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701.
Electro Energy Inc. (EEI) is developing high power, long life, bipolar nickel-metal hydride batteries for aerospace applications. Bipolar nickel-metal hydride designs allow for high energy and high power designs with a 25 percent reduction in both weight and volume as compared to prismatic and/or cylindrical Ni-MH designs. Utilizing a sealed wafer cell design EEI has demonstrated a 1.2 kW/kg power capability. Prototype designs have achieved 70 Wh/kg. Designs studies show 80 Wh/kg are achievable with EEI's state-of-the-art technology. The sealed wafer cell is the building block for EEI's high power and high voltage bipolar batteries making the assembly easy and significantly lower in cost. Satellite and aircraft batteries are being developed which provide high power and long life. Sealed cells now show excellent rate capability and life. Cells tested in a low earth orbit (LEO) cycle have reached 9000 cycles and continue on test. High power, bipolar battery designs are ideal in applications where using conventional aerospace battery technology would require excessive capacity; weight and volume, thereby reducing usable payload on the vehicle 相似文献
702.
A five-phase Power Management and Distribution System for a More-Electric Aircraft (MADMEL) program was awarded by the Air Force to Northrop/Grumman Military Aircraft Division in September 1991. The objective of the program is to design, develop, and demonstrate an advanced electrical power generation and distribution system for a More-Electric Aircraft (MEA). The MEA emphasizes the use of electrical power in place of hydraulics, pneumatic, and mechanical power to optimize the performance and life cycle cost of the aircraft. This paper presents an overview of the MADMEL program and a top-level summary of the program results, development and test of major components to date. In Phase I and Phase II studies, the electrical load requirements were established and the electrical power system architecture was defined for both near-term (NT-year 1996) and far-term (FT-year 2003) MEA application. The detailed design and specification for the Electrical Power System (EPS), its interface with the Vehicle Management System, and the test set-up were developed under Phase III. Phase IV, fabrication and testing of the subsystem level hardware, has been completed. Overall system level integration and testing, Phase V, is scheduled to be completed by September 1999 相似文献
703.
A possible variant presented for solving the equation of motion of a rotating flow is more general with respect to the variants known in the literature. On the basis of the simultaneous solution of the equations of motion and energy, the temperature fields are determined under changes of the rotation nature. 相似文献
704.
Aeronautical telemetry using multiple-antenna transmitters 总被引:1,自引:0,他引:1
Jensen M.A. Rice M.D. Anderson A.L. 《IEEE transactions on aerospace and electronic systems》2007,43(1):262-272
The placement of multiple antennas on an air vehicle is one possible practice for overcoming signal obstruction created by vehicle maneuvering during air-to-ground transmission. Unfortunately, for vehicle attitudes where more than one of these antennas has a clear path to the receiving station, this practice also leads to self-interference nulls, resulting in dramatic degradation in the average signal integrity. This paper discusses application of unitary space-time codes such as the Alamouti transmit diversity scheme and unitary differential space-time codes to overcome the self-interference effect observed in such systems. The mathematical foundations of these techniques within the context of this application as well as computational performance gains associated with their implementation are provided. Issues such as the cost of channel estimation for trained techniques as well as the throughput performance of nondifferential and differential schemes for realistic air-vehicle motion are analyzed 相似文献
705.
McEneaney W.M. Fitzpatrick B.G. Lauko I.G. 《IEEE transactions on aerospace and electronic systems》2004,40(4):1191-1216
A command and control (C/sup 2/) problem for military air operations is addressed. Specifically, we consider C/sup 2/ problems for air vehicles against ground-based targets and defensive systems. The problem is viewed as a stochastic game. We restrict our attention to the C/sup 2/ level where the problem may consist of a few unmanned combat air vehicles (UCAVs) or aircraft (or possibly teams of vehicles), less than say, a half-dozen enemy surface-to-air missile air defense units (SAMs), a few enemy assets (viewed as targets from our standpoint), and some enemy decoys (assumed to mimic SAM radar signatures). At this low level, some targets are mapped out and possible SAM sites that are unavoidably part of the situation are known. One may then employ a discrete stochastic game problem formulation to determine which of these SAMs should optimally be engaged (if any), and by what series of air vehicle operations. We provide analysis, numerical implementation, and simulation for full state-feedback and measurement feedback control within this C/sup 2/ context. Sensitivity to parameter uncertainty is discussed. Some insight into the structure of optimal and near-optimal strategies for C/sup 2/ is obtained. The analysis is extended to the case of observations which may be affected by adversarial inputs. A heuristic based on risk-sensitive control is applied, and it is found that this produces improved results over more standard approaches. 相似文献
706.
Solar wind turbulence during the solar cycle deduced from Galileo coronal radio-sounding experiments
A.I. Efimov L.N. Samoznaev M.K. Bird I.V. Chashei D. Plettemeier 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
Seven coronal radio-sounding campaigns were carried out during the active lifetime of the Galileo spacecraft in the years 1994–2002. The observational data analyzed in the present work are S-band frequency fluctuation measurements recorded during the solar conjunctions at different phases of solar activity cycle #23, specifically: periods near solar maximum (three conjunctions), near solar minimum (three conjunctions) and during the ascending phase (one conjunction). These data are all applicable to low heliographic latitudes, i.e. to the slow solar wind. The rms frequency fluctuation and power-law index of the frequency fluctuation temporal spectra are determined as a function of heliocentric distance. The turbulence power spectrum tends to be flatter inside ca. 20 solar radii during all phases of the solar cycle. This coincides with a transition in the flow from the inner acceleration region to the outer region of constant velocity. The radial falloff rate and absolute level of the rms frequency fluctuation are essentially invariant over the solar cycle. 相似文献
707.
When US President George W. Bush on 14 January 2004 announced a new US “Vision for Space Exploration”, he called for international participation in “a journey, not a race”, a call received with skepticism and concern elsewhere. But, after a slow start in implementing this directive, during 2006 NASA has increased the forward momentum of action on the program and of discussions on international cooperation in exploring “the Moon, Mars, and beyond”. There are nevertheless a number of significant top-level issues that must be addressed if a cooperative approach to human space exploration is to be pursued. These include the relationship between utilization of the ISS and the lunar exploration plans, integration of potential partners’ current and future capabilities into the exploration plans, and the evolving space-related intentions of other countries. 相似文献
708.
In preparation for the flyby of the Rosetta spacecraft, the state of the knowledge of 21 Lutetia and 2867 Steins obtained
by ground based observations is reported. Preliminary determination of shape and/or size, rotational properties and taxonomic
types are presented for both asteroids. The dusty environment of the targets has been studied in order to help in defining
safe fly-by trajectories without the risk of damaging collisions. The expected science return from the asteroid fly-by is
also discussed. 相似文献
709.
D P Hader M Lebert P Richter 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1998,21(8-9):1277-1284
Gravitactic orientation in the flagellate Euglena gracilis is mediated by an active physiological receptor rather than a passive alignment of the cells. During a recent space flight on the American shuttle Columbia the cells were subjected to different accelerations between 0 and 1.5 x g and tracked by computerized real-time image analysis. The dependence of orientation on acceleration followed a sigmoidal curve with a threshold at < or = 0.16 x g and a saturation at about 0.32 x g. No adaptation of the cells to the conditions of weightlessness was observed over the duration of the space mission (12 days). Under terrestrial conditions graviorientation was eliminated when the cells were suspended in a medium the density of which (Ficoll) equaled that of the cell body (1.04 g/ml) and was reversed at higher densities indicating that the whole cytoplasm exerts a pressure on the respective lower membrane. There it probably activates stretch-sensitive calcium specific ion channels since gravitaxis can be affected by gadolinium which is a specific inhibitor of calcium transport in these structures. The sensory transduction chain could involve modulation of the membrane potential since ion channel blockers, ionophores and ATPase inhibitors impair graviperception. 相似文献
710.
Richard Wagener John Caldwell 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(3):189-193
For the distant giant planets, Uranus and Neptune, the observation of aurorae may be the best astronomical technique for the detection of planetary magnetic fields, with implications for the structure and composition of their interiors. Aurorae may be detected by emssion of H I Ly α (1216 Å) and by H2 bands near 1600 Å. The latter are important for very faint aurorae because there is essentially no planetary, interplanetary or geocoronal scattering of sunlight to contaminate the signal. For Uranus, present IUE results suggest the presence of a strong aurora at Ly α, but the background and instrument noise levels are very high compared to the apparent signal. At 1600 Å, the IUE instrument noise renders the H2 emission bands on Uranus marginal at best. No aurora has yet been observed on Neptune. For Jupiter, where the existence and general characteristics of the magnetic field are well established, there is disagreement between ground-based infrared and space-borne ultraviolet observations of the location of the aurorae. For all four giant planets, Space Telescope can improve upon the quality of current optical observations. For spectroscopy, the low resolution mode of the High Resolution Spectrograph (HRS) is particularly well suited to auroral observations because of its spectral range, adequate resolution and high sensitivity. For ultraviolet imaging through appropriate filters, the ST spatial resolution, expected to be of order 5 hundredths of an arc second, is also well suited to determine the spatial properties of the aurorae. 相似文献