Fisk  L. A.  Jokipii  J. R.  Simnett  G. M.  Wenzel  K.-P. 《Space Science Reviews》1998,83(1-2):1-4

Space Science Reviews -  相似文献   

    

Lyne JE  Townsend LW 《Journal of spacecraft and rockets》1998,35(6):855-856

  相似文献   

  总被引：13，自引：0，他引：13  

Sandel  B.R.  Broadfoot  A.L.  Curtis  C.C.  King  R.A.  Stone  T.C.  Hill  R.H.  Chen  J.  Siegmund  O.H.W.  Raffanti  R.  Allred  DAVID D.  Turley  R. STEVEN  Gallagher  D.L. 《Space Science Reviews》2000,91(1-2):197-242

The Extreme Ultraviolet Imager (EUV) of the IMAGE Mission will study the distribution of He⁺ in Earth's plasmasphere by detecting its resonantly-scattered emission at 30.4 nm. It will record the structure and dynamics of the cold plasma in Earth's plasmasphere on a global scale. The 30.4-nm feature is relatively easy to measure because it is the brightest ion emission from the plasmasphere, it is spectrally isolated, and the background at that wavelength is negligible. Measurements are easy to interpret because the plasmaspheric He⁺ emission is optically thin, so its brightness is directly proportional to the He⁺ column abundance. Effective imaging of the plasmaspheric He⁺ requires global `snapshots in which the high apogee and the wide field of view of EUV provide in a single exposure a map of the entire plasmasphere. EUV consists of three identical sensor heads, each having a field of view 30° in diameter. These sensors are tilted relative to one another to cover a fan-shaped field of 84°×30°, which is swept across the plasmasphere by the spin of the satellite. EUVs spatial resolution is 0.6° or 0.1 R_E in the equatorial plane seen from apogee. The sensitivity is 1.9 count s^–1 Rayleigh^–1, sufficient to map the position of the plasmapause with a time resolution of 10 min.  相似文献   

  总被引：1，自引：0，他引：1  

Reinisch  B.W.  Haines  D.M.  Bibl  K.  Cheney  G.  Galkin  I.A.  Huang  X.  Myers  S.H.  Sales  G.S.  Benson  R.F.  Fung  S.F.  Green  J.L.  Boardsen  S.  Taylor  W.W.L.  Bougeret  J.-L.  Manning  R.  Meyer-Vernet  N.  Moncuquet  M.  Carpenter  D.L.  Gallagher  D.L.  Reiff  P. 《Space Science Reviews》2000,91(1-2):319-359

Radio plasma imaging uses total reflection of electromagnetic waves from plasmas whose plasma frequencies equal the radio sounding frequency and whose electron density gradients are parallel to the wave normals. The Radio Plasma Imager (RPI) has two orthogonal 500-m long dipole antennas in the spin plane for near omni-directional transmission. The third antenna is a 20-m dipole along the spin axis. Echoes from the magnetopause, plasmasphere and cusp will be received with the three orthogonal antennas, allowing the determination of their angle-of-arrival. Thus it will be possible to create image fragments of the reflecting density structures. The instrument can execute a large variety of programmable measuring options at frequencies between 3 kHz and 3 MHz. Tuning of the transmit antennas provides optimum power transfer from the 10 W transmitter to the antennas. The instrument can operate in three active sounding modes: (1) remote sounding to probe magnetospheric boundaries, (2) local (relaxation) sounding to probe the local plasma frequency and scalar magnetic field, and (3) whistler stimulation sounding. In addition, there is a passive mode to record natural emissions, and to determine the local electron density, the scalar magnetic field, and temperature by using a thermal noise spectroscopy technique.  相似文献   

  总被引：2，自引：0，他引：2  

Roelof  Edmond C.  Skinner  Andrew J. 《Space Science Reviews》2000,91(1-2):437-459

Energetic neutral atom (ENA) and extreme ultra-violet photon (EUV) imagers will soon be probing magnetospheric ion distributions from the NASA space missions IMAGE and TWINS. Although ENA and EUV images will differ greatly, the same basic mathematical approach can be applied to deducing the ion distributions: extracting the parameters of a model ion distribution in a model magnetic field (and, in the case of ENA, interacting with a model cold neutral population). The model ion distribution is highly non-linear in its many parameters (as many as 38 have been used) in order to describe the strong spatial gradients of ion intensities in the magnetosphere. We have developed several new computer algorithms to accomplish the extraction by minimizing the differences between a simulated (instrument-specific) image and an observed image (or set of images). Towards the goal of a truly automated `hands-off extraction algorithm, we have combined three algorithms into a Hierarchical Simplex Algorithm. At each step of the minimization, it first tries a sophisticated and efficient Adaptive Conjugate Gradient algorithm. Then, if the error function is not reduced, it defers to an intermediate Analytic Simplex algorithm, and (if this step also fails) it finally defaults to the robust but inefficient Downhill Simplex algorithm. Whenever a step is successful, the algorithm begins the next step at the top of the hierarchy. We also offer a completely different approach (without minimization) for the interpretation of sharp `edges in the images (e.g., the plasmapause in He⁺ 30.4 nm EUV images of the plasmasphere). We demonstrate mathematically that the equatorial shape of the plasmapause can be constructed directly from the image using a simple graphical algorithm.  相似文献   

    

Littlejohn  K. DelPrincipe  M.V. Preston  J.D. 《Aerospace and Electronic Systems Magazine, IEEE》2000,15(11):3-7

Currently fielded embedded information systems face readiness challenges imposed by evolving missions and extended service lifespans. The ability to overcome these challenges is constrained by such factors as shrinking budgets, limited computational capacity and diminished manufacturing sources effects that impact both hardware and software options. Wholesale redevelopment is often cost prohibitive, particularly since large portions of embedded applications continue to fulfil mission requirements. Solutions must preserve prior investments while providing efficient pathways for continued technology refresh. A technology solution for affordable modernization of legacy system software is being development. The Embedded Information System Re-engineering (EISR) project is developing an automation-assisted JOVIAL-to-C re-engineering capability that permits simultaneous modernization of both the structure and source language of legacy embedded applications. Engineers will be able to apply the proven labor-saving visualization and analysis features of modern CASE tools to legacy JOVIAL applications. EISR will thus allow the DoD to recapture previous investments in proven legacy algorithms and mission capabilities while permitting the full exploitation of COTS economies of scale. This paper describes in brief the goals and objectives of the EISR project, and provides the current status of the EISR capability.  相似文献   

    

Abdul-Baki  B. Baldwin  J. Rudel  M.-P. 《Aerospace and Electronic Systems Magazine, IEEE》2000,15(8):3-21

This paper describes the specification-based testing, analysis tools, and associated processes used to independently validate, verify, and ultimately, provide for certifying safety-critical software developed for the Traffic Alert and Collision Avoidance System (TCAS II) program. These tools and processes comprise an effective and Independent Validation and Verification (IV and V) activity applied to the Collision Avoidance Subsystem (GAS) software development process. A requirements specification language called the Requirements State Machine Language (RSML), originally developed by the University of California, Irvine (UCI), was employed for the specification of GAS. The end result is the next generation of TCAS II collision avoidance logic, referred to as Version 7, that is of a higher quality than its predecessors, meets the certification requirements of DO-178B Level B (Ref. 1), and can be shown to satisfy the new operational requirements it was developed to address  相似文献   

    

Drumheller  D.M. Glasser  M.L. 《IEEE transactions on aerospace and electronic systems》1997,33(3):784-794

In a recent paper, general expressions were derived for the density and cumulative probability functions of the amplitude of a linear matched-filter output given a nonfluctuating target in a clutter-limited environment. These expressions were based on the clutter amplitude density function. The results are extended to calculate the cumulative probability function of the output of a linear matched filter used to detect a chi-square fluctuating target in a clutter-limited environment. The resulting method is applied to a common radar clutter model, and experimental sonar data.  相似文献   

    

Wilson JR 《Aerospace America》1997,35(6):28-32, 38

The development and testing of a new emergency Crew Return Vehicle (CRV) prototype is discussed. The new CRV is being developed by NASA and ESA and is designed for use on the International Space Station as a supplement to the Soyuz ships of the Russians, which accommodate only three passengers. The new vehicle will provide a shirt-sleeve environment for up to six astronauts and will allow for emergency medical treatment to be provided.  相似文献   

    

Sharpin  D.L. Tsui  J.B.Y. 《IEEE transactions on aerospace and electronic systems》1995,31(1):248-256

An analysis of the relationship between a linear amplifier chain and an analog-to-digital converter (ADC) in a digital microwave receiver, with respect to sensitivity and dynamic range issues, is presented. The effects of gain, third-order intermodulation products and ADC characteristics on the performance of the receiver are illustrated and design criteria for the linear amplifier chain (given a specified ADC) are developed. A computer program is included which calculates theoretical receiver performance based on gain and third-order intermodulation product selections. Experimental results are also presented and compared with theoretical values  相似文献