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排序方式: 共有83条查询结果,搜索用时 15 毫秒
41.
Anuja MahashabdePhilip Wolfe Akshay AshokChristopher Dorbian Qinxian HeAlice Fan Stephen LukachkoAleksandra Mozdzanowska Christoph WollersheimSteven R.H. Barrett Maryalice LockeIan A. Waitz 《Progress in Aerospace Sciences》2011,47(1):15-52
With the projected growth in demand for commercial aviation, many anticipate increased environmental impacts associated with noise, air quality, and climate change. Therefore, decision-makers and stakeholders are seeking policies, technologies, and operational procedures that balance environmental and economic interests. The main objective of this paper is to address shortcomings in current decision-making practices for aviation environmental policies. We review knowledge of the noise, air quality, and climate impacts of aviation, and demonstrate how including environmental impact assessment and quantifying uncertainties can enable a more comprehensive evaluation of aviation environmental policies. A comparison is presented between the cost-effectiveness analysis currently used for aviation environmental policy decision-making and an illustrative cost-benefit analysis. We focus on assessing a subset of the engine NOX emissions certification stringency options considered at the eighth meeting of the International Civil Aviation Organization’s Committee on Aviation Environmental Protection. The FAA Aviation environmental Portfolio Management Tool (APMT) is employed to conduct the policy assessments. We show that different conclusions may be drawn about the same policy options depending on whether benefits and interdependencies are estimated in terms of health and welfare impacts versus changes in NOX emissions inventories as is the typical practice. We also show that these conclusions are sensitive to a variety of modeling uncertainties. While our more comprehensive analysis makes the best policy option less clear, it represents a more accurate characterization of the scientific and economic uncertainties underlying impacts and the policy choices. 相似文献
42.
43.
Unique springs, discharging from the surface of an arctic glacier, release H(2)S and deposit native sulfur, gypsum, and calcite. The presence of sulfur in three oxidation states indicates a complex series of redox reactions. Physical and chemical conditions of the spring water and surrounding environment, as well as mineralogical and isotopic signatures, suggest biologically mediated reactions. Cell counts and DNA analyses confirm bacteria are present in the spring system, and a limited number of sequenced isolates suggests that complex communities of bacteria live within the glacial system. 相似文献
44.
This paper deals with the difficulty of decoding the origins of natural structures through the study of their morphological features. We focus on the case of primitive life detection, where it is clear that the principles of comparative anatomy cannot be applied. A range of inorganic processes are described that result in morphologies emulating biological shapes, with particular emphasis on geochemically plausible processes. In particular, the formation of inorganic biomorphs in alkaline silica-rich environments are described in detail. 相似文献
45.
Peter W. A. Roming Thomas E. Kennedy Keith O. Mason John A. Nousek Lindy Ahr Richard E. Bingham Patrick S. Broos Mary J. Carter Barry K. Hancock Howard E. Huckle S D. Hunsberger Hajime Kawakami Ronnie Killough T Scott Koch Michael K. Mclelland Kelly Smith Philip J. Smith Juan Carlos Soto Patricia T. Boyd Alice A. Breeveld Stephen T. Holland Mariya Ivanushkina Michael S. Pryzby Martin D. Still Joseph Stock 《Space Science Reviews》2005,120(3-4):95-142
The Ultra-Violet/Optical Telescope (UVOT) is one of three instruments flying aboard the Swift Gamma-ray Observatory. It is designed to capture the early (∼1 min) UV and optical photons from the afterglow of gamma-ray
bursts in the 170–600 nm band as well as long term observations of these afterglows. This is accomplished through the use
of UV and optical broadband filters and grisms. The UVOT has a modified Ritchey–Chrétien design with micro-channel plate intensified
charged-coupled device detectors that record the arrival time of individual photons and provide sub-arcsecond positioning
of sources. We discuss some of the science to be pursued by the UVOT and the overall design of the instrument. 相似文献
46.
The plasma produced by a Kaufman (UK-25) ion thruster possesses four distinct regions. The interaction of two of these regions, the coupling and discharge plasmas, is important for thruster design and efficiency, since it controls the production of the primary electrons responsible for most of the ionisation in the thruster. This paper details the measurement and analysis techniques used to obtain two-dimensional experimental plasma parameter maps across a plasma double layer in the baffle aperture region of this type of ion thruster. This plasma-interaction region was mapped experimentally using Langmuir probes.The Langmuir probe data were collected and analysed to produce maps of plasma potential, Maxwellian and primary electron energy and number density. Detailed static magnetic field measurements using Hall-effect probes were also obtained. A number of derived plasma parameter maps were then made possible, such as electron pressure. The application of the analysis techniques used here allowed ion thruster plasma property maps to be constructed of a spatial extent and resolution previously unseen. Two-dimensional maps of the spatial location of primary electrons are presented, as effected by applied magnetic field changes, along with the detection of regions showing depletion of primary electron energies. 相似文献
47.
The Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) on the New Horizons Mission
Ralph L. McNutt Jr. Stefano A. Livi Reid S. Gurnee Matthew E. Hill Kim A. Cooper G. Bruce Andrews Edwin P. Keath Stamatios M. Krimigis Donald G. Mitchell Barry Tossman Fran Bagenal John D. Boldt Walter Bradley William S. Devereux George C. Ho Stephen E. Jaskulek Thomas W. LeFevere Horace Malcom Geoffrey A. Marcus John R. Hayes G. Ty Moore Mark E. Perry Bruce D. Williams Paul Wilson IV Lawrence E. Brown Martha B. Kusterer Jon D. Vandegriff 《Space Science Reviews》2008,140(1-4):315-385
The Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) comprises the hardware and accompanying science investigation on the New Horizons spacecraft to measure pick-up ions from Pluto’s outgassing atmosphere. To the extent that Pluto retains its characteristics similar to those of a “heavy comet” as detected in stellar occultations since the early 1980s, these measurements will characterize the neutral atmosphere of Pluto while providing a consistency check on the atmospheric escape rate at the encounter epoch with that deduced from the atmospheric structure at lower altitudes by the ALICE, REX, and SWAP experiments on New Horizons. In addition, PEPSSI will characterize any extended ionosphere and solar wind interaction while also characterizing the energetic particle environment of Pluto, Charon, and their associated system. First proposed for development for the Pluto Express mission in September 1993, what became the PEPSSI instrument went through a number of development stages to meet the requirements of such an instrument for a mission to Pluto while minimizing the required spacecraft resources. The PEPSSI instrument provides for measurements of ions (with compositional information) and electrons from 10 s of keV to ~1 MeV in a 160°×12° fan-shaped beam in six sectors for 1.5 kg and ~2.5 W. 相似文献
48.
James C. Leary Richard F. Conde George Dakermanji Carl S. Engelbrecht Carl J. Ercol Karl B. Fielhauer David G. Grant Theodore J. Hartka Tracy A. Hill Stephen E. Jaskulek Mary A. Mirantes Larry E. Mosher Michael V. Paul David F. Persons Elliot H. Rodberg Dipak K. Srinivasan Robin M. Vaughan Samuel R. Wiley 《Space Science Reviews》2007,131(1-4):187-217
The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft was designed and constructed to withstand the harsh environments associated with achieving and operating in Mercury
orbit. The system can be divided into eight subsystems: structures and mechanisms (e.g., the composite core structure, aluminum
launch vehicle adapter, and deployables), propulsion (e.g., the state-of-the-art titanium fuel tanks, thruster modules, and
associated plumbing), thermal (e.g., the ceramic-cloth sunshade, heaters, and radiators), power (e.g., solar arrays, battery,
and controlling electronics), avionics (e.g., the processors, solid-state recorder, and data handling electronics), software
(e.g., processor-supported code that performs commanding, data handling, and spacecraft control), guidance and control (e.g.,
attitude sensors including star cameras and Sun sensors integrated with controllers including reaction wheels), radio frequency
telecommunications (e.g., the spacecraft antenna suites and supporting electronics), and payload (e.g., the science instruments
and supporting processors). This system architecture went through an extensive (nearly four-year) development and testing
effort that provided the team with confidence that all mission goals will be achieved.
Larry E. Mosher passed away during the preparation of this paper. 相似文献
49.
Emilien Fabacher Stephen Kemble Christian Trenkel Neil Dunbar 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
LISA Pathfinder is an ESA mission due to be launched in the next two years. The gravity gradiometer onboard has the sensitivity required to test predictions by gravitational theories proposed as alternatives to Dark Matter such as TeVeS. Within the Solar System measurable effects are predicted only in the vicinity of gravitational saddle points (SP). For this reason it has been proposed to fly LPF by the Earth–Sun SP, at some 259,000 km from Earth. This could be done in an extension to the nominal mission which uses a Lissajous orbit about the Earth–Sun L1 point. The responsibility for LPF mission design lies with ESA/ESOC, who have designed the transfer trajectories, orbits about L1, and station keeping strategies. This article describes an analysis performed by Astrium to support a suggestion for a possible mission extension to a saddle point crossing. With only very limited fuel availability, reaching the saddle point is a significant challenge. In this article, we present recent advances in the work on trajectory design. It is demonstrated that reaching the SP is feasible once the LPF mission is completed. Furthermore, in a significant enhancement, it is demonstrated that trajectories including more than one SP flyby are possible, thus improving the science return for this proposed mission extension. 相似文献
50.
John M. Harlander Christoph R. Englert Charles M. Brown Kenneth D. Marr Ian J. Miller Vaz Zastera Bernhard W. Bach Stephen B. Mende 《Space Science Reviews》2017,212(1-2):601-613
The design and laboratory tests of the interferometers for the Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) instrument which measures thermospheric wind and temperature for the NASA-sponsored Ionospheric Connection (ICON) Explorer mission are described. The monolithic interferometers use the Doppler Asymmetric Spatial Heterodyne (DASH) Spectroscopy technique for wind measurements and a multi-element photometer approach to measure thermospheric temperatures. The DASH technique and overall optical design of the MIGHTI instrument are described in an overview followed by details on the design, element fabrication, assembly, laboratory tests and thermal control of the interferometers that are the heart of MIGHTI. 相似文献