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21.
Ananth Krishna N. S. Gopinath N. S. Hegde N. K. Malik 《Journal of Earth System Science》2005,114(6):739-748
The Chandrayaan-1 mission proposes to put a 550 kg lunarcraft into Geostationary Transfer Orbit (GTO) using the Polar Satellite
Launch Vehicle (PSLV) which will subsequently be transferred into a 100 km circular lunar polar orbit for imaging purposes.
In this paper, we describe certain aspects of mission strategies which will allow optimum power generation and imaging of
the lunar surface.
The lunar orbit considered is circular and polar and therefore nearly perpendicular to the ecliptic plane. Unlike an Earth
orbiting remote sensing satellite, the orbit plane of lunar orbiter is inertially fixed as a consequence of the very small
oblateness of the Moon. The Earth rotates around the Sun once a year, resulting in an apparent motion of Sun around this orbit
in a year. Two extreme situations can be identified concerning the solar illumination of the lunar orbit, noon/midnight orbit,
where the Sun vector is parallel to the spacecraft orbit plane and dawn/dusk orbit, where the Sun vector is perpendicular
to the spacecraft orbit plane. This scenario directly affects the solar panel configuration. In case the solar panels are
not canted, during the noon/midnight orbit, 100% power is generated, whereas during the dawn/dusk orbit, zero power is generated.
Hence for optimum power generation, canting of the panels is essential. Detailed analysis was carried out to fix optimum canting
and also determine a strategy to maintain optimum power generation throughout the year. The analysis led to the strategy of
180‡ yaw rotation at noon/midnight orbits and flipping the solar panel by 180‡ at dawn/dusk orbits. This also resulted in
the negative pitch face of the lunarcraft to be an anti-sun panel, which is very useful for thermal design, and further to
meet cooling requirements of the spectrometers.
In principle the Moon’s surface can be imaged in 28 days, because the orbit chosen and the payload swath provide adequate
overlap. However, in reality it is not possible to complete the imaging in 28 days due to various mission constraints like
maximum duration of imaging allowed keeping in view the SSR sizing and payloads data input rate, time required for downlinking
the payload data, data compression requirements and visibility of the lunarcraft for the Bangalore DSN. In each cycle, all
the latitudes are swept. Due to the constraints mentioned, only 60‡ latitude arc coverage is possible in each orbit. As Bangalore
DSN is the only station, half of the orbits in a day are not available. The longitudinal gaps because of non-visibility are
covered in the next cycle by Bangalore DSN. Hence, in the firstprime imaging season, only 25% of the prime imaging zones are covered, and an additional threeprime imaging seasons are required for a full coverage of the Moon in two years. Strategy is also planned to cover X-ray payload coverage considering
swath and orbit shift. 相似文献
22.
In spite of detailed geological investigations of the Dharwar craton since the 1890s, its principal lithological units, structure
and chronology remain contentious. Important new work on lithostratigraphy, basin development, structure, geochemistry and
geochronology has led to wide-ranging speculation on the Late Archaean plate tectonic setting. Much of the speculation is
based on uniformitarian models which contrast with a recent proposal that the evolution of the craton was controlled by gravity-driven
processes with no crustal shortening. 相似文献
23.
Temperature and wind data are used to describe variation in the strength of the Monsoon Low Level Jet (MLLJ) from an active
phase of the monsoon to a break phase. Also estimated are the characteristics of turbulence above and below MLLJ. 相似文献
24.
Lalitha M. Kumar K. S. Anil Nair K. M. Dharumarajan S. Koyal Arti Khandal Shivanand Kaliraj S. Hegde Rajendra 《Natural Hazards》2021,106(1):487-507
Natural Hazards - In the Western Ghats of India, the soil properties, particularly Atterberg limits, are of relevance to the landslides. Pedogenic processes in the Western Ghats and plateaus on it... 相似文献
25.
26.
K. Ram Chandar V. R. Sastry Chiranth Hegde Srisharan Shreedharan 《Geomechanics and Geoengineering》2017,12(3):207-214
Ground vibrations produced from blasting operations cause structural vibrations, which may weaken structure if it occurs at the resonant frequency. Measurable parameters associated with ground vibrations are peak particle velocity (PPV), amplitude and dominant frequency (frequency of highest PPV amongst translational, vertical and horizontal vibrations). In this paper, an attempt is made to correlate measurable parameters associated with ground vibrations with scaled distance. Using the correlated data, it was found that a predictor equation can be determined for the amplitude and PPV, but not for dominant frequency as it is dynamic and depends upon infinitesimal changes that occur within a number of other parameters. Another analysis of the same is made using multiple linear regression analysis. This included predicting the PPV using scaled distance, maximum charge per delay, amplitude as predictors. A considerable improvement is seen in the prediction on adding the interaction of the predictors in multiple regressions. A comparison of different combination of predictors is made so as to assess the best combination giving the best R2 value for the given mine. Frequency is also plotted using the aforementioned method. However, it was found that the dominant frequency cannot be predicted with high accuracy even with this method. 相似文献
27.
This paper presents an efficient procedure to determine the natural frequencies, modal damping ratios and mode shapes for torsionally coupled shear buildings using earthquake response records. It is shown that the responses recorded at the top and first floor levels are sufficient to identify the dominant modal properties of a multistoried torsionally coupled shear building with uniform mass and constant eccentricity even when the input excitation is not known. The procedure applies eigenrealization algorithm to generate the state‐space model of the structure using the cross‐correlations among the measured responses. The dynamic characteristics of the structure are determined from the state‐space realization matrices. Since the mode shapes are obtained only at the instrumented floor (top and first floors) levels, a new mode shape interpolation technique has been proposed to estimate the mode shape coefficients at the remaining floor levels. The application of the procedure has been demonstrated through a numerical experiment on an eight‐storied torsionally coupled shear building subjected to earthquake base excitation. The results show that the proposed parameter identification technique is capable of identifying dominant modal parameters and responses even with significant noise contamination of the response records. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
28.
A new high-resolution radio spectropolarimeter instrument operating in the frequency range of 15?–?85 MHz has recently been commissioned at the Radio Astronomy Field Station of the Indian Institute of Astrophysics at Gauribidanur, 100 km north of Bangalore, India. We describe the design and construction of this instrument. We present observations of a solar radio noise storm associated with Active Region (AR) 12567 in the frequency range of \({\approx}\,15\,\mbox{--}\,85~\mbox{MHz}\) during 18 and 19 July 2016, observed using this instrument in the meridian-transit mode. This is the first report that we are aware of in which both the burst and continuum properties are derived simultaneously. Spectral indices and degree of polarization of both the continuum radiation and bursts are estimated. It is found that The results obtained here indicate that the continuum emission is due to bursts occurring in rapid succession. We find that the derived parameters for Type I bursts are consistent with suprathermal electron acceleration theory and those of Type III favor fundamental plasma emission.
相似文献
- i)Type I storm bursts have a spectral index of \({\approx}\,{+}3.5\),
- ii)the spectral index of the background continuum is \({\approx}\,{+}2.9\),
- iii)the transition frequency between Type I and Type III storms occurs at \({\approx}\,55~\mbox{MHz}\),
- iv)Type III bursts have an average spectral index of \({\approx}\,{-}2.7\),
- v)the spectral index of the Type III continuum is \({\approx}\,{-}1.6\), and
- vi)the degree of circular polarization of all Type I (Type III) bursts is \({\approx}\,90\%\) (\(30\%\)).
29.
Mooring forces in horizontal interlaced moored floating pipe breakwater with three layers 总被引:2,自引:0,他引:2
The paper presents the results from model scale experiments on the study of forces in the moorings of horizontally interlaced, multi-layered, moored floating pipe breakwaters. The studies are conducted with breakwater models having three layers subjected to waves of steepness Hi/L (Hi is the incident wave height and L the wavelength) varying from 0.0066 to 0.0464, relative width W/L (W is the width of breakwater) varying from 0.4 to 2.65, and relative spacing S/D (S is the spacing of pipes and D the diameter of pipe) of 2 and 4. The variation of measured normalized mooring forces on the seaward side and leeward side are analyzed by plotting non-dimensional graphs depicting f/γW2 (f is the force in the mooring per unit length of the breakwater, γ the weight density of sea water) as a function W/L for various values of Hi/d (d is the depth of water). It is found that the force in the seaward side mooring increases with an increase in Hi/L for d/W values ranging between 0.081 and 0.276. The experimental results also reveal that the forces in the seaward side mooring decrease as W/L increases, up to a value of W/L=1.3, and then increases with an increase in W/L. It is also observed that the wave attenuation characteristics of breakwater model with relative spacing of 4 is better than that of the model with relative spacing of 2. The maximum force in the seaward side mooring for model with S/D=4 is lower compared to that for the breakwater model with S/D=2. A multivariate non-linear regression analysis has been carried out for the data on mooring forces for the seaside and leeside. 相似文献
30.
Sikta Patnaik G. N. Hegde A. Panneerselvam M. B. Verma R. Mohanty A. K. Rai 《Journal of the Geological Society of India》2016,88(2):151-158
Granite core samples (n=14) from the Gogi-Kurlagere fault zone in the central part of the Bhima basin were studied in terms of LREE, Y and Zr mobility during uranium mineralization. LREE, Zr and Y along with LILE (Ba, Rb) and P show behavioral differences in the mineralised and the non-mineralised samples. Average ΣLREE in mineralised granite (240 ppm) is higher than in non-mineralised samples (157 ppm). The average Zr and Y in the mineralised granite are 193 ppm and 17 ppm, while the corresponding abundances of these elements in non-mineralised portion are 148 ppm and 11 ppm respectively. Besides enrichment of U, Th, Ba, Pb and Rb and depletion of Sr are observed in mineralized granite in comparison to non-mineralized granite. Hydrothermal alteration has led to the mobility of these elements, which again dependent on the overall geochemical behavior of the migrating fluid. REE and Y in association with uranyl [(UO2)2+] ion were transported as carbonate complexes like [UO2(CO3)3]4- and [REE (CO3)3]3- and were later incorporated into favourable structural loci by precipitating minerals like pitchblende and coffinite. 相似文献