Optimum Angle Demodulation with Saturation Nonlinearity in the Modulator

The problem of optimum demodulation of PM and FM signals when the phase modulator employed in the transmitter of the communication system exhibits saturation effects is studied. Quasi-optimum receivers with zero and finite lag are designed by making use of the state variable techniques. Performance results are presented graphically for a class of message signals, and it turns out that the effect of saturation in the phase modulator on the average performance of the system is essentially to reduce the modulation index.     

Technical and legal issues surrounding space debris—India''s position in the UN

This article briefly presents the historical background, as seen by ISRO and India, to the growing problem of space debris. It describes the technical aspects of ISRO's activities in the field of space debris, and the grey areas in technical understanding, which may impede legal discussions. Analysis of the cost and technical aspects of reorbiting satellites from geostationary Earth orbit (GEO) is detailed, since this is an important area for India and other developing countries. The article also briefly describes ISRO's views of the applicability and relevance of the existing space treaties to a possible future legal regime for space debris. Debates are currently taking place in the UN and other multilateral fora on the subject of space debris and the situation is dynamic. The main aim of this article is to inform readers of ISRO's and India's position in the UN on the subject of space debris, in terms of its technical, political and legal aspects. Certain issues of importance from the legal point of view, though not of immediate urgency, are also discussed.     

Bifurcation analysis of ion-acoustic waves for Schrödinger equation in nonextensive Solar wind plasma

Bifurcation analysis of ion-acoustic wave (IAWs) solutions of the nonlinear Schrödinger equation (NLSE) is explored for the first time in an electron-ion (e-i) magnetized solar wind plasma. The existence of ion-acoustic (IA) periodic, superperiodic, kink, antikink, compressive and rarefactive solitary wave solutions are revealed. Special values of Solar wind plasma parameters at a normalized distance from the Sun are considered for numerical simulation. The IA wave solutions are derived analytically. These solutions are analyzed numerically considering the influence of parameters, namely, wave number (k), velocity (V) of traveling wave and nonextensive parameter (q). Computational simulation reveals that only IA periodic wave grows in amplitude as waves moves from the Sun.     

Flux emergence,flux imbalance,magnetic free energy and solar flares

Emergence of complex magnetic flux in the solar active regions lead to several observational effects such as a change in sunspot area and flux embalance in photospheric magnetograms. The flux emergence also results in twisted magnetic field lines that add to free energy content. The magnetic field configuration of these active regions relax to near potential-field configuration after energy release through solar flares and coronal mass ejections. In this paper, we study the relation of flare productivity of active regions with their evolution of magnetic flux emergence, flux imbalance and free energy content. We use the sunspot area and number for flux emergence study as they contain most of the concentrated magnetic flux in the active region. The magnetic flux imbalance and the free energy are estimated using the HMI/SDO magnetograms and Virial theorem method. We find that the active regions that undergo large changes in sunspot area are most flare productive. The active regions become flary when the free energy content exceeds 50% of the total energy. Although, the flary active regions show magnetic flux imbalance, it is hard to predict flare activity based on this parameter alone.     

Space applications for input pulse shaping filter

A pulse-shaping technique superior to various other existing pulse shaping techniques has been suggested. A practical way of implementing the scheme has been discussed and the results found to be encouraging. New spike suppression (SS). Window function has also been suggested for obtaining low side lobe levels and to suppress spikes in phase shift keying spectrums that exists at high bit rate data transmission. The characteristics such as low side lobe levels and spike elimination have been achieved using new techniques that are essential for space applications     

Sensitivity Analysis of Finite-Lag Receivers

This paper presents the sensitivity analysis of a class of receivers called finite-lag receivers, introduced by the authors in [1] through [3]. Since these receivers are based on the use of fixed-lag smoothing techniques, algorithms for the calculation of large-scale and small-scale sensitivities of fixed-lag smoothing are derived using a state augmentation approach. Steady-state analysis of these algorithms shows that an explicit relation can be obtained between sensitivity coefficients of fixed-lag smoothing and filtering. The specific case of sensitivity to variations in the measurement (channel) noise is considered as an example. These results are applied to study the sensitivity performance of the finite-lag receivers for analog communication. It is shown, for example, that finite-lag receivers for AM signals, besides being superior in performance [1]-[3], [11], in terms of output SNR or error variance, are also much less sensitive to the additive noise power level, compared to zero-lag receivers.     

Strategic, technological and ethical aspects of establishing colonies on Moon and Mars

With the vast experience gained by Aerospace Community in the last five decades, the natural future course of action will be to expand Space Exploration. Our understanding of Moon is relatively better with a number of unmanned satellite missions carried out by the leading Space Agencies and manned missions to Moon by USA. Also a number of unmanned satellite missions and surface rover missions were carried out to Mars by those Space agencies generating many new details about Mars. While the future exploration efforts by global community will also be centered obviously on Moon and Mars, it is noteworthy that already NASA had declared its plans for establishing a Surface Base on Moon and developing the technical infrastructure required. Surface Bases on Moon and Mars give rise to a number of strategic, technical and ethical issues both in the process of development, and in the process of establishing the bases. The strategic issues related to Moon and Mars Surface Bases will be centered around development of enabling technologies, cost of the missions, and international cooperation. The obvious path for tackling both the technological development and cost issues will be through innovative and new means of international cooperation. International cooperation can take many forms like—all capable players joining a leader, or sharing of tasks at system level, or all players having their independent programmes with agreed common interfaces of the items being taken to and left on the surface of Moon/Mars. Each model has its own unique features. Among the technical issues, the first one is that of the Mission Objectives—why Surface Bases have to be developed and what will be the activity of crew on Surface Bases? Surface Bases have to meet mainly the issues on long term survivability of humans on the Mars/Moon with their specific atmosphere, gravity and surface characteristics. Moon offers excellent advantages for astronomy while posing difficulties with respect to solar power utilization and extreme temperature variations. Hence the technical challenges depend on a number of factors starting from mission requirements. Obviously the most important technical challenge to be addressed will be in the areas of crew safety, crew survivability, adequate provision to overcome contingencies, and in-situ resource utilization. Towards this, new innovations will be developed in areas such as specialized space suits, rovers, power and communication systems, and ascent and descent modules. The biggest ethical issue is whether humankind from Earth is targeting ‘habitation’ or ‘colonization’ of Moon/Mars. The next question will be whether the in-situ resource exploitation will be only for carrying out further missions to other planets from Moon/Mars or for utilization on Earth. The third ethical issue will be the long term impact of pollution on Moon/Mars due to technologies employed for power generation and other logistics on Surfaces. The paper elaborates the views of the authors on the strategic, technical and ethical aspects of establishing Surface Bases and colonies on Moon and Mars. The underlying assumptions and gray areas under each aspect will be explained with the resulting long-term implications.     

Retrieval of spinach crop parameters by microwave remote sensing with back propagation artificial neural networks: A comparison of different transfer functions

Back propagation artificial natural network (BPANN) is a well known and widely used machine learning methodology in the field of remote sensing. In this paper an attempt is made to retrieve the spinach crop parameters like biomass, leaf area index, average plant height and soil moisture content by using the X-band scattering coefficients with BPANN at different growth stages of this crop. The maturity age of this crop was found to be 45 days from the date of sowing. After 45 days from the date of sowing, this crop was cut at a certain height for production. Then, it is a point of interest to investigate the microwave response of variation in production. Significant variations in all the crop parameters were observed after cutting the crop and consequently made the problem more critical. Our work confirms the utility of BPANN in handling such a non-linear data set. The BPANN is essentially a network of simple processing nodes arranged into different layers as input, hidden and the output. The input layer propagates components of a particular input vector after weighting these with synaptic weights to each node in the hidden layer. At each node, these weighted input vector components are added. Each hidden layer computes output corresponding to these weighted sum through a non-linear/linear function (e.g. LOGSIG, TANSIG and PURLIN). These functions are known as transfer functions. Thus, each of the hidden layer nodes compute output values, which become inputs to the nodes of the output layer. At nodes of output layer also a weighted sum of outputs of previous layer (hidden layer) are obtained and processed through a transfer function. Thus, the output layer nodes compute the network output for the particular input vector. In this paper, output nodes use linear transfer function. Different transfer functions e.g. TANSIG, LOGSIG and PURELIN were used and the performance of the ANN was optimized by changing the number of neurons in the hidden layers. The present analysis suggests the need of critical analysis of the BPANN in terms of selection of the best transfer function and other network parameters for the better results.     

Effect of spectral distribution of energetic electrons on wave-particle interaction and precipitated energy input

The precipitated energy flux as affected by the presence of parallel electric field and geomagnetic field distortions have been obtained using a complete kinetic treatment of pitch angle scattering by whistler waves. Four different energy spectra have been used to show that the precipitated energy flux depends on the spectral details of the interacting electron ensemble.