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1.
Rhoda Shaller Hornstein Gerald L. Shinkle Jerry D. Weiler John K. Willoughby 《Acta Astronautica》1991,25(12):793-798
The widely distributed nature of the Space Station Freedom program, plus continuous multi-year operations will force program planners to develop innovative planning concepts. The traditional centralized planning operation will not be adequate. It will be replaced by multiple small planning centers working within guidelines issued by a central planning authority. Plans will not be optimized; rather, operating efficiency and user flexibility will be blended to satisfy program goals. The key to this new approach is the application of new planning methodologies and system development technologies to accommodate distributed resources that must be integrated. Resources will be distributed to the multiple planning entities in such a way that, when the several plans are built and then integrated, they will fit together with minimal modification. The plan itself will be an envelope schedule containing resource limits and constraint boundaries within which users will be free to make choices of the specific activities they will execute, up to the time of execution. Some level of margin within program guidelines will be built in to allow for variation and unforeseen change. This paper presents the authors' recommended planning approach and cites two NASA systems being developed that will utilize these resource distribution/integration planning concepts, methodologies and development technologies. 相似文献
2.
An experimental program is described that had the objective of measuring the effects of the time-dependent structure of downlink (air craft to ground) interference generated by the Air Traffic Control Radar Beacon System (ATCRBS) in an active air traffic terminal area that are relevant to system and ground controller response time. The results of this program indicate a number of interesting details concerning the correlation of the level of the downlink interference with changes in the arrival and departure rates of aircraft at the local terminal sites. 相似文献
3.
Gerald T. Davidson 《Space Science Reviews》1990,53(1-2):45-82
Morningside aurorae at latitudes below about 70° display complex spatial and temporal structures unlike anything seen in the evening or midnight sectors. The morningside structures are believed to be formed by the precipitation of trapped electrons injected in auroral substorms; no significant role has yet been identified in the morningside auroral regions for the large-scale parallel electric fields that dominate the evening side. How those spatial and temporal structures originate has been the subject of much speculation; most theoretical mechanisms focus on the wave-particle interactions that drive pitch-angle diffusion. The principal evidence pertaining to the role of pitch-angle diffusion in the auroral regions is reviewed here. The observational evidence concerns mainly auroral emissions in the atmosphere, energetic particles observed from rockets and satellites, VLF waves at high altitudes, magnetospheric cold plasma, and magnetic pulsations detected on the ground. With the aid of such evidence, plus observations and theories related to the outer permanently trapped radiation belts, several theoretical models for the modulation of VLF wave growth in the equatorial regions have been pieced together. Those models, and the observational data supporting them, are examined to see how well they fit the observational picture and to see where they might lead in future research. The models fall into two categories: those in which the modulations are externally imposed and those in which the modulations are self-excited. For the temporal variations the self-excited mechanisms are now favored. The leading candidate involves a nonlinear relaxation oscillator; the nonlinearity may have important consequences. There are several contenders in both categories for the origin of the spatial structures, none of which agrees fully with inferences from the observations. All the theories involve critical parameters that have not yet been precisely fixed. The critical research needs are listed and discussed. 相似文献
4.
Louise M. Prockter Rosaly M. C. Lopes Bernd Giese Ralf Jaumann Ralph D. Lorenz Robert T. Pappalardo Gerald W. Patterson Peter C. Thomas Elizabeth P. Turtle Roland J. Wagner 《Space Science Reviews》2010,153(1-4):63-111
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. 相似文献
5.
Lehman D. Clark K. Cook B. Gavit S. Kayali S. McKinney J. Milkovich D. Reh K. Taylor R. Casani J. Griebel T. 《Aerospace and Electronic Systems Magazine, IEEE》2009,24(3):12-21
Congress authorized NASA's Prometheus Project in February 2003, with the first Prometheus mission slated to explore the icy moons of Jupiter. The project had two major objectives: 1) to develop a nuclear reactor that would provide unprecedented levels of power and show that it could be processed safely and operated reliably in space for long-duration, deep-space exploration; and 2) to explore the three icy moons of Jupiter - Callisto, Ganymede, and Europa - and return science data that would meet the scientific goals as set forth in the Decadal Survey Report of the National Academy of Sciences. Early in project planning, it was determined that the development of the Prometheus nuclear-powered spaceship would be complex and require the intellectual knowledge residing at numerous organizations across the country. In addition, because of the complex nature of the project and the multiple partners, approaches beyond those successfully used to manage a typical JPL project would be needed. This describes the key experiences in managing Prometheus, which should prove useful for future projects of similar scope and magnitude. 相似文献
6.
A.F. Cook 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1983,3(3):83-86
Saturn lies at nearly twice Jupiter's distance from the Sun and nearly all parts of its system are characterized by much smaller scales than those which are important in the case of Jupiter. This appears in the structures of the planet's atmosphere, in the sizes of classical satellites other than Titan vis-à-vis those of the Galilean satellites, in the plethora of small Saturnian satellites, especially Lagrangian co-orbiters, in the structure of Saturn's F-Ring as contrasted with that of Jupiter's Ring and finally in the highly structured detail in Saturn's Rings, much finer than seriously considered in past theoretical discussions. Uranus' Rings were unknown until five years ago. The discovery and observation of these rings have revived contributions to theory originally intended for application to Saturn's Rings. Models have also been generated for eccentric rings for application to Uranus' Rings which also apply to those of Saturn. These two classes of model are reviewed in the present paper along with the first tentative steps made down the road to unravelling the complexity of Saturn's Rings. 相似文献
7.
A general performance index is developed for evaluating aircraft landing trajectories. The primary term in the index is the effect of noise on people residing near the air terminal. Other terms included are passenger comfort, fuel consumed, and the time spent in the near-terminal area. Models are developed for aircraft engine noise, passenger comfort, the population distribution about a specific airport, and the aircraft flight behavior. While this performance index may be used in computing optimal trajectories, it is also useful for comparing nonoptimal trajectories which, for one reason or another, may be worthy of consideration. Some examples of such comparisons are included through simulations of landing. The aircraft considered is a Boeing 737. 相似文献
8.
Linear FM Signal Formats for Beacon and Communication Systems 总被引:2,自引:0,他引:2
This paper examines the capabilities of the class of linear FM spread-spectrum signals within the context of potential communications systems usage in order to establish some performance criteria and bounds that permit comparison with other spread-spectrum formats. A systematic basis is provided for parameter selection for this class of signals by examining the interaction a mong the frequency-modulation indices, time-bandwidth product, and cross-talk criteria that determine the number of effective linear FM signals (or channels) that can be used within the constraints of a bounded time-frequency region. A general expression is derived relating N, the number of useful signals, R2, a cross-talk parameter, ToWo, the mean time-bandwidth product, and ?max and ?min, the maximum and minimum FM rates of the signal set. Canonic signal processor structures are described for ensembles of linear FM signals that have either constant duration or constant bandwidth. It is then shown that the signal modulation format can be modified in accordance with classical paired-echo theory to expand the utility of this class of signals in both synchronous and nonsynchronous operations to yield the equivalent of time-division and code multiplexing. Possible applications for this signal format are discussed. 相似文献
9.
Stone E.C. Cohen C.M.S. Cook W.R. Cummings A.C. Gauld B. Kecman B. Leske R.A. Mewaldt R.A. Thayer M.R. Dougherty B.L. Grumm R.L. Milliken B.D. Radocinski R.G. Wiedenbeck M.E. Christian E.R. Shuman S. von Rosenvinge T.T. 《Space Science Reviews》1998,86(1-4):357-408
The Solar Isotope Spectrometer (SIS), one of nine instruments on the Advanced Composition Explorer (ACE), is designed to provide
high- resolution measurements of the isotopic composition of energetic nuclei from He to Zn (Z=2 to 30) over the energy range
from ∼10 to ∼100 MeV nucl−1. During large solar events SIS will measure the isotopic abundances of solar energetic particles
to determine directly the composition of the solar corona and to study particle acceleration processes. During solar quiet
times SIS will measure the isotopes of low-energy cosmic rays from the Galaxy and isotopes of the anomalous cosmic-ray component,
which originates in the nearby interstellar medium. SIS has two telescopes composed of silicon solid-state detectors that
provide measurements of the nuclear charge, mass, and kinetic energy of incident nuclei. Within each telescope, particle trajectories
are measured with a pair of two-dimensional silicon-strip detectors instrumented with custom, very large-scale integrated
(VLSI) electronics to provide both position and energy-loss measurements. SIS was especially designed to achieve excellent
mass resolution under the extreme, high flux conditions encountered in large solar particle events. It provides a geometry
factor of ∼40 cm2 sr, significantly greater than earlier solar particle isotope spectrometers. A microprocessor controls the
instrument operation, sorts events into prioritized buffers on the basis of their charge, range, angle of incidence, and quality
of trajectory determination, and formats data for readout by the spacecraft. This paper describes the design and operation
of SIS and the scientific objectives that the instrument will address.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
10.
Hart Walter G. McGowan Gerald F. DuPont T. E. 《IEEE transactions on aerospace and electronic systems》1968,(4):592-606
The design of an adaptive tracking filter control system and its application to large flexible booster vehicles is described. The problem of elastic vehicle stability is considered along with its solution by conventional and adaptive techniques. The improvement in vehicle stability, which may be achieved with the adaptive tracking filter technique as compared to conventional techniques, is shown. The control system evolved uses two adaptive tracking filters to phase stabilize the first and second bending modes, in addition to conventional compensation techniques. The application of this adaptive technique to a vehicle in which the modal frequencies are in close proximity (<2.5 percent separation) is discussed. The mechanization of the adaptive control system involves the selection of design techniques and components that are electrically and physically compatible with the intended airborne application. The development of a suitable frequency tracking technique and tracking filter is described, in addition to the electronic and mechanical design of the adaptive control system prototype. 相似文献