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11.
Timothy G. Hawarden Robert Crane Harley A. Thronson Jr. Alan J. Penny Anna H. Orlowska Thomas W. Bradshaw 《Space Science Reviews》1995,74(1-2):45-56
The designs of cold space telescopes, cryogenic and radiatively cooled, are similar in most elements and both benefit from orbits distant from the Earth. In particular such orbits allow the anti-sunward side of radiatively-cooled spacecraft to be used to provide large cooling radiators for the individual radiation shields. Designs incorporating these features have predictedT
tel near 20 K. The attainability of such temperatures is supported by limited practical experience (IRAS, COBE). Supplementary cooling systems (cryogens, mechanical coolers) can be advantageously combined with radiative cooling in hybrid designs to provide robustness against deterioration and yet lower temperatures for detectors, instruments, and even the whole telescope. The possibility of such major additional gains is illustrated by the Very Cold Telescope option under study forEdison, which should offerT
tel5 K for a little extra mechanical cooling capacity. 相似文献
12.
Robert A. Bettinger 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(10):3267-3281
A unique logic-based algorithm for atmospheric reentry hemisphere prediction is presented for spacecraft in low-eccentricity, prograde low Earth orbits at altitudes of 300 km and lower. Using two-line element (TLE) data for initial orbit conditions, coupled with coarse estimates for spacecraft aerodynamic characteristics, the algorithm relies on logical disjunction operations based on a dual analysis of histogram and two-weighted Gaussian probability density function (PDF) fits of predicted reentry latitude data. The algorithm requires the execution of a series of parametric simulations to determine the reentry hemisphere for variations in spacecraft aerodynamic coefficients and drag reference area. When implemented, the algorithm yields accurate hemisphere predictions on average 15 days from reentry as demonstrated by historical reentry cases from 1979 to 2018. All reentry cases were selected to demonstrate the algorithm’s ability to deliver accurate reentry hemisphere predictions for spacecraft with varying physical size and mass, and reentering during different periods of solar cycle activity. 相似文献
13.
Nathan R. Boone Robert A. Bettinger 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(8):2319-2332
The theoretical analysis of the motion of natural space debris near the stable Earth-Moon Lagrange Points, and , is presented with a focus on the potential debris risks to spacecraft operating near these points. Specifically, the research formulates a debris propagation model using four-body dynamics, then applies candidate probabilistic survivability models to a notional spacecraft operating at the and Lagrange points to quantify the collision risks to the spacecraft from natural debris particles. Of the survivability models implemented, the natural debris collision risks to spacecraft survivability are found to be incredibly low, but mitigation strategies to reduce the risk further are identified in this study. Overall, research into stable Lagrange point natural debris propagation improves understanding of the collision risks posed by the naturally occurring Kordylewski clouds and enhances operational planning for Lagrange point space missions. 相似文献
14.
David Blake David Vaniman Cherie Achilles Robert Anderson David Bish Tom Bristow Curtis Chen Steve Chipera Joy Crisp David Des?Marais Robert T. Downs Jack Farmer Sabrina Feldman Mark Fonda Marc Gailhanou Hongwei Ma Doug W. Ming Richard V. Morris Philippe Sarrazin Ed Stolper Allan Treiman Albert Yen 《Space Science Reviews》2012,170(1-4):341-399
A principal goal of the Mars Science Laboratory (MSL) rover Curiosity is to identify and characterize past habitable environments on Mars. Determination of the mineralogical and chemical composition of Martian rocks and soils constrains their formation and alteration pathways, providing information on climate and habitability through time. The CheMin X-ray diffraction (XRD) and X-ray fluorescence (XRF) instrument on MSL will return accurate mineralogical identifications and quantitative phase abundances for scooped soil samples and drilled rock powders collected at Gale Crater during Curiosity’s 1-Mars-year nominal mission. The instrument has a Co X-ray source and a cooled charge-coupled device (CCD) detector arranged in transmission geometry with the sample. CheMin’s angular range of 5° to 50° 2θ with <0.35° 2θ resolution is sufficient to identify and quantify virtually all minerals. CheMin’s XRF requirement was descoped for technical and budgetary reasons. However, X-ray energy discrimination is still required to separate Co?Kα from Co?Kβ and Fe?Kα photons. The X-ray energy-dispersive histograms (EDH) returned along with XRD for instrument evaluation should be useful in identifying elements Z>13 that are contained in the sample. The CheMin XRD is equipped with internal chemical and mineralogical standards and 27 reusable sample cells with either Mylar? or Kapton? windows to accommodate acidic-to-basic environmental conditions. The CheMin flight model (FM) instrument will be calibrated utilizing analyses of common samples against a demonstration-model (DM) instrument and CheMin-like laboratory instruments. The samples include phyllosilicate and sulfate minerals that are expected at Gale crater on the basis of remote sensing observations. 相似文献
15.
双盘转子碰摩的弯曲和扭转振动实验研究 总被引:1,自引:1,他引:1
设计了 1个新型多自由度的双盘转子动静件碰摩实验器。应用该实验装置 ,重点研究了转子动、静碰摩后的转子弯曲和扭转振动。实验结果表明 ,转静件碰摩主要激起系统扭转自然频率振动 ;同时 ,弯曲振动复杂。不同情况下的转静件碰摩 ,转子具有不同的弯曲和扭转振动响应。根据转子扭转振动的变化可诊断转静件碰摩故障 ,与理论研究的结果相吻合 相似文献
16.
Sean C. Solomon Ralph L. McNutt Jr. Robert E. Gold Deborah L. Domingue 《Space Science Reviews》2007,131(1-4):3-39
The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, launched on August 3, 2004, is nearing the halfway point on its voyage to become the first probe to orbit the planet Mercury. The mission, spacecraft, and payload are designed to answer six fundamental questions regarding the innermost planet: (1) What planetary formational processes led to Mercury’s high ratio of metal to silicate? (2) What is the geological history of Mercury? (3) What are the nature and origin of Mercury’s magnetic field? (4) What are the structure and state of Mercury’s core? (5) What are the radar-reflective materials at Mercury’s poles? (6) What are the important volatile species and their sources and sinks near Mercury? The mission has focused to date on commissioning the spacecraft and science payload as well as planning for flyby and orbital operations. The second Venus flyby (June 2007) will complete final rehearsals for the Mercury flyby operations in January and October 2008 and September 2009. Those flybys will provide opportunities to image the hemisphere of the planet not seen by Mariner 10, obtain high-resolution spectral observations with which to map surface mineralogy and assay the exosphere, and carry out an exploration of the magnetic field and energetic particle distribution in the near-Mercury environment. The orbital phase, beginning on March 18, 2011, is a one-year-long, near-polar-orbital observational campaign that will address all mission goals. The orbital phase will complete global imaging, yield detailed surface compositional and topographic data over the northern hemisphere, determine the geometry of Mercury’s internal magnetic field and magnetosphere, ascertain the radius and physical state of Mercury’s outer core, assess the nature of Mercury’s polar deposits, and inventory exospheric neutrals and magnetospheric charged particle species over a range of dynamic conditions. Answering the questions that have guided the MESSENGER mission will expand our understanding of the formation and evolution of the terrestrial planets as a family. 相似文献
17.
利用简化的飞机模型,通过改变尾翼的迎角及展弦比,试图建立一种能加速自我消亡的尾流涡系统.该实验在拖曳水槽中进行,运用SPIV(体视粒子图像测速技术)系统进行测量,获得了一系列空间切面的2D/3C(二维/三分量)数据,给出了三种不同尾翼情况(两种有尾翼情况及一种无尾翼情况)下的SPIV观测结果,并将这几种情况作了对比. 相似文献
18.
航空维修业正处在发展的十字路口.一些航空公司将其维修业务剥离出去以增加现金流,独立的航空维修企业正在进行调整以应对不断改变的市场环境,更多的维修企业则在寻求新的投资和合作伙伴. 相似文献
19.
Louise M. Prockter Rosaly M. C. Lopes Bernd Giese Ralf Jaumann Ralph D. Lorenz Robert T. Pappalardo Gerald W. Patterson Peter C. Thomas Elizabeth P. Turtle Roland J. Wagner 《Space Science Reviews》2010,153(1-4):63-111
The surfaces of the Solar System’s icy satellites show an extraordinary variety of morphological features, which bear witness to exchange processes between the surface and subsurface. In this paper we review the characteristics of surface features on the moons of Jupiter, Saturn, Uranus and Neptune. Using data from spacecraft missions, we discuss the detailed morphology, size, and topography of cryovolcanic, tectonic, aeolian, fluvial, and impact features of both large moons and smaller satellites. 相似文献
20.
Cassini Imaging Science: Instrument Characteristics And Anticipated Scientific Investigations At Saturn 总被引:1,自引:0,他引:1
Carolyn C. Porco Robert A. West Steven Squyres Alfred Mcewen Peter Thomas Carl D. Murray Anthony Delgenio Andrew P. Ingersoll Torrence V. Johnson Gerhard Neukum Joseph Veverka Luke Dones Andre Brahic Joseph A. Burns Vance Haemmerle Benjamin Knowles Douglas Dawson Thomas Roatsch Kevin Beurle William Owen 《Space Science Reviews》2004,115(1-4):363-497
The Cassini Imaging Science Subsystem (ISS) is the highest-resolution two-dimensional imaging device on the Cassini Orbiter and has been designed for investigations of the bodies and phenomena found within the Saturnian planetary system. It consists of two framing cameras: a narrow angle, reflecting telescope with a 2-m focal length and a square field of view (FOV) 0.35∘ across, and a wide-angle refractor with a 0.2-m focal length and a FOV 3.5∘ across. At the heart of each camera is a charged coupled device (CCD) detector consisting of a 1024 square array of pixels, each 12 μ on a side. The data system allows many options for data collection, including choices for on-chip summing, rapid imaging and data compression. Each camera is outfitted with a large number of spectral filters which, taken together, span the electromagnetic spectrum from 200 to 1100 nm. These were chosen to address a multitude of Saturn-system scientific objectives: sounding the three-dimensional cloud structure and meteorology of the Saturn and Titan atmospheres, capturing lightning on both bodies, imaging the surfaces of Saturn’s many icy satellites, determining the structure of its enormous ring system, searching for previously undiscovered Saturnian moons (within and exterior to the rings), peering through the hazy Titan atmosphere to its yet-unexplored surface, and in general searching for temporal variability throughout the system on a variety of time scales. The ISS is also the optical navigation instrument for the Cassini mission. We describe here the capabilities and characteristics of the Cassini ISS, determined from both ground calibration data and in-flight data taken during cruise, and the Saturn-system investigations that will be conducted with it. At the time of writing, Cassini is approaching Saturn and the images returned to Earth thus far are both breathtaking and promising.This revised version was published online in July 2005 with a corrected cover date. 相似文献