures leading to the development of intense storms were: magnetic clouds, sheath fields, sheath fields followed by a magnetic cloud and corotating interaction regions at the leading fronts of high speed streams. However, the relative importance of each of those driving structures has been shown to vary with the solar cycle phase. Superintense storms (Dst≤−250 nT) have been also studied in more detail for solar cycle 23, confirming initial studies done about their main interplanetary causes. The storms are associated with magnetic clouds and sheath fields following interplanetary shocks, although they frequently involve consecutive and complex ICME structures. Concerning extreme storms (Dst≤−400 nT), due to the poor statistics of their occurrence during the space era, only some indications about their main interplanetary causes are known. For the most extreme events, we review the Carrington event and also discuss the distribution of historical and space era extreme events in the context of the sunspot and Gleissberg solar activity cycles, highlighting a discussion about the eventual occurrence of more Carrington-type storms.     

The Dawn Spacecraft

The Dawn spacecraft is designed to travel to and operate in orbit around the two largest main belt asteroids, Vesta and Ceres. Developed to meet a ten-year life and fully redundant, the spacecraft accommodates an ion propulsion system, including three ion engines and xenon propellant tank, utilizes large solar arrays to power the engines, carries the science instrument payload, and hosts the hardware and software required to successfully collect and transmit the scientific data back to Earth. The launch of the Dawn spacecraft in September 2007 from Cape Canaveral Air Force Station was the culmination of nearly five years of design, development, integration and testing of this unique system, one of the very few scientific spacecraft to rely on ion propulsion. The Dawn spacecraft arrived at its first destination, Vesta, in July 2011, where it will conduct science operations for twelve months before departing for Ceres.     

Optimum Power Division for Phase-Modulated Deep-Space Communications Links

Optimum power division is required in deep-space communications links to maximize transmission range or data rate and to permit efficient performance of both carrier tracking and data reception functions. A simple, graphical technique has been developed for phase-modulated links to determine the particular set of peak phase deviations, or modulation indexes, which results in an optimum power division between the carrier and any combination of sine-wave and square-wave subcarriers. Whereas previous methods for the selection of modulation indexes generally necessitated either lengthy solutions of simultaneous equations or complex computer programs, the methods developed in this paper involve simplified graphical procedures, using the trigonometric and Bessel function expressions which describe the power balance between carrier and subcarriers. The optimization procedure is a valuable tool for preliminary design analysis and should be of interest to communications-system engineers, The techniques developed here are particularly applicable when subcarriers have wide differences in data rates, since under these conditions, it becomes increasingly difficult to select arbitrarily the proper modulation indexes. Channel optimization is developed for both nominal and worst-case link conditions and examples are presented to demonstrate the techniques involved.