Entity

Time filter

Source Type


Selvakumar N.,National Aerospace Laboratories, Bangalore | Biswas A.,Bhabha Atomic Research Center | Rajaguru K.,National Aerospace Laboratories, Bangalore | Gouda G.M.,Laboratory for Electro Optics Systems LEOS | Barshilia H.C.,National Aerospace Laboratories, Bangalore
Solar Energy Materials and Solar Cells | Year: 2015

Abstract A novel AlHfN(H)/AlHfN(L) coating with tunable optical properties was designed and developed for high temperature solar thermal applications. The transition from absorber to antireflection behavior was achieved by varying the chemical composition of AlHfN coatings. The aluminum and hafnium target power densities and nitrogen flow rates were varied in order to attain the different chemical compositions of AlHfN layers, which resulted in different optical constant values. The ellipsometric measurements indicated that bottom AlHfN(H)) is the main absorber layer and the top AlHfN(L) acts as an antireflection coating. The AlHfN(H)/AlHfN(L) coating deposited on stainless steel (SS) substrates exhibited absorptance of 0.93 with an emittance of 0.13. In order to decrease the emittance, approximately 1 μm thick tungsten coating was deposited on SS substrates. The tungsten coating acts as an infrared reflector due to which the emittance decreased drastically from 0.13 to 0.06, without affecting the absorptance. The optimized W/AlHfN(H)/AlHfN(L) coating deposited on SS substrates was thermally stable in air at 425 C for 2 h. These coatings also exhibited high thermal stability in vacuum at 580 C for 260 h. © 2015 Elsevier B.V. All rights reserved. Source


Selvakumar N.,Nanomaterials Research Laboratory | Rajaguru K.,Nanomaterials Research Laboratory | Gouda G.M.,Laboratory for Electro Optics Systems LEOS | Barshilia H.C.,Nanomaterials Research Laboratory
Solar Energy | Year: 2015

A novel AlMoN(H)/AlMoN(L) coating with improved thermal stability was developed for high temperature solar thermal applications. The aluminum and molybdenum target power densities and nitrogen flow rates were varied in order to attain the different chemical composition of AlMoN layers, which resulted in different optical properties. The coating deposited at a nitrogen flow rate of 1 sccm (AlMoN(H)) acts as an absorber, whereas coating deposited at a nitrogen flow rate of 4 sccm (AlMoN(L)) acts as an antireflection coating. By combining these two layers (i.e., AlMoN(H)/AlMoN(L)) an absorptance of 0.93 and an emittance of 0.13 were achieved. In order to decrease the emittance, approximately 1 lm thick tungsten coating was deposited on SS substrates. The tungsten coating acts as an infrared reflector due to which the emittance decreased drastically from 0.13 to 0.06, without affecting the absorptance. The optimized AlMoN(H)/AlMoN(L) coating deposited on SS substrates was thermally stable in air at 300 and 450 °C for 200 and 2 h, respectively. These coatings also exhibited high thermal stability in vacuum (600 °C for 435 h). © 2015 Elsevier Ltd. All rights reserved. Source


Lohar K.A.,Laboratory for Electro Optics Systems LEOS | Ramana Reddy V.V.,Laboratory for Electro Optics Systems LEOS | Viswanatha N.,Laboratory for Electro Optics Systems LEOS | Laxmi Prasad A.S.,Laboratory for Electro Optics Systems LEOS | Patnaik M.M.M.,Laboratory for Electro Optics Systems LEOS
Journal of Spacecraft Technology | Year: 2010

This paper describes the mathematical formulation to develop an analytical model of solar panel sun sensor onboard Chandrayaan-1. A MATLAB code was developed to generate the plots which show the characteristics of the sensors. Sensor hardware dependent behaviors like slope variations over cross field of view and blocking of input sun signal due to the aperture window are also incorporated in MATLAB model. The code was validated against the lab simulated sensor outputs and then the model was further used to analyze the onboard data of both main and redundant SPSS. Source


Saxena G.D.,Laboratory for Electro Optics Systems LEOS | Agarwal E.,Laboratory for Electro Optics Systems LEOS | Selveraj P.,Laboratory for Electro Optics Systems LEOS | Thamarai V.,Laboratory for Electro Optics Systems LEOS | And 3 more authors.
Proceedings of the 2013 International Conference on Advances in Computing, Communications and Informatics, ICACCI 2013 | Year: 2013

This paper presents a high performance space grade MEMS based Seismometer targeted for ground applications as well as for Chandrayaan-2 moon mission. Motivation of this paper is to develop a very light weight and high resolution seismometer using MEMS accelerometer sensor fabricated at LEOS-ISRO. It reports on the design and development of MEMS seismometer working on single power supply of +5V with a very small size of 50×32×6 mm3, weight of 30grams and very low power consumption of 10-15mW. MEMS accelerometer sensor and associated capacitive readout is realized in the form of HMC. Readout console is used for reading the acceleration data from the HMC and performing integration to extract velocity information. The functionality and performance of the full system was studied and tested on actual test-bed at NGRI (National Geophysics Research Institute) Measurements demonstrate that developed seismometer is having a good noise performance of 0.0007m/sec with a negligible non-linearity of 387 ppm over the frequency range of 0.01 to 20 Hz. © 2013 IEEE. Source


Muralidhara K.R.,Laboratory for Electro Optics Systems LEOS | Ashrita M.S.,Laboratory for Electro Optics Systems LEOS | Arpana A.,Laboratory for Electro Optics Systems LEOS | Padmasree S.,Laboratory for Electro Optics Systems LEOS | And 3 more authors.
Proceedings of the 2013 International Conference on Advanced Electronic Systems, ICAES 2013 | Year: 2013

A star sensor is an embedded system used in modern spacecraft for estimating the orientation of the spacecraft. Star trackers capture image of star in the sky, process them and gave highly accurate attitude in all 3 axis. Basically a star tracker is an electronic camera connected to a microcomputer. First generation star trackers are characterized by acquiring and processing few stars information to estimate attitude with limited software modules. The availability of space qualified microcomputers enables generation shift in the star trackers development for attitude determination onboard. Laboratory for Electro-Optics Systems (LEOS) is actively involved in design and development of indigenous star trackers for different ISRO. Current star trackers employs traditional method of acquiring and processing star image and don't meet the many spacecraft requirements in terms of number of stars tracking, accuracy and update rate. In order to meet the current generation spacecraft requirements, LEOS has designed and developed second generation star trackers which are characterized by low weight, volume and power. These sensors are based on ERC-32 processor, here after referred as Mark-II sensor. The essential features expected from onboard software are robustness in operations, run-time and ability to give solutions especially during satellite injection with high angular rate. This paper presents the details of state-of-art software designed and developed for these star trackers to provide high accuracy and higher bandwidth with existing hardware limitations even with harsh space environment with limited resources and constraints. ©2013 IEEE. Source

Discover hidden collaborations