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71.
Israel G. Cabane M. Brun J-F. Niemann H. Way S. Riedler W. Steller M. Raulin F. Coscia D. 《Space Science Reviews》2002,104(1-4):433-468
ACP's main objective is the chemical analysis of the aerosols in Titan's atmosphere. For this purpose, it will sample the
aerosols during descent and prepare the collected matter (by evaporation, pyrolysis and gas products transfer) for analysis
by the Huygens Gas Chromatograph Mass Spectrometer (GCMS). A sampling system is required for sampling the aerosols in the
135'32 km and 22'17 km altitude regions of Titan's atmosphere. A pump unit is used to force the gas flow through a filter.
In its sampling position, the filter front face extends a few mm beyond the inlet tube. The oven is a pyrolysis furnace where
a heating element can heat the filter and hence the sampled aerosols to 250 °C or 600 °C. The oven contains the filter, which
has a thimble-like shape (height 28 mm). For transferring effluent gas and pyrolysis products to GCMS, the carrier gas is
a labeled nitrogen 15N2, to avoid unwanted secondary reactions with Titan's atmospheric nitrogen.
Aeraulic tests under cold temperature conditions were conducted by using a cold gas test system developed by ONERA. The objective
of the test was to demonstrate the functional ability of the instrument during the descent of the probe and to understand
its thermal behavior, that is to test the performance of all its components, pump unit and mechanisms.
In order to validate ACP's scientific performance, pyrolysis tests were conducted at LISA on solid phase material synthesized
from experimental simulation. The chromatogram obtained by GCMS analysis shows many organic compounds. Some GC peaks appear
clearly from the total mass spectra, with specific ions well identified thanks to the very high sensitivity of the mass spectrometer.
The program selected for calibrating the flight model is directly linked to the GCMS calibration plan. In order not to pollute
the two flight models with products of solid samples such as tholins, we excluded any direct pyrolysis tests through the ACP
oven during the first phase of the calibration. Post probe descent simulation of flight results are planned, using the much
representative GCMS and ACP spare models.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
72.
Peter C. Thomas Joseph Veverka Michael F. A’Hearn Lucy Mcfadden Michael J. S. Belton Jessica M. Sunshine 《Space Science Reviews》2005,117(1-2):193-205
The Deep Impact mission will provide the highest resolution images yet of a comet nucleus. Our knowledge of the makeup and
structure of cometary nuclei, and the processes shaping their surfaces, is extremely limited, thus use of the Deep Impact
data to show the geological context of the cratering experiment is crucial. This article briefly discusses some of the geological
issues of cometary nuclei. 相似文献
73.
Transient Modeling of Synchronous Machine-Transformer-SCR Bridge 总被引:1,自引:0,他引:1
A rigorous mathematical model of a synchronouschine-machine-transformer-thyristor bridge unit is presented in state-space form with coefficients that are explicit functions of standard parameters. The developed model has a minimum order for each of the various operation modes of the bridge, and its form is such that it can be readily interfaced with any type of dc network connected to the bridge. In addition, the model has the capability to consider different types of transformer winding connections. In a digital simulation, the explicit form of the state model eliminates the need of matrix inversions at each integration step. This and the use of the ?, ? reference frame result in a high computing efficiency and accuracy. As an illustration, simulation results are shown of a case study where the unit is part of a high-power pulse generating system. 相似文献
74.
Eberhard Grün Hugo Fechtig Martha S. Hanner Jochen Kissel Bertil-Anders Lindblad Dietmar Linkert Dieter Maas Gregor E. Morfill Herbert A. Zook 《Space Science Reviews》1992,60(1-4):317-340
The Galileo Dust Detector is intended to provide direct observations of dust grains with masses between 10-19 and 10-9 kg in interplanetary space and in the Jovian system, to investigate their physical and dynamical properties as functions of the distances to the Sun, to Jupiter and to its satellites, to study its interaction with the Galilean satellites and the Jovian magnetosphere. Surface phenomena of the satellites (like albedo variations), which might be effects of meteoroid impacts will be compared with the dust environment. Electric charges of particulate matter in the magnetosphere and its consequences will be studied; e.g., the effects of the magnetic field on the trajectories of dust particles and fragmentation of particles due to electrostatic disruption. The investigation is performed with an instrument that measures the mass, speed, flight direction and electric charge of individual dust particles. It is a multicoincidence detector with a mass sensitivity 106 times higher than that of previous in-situ experiments which measured dust in the outer solar system. The instrument weighs 4.2 kg, consumes 2.4 W, and has a normal data transmission rate of 24 bits s-1 in nominal spacecraft tracking mode. On December 29, 1989 the instrument was switched-on. After the instrument had been configured to flight conditions cruise science data collection started immediately. In the period to May 18, 1990 at least 168 dust impacts have been recorded. For 81 of these dust grains masses and impact speeds have been determined. First flux values are given. 相似文献
75.
Lee F.C. Carter R.A. Fang Z.D. 《IEEE transactions on aerospace and electronic systems》1983,(2):274-287
The stability and dynamic performances of a buck/boost regulator employing a current-injected control are examined. Small-signal models for the power state, the multiloop error processor, and the duty-cycle pulse modulator are developed. The error-processor model which incorporates the current-injected loop, the dc loop, and the compensation network permits evaluation of the effects of each individual control loop and their combined efforts toward shaping the performance characteristics of the closed-loop system. Comparisons are made between this modeling approach and earlier approaches. Some important yet subtle dissimilarities are discussed. This model predicts the constant-frequency 50-percent duty-cycle instability which is inherent to the current-injected control. 相似文献
76.
Rijsdijk F.B. van der Spek G.A. 《IEEE transactions on aerospace and electronic systems》1978,(2):226-236
For a planar-array antenna with a monopulse feed horn, this study describes a simple algorithm for the determination of the direction of target echoes. Antenna pattern measurements of the array indicate that the direction sines of a received wavefront can be independently obtained with one simple relation between a normalized difference channel output and a direction sine. This paper determines the accuracy of the algorithm. 相似文献
77.
S. J. Bauer L. H. Brace D. M. Hunten D. S. Intriligator W. C. Knudsen A. F. Nagy C. T. Russell F. L. Scarf J. H. Wolfe 《Space Science Reviews》1977,20(4):413-430
The current state of knowledge of the chemistry, dynamics and energetics of the upper atmosphere and ionosphere of Venus is reviewed together with the nature of the solar wind-Venus interaction. Because of the weak, though perhaps not negligible, intrinsic magnetic field of Venus, the mutual effects between these regions are probably strong and unique in the solar system. The ability of the Pioneer Venus Bus and Orbiter experiments to provide the required data to answer the questions outstanding is discussed in detail. 相似文献
78.
Multipath-adaptive GPS/INS receiver 总被引:2,自引:0,他引:2
Erickson J.W. Maybeck P.S. Raquet J.F. 《IEEE transactions on aerospace and electronic systems》2005,41(2):645-657
Multipath interference is one of the contributing sources of errors in precise global positioning system (GPS) position determination. This paper identifies key parameters of a multipath signal, focusing on estimating them accurately in order to mitigate multipath effects. Multiple model adaptive estimation (MMAE) techniques are applied to an inertial navigation system (INS)-coupled GPS receiver, based on a federated (distributed) Kalman filter design, to estimate the desired multipath parameters. The system configuration is one in which a GPS receiver and an INS are integrated together at the level of the in-phase and quadrature phase (I and Q) signals, rather than at the level of pseudo-range signals or navigation solutions. The system model of the MMAE is presented and the elemental Kalman filter design is examined. Different parameter search spaces are examined for accurate multipath parameter identification. The resulting GPS/INS receiver designs are validated through computer simulation of a user receiving signals from GPS satellites with multipath signal interference present The designed adaptive receiver provides pseudo-range estimates that are corrected for the effects of multipath interference, resulting in an integrated system that performs well with or without multipath interference present. 相似文献
79.
J. Scudder F. Hunsacker G. Miller J. Lobell T. Zawistowski K. Ogilvie J. Keller D. Chornay F. Herrero R. Fitzenreiter D. Fairfield J. Needell D. Bodet J. Googins C. Kletzing R. Torbert J. Vandiver R. Bentley W. Fillius C. McIlwain E. Whipple A. Korth 《Space Science Reviews》1995,71(1-4):459-495
HYDRA is an experimental hot plasma investigation for the POLAR spacecraft of the GGS program. A consortium of institutions has designed a suite of particle analyzers that sample the velocity space of electron and ions between 2 keV/q – 35 keV/q in three dimensions, with a routine time resolution of 0.5 s. Routine coverage of velocity space will be accomplished with an angular homogeneity assumption of 16°, appropriate for subsonic plasmas, but with special 1.5° resolution for electrons with energies between 100 eV and 10 keV along and opposed to the local magnetic field. This instrument produces 4.9 kilobits s–1 to the telemetry, consumes on average 14 W and requires 18.7 kg for deployment including its internal shielding. The scientific objectives for the polar magnetosphere fall into four broad categories: (1) those to define the ambient kinetic regimes of ions and electrons; (2) those to elucidate the magnetohydrodynamic responses in these regimes; (3) those to assess the particle populations with high time resolution; and (4) those to determine the global topology of the magnetic field. In thefirst group are issues of identifying the origins of particles at high magnetic latitudes, their energization, the altitude dependence of the forces, including parallel electric fields they have traversed. In thesecond group are the physics of the fluid flows, regimes of current, and plasma depletion zones during quiescent and disturbed magnetic conditions. In thethird group is the exploration of the processes that accompany the rapid time variations known to occur in the auroral zone, cusp and entry layers as they affect the flow of mass, momentum and energy in the auroral region. In thefourth class of objectives are studies in conjunction with the SWE measurements of the Strahl in the solar wind that exploit the small gyroradius of thermal electrons to detect those magnetic field lines that penetrate the auroral region that are directly open to interplanetary space where, for example, the Polar Rain is observed. 相似文献
80.
The nonlinear modeling and analysis of dc-dc converters has been done by averaging and discrete-sampling techniques. The averaging technique is simple, but inaccurate, as the modulation frequencies approach the theoretical limit of one-half the switching frequency. The discrete technique is accurate even at high frequencies, but is very complex and cumbersome. An improved model is developed by combining the aforementioned techniques. This new model is easy to implement in circuit and state variable forms and is accurate to the theoretical limit. 相似文献