Understanding magnetotail current sheet meso-scale structures using MHD simulations

Recent Cluster observations have strongly supported the existence of meso-scale structure in the magnetotail current sheet. In our study, a magnetohydrodynamic simulation event study exhibited current sheet behavior comparable to that seen in the Cluster observations. Geotail and DoubleStar observations also show that the simulation is providing a realistic representation of the magnetosphere during the period of interest; that is, when the current sheet evidently becomes bifurcated. The magnetohydrodynamic simulation allows us to place the local observations into a global contest. It shows that the observations can be explained in terms of localized reconnection tailward of the Cluster location and the formation of a flux rope nearby. The simulation also features wave-like structure across the current sheet.     

Pilots for space tourism

This article sheds light on the key player needed for any space tourism adventure: the pilot who flies the spacecraft. The paper addresses the potential benefits of including a pilot at the controls when designing a space tourism spacecraft. It examines the basic qualifications and advanced skills required of space tourism pilots and discusses key training requirements for selected pilots and space pilots' pay and benefits. In addition, the research concludes that, just as the pioneers of passenger transport in aviation entertained and captured the interest of their passengers, the space pilot should have the skills of a tour guide.     

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.     

1. Transport of Mass,Momentum and Energy in Planetary Magnetodisc Regions

The rapid rotation of the gas giant planets, Jupiter and Saturn, leads to the formation of magnetodisc regions in their magnetospheric environments. In these regions, relatively cold plasma is confined towards the equatorial regions, and the magnetic field generated by the azimuthal (ring) current adds to the planetary dipole, forming radially distended field lines near the equatorial plane. The ensuing force balance in the equatorial magnetodisc is strongly influenced by centrifugal stress and by the thermal pressure of hot ion populations, whose thermal energy is large compared to the magnitude of their centrifugal potential energy. The sources of plasma for the Jovian and Kronian magnetospheres are the respective satellites Io (a volcanic moon) and Enceladus (an icy moon). The plasma produced by these sources is globally transported outwards through the respective magnetosphere, and ultimately lost from the system. One of the most studied mechanisms for this transport is flux tube interchange, a plasma instability which displaces mass but does not displace magnetic flux—an important observational constraint for any transport process. Pressure anisotropy is likely to play a role in the loss of plasma from these magnetospheres. This is especially the case for the Jovian system, which can harbour strong parallel pressures at the equatorial segments of rotating, expanding flux tubes, leading to these regions becoming unstable, blowing open and releasing their plasma. Plasma mass loss is also associated with magnetic reconnection events in the magnetotail regions. In this overview, we summarise some important observational and theoretical concepts associated with the production and transport of plasma in giant planet magnetodiscs. We begin by considering aspects of force balance in these systems, and their coupling with the ionospheres of their parent planets. We then describe the role of the interaction between neutral and ionized species, and how it determines the rate at which plasma mass and momentum are added to the magnetodisc. Following this, we describe the observational properties of plasma injections, and the consequent implications for the nature of global plasma transport and magnetodisc stability. The theory of the flux tube interchange instability is reviewed, and the influences of gravity and magnetic curvature on the instability are described. The interaction between simulated interchange plasma structures and Saturn’s moon Titan is discussed, and its relationship to observed periodic phenomena at Saturn is described. Finally, the observation, generation and evolution of plasma waves associated with mass loading in the magnetodisc regions is reviewed.     

Characteristics of Icy Surfaces

The surfaces of the Solar System’s icy satellites show an extraordinary variety of morphological features, which bear witness to exchange processes between the surface and subsurface. In this paper we review the characteristics of surface features on the moons of Jupiter, Saturn, Uranus and Neptune. Using data from spacecraft missions, we discuss the detailed morphology, size, and topography of cryovolcanic, tectonic, aeolian, fluvial, and impact features of both large moons and smaller satellites.     

The Solar System d/h Ratio: Observations and Theories

The measured D/H ratios in interstellar environments and in the solar system are reviewed. The two extreme D/H ratios in solar system water - (720±120)×10⁻⁶ in clay minerals and (88±11)×10⁻⁶ in chondrules, both from LL3 chondritic meteorites - are interpreted as the result of a progressive isotopic exchange in the solar nebula between deuterium-rich interstellar water and protosolar H₂. According to a turbulent model describing the evolution of the nebula (Drouart et al., 1999), water in the solar system cannot be a product of thermal (neutral) reactions occurring in the solar nebula. Taking 720×10⁻⁶ as a face value for the isotopic composition of the interstellar water that predates the formation of the solar nebula, numerical simulations show that the water D/H ratio decreases via an isotopic exchange with H₂. During the course of this process, a D/H gradient was established in the nebula. This gradient was smoothed with time and the isotopic homogenization of the solar nebula was completed in 10⁶ years, reaching a D/H ratio of 88×10⁻⁶. In this model, cometary water should have also suffered a partial isotopic re-equilibration with H₂. The isotopic heterogeneity observed in chondrites result from the turbulent mixing of grains, condensed at different epochs and locations in the solar nebula. Recent isotopic determinations of water ice in cold interstellar clouds are in agreement with these chondritic data and their interpretation (Texeira et al., 1999). This revised version was published online in June 2006 with corrections to the Cover Date.     

A new polyethylene balloon film

After over twenty years there is a new film introduced in the United States for fabricating scientific balloons. The film was developed by Raven and is designated Astrofilm.The film is a result of a critical selection of both the resin and extruding parameters. The film's physical properties and results of a test flight are reported. Also reported are a proposed design modification and failure analysis.     

Oxygen Isotopes in the Solar System

The oxygen three-isotope system has major advantages over the two-isotope systems of hydrogen, carbon, and nitrogen because different fractionation laws govern intraplanetary and interplanetary processes. This permits discriminating between solar nebular processes and parent-body processes. Oxygen isotopes also serve as a sensitive natural tracer for meteorite classification. This revised version was published online in August 2006 with corrections to the Cover Date.     

RF communications subsystem for the Radiation Belt Storm Probes mission

The NASA Radiation Belt Storm Probes (RBSP) mission, currently in Phase B, is a two-spacecraft, Earth-orbiting mission, which will launch in 2012. The spacecraft's S-band radio frequency (RF) telecommunications subsystem has three primary functions: provide spacecraft command capability, provide spacecraft telemetry and science data return, and provide accurate Doppler data for navigation. The primary communications link to the ground is via the Johns Hopkins University Applied Physics Laboratory's (JHU/APL) 18 m dish, with secondary links to the NASA 13 m Ground Network and the Tracking and Data Relay Spacecraft System (TDRSS) in single-access mode. The on-board RF subsystem features the APL-built coherent transceiver and in-house builds of a solid-state power amplifier and conical bifilar helix broad-beam antennas. The coherent transceiver provides coherency digitally, and controls the downlink data rate and encoding within its field-programmable gate array (FPGA). The transceiver also provides a critical command decoder (CCD) function, which is used to protect against box-level upsets in the C&DH subsystem. Because RBSP is a spin-stabilized mission, the antennas must be symmetric about the spin axis. Two broad-beam antennas point along both ends of the spin axis, providing communication coverage from boresight to 70°. An RF splitter excites both antennas; therefore, the mission is designed such that no communications are required close to 90° from the spin axis due to the interferometer effect from the two antennas. To maximize the total downlink volume from the spacecraft, the CCSDS File Delivery Protocol (CFDP) has been baselined for the RBSP mission. During real-time ground contacts with the APL ground station, downlinked files are checked for errors. Handshaking between flight and ground CFDP software results in requests to retransmit only the file fragments lost due to dropouts. This allows minimization of RF link margins, thereby maximizing data rate and thus data volume.     

中东MRO市场:谨慎的乐观

尽管全球经济形势不断恶化,航空市场缩水,但中东地区丰富的石油资源和现金流,依然是航空维修业发展的沃土.中东各国政府、航空公司及其合作伙伴不惜花巨资开发和提升维修能力,成为飞机机体或发动机的维修中心.其中以迪拜的航空维修设施的发展最为抢眼.