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121.
M. van der Klis A. Peacock A. Smith N. White K. Mason G. Manzo 《Space Science Reviews》1985,40(1-2):297-304
Cygnus X-3 was observed with the GSPC on board EXOSAT on several occasions, one observation lasting for 7 orbital cycles. The width W and centroid energy E of the iron emission feature near 6.7 keV show a smooth, correlated, sinusoidal-type modulation, the iron line being widest and E being lowest just before X-ray maximum. The line profile may show a low-energy wing, but apart from this does not deviate strongly from a symmetric, Gaussian-type shape. The continuum at higher energies than the line is not completely smooth, but shows bumps which remain stable in time. Two possible explanations are discussed for the correlated variation of E and W as a function of orbital phase. 相似文献
122.
V. Wakelam I. W. M. Smith E. Herbst J. Troe W. Geppert H. Linnartz K. Öberg E. Roueff M. Agúndez P. Pernot H. M. Cuppen J. C. Loison D. Talbi 《Space Science Reviews》2010,156(1-4):13-72
We survey the current situation regarding chemical modelling of the synthesis of molecules in the interstellar medium. The present state of knowledge concerning the rate coefficients and their uncertainties for the major gas-phase processes—ion-neutral reactions, neutral-neutral reactions, radiative association, and dissociative recombination—is reviewed. Emphasis is placed on those key reactions that have been identified, by sensitivity analyses, as ‘crucial’ in determining the predicted abundances of the species observed in the interstellar medium. These sensitivity analyses have been carried out for gas-phase models of three representative, molecule-rich, astronomical sources: the cold dense molecular clouds TMC-1 and L134N, and the expanding circumstellar envelope IRC +10216. Our review has led to the proposal of new values and uncertainties for the rate coefficients of many of the key reactions. The impact of these new data on the predicted abundances in TMC-1 and L134N is reported. Interstellar dust particles also influence the observed abundances of molecules in the interstellar medium. Their role is included in gas-grain, as distinct from gas-phase only, models. We review the methods for incorporating both accretion onto, and reactions on, the surfaces of grains in such models, as well as describing some recent experimental efforts to simulate and examine relevant processes in the laboratory. These efforts include experiments on the surface-catalyzed recombination of hydrogen atoms, on chemical processing on and in the ices that are known to exist on the surface of interstellar grains, and on desorption processes, which may enable species formed on grains to return to the gas-phase. 相似文献
123.
M. P. Miralles L. Strachan L. D. Gardner P. L. Smith J. L. Kohl M. Guhathakurta R. R. Fisher 《Space Science Reviews》1999,87(1-2):277-281
The Spartan 201 flights from 1993 to 1995 provided us with observations in H I Lyman-α of several coronal hole/streamer boundaries
and adjacent streamers during the declining phase of the current solar cycle: Analysis of the latitudinal dependence of the
line intensities clearly shows that there is a boundary region at the coronal hole/streamer interface where the H I Lyman-α
intensity reaches a minimum value. Similar results are also found in UVCS/SOHO observations. We also discuss differences in
the coronal hole/streamer boundaries for different types of streamers and their changes over the three year period of Spartan
201 observations.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
124.
J.C. Bennett J. Sang C.H. Smith K. Zhang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Orbit manoeuvre of low Earth orbiting (LEO) debris using ground-based lasers has been proposed as a cost-effective means to avoid debris collisions. This requires the orbit of the debris object to be determined and predicted accurately so that the laser beam can be locked on the debris without the loss of valuable laser operation time. This paper presents the method and results of a short-term accurate LEO (<900 km in altitude) debris orbit prediction study using sparse laser ranging data collected by the EOS Space Debris Tracking System (SDTS). A main development is the estimation of the ballistic coefficients of the LEO objects from their archived long-term two line elements (TLE). When an object is laser tracked for two passes over about 24 h, orbit prediction (OP) accuracy of 10–20 arc seconds for the next 24–48 h can be achieved – the accuracy required for laser debris manoeuvre. The improvements in debris OP accuracy are significant in other applications such as debris conjunction analyses and the realisation of daytime debris laser tracking. 相似文献
125.
Maria T. Zuber Oded Aharonson Jonathan M. Aurnou Andrew F. Cheng Steven A. Hauck II Moritz H. Heimpel Gregory A. Neumann Stanton J. Peale Roger J. Phillips David E. Smith Sean C. Solomon Sabine Stanley 《Space Science Reviews》2007,131(1-4):105-132
Current geophysical knowledge of the planet Mercury is based upon observations from ground-based astronomy and flybys of the
Mariner 10 spacecraft, along with theoretical and computational studies. Mercury has the highest uncompressed density of the
terrestrial planets and by implication has a metallic core with a radius approximately 75% of the planetary radius. Mercury’s
spin rate is stably locked at 1.5 times the orbital mean motion. Capture into this state is the natural result of tidal evolution
if this is the only dissipative process affecting the spin, but the capture probability is enhanced if Mercury’s core were
molten at the time of capture. The discovery of Mercury’s magnetic field by Mariner 10 suggests the possibility that the core
is partially molten to the present, a result that is surprising given the planet’s size and a surface crater density indicative
of early cessation of significant volcanic activity. A present-day liquid outer core within Mercury would require either a
core sulfur content of at least several weight percent or an unusual history of heat loss from the planet’s core and silicate
fraction. A crustal remanent contribution to Mercury’s observed magnetic field cannot be ruled out on the basis of current
knowledge. Measurements from the MESSENGER orbiter, in combination with continued ground-based observations, hold the promise
of setting on a firmer basis our understanding of the structure and evolution of Mercury’s interior and the relationship of
that evolution to the planet’s geological history. 相似文献
126.
T.G. Guzik S. BesseA. Calongne A. DominiqueS.B. Ellison R. GouldD. Granger D. OlanoD. Smith M. StewartJ.P. Wefel 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
The High Altitude Student Platform (HASP) was originally conceived to provide student groups with access to the near-space environment for flight durations and experiment capabilities intermediate between what is possible with small sounding balloons and low Earth orbit rocket launches. HASP is designed to carry up to twelve student payloads to an altitude of about 36 km with flight durations of 15–20 h using a small zero-pressure polyethylene film balloon. This provides a flight capability that can be used to flight-test compact satellites, prototypes and other small payloads designed and built by students. HASP includes a standard mechanical, power and communication interface for the student payload to simplify integration and allows the payloads to be fully exercised. Over the last two years a partnership between the NASA Balloon Program Office (BPO), Columbia Scientific Balloon Facility (CSBF), Louisiana State University (LSU), the Louisiana Board of Regents (BoR), and the Louisiana Space Consortium (LaSPACE) has led to the development, construction and, finally, the first flight of HASP with a complement of eight student payloads on September 4, 2006. Here we discuss the primary as-built HASP systems and features, the student payload interface, HASP performance during the first flight and plans for continuing HASP flights. The HASP project maintains a website at http://laspace.lsu.edu/hasp/ where flight application, interface documentation and status information can be obtained. 相似文献
127.
The Juno Magnetic Field Investigation 总被引:2,自引:0,他引:2
J. E. P. Connerney M. Benn J. B. Bjarno T. Denver J. Espley J. L. Jorgensen P. S. Jorgensen P. Lawton A. Malinnikova J. M. Merayo S. Murphy J. Odom R. Oliversen R. Schnurr D. Sheppard E. J. Smith 《Space Science Reviews》2017,213(1-4):39-138
The Juno Magnetic Field investigation (MAG) characterizes Jupiter’s planetary magnetic field and magnetosphere, providing the first globally distributed and proximate measurements of the magnetic field of Jupiter. The magnetic field instrumentation consists of two independent magnetometer sensor suites, each consisting of a tri-axial Fluxgate Magnetometer (FGM) sensor and a pair of co-located imaging sensors mounted on an ultra-stable optical bench. The imaging system sensors are part of a subsystem that provides accurate attitude information (to ~20 arcsec on a spinning spacecraft) near the point of measurement of the magnetic field. The two sensor suites are accommodated at 10 and 12 m from the body of the spacecraft on a 4 m long magnetometer boom affixed to the outer end of one of ’s three solar array assemblies. The magnetometer sensors are controlled by independent and functionally identical electronics boards within the magnetometer electronics package mounted inside Juno’s massive radiation shielded vault. The imaging sensors are controlled by a fully hardware redundant electronics package also mounted within the radiation vault. Each magnetometer sensor measures the vector magnetic field with 100 ppm absolute vector accuracy over a wide dynamic range (to 16 Gauss = \(1.6 \times 10^{6}\mbox{ nT}\) per axis) with a resolution of ~0.05 nT in the most sensitive dynamic range (±1600 nT per axis). Both magnetometers sample the magnetic field simultaneously at an intrinsic sample rate of 64 vector samples per second. The magnetic field instrumentation may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. The attitude determination system compares images with an on-board star catalog to provide attitude solutions (quaternions) at a rate of up to 4 solutions per second, and may be configured to acquire images of selected targets for science and engineering analysis. The system tracks and catalogs objects that pass through the imager field of view and also provides a continuous record of radiation exposure. A spacecraft magnetic control program was implemented to provide a magnetically clean environment for the magnetic sensors, and residual spacecraft fields and/or sensor offsets are monitored in flight taking advantage of Juno’s spin (nominally 2 rpm) to separate environmental fields from those that rotate with the spacecraft. 相似文献
128.
Zwickl R.D. Doggett K.A. Sahm S. Barrett W.P. Grubb R.N. Detman T.R. Raben V.J. Smith C.W. Riley P. Gold R.E. Mewaldt R.A. Maruyama T. 《Space Science Reviews》1998,86(1-4):633-648
The Advanced Composition Explorer (ACE) RTSW system is continuously monitoring the solar wind and produces warnings of impending
major geomagnetic activity, up to one hour in advance. Warnings and alerts issued by NOAA allow those with systems sensitive
to such activity to take preventative action. The RTSW system gathers solar wind and energetic particle data at high time
resolution from four ACE instruments (MAG, SWEPAM, EPAM, and SIS), packs the data into a low-rate bit stream, and broadcasts
the data continuously. NASA sends real-time data to NOAA each day when downloading science data. With a combination of dedicated
ground stations (CRL in Japan and RAL in Great Britain), and time on existing ground tracking networks (NASA's DSN and the
USAF's AFSCN), the RTSW system can receive data 24 hours per day throughout the year. The raw data are immediately sent from
the ground station to the Space Environment Center in Boulder, Colorado, processed, and then delivered to its Space Weather
Operations center where they are used in daily operations; the data are also delivered to the CRL Regional Warning Center
at Hiraiso, Japan, to the USAF 55th Space Weather Squadron, and placed on the World Wide Web. The data are downloaded, processed
and dispersed within 5 min from the time they leave ACE. The RTSW system also uses the low-energy energetic particles to warn
of approaching interplanetary shocks, and to help monitor the flux of high-energy particles that can produce radiation damage
in satellite systems.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
129.
Maxwell's equations govern the eddy-current phenomenon, and are the starting point of this analysis. It is shown that Maxwell's equations, as applied to steady-state ac conditions, can be transformed to a Fredholm-type integral equation in eddy-current density. In turn, it is demonstrated that the method of subareas can be used to solve the Fredholm equation. This approach leads to the familiar circuit-analysis concepts of resistance and inductance in finite coupled circuits. The coupledcircuit method can be utilized in cases of complex, mixed boundary conditions without difficulty, as is illustrated by an example of the eddy-current losses in a conducting disk of finite thickness and finite radius, in the presence of a current-carrying loop. Experimental data is presented which confirms the theory, for a range of disk thicknesses. References are included to previous work. 相似文献
130.
Bozdağ Ebru Ruan Youyi Metthez Nathan Khan Amir Leng Kuangdai van Driel Martin Wieczorek Mark Rivoldini Attilio Larmat Carène S. Giardini Domenico Tromp Jeroen Lognonné Philippe Banerdt Bruce W. 《Space Science Reviews》2017,211(1-4):571-594
Space Science Reviews - We present global and regional synthetic seismograms computed for 1D and 3D Mars models based on the spectral-element method. For global simulations, we implemented a... 相似文献