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201.
Campbell James P. Blinn John C. 《IEEE transactions on aerospace and electronic systems》1968,(4):620-626
Experiments were conducted to determine the feasibility of using a passive microwave sensor of velocity/altitude ratio (V/H) as the basis for an aircraft navigation system. This sensor, combined with a radar altimeter, yields the velocity information needed for navigation. Airborne measurements were made with a two-beam X-band radiometer in a C-47 test aircraft. Radiometer signals and auxiliary information were recorded on magnetic tape. Ground-based data processing provided a comparison of radiometer-derived V/H measurements with those derived from independent sensors. Good results (fluctuating errors comparable to experimental uncertainties) were obtained over green farmland, urban areas, rice paddies, and certain desert areas; marginal results were obtained over other deserts and winter farmland. It was concluded that a microwave V/H sensor is feasible as the basis for a navigation system at low altitude over favorable terrains. 相似文献
202.
James B. Pollack 《Space Science Reviews》1975,18(1):3-93
This paper reviews observations of the rings of Saturn at visual, infrared, and radio wave-lengths. Critical assessments are made of attempts to derive the physical characteristics of the rings from these measurements. A discussion is also given of the origin and evolution of the rings. 相似文献
203.
204.
James B. Pezent Rohan Sood Andrew Heaton 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(9):2981-2994
Regions outside the reach of traditional propulsion systems or the ones that require significant propellant, may be reached by harnessing the solar radiation pressure and leveraging coupled dynamics to maneuver a sail-based spacecraft. Earth-trailing orbits have recently been investigated for getting a unique perspective of the Sun while maintaining the spacecraft in close proximity to Earth. Vertical orbits trailing the Earth exhibit the additional capability to view the Sun from above and below the ecliptic plane. In this work, families of sail-based orbits are explored for varying Earth-trailing angles and Z amplitudes in the Sun-Earth circular restricted three-body problem. Optimization is carried out to ensure that the non-traditional vertical orbits exhibit a constant pitch angle control history, as well as symmetry across the X-Y plane. The stability of the resulting orbit families is assessed using an extension of Flouquet theory to Differential Algebraic Equations. Results indicate that sail-based Earth-trailing vertical orbits can be more stable than traditional sub-L1 sail-based vertical orbits. 相似文献
205.
James A. Blake Paul Chote Don Pollacco William Feline Grant Privett Andrew Ash Stuart Eves Arthur Greenwood Nick Harwood Thomas R. Marsh Dimitri Veras Christopher Watson 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(1):360-370
Recent anomalies exhibited by satellites and rocket bodies have highlighted that a population of faint debris exists at geosynchronous (GEO) altitudes, where there are no natural removal mechanisms. Despite previous optical surveys probing to around 10–20 cm in size, regular monitoring of faint sources at GEO is challenging, thus our knowledge remains sparse. It is essential that we continue to explore the faint debris population using large telescopes to better understand the risk posed to active GEO satellites. To this end, we present photometric results from a survey of the GEO region carried out with the 2.54 m Isaac Newton Telescope in La Palma, Canary Islands. We probe to 21st visual magnitude (around 10 cm, assuming Lambertian spheres with an albedo of 0.1), uncovering 129 orbital tracks with GEO-like motion across the eight nights of dark-grey time comprising the survey. The faint end of our brightness distribution continues to rise until the sensitivity limit of the sensor is reached, suggesting that the modal brightness could be even fainter. We uncover a number of faint, uncatalogued objects that show photometric signatures of rapid tumbling, many of which straddle the limiting magnitude of our survey over the course of a single exposure, posing a complex issue when estimating object size. This work presents the first instalment of DebrisWatch, an ongoing collaboration between the University of Warwick and the Defence Science and Technology Laboratory (UK) investigating the faint population of GEO debris. 相似文献
206.
据《航空周刊》预测,2020年商用飞机发动机售后市场的MRO总支出将跃升至347亿美元,其中窄体飞机发动机MRO总支出的占比将达到42%,返厂维修量将激增,许多MRO供应商在全球的车间内将全年12个月的产能都调至接近最大。鉴于这种产能供不应求的局面,发动机OEM和MRO企业都在不断调整战略。 相似文献
207.
Martin M. Sirk Eric J. Korpela Yuzo Ishikawa Jerry Edelstein Edward H. Wishnow Christopher Smith Jeremy McCauley Jason B. McPhate James Curtis Travis Curtis Steven R. Gibson Sharon Jelinsky Jeffrey A. Lynn Mario Marckwordt Nathan Miller Michael Raffanti William Van Shourt Andrew W. Stephan Thomas J. Immel 《Space Science Reviews》2017,212(1-2):631-643
We present the design, implementation, and on-ground performance measurements of the Ionospheric Connection Explorer EUV spectrometer, ICON EUV, a wide field (\(17^{\circ}\times 12^{\circ}\)) extreme ultraviolet (EUV) imaging spectrograph designed to observe the lower ionosphere at tangent altitudes between 100 and 500 km. The primary targets of the spectrometer, which has a spectral range of 54–88 nm, are the Oii emission lines at 61.6 nm and 83.4 nm. Its design, using a single optical element, permits a imaging resolution perpendicular to the spectral dispersion direction with a large (\(12^{\circ} \)) acceptance parallel to the dispersion direction while providing a slit-width dominated spectral resolution of \(R\sim25\) at 58.4 nm. Pre-flight calibration shows that the instrument has met all of the science performance requirements. 相似文献
208.
The Lunar Orbiter Laser Altimeter Investigation on the Lunar Reconnaissance Orbiter Mission 总被引:3,自引:0,他引:3
David E. Smith Maria T. Zuber Glenn B. Jackson John F. Cavanaugh Gregory A. Neumann Haris Riris Xiaoli Sun Ronald S. Zellar Craig Coltharp Joseph Connelly Richard B. Katz Igor Kleyner Peter Liiva Adam Matuszeski Erwan M. Mazarico Jan F. McGarry Anne-Marie Novo-Gradac Melanie N. Ott Carlton Peters Luis A. Ramos-Izquierdo Lawrence Ramsey David D. Rowlands Stephen Schmidt V. Stanley Scott III George B. Shaw James C. Smith Joseph-Paul Swinski Mark H. Torrence Glenn Unger Anthony W. Yu Thomas W. Zagwodzki 《Space Science Reviews》2010,150(1-4):209-241
The Lunar Orbiter Laser Altimeter (LOLA) is an instrument on the payload of NASA’s Lunar Reconnaissance Orbiter spacecraft (LRO) (Chin et al., in Space Sci. Rev. 129:391–419, 2007). The instrument is designed to measure the shape of the Moon by measuring precisely the range from the spacecraft to the lunar surface, and incorporating precision orbit determination of LRO, referencing surface ranges to the Moon’s center of mass. LOLA has 5 beams and operates at 28 Hz, with a nominal accuracy of 10 cm. Its primary objective is to produce a global geodetic grid for the Moon to which all other observations can be precisely referenced. 相似文献
209.
Sharon Kedar Jose Andrade Bruce Banerdt Pierre Delage Matt Golombek Matthias Grott Troy Hudson Aaron Kiely Martin Knapmeyer Brigitte Knapmeyer-Endrun Christian Krause Taichi Kawamura Philippe Lognonne Tom Pike Youyi Ruan Tilman Spohn Nick Teanby Jeroen Tromp James Wookey 《Space Science Reviews》2017,211(1-4):315-337
InSight’s Seismic Experiment for Interior Structure (SEIS) provides a unique and unprecedented opportunity to conduct the first geotechnical survey of the Martian soil by taking advantage of the repeated seismic signals that will be generated by the mole of the Heat Flow and Physical Properties Package (HP3). Knowledge of the elastic properties of the Martian regolith have implications to material strength and can constrain models of water content, and provide context to geological processes and history that have acted on the landing site in western Elysium Planitia. Moreover, it will help to reduce travel-time errors introduced into the analysis of seismic data due to poor knowledge of the shallow subsurface. The challenge faced by the InSight team is to overcome the limited temporal resolution of the sharp hammer signals, which have significantly higher frequency content than the SEIS 100 Hz sampling rate. Fortunately, since the mole propagates at a rate of \(\sim1~\mbox{mm}\) per stroke down to 5 m depth, we anticipate thousands of seismic signals, which will vary very gradually as the mole travels.Using a combination of field measurements and modeling we simulate a seismic data set that mimics the InSight HP3-SEIS scenario, and the resolution of the InSight seismometer data. We demonstrate that the direct signal, and more importantly an anticipated reflected signal from the interface between the bottom of the regolith layer and an underlying lava flow, are likely to be observed both by Insight’s Very Broad Band (VBB) seismometer and Short Period (SP) seismometer. We have outlined several strategies to increase the signal temporal resolution using the multitude of hammer stroke and internal timing information to stack and interpolate multiple signals, and demonstrated that in spite of the low resolution, the key parameters—seismic velocities and regolith depth—can be retrieved with a high degree of confidence. 相似文献
210.
Paul R. Mahaffy Mehdi Benna Todd King Daniel N. Harpold Robert Arvey Michael Barciniak Mirl Bendt Daniel Carrigan Therese Errigo Vincent Holmes Christopher S. Johnson James Kellogg Patrick Kimvilakani Matthew Lefavor Jerome Hengemihle Ferzan Jaeger Eric Lyness John Maurer Anthony Melak Felix Noreiga Marvin Noriega Kiran Patel Benito Prats Eric Raaen Florence Tan Edwin Weidner Cynthia Gundersen Steven Battel Bruce P. Block Ken Arnett Ryan Miller Curt Cooper Charles Edmonson J. Thomas Nolan 《Space Science Reviews》2015,196(1-4):49-77