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771.
Kwon W.H. Lee K.S. Kwon O.K. 《IEEE transactions on aerospace and electronic systems》1990,26(6):1011-1021
An optimal FIR (finite impulse response) filter and smoother is introduced for the time-varying state-space model. The suggested filter has an FIR structure and utilizes finite observation. It is shown that the impulse response of the optimal FIR filter can be obtained by a simple Riccati-type matrix differential equation. Especially for time-invariant systems, this FIR filter reduces to previously known simple forms. For implementation, a recursive form of the optimal FIR filter and smoother is derived by using adjoint variables, and computational algorithms are suggested. It is also shown by sensitivity analysis that the proposed optimal FIR filter alleviates potential divergence characteristics of the standard Kalman filter 相似文献
772.
K E Gartenbach M Pickert M W Zimmermann A R Kranz 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1994,14(10):105-108
Recently, comparison of biophysical data obtained from orbital flights of short and long duration led to results which will be significant for long and/or repeated stay of man in space. Under orbital conditions biological stress is induced in dry seeds of Arabidopsis thaliana by cosmic radiation especially its high energetic, densely ionizing component, the heavy ions (HZE). For comparison of radiation impact during different space flights a biological attempt at estimating the impact of single particles with high mass and energy (HZE-particles) on seeds was developed. Subdivision into LET-groups showed a remarkable contribution of an intermediate group (LET = 35 to 100 keV/micrometer) due to medium heavy ions (Z = 6 to 10). Efficiency factors for radiation damage experimentally determined and assigned to different LET-classes were compared to radiation quality factors discussed in literature. 相似文献
773.
An assessment is presented of the probable magnitude of ocean signals causing aliasing in ocean bottom pressure measurements
from the GRACE satellite mission. Even after modelling as much of the high frequency signal as possible, variability between
1 mbar (in quiet ocean regions) and 10 mbar (on some shelves) is likely to remain. Interpretation of the resulting retrievals
will therefore rely on the facts that the satellite sampling will average the aliasing signal to some extent, and that the
spatial patterns of aliased signal and true signal will be different. To this end, a theoretical argument is given, and supported
by model diagnostics, suggesting that observable bottom pressure signals will be strongly constrained by the shape of the
ocean floor. The modelled magnitudes offer the prospect of significant detectable signals and, while the model accuracy can
be called into question, there are hints from Earth rotation and satellite orbit measurements that significant mass redistributions
occur in the ocean. It seems certain that we will learn something new about the oceans from GRACE.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
774.
O'Neill M.J. McDanal A.J. Piszczor M.F. George P.J. Edwards D.L. Brandhorst H.W. Eskenazi M.I. Botke M.M. Jaster P.M. 《Aerospace and Electronic Systems Magazine, IEEE》2003,18(1):3-9
At IECEC 2001, this team presented a paper on the new stretched lens array (SLA), including its evolution from the successful SCARLET array on the NASA/JPL Deep Space 1 spacecraft. Since that conference, the SLA team has made significant advances in SLA technology, including component-level improvements, array-level optimization, space environment exposure testing, and prototype hardware fabrication and evaluation. This paper describes the evolved version of the SLA, highlighting recent improvements in the lens, solar cell, photovoltaic receiver, rigid panel structure, and complete solar array wing. In addition to excellent durability in the space environment, the near-term SLA will provide outstanding wing-level performance parameters: 180 W/kg specific power; 300 W/m/sup 2/ power density; 300 V operational voltage; 85% savings in cell area (cm/sup 2//W) and cell-related cost ($/W) compared to planar arrays; 9 kW/m/sup 3/ stowed power at launch. 相似文献
775.
G. Li G.P. Zank W.K.M. Rice 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2003,32(12):2597-2602
Historically, solar energetic particle (SEP) events are classified in two classes as “impulsive” and “gradual”. Whether there is a clear distinction between the two classes is still a matter of debate, but it is now commonly accepted that in large “gradual” SEP events, Fermi acceleration, also known as diffusive shock acceleration, is the underlying acceleration mechanism. At shock waves driven by coronal mass ejections (CMEs), particles are accelerated diffusively at the shock and often reach > MeV energies (and perhaps up to GeV energies). As a CME-driven shock propagates, expands and weakens, the accelerated particles can escape ahead of the shock into the interplanetary medium. These escaping energized particles then propagate along the interplanetary magnetic field, experiencing only weak scattering from fluctuations in the interplanetary magnetic field (IMF). In this paper, we use a Monte-Carlo approach to study the transport of energetic particles escaping from a CME-driven shock. We present particle spectra observed at 1 AU. We also discuss the particle “crossing number” at 1AU and its implication to particle anisotropy. Based on previous models of particle acceleration at CME-driven shocks, our simulation allows us to investigate various characteristics of energetic particles arriving at various distances from the sun. This provides us an excellent basis for understanding the observations of high-energy particles made at 1 AU by ACE and WIND. 相似文献
776.
M Nelson J Allen A Alling W F Dempster S Silverstone 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2003,31(7):1649-1655
The parallels between the challenges facing bioregenerative life support in artificial closed ecological systems and those in our global biosphere are striking. At the scale of the current global technosphere and expanding human population, it is increasingly obvious that the biosphere can no longer safely buffer and absorb technogenic and anthropogenic pollutants. The loss of biodiversity, reliance on non-renewable natural resources, and conversion of once wild ecosystems for human use with attendant desertification/soil erosion, has led to a shift of consciousness and the widespread call for sustainability of human activities. For researchers working on bioregenerative life support in closed systems, the small volumes and faster cycling times than in the Earth's biosphere make it starkly clear that systems must be designed to ensure renewal of water and atmosphere, nutrient recycling, production of healthy food, and safe environmental methods of maintaining technical systems. The development of technical systems that can be fully integrated and supportive of living systems is a harbinger of new perspectives as well as technologies in the global environment. In addition, closed system bioregenerative life support offers opportunities for public education and consciousness changing of how to live with our global biosphere. 相似文献
777.
C.F. Chen B.W. Reinisch J.L. Scali X. Huang R.R. Gamache M.J. Buonsanto B.D. Ward 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1994,14(12):43-46
At the Millstone Hill station the Incoherent Scatter Radar (ISR) and a Digisonde 256 are simultaneously operating. Some characteristic true heights determined by both instruments are compared with each other, possible reasons for observed difference are indicated. 相似文献
778.
W.C. Carey J.A.M. McDonnell C.S. Welch J.C. Zarnecki 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(9):217-220
Modelling of the cometary coma with respect to the distribution of dust particles within the coma and tail have been performed by a number of authors /1,2,3/. Applications of the Divine model using a program coded for the Giotto DIDSY sensors have also been made to calculate expected sensor response of the instrument and spacecraft impact rates /4/. For a chosen mass of ~ 10?10g we use the Divine Reference model /1/ to investigate the effect on the mass envelope of i) a velocity spread in dust particle ejection; and ii) a variation in the particle type. The results show that effects i) and ii) lead to a smoothing-out of the anticipated peak flux at an envelope boundary. A conceptual model to follow the formation and development of dust jets is also presented and effects illustrated for various nucleus rotation periods. 相似文献
779.
E. Grün G.W. Garneau R.J. Terrile T.V. Johnson G.E. Morfill 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(9):143-148
Voyager 2 images of Saturn's rings have been analyzed for spoke activity. More than 80 and 40 different spokes have been measured at the morning and at the evening ansa, respectively. Higher rate of spoke formation has been found at 145° ± 15° SLS and at 305° ± 15° SLS which persisted for at least 3 Saturn revolutions. Higher spoke activity (formation and growth in width) by more than a factor 3 has been observed over the nightside hemisphere of Saturn than over the dayside hemisphere. The age distribution (i.e. time from radial formation until observation, assuming Keplerian shear) of the leading (old) edges of spokes has its maximum at ~ 9,000 s and ~ 6,000 s for spokes observed at the morning ansa and at the evening ansa, respectively. The highest spoke age observed is ~ 20,000 s. The age distribution of the trailing (young) edges of spokes peaks at < 2,000 s at both ansae but has its mean at ~ 4,500 s and ~ 3,500 s, respectively. On the average the observed spokes grew in width for ~ 4,500 s at the morning ansa and for ~ 2,500 s at the evening ansa. The maximum time of growth in width was ~ 12,000 s. 相似文献
780.