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Faisal Hossain 《Natural Hazards》2006,37(3):263-276
The three most important components necessary for functioning of an operational flood warning system are: (1) a rainfall measuring
system; (2) a soil moisture updating system; and, (3) a surface discharge measuring system. Although surface based networks
for these systems can be largely inadequate in many parts of the world, this inadequacy particularly affects the tropics,
which are most vulnerable to flooding hazards. Furthermore, the tropical regions comprise developing countries lacking the
financial resources for such surface-based monitoring. The heritage of research conducted on evaluating the potential for
measuring discharge from space has now morphed into an agenda for a mission dedicated to space-based surface discharge measurements.
This mission juxtaposed with two other upcoming space-based missions: (1) for rainfall measurement (Global Precipitation Measurement,
GPM), and (2) soil moisture measurement (Hydrosphere State, HYDROS), bears promise for designing a fully space-borne system
for early warning of floods. Such a system, if operational, stands to offer tremendous socio-economic benefit to many flood-prone
developing nations of the tropical world. However, there are two competing aspects that need careful assessment to justify
the viability of such a system: (1) cost-effectiveness due to surface data scarcity; and (2) flood prediction uncertainty
due to uncertainty in the remote sensing measurements. This paper presents the flood hazard mitigation opportunities offered
by the assimilation of the three proposed space missions within the context of these two competing aspects. The discussion
is cast from the perspective of current understanding of the prediction uncertainties associated with space-based flood prediction.
A conceptual framework for a fully space-borne system for early-warning of floods is proposed. The need for retrospective
validation of such a system on historical data comprising floods and its associated socio-economic impact is stressed. This
proposal for a fully space-borne system, if pursued through wide interdisciplinary effort as recommended herein, promises
to enhance the utility of the three space missions more than what their individual agenda can be expected to offer. 相似文献
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Understanding our star, the Sun, is of fundamental interest for life on Earth. In this paper, the status of knowledge in solar physics of roughly two decades ago is summarised, and the most recent developments in this very active field are shown, many of them achieved by means of space based missions. The Sun–Earth connection is described and, finally, an outlook on future solar research is given. 相似文献
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航天器工作环境中的地磁场可以用于定向和姿态控制，为空间飞行提供了一个天然的坐标系，但地磁场与带电、带磁的航天器相互作用又在一定程度上影响着航天器的运动参数（如自旋、定向、轨道等），地磁场的变化，特别是磁暴和亚暴期间剧烈的磁场扰动会对航天器的正常运行和航天器仪器的有效工作造成重大影响，与磁场变化相伴随的磁层、电离层扰动，高能粒子流对航天器的工作、空间通讯、对宇航员的安全都可能有严重影响。磁扰期间，中性大气的密度、温度的变化也会影响航天器的轨道和姿态，本文从地磁场结构和变化综合评价航天器工作的地磁场环境，为航天器利用地磁场和防护地磁场变化带来的有害影响提供一些背景材料。 相似文献
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In this paper, a new approach to planetary mission design is described which automates the search for gravity-assist trajectories. This method finds all conic solutions given a range of launch dates, a range of launch energies and a set of target planets. The new design tool is applied to the problems of finding multiple encounter trajectories to the outer planets and Venus gravity-assist trajectories to Mars. The last four-planet grand tour opportunity (until the year 2153) is identified. It requires an Earth launch in 1996 and encounters Jupiter, Uranus, Neptune, and Pluto. Venus gravity-assist trajectories to Mars for the 30 year period 1995–2024 are examined. It is shown that in many cases these trajectories require less launch energy to reach Mars than direct ballistic trajectories.Assistant Professor, School of Aeronautics and AstronauticsGraduate Student, School of Aeronautics and Astronautics 相似文献
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The science requirements on future gravity satellite missions, following from the previous contributions of this issue, are
summarized and visualized in terms of spatial scales, temporal behaviour and accuracy. This summary serves the identification
of four classes of future satellite mission of potential interest: high-altitude monitoring, satellite-to-satellite tracking,
gradiometry, and formation flights. Within each class several variants are defined. The gravity recovery performance of each
of these ideal missions is simulated. Despite some simplifying assumptions, these error simulations result in guidelines as
to which type of mission fulfils which requirements best. 相似文献
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The scientific objectives of a geodetic experiment based on a network of landers, such as NEIGE (NEtlander Ionosphere and Geodesy Experiment) are to improve the current knowledge of Mars' interior and atmosphere dynamics. Such a network science experiment allows monitoring the motions of the Martian rotation axis with a precision of a few centimeters (or milli-arc-seconds (mas)) over annual and sub-annual periods. Thereto, besides radio tracking of a Mars orbiter from the Earth, radio Doppler shifts between this orbiter and several landers at the planet's surface will be performed. From the analysis of these radio Doppler data, it is possible to reconstruct the orbiter motion and Mars' orientation in space. The errors on the orbit determination (position and velocity of the orbiter) have an impact on the geodetic parameters determination from the Doppler shifts and must be removed from the signal in order to achieve a high enough accuracy. In this paper, we perform numerical simulations of the two Doppler signals involved in such an experiment to estimate the impact of the spacecraft angular momentum desaturations on the determination of Mars' orientation variations. The attitude control of the orbiter needs such desaturation maneuvers regularly repeated. They produce velocity variations that must be taken into account when determining the orbit. For our simulations, we use a priori models of the Martian rotation and introduce the spacecraft velocity variations induced by each desaturation event. By a least-squares adjustment of the simulated Doppler signals, we then estimate the orbiter velocity variations and the parameters of the Mars' rotation model. We show that these velocity variations are ill resolved when the spacecraft is not tracked, therefore requiring a near-continuous tracking from the Earth to accurately determine the orbit. In such conditions we show that only 15- of lander-orbiter tracking per week allows recovering Mars' orientation parameters with a precision of a few mas over a period of 1 Martian year. 相似文献
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Jonathan Horner Olivier Mousis Jonathan I. Lunine 《Planetary and Space Science》2008,56(12):1585-1595
We consider the role of deuterium as a potential marker of location and ambient conditions during the formation of small bodies in our Solar system. We concentrate in particular on the formation of the regular icy satellites of Jupiter and the other giant planets, but include a discussion of the implications for the Trojan asteroids and the irregular satellites. We examine in detail the formation of regular planetary satellites within the paradigm of a circum-Jovian subnebula. Particular attention is paid to the two extreme potential subnebulae—“hot” and “cold”. In particular, we show that, for the case of the “hot” subnebula model, the D:H ratio in water ice measured from the regular satellites would be expected to be near-Solar. In contrast, satellites which formed in a “cold” subnebula would be expected to display a D:H ratio that is distinctly over-Solar. We then compare the results obtained with the enrichment regimes which could be expected for other families of icy small bodies in the outer Solar system—the Trojan asteroids and the irregular satellites. In doing so, we demonstrate how measurements by Laplace, the James Webb Space Telescope, HERSCHEL and ALMA will play an important role in determining the true formation locations and mechanisms of these objects. 相似文献
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Vishnu Reddy Andreas Nathues Michael J. Gaffey Sven Schaeff 《Planetary and Space Science》2011,59(8):772-778
In-situ investigation of asteroids is the next logical step in understanding their exact surface mineralogy, petrology, elemental abundances, particle size distribution, internal structure, and collisional evolution. Near-Earth asteroids (NEAs) provide us with ample opportunities for in-situ scientific exploration with lower Δv requirements and subsequently lower costs than their main belt counterparts. The ASTEX mission concept aims at surface characterization of two compositionally diverse NEAs, one with primitive and the other with a strong thermally evolved surface mineralogy. Here we present the first results of our ground-based characterization of potential ASTEX mission targets using the SpeX instrument on the NASA IRTF. Of the four potential targets we characterized, two (1991 JW and 1998 PA) have compositions similar to ordinary chondrite mineralogy. The other two targets (1994 CC and 1999 TA10) are thermally evolved objects with igneous formation histories. While 1994 CC is a triplet system and thus very challenging to orbit the V-type NEA, 1999 TA10 is the most interesting scientific ASTEX target identified so far. 相似文献