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211.
New Horizons Mission Design 总被引:1,自引:0,他引:1
In the first mission to Pluto, the New Horizons spacecraft was launched on January 19, 2006, and flew by Jupiter on February 28, 2007, gaining a significant speed boost from Jupiter’s gravity assist. After a 9.5-year journey, the spacecraft will encounter Pluto on July 14, 2015, followed by an extended mission to the Kuiper Belt objects for the first time. The mission design for New Horizons went through more than five years of numerous revisions and updates, as various mission scenarios regarding routes to Pluto and launch opportunities were investigated in order to meet the New Horizons mission’s objectives, requirements, and goals. Great efforts have been made to optimize the mission design under various constraints in each of the key aspects, including launch window, interplanetary trajectory, Jupiter gravity-assist flyby, Pluto–Charon encounter with science measurement requirements, and extended mission to the Kuiper Belt and beyond. Favorable encounter geometry, flyby trajectory, and arrival time for the Pluto–Charon encounter were found in the baseline design to enable all of the desired science measurements for the mission. The New Horizons mission trajectory was designed as a ballistic flight from Earth to Pluto, and all energy and the associated orbit state required for arriving at Pluto at the desired time and encounter geometry were computed and specified in the launch targets. The spacecraft’s flight thus far has been extremely efficient, with the actual trajectory error correction ΔV being much less than the budgeted amount. 相似文献
212.
Loehr J. Siskaninetz W. Wiemeri J. Feld S. 《Aerospace and Electronic Systems Magazine, IEEE》1998,13(4):9-12
Avionic information processing and transmission requirements are increasing geometrically, with no end in sight, The only feasible way to meet them is to incorporate fiber-optic communication systems into avionic platforms, Such systems can be employed to replace standard electronic components, to augment existing systems, or to enable new technologies. In this paper, we survey the field of low-power communication systems from the avionics engineering perspective. We review the fundamental merits of optical fiber for information transmission and discuss various information modulation schemes. These modulation techniques determine the performance requirements for laser transmitters, We describe the horizontal- and vertical-cavity semiconductor lasers currently available for these systems, and measure their performance against the additional environmental constraints of avionics platforms. Finally, we outline expected near- and far-term trends in system and device development 相似文献
213.
The original basis for the Lorentz transformations, and thus special relativity, was the assumption that the observed velocity of interaction of light with matter represents a unique velocity of the electromagnetic wave. This arbitrary decision is not borne out by Maxwell's theories or by any test that might prove that EM energy actually travels in a continuum of velocities. The second postulate as stated by Einstein does not deserve the status of a postulate, as it is at once overly restrictive and ultimately phenomenological-the nature of c is based on experimental measurement rather than on analysis of first principles. The radiation continuum model's (RCM) modified second postulate, however, says nothing about the actual propagation of EM energy, but only of the relative speed with which it must interact with matter to be detected. Utilizing this modified light principle we obtain an intuitive Galilean form invariance for Maxwell's equations. RCM places no upper limit on attainable velocities, and allows for the possibility of communications between humans or particles at speeds far in excess of c. This precludes many of the compatibility problems between the highly successful quantum mechanics and relativity theory 相似文献
214.
H.G. Mayr I. Harris F.A. Herrero N.W. Spencer A.E. Hedin R.E. Hartle H.A. Taylor L.E. Wharton F. Varosi H. Volland G.R. Carignan 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(4):283-288
Thermospheric temperature, composition and wind measurements from the Dynamics Explorer satellite (DE-2) are interpreted using a three dimensional, multiconstituent spectral model. The analysis accounts for tides driven by the absorbed solar radiation as well as energy and momentum coupling involving the magnetosphere and lower atmosphere. We discuss phenomena associated with the annual tide, polar circulation, magnetic storms and substorms. 相似文献
215.
H. Fuke J.E. Koglin T. Yoshida T. Aramaki W.W. Craig L. Fabris F. Gahbauer C.J. Hailey F.J. Jou N. Madden K. Mori H.T. Yu K.P. Ziock 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(12):2056-2060
We discuss current progress and future plans for the general antiparticle spectrometer experiment (GAPS). GAPS detects antideuterons through the X-rays and pions emitted during the deexcitation of exotic atoms formed when the antideuterons are slowed down and stopped in targets. GAPS provides an exceptionally sensitive means to detect cosmic-ray antideuterons. Cosmic-ray antideuterons can provide indirect evidence for the existence of dark matter in such form as neutralinos or Kaluza–Klein particles. We describe results of accelerator testing of GAPS prototypes, tentative design concepts for a flight GAPS detector, and near-term plans for flying a GAPS prototype on a balloon. 相似文献
216.
David W. Forslund 《Space Science Reviews》1985,42(1-2):3-16
With the increasing size and speed of modern supercomputers, the incredibly complex nonlinear properties of plasmas in the
laboratory and in space are being successfully explored in increasing depth. Of particular importance have been numerical
simulation techniques involving finite size particles on a discrete mesh. After discussing the importance of this means of
understanding a variety of nonlinear plasma phenomena, we describe the basic elements of particle-in-cell simulation and their
limitations and advantages. The differencing techniques, stability and accuracy issues, data management and optimization issues
are discussed by a simple example of a particle-in-cell code. Recent advances in simulation methods allowing large space and
time scales to be treated with minimal sacrifice in physics are reviewed. Various examples of nonlinear processes successfully
studied by plasma simulation are given. 相似文献
217.
218.
Sanneman Richard W. Gupta Someshwar C. 《IEEE transactions on aerospace and electronic systems》1966,(5):570-581
Pontryagin's maximum principle is applied to minimize the time for a phase-locked loop to lock to a step change in frequency. In particular, a Type II phase-locked loop is considered in detail. Phase control and frequency control of the input signal are analyzed with the nonlinearity of the phase detector taken into consideration. It is shown that application of Pontryagin's maximum principle offers a decided advantage in shortening this time by proper control. 相似文献
219.
Maxwell W. Hunter II 《Space Science Reviews》1967,6(5):601-654
Velocity requirements for scientific probe vehicles operating throughout the entire solar system are presented. Both direct flights and those using planetary swingby modes are considered. Launch-vehicle and payload sizes necessary to perform useful scientific missions are examined. Scientific investigation of the solar system is shown to be much less difficult than is commonly believed. 相似文献
220.
J.B. Cladis W.E. Francis 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(4):415-419
The transport of ions from the polar ionosphere to the inner magnetosphere during stormtime conditions has been computed using a Monte Carlo diffusion code. The effect of the electrostatic turbulence assumed to be present during the substorm expansion phase was simulated by a process that accelerated the ions stochastically perpendicular to the magnetic field with a diffusion coefficient proportional to the energization rate of the ions by the induced electric field. This diffusion process was continued as the ions were convected from the plasma sheet boundary layer to the double-spiral injection boundary. Inward of the injection boundary, the ions were convected adiabatically. By using as input an O+ flux of 2.8 × 108 cm?2 s?1 (w > 10 eV) and an H+ flux of 5.5 × 108 cm?2 s?1 (w > .63 eV), the computed distribution functions of the ions in the ring current were found to be in good agreement, over a wide range in L (4 to 8), with measurements made with the ISEE-1 satellite during a storm. This O+ flux and a large part of the H+ flux are consistent with the DE satellite measurements of the polar ionospheric outflow during disturbed times. 相似文献