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721.
This is the second part of a two-part paper which summarizes work pursued by the author in 1967 [2]. The paper describes the application of minimum-variance estimation techniques for in-flight alignment and calibration of an inertial measurement unit (IMU) relative to another IMU and/or some other reference. The first paper [1] formulates the problem, and this paper reports numerical results and analyses. The approach taken is to cast the problem into the framework of Kalman-Bucy estimation theory, where velocity and position differences between the two IMU's are used as observations and the IMU parameters of interest become part of the state vector. Instrument quantization and computer roundoff errors are considered as measurement noise, and environmental induced random accelerations are considered as state noise. In this paper, numerical results for three important IMU error parameter configurations are presented and discussed. The main results of the paper determine the effects of state and observation noise levels and the nominal trajectory on the identifications of the errors for these configurations. A discussion of the minimum number of trajectory maneuvers and of the optimal trajectory maneuvering is given. 相似文献
722.
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
723.
F.J. Montojo T. López Moratalla C. Abad 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
In the project titled “Astrometric Positioning of Geostationary Satellite” (PASAGE), carried out by the Real Instituto y Observatorio de la Armada (ROA), optical observation techniques were developed to allow satellites to be located in the geostationary ring with angular accuracies of up to a few tenths of an arcsec. These techniques do not necessarily require the use of large telescopes or especially dark areas, and furthermore, because optical observation is a passive method, they could be directly applicable to the detection and monitoring of passive objects such as space debris in the geostationary ring. 相似文献
724.
A prominent neuroscientist A. Damasio has observed that “More may have been learned about the brain and the mind in the 1990s... than during the entire previous history of psychology and neuroscience” (1999). This progress, which should continue at an exponentially increasing pace as we move into the 21st century, sets the stage for another revolution-in the scientific formulation of intentional behavior. Just as applied sciences such as fluid mechanics and solid-state electronics benefited from breakthroughs in physics, so it may be expected that social psychology and economics, for example, will similarly benefit from our expanding knowledge of psychosomatic and psychological function. Economics, however, with its basic concepts dating from the nineteenth century, must endure an extensive renewal. Toward this end, a new mathematical theory of behavior was formulated in the early 1990s based on the contributions of prominent psychologists and economists over the past two centuries. Presentation of the new approach at international conferences continued in 2000 with attention moving beyond the fundamentals into macroeconomic concerns including business cycles, productivity, and unemployment 相似文献
725.
726.
Margarita Karovska Brian E. Wood John W. Cook Russell A. Howard Guenter E. Brueckner 《Space Science Reviews》1999,87(1-2):219-222
We present the results from a study of the dynamical properties of polar jets in the Sun's polar regions using LASCO C2 coronagraph
and EIT observations. In the simplest impulsive acceleration scenarios for jets, gravity is expected to be the dominant force
on the jet following the initial acceleration, especially in the Sun's polar regions where the open magnetic fields should
not significantly impede the jet's motion. Our analysis shows that although at low heights the kinematics of the jets could
be consistent with a gravitational deceleration of the ejected plasma, at higher heights their motions may simply follow the
ambient solar wind outflow. If so, the polar jets can be used as tracers of the solar wind in coronal holes.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
727.
Formation and Evolution of Corotating Interaction Regions and their Three Dimensional Structure 总被引:1,自引:0,他引:1
Corotating interaction regions are a consequence of spatial variability in the coronal expansion and solar rotation, which
cause solar wind flows of different speeds to become radially aligned. Compressive interaction regions are produced where
high-speed wind runs into slower plasma ahead. When the flow pattern emanating from the Sun is roughly time-stationary these
compression regions form spirals in the solar equatorial plane that corotate with the Sun, hence the name corotating interaction
regions, or CIRs. The leading edge of a CIR is a forward pressure wave that propagates into the slower plasma ahead, while
the trailing edge is a reverse pressure wave that propagates back into the trailing high-speed flow. At large heliocentric
distances the pressure waves bounding a CIR commonly steepen into forward and reverse shocks. Spatial variation in the solar
wind outflow from the Sun is a consequence of the solar magnetic field, which modulates the coronal expansion. Because the
magnetic equator of the Sun is commonly both warped and tilted with respect to the heliographic equator, CIRs commonly have
substantial north-south tilts that are opposed in the northern and southern hemispheres. Thus, with increasing heliocentric
distance the forward waves in both hemispheres propagate toward and eventually across the solar equatorial plane, while the
reverse shocks propagate poleward to higher latitudes. This paper provides an overview of observations and numerical models
that describe the physical origin and radial evolution of these complex three-dimensional (3-D) heliospheric structures.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
728.
John M. Logsdon 《Space Policy》2011,27(3):153-156
A newly released tape of a 18 September 1963 conversation between President Kennedy and NASA Administrator James Webb has been interpreted by some as showing that the president was looking for a way out of his Apollo commitment. This commentary analyses the meeting – in which Webb did most of the talking – and concludes instead that Kennedy was concerned about how to keep the program going in the face of growing criticism of its cost and goals. In particular there was discussion of how to ensure that his support for Apollo did not harm his chances of re-election. To Kennedy, giving Apollo a military rationale seemed the best way to ensure its support. 相似文献
729.
730.
The DoD has many acquisition programs that are aggressively implementing open architecture principles in new avionics systems. Since “open” is an unclear attribute, projects eventually give in to a point solution that has no flexibility to cost effectively keep up with rapid changes in technology. The Open Systems Development Initiative (OSDI) project utilized COTS products to study the feasibility of building an open system that has plug-and-play capabilities. Lessons learned from the AV-8B Open Systems Core Avionics Requirements (OSCAR) and the F/A-18 Advanced Mission Computers and Displays (AMC&D) programs clearly indicated that understanding the underlying interfaces is crucial to keeping the system as open as possible to take advantage of the rapid changes in technology. A matrix of Key Open Standard Interfaces (KOSI), called the KOSI matrix, was developed and an applicable standard was identified for each interface. A list of non-conforming interfaces was also identified and the use of extensions or wrappers was investigated in an attempt to comply with standards. Standardization, rather than optimization of such interfaces, was considered more beneficial. It became evident that, with the exception of ruggedization, there is no difference in the use of COTS products for either commercial or military systems. Performing a KOSI analysis helped identify the key interfaces and standards, thus enabling the OSDI system to be scalable, portable and interoperable. A good KOSI matrix provides a vehicle for clear communication and helps systems integration and technology insertion to be less painful than what it is today. It helps reduce time-to-market and provides guidance to systems engineers and vendors to keep the system open 相似文献