Pakistan Space & Upper Atmosphere Research Commission
The National Space Agency of Pakistan

Research Studies

SRS/GIS/ Application

Case Study of Drought in Pakistan using Satellite Data

Abstract
Droughts are chronic climatic events, which often affect South Asia. Pakistan is predominantly arid with low rainfall and higher solar radiation over most parts of the country. Pakistan is basically an Agricultural country and its economy is mainly agrarian. Water is one of the most limiting constraints for agricultural production in Pakistan.

Analysis of the drought condition made in this study for the areas of Sindh particularly along Indus River, is based on calculation of Normalized Difference Vegetation Index (NDVI) and DEVNDVI using Advanced Very High Resolution Radiometer (AVHRR) data on board National Oceanic and Atmospheric Administration (NOAA) series of satellites. Data analysis for February and October (1996-2006) and deviation of rainfall from its mean based on precipitation data for the period: 1986-2006 has been carried out. NDVI describes vegetation health based on chlorophyll concentration and its deviation DEVNDVI indicates the severity of drought. The values of vegetation index for February and October (1996- 2006) show that the drought was severe during the year 2000 and 2003 as it affected most areas of Sindh.

Results show strong relationships among NDVI, DEVNDVI, precipitation and drought conditions.
Satellite technology combined with meteorological data (like precipitation) can be effectively used for agricultural drought monitoring.

Monitoring of Mountain Glacial Variations in Northern Pakistan, from 1992 to 2008 using Landsat and ALOS Data

Abstract
Glacier changes, especially recent melting, can affect our resources including drinking water supplies, agriculture, hydroelectric power, transportation, tourism, coastlines, and ecological habitats. Glacial changes can also have a more immediate impact on communities that rely on glaciers for their water supply, or on regions susceptible to floods, avalanches, or landslides triggered by abrupt glacial melt. Monitoring of glaciers for estimation of glaciated area is felt essential. Satellite data can be effectively used for such monitoring, where the area is vast and inaccessible. Multi temporal data will help in estimation of future changes in glaciated area and also track size and movement of glaciers. In continuation to previous study (“A Study of Glaciers in Northern Pakistan” published in proceeding of ALOS First Joint PI Symposium of ALOS Data Nodes for ALOS Science Program in Kyoto), the study has been extended to monitor Ghulkin and Passu Glaciers, situated in the south of Batura Glacier, these glaciers have experienced GLOF on 21 May 2008, causing massive damage to houses and crops and blocked Karakoram Highway. The purpose of this study is to analyze the variations in Ghulkin and Passu Glaciers during 1992 and 2008. Analyses of Batura, Biafo, Yazghil and Jutmau have also been included in the study. Landsat (TM Oct 1992, ETM+ Oct 2000) and ALOS (AVNIR Oct 2007) cloud free images were selected for the study. Spectral signatures of glaciated, non glaciated and transition (mixed snow & ice) areas have been identified using supervised, unsupervised and band ratios techniques. The glaciers retreat in the region is due to global warming.

Application of ALOS Data in Flood Monitoring in Pakistan

Abstract
Natural hazard such as flood is a water-related natural disaster which affects a wide range of environmental factors and activities related to agriculture, vegetation, human and wild life and local economies. Recently Pakistan’s southern provinces, Balochistan and Sindh were severely affected by flash floods, from 26 June to 10 July 2007. The floods were caused by torrential rains, gushing water from high altitudes of Kirthar to plains of Sindh significantly contributed in flooding. In this study the damage assessed by UNOSAT using data of Phased Array L-band Synthetic Aperture Radar (PALSAR) onboard Advanced Land Observing Satellite (ALOS) in combination with Tropical Rain Measurement Mission Satellite (TRMM) and other ancillary data greatly helped in finding the most affected areas. Also the unprocessed PALSAR images of pre and post flood periods downloaded from JAXA-ALOS site were used to assess change detection. As Pakistan is frequently affected by such disastrous situations, it is recommended that Digital Elevation Model (DEM) generated from Panchrometric Remote Sensing Instrument for Stereo Mapping (PRISM) onboard ALOS along with other optical data can be effectively used for flood mapping along River Indus for identification of most vulnerable areas.

A Study of Glaciers in Northern Pakistan

Abstract
Glaciers serve as a natural regulator of regional water supplies. Pakistan’s glaciers are spread over an area of about 16933 Km². Pakistan is a home of 108 peaks above 6000m, and numerous peaks above 5000 and 4000. Five of the 14 highest independent peaks in the world are here. These glaciers are enormous reservoirs of fresh water and their melt water is an important resource which feed rivers in Pakistan. Glacier depletion, especially recent melting can affect agriculture, drinking water supplies, hydro-electric power, and ecological habitats. This can also have a more immediate impact on Pakistan’s economy that depends mainly on water from glacier melt. Melting of seasonal snowfall and permanent glaciers has resulted not only in reduction of water resources but also caused flash floods in many areas of Pakistan. Using satellite data the study of glaciers, has become possible. Comparison of Landsat images of Batura glacier for the year October 1992 and October 2000 has revealed that there is decrease of about 17 km2 in Batura glaciers. Biafo glacier has also retreated. Through this study efforts have been made to analyze future changes in glaciers because, changes cannot be assessed without baseline information on glacier extent.

ALOS data could be effectively used to compare with the historical data to detect changes in the glaciated area. ALOS PRISM data can also help in DEM generation for volume assessment.

Use of Satellites in Natural and Anthropogenic Hazards Monitoring

Abstract
Natural and anthropogenic disasters such as tropical cyclones, tsunamis, floods, earthquakes, volcanic, fires, fog, oil spills, land slides, inflict substantial damages to life and property every year. Monitoring, forecasting and mitigating the harm is very important. SUPARCO acquires various satellite data which have variety of applications including prediction, monitoring of hazards, damage assessment, their management and mitigation. Situations during recent flood in Balochistan, heavy snow-fall in northern Pakistan were monitored. Effect of oil spill due to accident of oil tanker in August 2003 near Karachi Coast was assessed using Canadian Radarsat images. Phenomena of winter fog in northern Pakistan is monitored every year, the situation is conveyed to concerned agencies for preparedness to deal with the situation. This paper discusses how satellites are helpful in damage assessment, its contribution to improving disaster response and prevention. Some disasters might be foreseen and developing trends may be understood from the observations made from the ground-based facilities. Space Technology provides an effective means to monitoring the hazards by providing information on a regular basis to aid prediction, damage assessment and their management and mitigation. Satellites dedicated to the study of earth’s land surface, oceans and atmospheric can keep on monitoring environmental/ecological/climatic changes that could trigger off or aggravate disaster. Processes like deforestation, erosion and atmospheric and marine pollution can be monitored by remote sensing satellites for timely measures to avert future catastrophes.

Remote Sensing and GIS Applications in Crop Sector

Abstract
Availability of timely and precise information on the area and size of crops is the basic need for sound agricultural development planning and policy formulation. The main constraints in collection of data are inordinate time lags, quality concerns and a heavy overhead expenditure on manpower and wherewithal.

With introduction of RS/GIS technology in agriculture sector, Ministry of Food, Agriculture and Livestock (MINFAL) mandated Pakistan Space and upper Atmosphere Research commission (SUPARCO) to devise a satellite based Crop Reporting and Forecasting system in collaboration with stakeholders. Three contiguous districts of Bahawalpur, Rahim Yar Khan and Ghotki in the cotton –wheat cropping system were selected. Images of the program areas were obtained through constellation of SPOT satellites with resolution of 2.5 and 5 meter in panchromatic and 10 meter in multispectral mode during June, July and September 2005 for cotton and December 2005 and January 2006 for wheat crop. Ground Truthing Surveys were carried out in 15 villages from among the area frame villages, in vogue. The digitization of irrigation /communication networks and mosaicing, merging, integration, processing of the data /development of algorithm was carried out at Space Application and Research Center, Islamabd. The results were reported to MINFAL. The cotton data showed a divergence of 2.4 percent from the area reported by provinces, with lag of three months. Similar results have also been reported for wheat crop.

SUPARCO in cooperation with MINFAL and Planning Commission of Pakistan intends to further expand the program to other provinces/areas and also cover additional crops. Yield forecasting models are also being developed. The aim is to develop algorithms to provide a synoptic view of cropping systems in Pakistan by gathering temporal satellite data. This will help to minimize /alleviate the gaps in timely availability of data and also address the data quality concerns.

Monitoring of Drought in Pakistan Using Ndvi and Rainfall Data

Abstract
The natural disaster such as drought is observed in some areas of Pakistan during 1998-2003 (2001 was relatively wet year). This paper presents some results of detection of drought-affected regions by comparing the Normalized Difference Vegetation Index (NDVI) and the rainfall data of the drought and wet years. Course/ Medium spatial resolution, high temporal frequency satellite data from the NOAA / AVHRR / MODIS/ Landsat have been used to monitor vegetation cover and drought throughout Pakistan. NDVI has been used for assessment and detection of drought affected areas in Sindh and Balochistan provinces of Pakistan, by comparing it against rainfall data of the same period. The results show a decrease in NDVI in the year 2000, which matches very well with the decreased rainfall data in the same year. On the other hand in 2001 (taken as wet year) the vegetation is quite green and healthy. Moreover statistical data of crop yield of the two years show more production in the year 2001 as compared to year 2000.

Impact of Arabian Sea Cyclones on Pakistan

Abstract
SUPARCO’s ‘Hazards Monitoring’ group has been studying Arabian Sea cyclones with satellite data / imageries since 1989. In this presentation, cyclone formation in the Arabian Sea, its development and possibility of predicting its course will be discussed. Statistical analysis of 60-years (since 1945) Arabian Sea cyclone data, including those traveling northward towards Pakistan has been worked out. Case study of the Thatta cyclone of May 1999 will be presented. The recurving phenomena and other characteristics for determining cyclone danger for Pakistan will be discussed. Coastal zones of Pakistan vulnerable to cyclone damages and mitigation measures that can be taken up will be presented. Finally, present and future developments in monitoring cyclones will be discussed.

Flood Assessment along River Kabul Using MODIS Data

Abstract
Northern mountains of Pakistan received a 30 years record snow fall in the month of February 2005. This was followed by a heat wave in third week of June 2005 which caused snowmelt and consequent stream runoff causing flooding in river Kabul. Low lying areas in the districts of Charsadda, Noshehra and Peshawar in NWFP province were inundated and remained flooded for at least two months. The River Kabul is mainly snow fed originating from the Unai pass of the southern Hindukush range. Satellite images (MODIS onboard Terra/Aqua satellites) pertaining to pre and post-flooding periods have been processed using ER Mapper software for quantitative assessment of flood inundation. Approximately 140 sq km (excluding the normal flow area which is 18 sq km) has been estimated to be affected by flood inundation in Charsadda, Noshehra and Peshawar. It has been analyzed that River Swat, which originates from Hindukush range and passes through Swat, Malakand and Charsadda districts, is one of the main contributors of flooding at the point where it joins river Kabul. This analysis has been possible due to the synoptic coverage of multi-temporal satellite images which enabled visualization of the land features and associated dynamic phenomena. Construction of the proposed Munda Dam and Kalam Dam on River Swat, and increase in the storage capacity of Warsak Dam will help to avoid flooding along the low lying areas of river Kabul.

Using Satellite Remote Sensing and Geographic Information System for Monitoring Agriculture Sector

SUPARCO, in collaboration with Ministry of Food, Agriculture and Livestock (MINFAL), initiated the program for monitoring of crops through satellite technology during 2005-06.Three contiguous districts of Bahawalpur, R.Y.Khan and Ghotki were selected for this study. Data for cotton and wheat crops were acquired from Spot constellation of satellites in panchromatic (5 meter) and multispectral resolutions (2.5 and 10 meters). The satellite images were processed and classified using training sample from the field. The area sown under cotton and wheat crops was worked from these classified images and reported to MINFAL.

For 2006-07, the scope of work was expanded to cover 43 districts. This includes 5 districts in NWFP, 25 districts in Punjab, 11 districts in Sindh and 2 districts in Balochistan. The expanded work was activated in Kharif (summer) season covering cotton, sugarcane, rice, maize crops and wheat crop will be covered during coming rabi (winter) season. SUPARCO is conducting this assignment in close association of provincial crop reporting services.

SUPARCO also imparted training to the scientists/functionaries of stakeholders viz. provincial crop reporting services (PRCS), Pakistan Meteorology Department (PMD), Federal Bureau of Statistics (FBS) and MINFAL. In addition, technology is being transferred from SPOT Image, France and Food and Agricultural Organization of United Nations to further perfect and upgrade the techniques. Hopefully, this system will be shortly used to cover the entire spectrum of agriculture sector.

Monitoring Disasters in Pakistan Using Satellite Data

Abstract
Pakistan is facing serious threat and great challenges from large-scale natural as well as anthropogenic disasters, such as, seismic events, landslides, droughts, floods, fog, torrential rains, tropical cyclones, dust storms, fires, locusts, oil-spills, etc. Earth observation satellites are widely used for identifying, examining and forecasting natural / anthropogenic disasters. SUPARCO has vast experience and the requisite skills in using satellite technology. It has played effective role in the context of disaster monitoring. This paper attempts to highlight the role of space technology in disaster monitoring, mitigation and management in Pakistan.

GIS in Fleet Management & Asset Tracking

Abstract
GIS has boundless falloff. Its usefulness has already been realized and the technology has already been implemented in the developed world for quite a long time, however, recognition of its applicability in developing world is still in some what initial period and a lot is still needed for this technology’s operationalization. In the developing world the applicability of GIS in Fleet Management & Asset Tracking has been recognized and is under implementation in many countries including Pakistan. In most of the developing countries this technology is used on is a limited aspect only. This paper focuses on possible applications of GIS in Fleet Management & Asset Management. There are three basic elements of a tracking system and these include: a. Tracking Device, b. Raster / Vector Maps of the area 3. Software Interface between moving asset and remotely situated control center. This paper would throw light on technical its aspects and its potential applications. Furthermore, it also discusses the areas of this technology’s potential usage that are ignored in developing countries like Pakistan.

Security Information System

Abstract
Security is a great apprehension in recent flux of terrorism and crime vulnerabilities in general but particularly in mega cities. The major concerns to deal with security matters are monitoring of unforeseen as well as planned or regular criminal activities on regular basis and planning of the available resources to combat the same in an efficient way. Satellite technology coupled with Geographic Information System (GIS) has been used to tackle such issues.

A Security Information System (SIS) based on satellite technologies has been developed for Karachi metropolitan to handle terrorism as well as criminal activities with efficient counter part planning. SIS is mainly capable of mapping/feeding, monitoring, and analyzing both types of datasets; criminal activities as well as available resources. The System has also the capability of real time vehicle tracking used for monitoring anti-criminal and rescue operations.

Satellite Technologies like Remote Sensing and GPS for real time position monitoring along with GIS tool are highly useful to deal with security issues at local as well as regional level.

Optical Imaging Systems on Earth Observation Satellites

Abstract
A typical imaging system mainly consists of an Image acquisition, processing & storage system. The acquisition system is mainly based upon the telescope and detector. The imager requires a telescope to collect and focus energy from the Earth scene. The wavelength requirements impact the telescope type and aperture size through considerations of chromatic dispersion and diffraction limitations. Telescopes fall into the categories of reflective, refractive, and catadioptric designs. Out of imaging with photographic film & detector arrays , the later consist of many thousands to millions of detector pixels, along with a multiplexing and readout system. The type of material and configuration of detector depends upon desired wavelength. In this paper we will discuss performance parameters, goals & design considerations for an imaging system. We examine the impacts from wavelength, resolution, weight, and radiometric performance requirements on telescope design, focal plane array size & material Radiometric performance estimates are considered for different channels. Design issues regarding spectral separation and common focal planes are considered. Characteristics of different earth observation satellite are also compared along with a brief description of limitations of different sensors employed on various earth observation satellites.

Image Compression Techniques for Earth-Observation Satellites

Abstract
The size of data to be processed by the earth observation satellite is very large and it needs a lot of memory for storage and higher band-width for transmission. Compression techniques are applied to reduce the amount of data to be stored on board and transmitted to ground. A variety of data compression techniques have been developed for earth observation applications. Such techniques can be divided into lossless and lossy compression. In lossless Compression the image can be reproduced exactly as the original. Rice code and DPCM coding are examples of lossless compression techniques. Lossless compression ratios vary from image to image but, in general, do not provide as high compression ratios as Lossy algorithms and are not suitable for fixed packet size applications. In Lossy Compression, higher compression ratio may be achieved by not keeping all the image information. There are many different ways of carrying out the compression, but all try to pick out the more important information components of the image, and keep those. JPEG and Moment Preserving Block Truncation Coding (MPBTC) are examples of Lossy compression. The requirements for the compression algorithm are governed by the limited resources on-board the spacecraft in such a way that the necessary compression hardware should be as simple as possible on-board. In this paper we try to provide a survey of current image/data compression techniques implemented on the Earth observatory satellites. And the aspect of this survey is far from completion, reflecting the substantial research in this field.

SATELLITE COMMUNICATION

Analysis, Design and Optimization of a Cirularly Polarised Truncated Corner Patch Antenna

Abstract
This paper discusses the design and optimization of a circularly polarized printed patch for an S-Band on board LEOsatellite Transmitter. Circular polarization is achieved with single point feed by a so called perturbation segment, in this case a pair of truncated corners. First an analysis based on the cavity model approach for the single CP patch is carried out, which is used to determine the normalized perturbation parameter. The initial dimensions are calculated using perturbation analysis. Optimization is performed using full wave analysis tools based on Method of Moments (MoM), and Finite Difference Time domain (FDTD). The measured minimum axial ratio is 0.3 dB for the truncated-corner square-patch antenna operating at 2.25 GHz. Peak antenna gain across the overall operating band is measured to be 6.6 dBi. Finally, the measured input impedance and radiation patterns are correlated with the calculated results.

Strategies for Effective Frequency Allocations for Satellite Communications

Abstract
This paper discusses various strategies that are currently being employed to prevent the frequency spectra from getting saturated due to the dramatically increasing growth of users & applications requiring radio spectrum. It discusses the optimal spectrum management mainly for satellite systems. It also goes on to discuss the future actions that can be taken to effectively utilize the spectrum.

Optical Tracking of Man Made Satellites in Low Earth Orbit

Abstract
Russian Space Station (MIR), International Space Station (ISS), and Hubble Space Telescope (HST) were optically tracked by SUPARCO, from its Space and Atmospheric Research Center (SPARCENT), Karachi. The tracking of MIR became more interesting during its decay phase in low earth orbit. The optical tracking of these objects was carried out using traditional low cost equipment. Orbits and the look angles were calculated to determine time and direction of appearance Time exposure images of these orbiting objects using ordinary cameras with 600-mm Tele lens and movie using video cameras were prepared. Observing techniques and strategies using low cost equipment are discussed in the paper. These objects were visible when the sky was dark and was able to reflect sunlight back to the observer. These conditions prevailed for about an hour before sunrise (before the sky became too light) and about an hour after sunset. Regardless of the fact that how bright these objects are, clear and relatively dark skies are needed to observe them. The main objective of this activity was to determine look angle and time of appearance of these objects, so as to locate and observe them.

Implementation of the Jacobi-Bessel Series Method for Radiation Pattern Equations of an Offset Parabolic Reflector Antenna Using MathCAD®

Abstract
The physical optics radiation integral expressed in terms of a summation of Fourier transformations is implemented in MathCAD software. The Jacobi-Bessel series has been used to evaluate the Fourier transforms. The mathematical formulation given provides a fast and accurate approach for the prediction of the far-field radiation pattern of offset reflector antennas. The accurate and rapid numerical evaluation of the expressions obtained is demonstrated through the design of a multi-feed offset reflector. Furthermore, the formulation can be slightly modified and implemented in MathCAD for axially symmetric reflectors and other types of aperture antennas as well.

Atmospheric Heating by F10.7cm Solar Radio Flux and its Effects on Leo Satellites

Abstract
This study discusses the effects of atmospheric heating caused by F10.7 cm (at 2800 MHz) solar radio flux on LEO satellites (100-1000 Km altitudes). The excessive atmospheric heating can damage telemetry / communication antennas and solar panels. These two items are most vulnerable parts of a satellite. The contact of a satellite so damaged can be lost from ground though the satellite may complete its natural life in the orbit. Also, during the period of high solar activity (i. e. high solar flux F10.7 cm), the upper most atmosphere expands, increasing the drag on satellite and accelerating the descent. The events of excessive heating of atmosphere are most frequent at and around solar maximum. Therefore, the ample care should be taken to such unusual atmospheric heating effects while designing, fabricating and launching LEO satellite. So far there’s little warning of solar-related disturbances so there’s little any one can do except design the system to cop. In order to find out the atmospheric heating, the atmospheric temperature is determined during the events of enhanced F10.7 cm flux. For this purpose, the standard formula Jacchia and Slowey, 1966 has been employed.

Accurate and Rapid Computation of Radiation Pattern of an Offset Parabolic Reflector Antenna Using MathCAD®

Abstract
The physical optics radiation integral expressed in terms of a summation of Fourier transformations is implemented in MathCAD software. The Jacobi-Bessel series has been used to evaluate the Fourier transforms. The mathematical formulation given provides a fast and accurate approach for the prediction of the far-field radiation pattern of offset reflector antennas. The accurate and rapid numerical evaluation of the expressions obtained is demonstrated through the design of a multi-feed offset reflector. Furthermore, the formulation can be slightly modified and implemented in MathCAD for axially symmetric reflectors and other types of aperture antennas as well.

Real Time Implementation of MIL-STD-1553 Data Bus

Abstract
MIL-STD-1553 is a military standard that defines the electrical and protocol characteristics for a data bus. This bus is being widely used in aerospace industry. This standard was implemented at SRDC-L basically to be used in Prototype Paksat-1R. The components used in this bus are restricted items and very difficult to procure. Therefore most of the hardware was implemented using components which are easily available from the market. The software was also developed and successfully tested with the hardware. The paper presents the introduction to the electrical and protocol characteristics of the data bus along with the steps to be taken to design and develop the hardware and software for the bus. System level diagrams and top level software design are also provided.

Navigation Using Global Positioning Satellite & Low Cost Sensors

Abstract
This paper describes integrated navigation using Global Positioning Satellites for low speed & low altitude vehicle. Global positioning satellite’s commercial services are accurate for estimating velocity & position of slow moving land or air vehicles .GPS errors contribute to constant & deterministic drifts in position; however the health & availability of signal is limited & uncertain. On the other hand low cost Inertial Navigation Systems are also suitable for same type of applications, are self contained, uninterrupted, require no external signals but position errors grow with time or are unbounded .So GPS & INS have almost contradictory properties ,this makes these an appropriate choice for integrated navigation. INS works in standalone mode for the measure portion of flight with out interruption & whenever GPS measurements are available usually at a slower rate than of INS, it corrects its position & velocity accordingly. Commercially available GPS can not give proper estimates of height so another sensor i-e pressure sensor is used to estimate errors in vertical channel. To integrate all these measurements Kalman Filter is used.

SUPARCO Telemedicine Pilot Project

Abstract
Telemedicine is defined as, the delivery of e-health services, where distance is a critical factor, by all e-health professionals using telecommunication technologies for the exchange of medical information for diagnosis, treatment and prevention of diseases and injuries, research and evaluation, and for continuing education of health care providers, all in the interests of advancing the health of individuals and their communities.

Many developing countries have inadequate health care and medical services and suffer from a shortage of doctors and other health care professionals. The inadequate distribution of doctors/specialists, infrastructures of telecommunications, roads and transport make it even more difficult to provide health care in remote and rural areas. Where clinics and hospitals exist, they are often ill-equipped and, especially, outside urban areas beyond the reach of normal communications.

Keeping in view natural disasters which severely damage landline communications, therefore, affected areas become isolated to provide medical facilities, in these situations; satellite communication by using VSAT technology is the reliable means of direct connection to the disaster areas where communication is critical for tele-medical consultations and patient treatment.

SUPARCO, being a national space agency of Pakistan and having an experience in satellite communications has initiated a Satellite Communication based Telemedicine network as pilot project which has been successfully established. VSAT (Very Small Aperture Terminal), state of art technology has been selected to provide broad band (satellite) connectivity, for live video conferencing, transfer of high quality biomedical images i.e. CT scan, MRI, X-rays etc, that best meets the requirements of doctors/specialists. Two sites have been connected through Paksat-1 satellite transponder, one at Jinnah Post Graduate Medical Center (JPMC), Karachi as hub and other at Shikarpur civil hospital (interior Sindh) as remote site.

Furthermore, SUPARCO has joint venture with JPMC for better utilization of satellite based network infrastructure regarding telemedicine applications, including tele-consultations and tele-trainings etc.

Performance and Reliability Determination of Leo Satellite Data Transmission System

Abstract
In recent years satellite mobile communications systems and market have entered into the era of maturation. Systems like Iridium and Global Star are technically considered as state of the art. This research paper is the result of a feasibility study of utilizing the Low Earth Orbit, Iridium satellite network for the data transfer. The findings of this research, also demonstrate the performance and reliability of the satellite link. A system of data transfer is developed according to a set of specifications, along with the selection of a suitable satellite link. This data collection system is realized in such a way, that there is a software which interfaces the PC of the data transmitting station, with the Iridium satellite constellation; a similar system configuration is present at the data receiving station.

Bandwidth Efficient Speech Processing Techniques used in Satellite Communication

Abstract
Speech is one of the most complex signals to be handled in the design of communication system. Digitizing speech at reduced rate in order to make efficient use of transmission bandwidth is called speech compression. Satellite communication requires optimum bandwidth utilization with minimum loss, delay and good quality, for speech transmission. In this paper, we analyze the techniques that can be employed in satellite communication in terms of efficient bandwidth, quality, robustness, bit rate, redundancy, complexity, processing time, delays and noise/error. MOS (Mean Optimum Score) and some other quality measure testing methods have been used to compare various speech compressions and coding techniques. INMARSAT (International Maritime Satellite Cooperation), ITU (International Telecommunication Union), FS (Federal Standard) and some other standards of speech compression have been followed.

COSPAS-SARSAT Beacons and Their Possible Applications

Abstract
COSPAS-SARSAT is a satellite-based Search and Rescue (SAR) System to detect and locate aviators, mariners and land-based users in distress and to pass on this information to the search and rescue agencies worldwide. This system consists of satellites in low-earth and geostationary orbits, ground receiving stations – called Local User Terminals (LUT), Missions Control Centers (MCCs), Rescue Coordination Centers (RCCs) and Emergency Beacons. The Emergency Beacons are used to transmit signals in distress situations to the COSPAS-SARSAT satellites on 121.5, 243 and 406 MHz frequencies. These signals are received by the COSPAS-SARSAT satellites, and are re-transmitted to the ground receiving stations (LUTs), where after being processed are transmitted to the Mission Control Centers (MCCs), and then distributed to the Rescue Coordination Centers (RCCs) and MCCs of the other countries. The information provided to the rescue agencies includes alert, identification and location data of the person(s) in distress and this information has proved very useful in rescuing the person(s) in distress situations and for the rescuing agencies in mounting a successful search and rescue operation. The COSPAS-SARSAT beacons have proved tremendously useful in saving the lives of the person(s) in distress situations and since there use from September, 1982 till December 2005, they have saved the lives of 20,331 peoples in distress at sea and on land all over the world.

A Simulation framework for a Reaction Wheel based AOCS

Abstract
A satellite poses a challenge to a control system designer due to the tradeoff between limited number of actuation techniques available and the robustness of the system. The reaction wheels present an economical solution in terms of energy and also enable a smooth control technique as opposed to a chattering control exhibited by thruster techniques. By continuously exchanging momentum between the spacecraft body and reaction/momentum wheels a fine pointing control can be implemented. This paper describes a simulation framework built for the design of an attitude control system for an indigenous communication satellite. It describes the modeling of the dynamics of the spacecraft structure carrying reaction wheels and its capacity for external disturbance rejection. The controller and the associated compensator algorithms are discussed in the context of pitch axis control. Finally an integrated model allowing 3-degrees of freedom to the spacecraft structure carrying three separate reaction wheels is implemented. The expected performance of the control system will be demonstrated through a simulation showing a graphic reorientation of a multi-faced body in accordance with the attitude control command issued by the autopilot.

Programming a Real-Time Operating System for Satellite

Abstract
With the realisation of ideas like formation flights and multi-body space vehicles the demands on an attitude control system have become increasingly complex. Even in its most simplified form, the control system for a typical geostationary satellite has to run various supervisory functions along with determination and control algorithms side by side. Within each algorithm it has to employ multiple actuation and sensing mechanisms and service real time interrupts, for example, in the case of actuator saturation and sensor data fusion. This entails the idea of thread scheduling and program synchronization, tasks specifically meant for a real time OS. This paper explores the embedding of attitude determination and control loop within the framework of a real time operating system provided for TI’s DSP C6xxx series. The paper details out the much functionality provided within the scaleable real time kernel and the analysis and configuration tools available. It goes on to describe a layered implementation stack associated with a typical control loop for Geo Stationary satellites. An application for control is then presented in which state of the art analysis tools are employed to view program threads, synchronization semaphores, hardware interrupts and data exchange pipes operating in real time.

ATMOSPHERIC SCIENCE

Revalidation of TRMM Precipitation Data with Ground Based Measurements for Selected Cities of Pakistan

Abstract
TRMM satellite is a joint venture project of JAXA, Japan and NASA, USA. It has been launched for assessment of rainfall in global and regional perspective. The objectives of this paper include validation of TRMM satellite data for Pakistan. In this paper a detailed comparison of 07 years TRMM based precipitation data (product 3B43 V6 0.25oX0.25 o latitude/longitude grid box monthly data) has been carried out for Karachi, Lahore, Multan and Bahawalpur cities of Pakistan with the ground observation data. The behavior of correlation factor R2 over last 07 years has also been calculated to estimate the pattern of relevance of TRMM data. The average value of R2 for the best matching is 0.85 whereas for average matching it is 0.72. The values of R2 show quite good results indicating TRMM satellite equally useful for rainfall estimation for Pakistan.

Black carbon aerosols in urban air in South Asia

Abstract
We report data from a yearlong (2006–2007) study of black carbon concentrations ([BC]) measured at 5-min intervals with an Aethalometer in Karachi, Pakistan. Daily mean [BC] varied from about 1 to 15 mgm_3. However, short-term spikes exceeding 40 mgm_3 were common, occurring primarily during the morning and evening rush-hour periods. The [BC] values were highest during November through February, w10 mgm_3, and lowest during June through September, w2 mgm_3. Diurnal, seasonal, and day-of-the-week trends are discussed. It is demonstrated that these trends are strongly affected by meteorological patterns. A simple expression is applied to the concentration profiles to separate the effects of meteorological conditions and elucidate the underlying emissions patterns. Daily emissions varied from 14,000 to 22,000 kg of BC per day. When integrated over the year emissions for Karachi Proper were estimated at 6.7 kilometric tons per year and emissions for greater Karachi were 17.5 kilometric tons per year. Folding in the populations of each area yields BC emissions of 0.74 and 1.1 kg per person per year, respectively. Applying the model to previously collected data at Lahore, Pakistan yields emissions during November–January that are around a factor of two higher than those in Karachi, but because the BC measurements in Lahore covered only three months, no estimates of annual emissions were attempted. Given the large populations of these cities the local health impact from PM alone is expected to be severe but because of the high [BC] emissions the impact on the global climate may be equally significant.

Study of Fine Aerosols by In-Situ Monitoring in Karachi-Pakistan and their correlation with MODIS-Derived Fine Mode Fractions

Abstract
Particulate matter (PM) is an important component of air pollution, having both long-term as well as short-term effects on human health such as cardiovascular, lung and skin diseases, which sometimes leads to premature deaths. Particulate Matter assessment is one of major concerns of the world and many environmental protection agencies are working towards continuous monitoring and assessment of air quality from surface-based stations. Variations in fine particulate matter (PM1.0 and PM2.5) concentrations from September 2007 to August 2008 were investigated in, Karachi, the biggest city of Pakistan. We compared the DustTrak 8520 Aerosol Monitor in-situ measurements of PM with remote sensing satellite data obtained from Moderate Resolution Imaging Spectroradiometer (MODIS) on board Terra and Aqua satellites fine mode fraction (FMF) data. Frequency distribution of PM and FMFs are consistent, showing similar trends of variations in different seasons. Seasonal variations of particulate matter were significant, with the highest concentrations observed from mid-November through January and the lowest from May through September. Concentrations were maximum (PM2.5 179.6µg/m3, PM1.0 179.6 µg/m3, FMF 0.754) during mid of winter, while lowest concentrations were observed in monsoon (May 08 to August 08). Both maximum and minimum concentrations of fine PM2.5 were found 2 ~ 5 times that of USEPA standard (35µg/m3). Similarly Black Carbon (BC) concentration measured at 5 min intervals with an Aethalometer in Karachi shows short term spikes exceeding 40µg/m3 which were common during morning and evening rush hours. Non availability of in-situ data could therefore be compensated with satellite data, thus satellites can be used to forecast air quality in an area. As the fine fraction (diameters below 2.5µm) are mainly generated from the anthropogenic activities involving combustion processes or as secondary aerosols produced through atmospheric processes, i.e. due to chemical interaction in the atmosphere involving gases again released mainly from anthropogenic activities. Thus PM observed in Karachi is mainly due to the industrials activities and the road transport.

Study of MODIS-Derived Cloud Top Temperature / Pressure and Aerosol Optical Thickness

Abstract
Aerosols influence the earth’s radiation balance and climate directly, by scattering shortwave (solar) radiation in cloud-free conditions and indirectly, by increasing concentrations of cloud droplets thereby, enhancing cloud shortwave reflectivity. In this paper level-2 data of Moderate Resolution Imaging Spectroradiometer (MODIS) onboard Aqua and Terra satellites have been used to study Cloud Top Temperature (CTT), Cloud Top Pressure (CTP) and Aerosol Optical Thickness (AOT) over Pakistan. These data were obtained for winter (Dec-Feb), pre-monsoon (Mar-May), monsoon (June-Aug) and post-monsoon (Sep-Nov) seasons over the area covering 22-36oN, 60-80oE for the period 2000-03. The study shows that maximum values of CTT and CTP are in the range of 293-299° K and 800-875hpa respectively in monsoon over the areas covering (25-36)°N/60-75°E implying that maximum amount of infrared radiation were emitted by the clouds in this season during the study period. Similarly minimum values of these parameters were observed in the range of 243-253°K and 400-450 hpa in the winter season over the areas covering (25- 36)°N/75-80°E and 31°N/65-70°E. The maximum value of AOT is in the range 0.9-1.0 at 22°N, 25N/60-75°E during monsoon season while at 22°N/60-68°E it is in the range of 0-0.4 during post-monsoon season.

Satellite-based Study of Aerosols’ Influence on Pakistan’s Weather

Abstract
The atmosphere contains suspended particles, ranging in size from about 0.01 µm to 10 µm called aerosols reflecting sunlight and so tend to cool the earth. The main sources of aerosols are fossil fuel combustion, which emits SO2 (converted to sulphates in the atmosphere) and biomass burning which releases organic and elemental carbon. Aerosols influence the radiative balance by absorbing and scattering solar radiation back to space, and by acting as nuclei for condensation and so influencing the properties of clouds. These aerosols are produced directly by natural processes and human activities. Natural aerosols include volcanic dust, sea spray and its particulate product etc. Aerosols not only scatter but also significantly absorb the incoming solar radiation covering the entire spectrum. This paper is based on aerosol data level-2 as obtained from Moderate Resolution Imaging Spectroradiometer (MODIS) onboard Aqua and Terra satellites and cloud data of Automatic Picture Transmission (APT) onboard NOAA (12,15,16) satellites. These data were obtained at different lat/long over Pakistan for the period 2000-2003. Aerosol Optical Thickness (AOT) was studied for area covering 22-36oN, 60-68oE. The maximum value is in the range 0.9-1.0 at 22oN, 25oN/60-75oE during Monsoon season. The reason is, during the northern hemisphere summer, pressure becomes low over Asia, where there is intense surface heating but remains quite high over the cool seas to the south. The moist equatorial air moves north under this pressure gradient, which decreases the optical thickness. As the air moves north, away from the equator the Coriolis force has more and more effect, so the winds are south and southwesterly over Pakistan. Similarly aerosol optical thickness at 22oN/60-68o E shows that it is in the range of 0-0.4 during Post Monsoon season. Like aerosols, clouds also affect the weather, therefore, the APT cloud data for the period 2000-2003 were used to study over well distributed places of Pakistan, which implied that during this period the northern areas of Pakistan remained most cloudy and the southern part of the country remained least cloudy in the winter and post monsoon seasons.

Long-term Trends in total Ozone over Pakistan using TOMS Data (1979-2005)

Abstract
Ozone measurement from the American satellite, Nimbus 7 Total Ozone Mapping Spectrometer (TOMS) instrument, which operated from November 1978 through early May 1993, and later on data from the TOMS instrument on-board the Russian Meteor 3 satellite till Dec., 1994 have been used to determine trends in total ozone over Pakistan. Both TOMS data records with spectral range 311-380 nm, and spectral resolution 1 nm, provide global measurements of total column of ozone on daily basis. Ozone data from 1995 onwards was obtained from Earth Probe and Japanese Advance Earth Observation Satellite (ADEOS) measurements. However, data gap existed for the period between mid 1994 to mid 1995. The reprocessed (version 7) daily total ozone observations made by these satellites over Pakistan (Karachi 24°N, 67°E, Lahore 31°N, 74°E, Quetta 31°N, 67°E, Chitral 35°N, 71°E) for the period from November 1978 till December 2005 have been used to investigate total ozone trends. Long term trend estimates obtained from the linear multiple regression analysis show no significant ozone trend in the south of the country (Karachi). However, the measurement for mid latitude (Lahore, Quetta) northern region (Chitral 35°N, 71°E) have shown significant negative trend in ozone. The objective of this paper is to present the result of an analysis of the TOMS total ozone data over Pakistan.

Aerosol optical properties derived from remote sensing ground-based and satellite system over Pakistan

Abstract
Knowledge of aerosol concentration on global scale, their temporal change and interrelation with other atmospheric parameters like cloud, water vapor, etc is of great importance. Remote sensing satellites in combination with and ground-based systems provide the best information on regional characterization of aerosol particles. This study is based on ground based data of Aerosol Optical Thickness (AOT) and Single Scattering Albedo (SSA) received from sun-photometers installed at Karachi (24.87oN,67.03oE) and Lahore (31.58oN, 74.3oE) and satellite-based data of AOT 22oN – 36oN / 60oE – 80oE) received from Moderate Resolution Imaging Spectro-radiometer (MODIS) onboard Aqua and Terra satellites. These properties of aerosol particles have been studied to investigate their temporal and spatial variation. This study shows that AOT value always remained high in the monsoon season as compared to post monsoon and winter seasons over the Sindh and Punjab. This area is crops yield and biomass burning region and largely contributing seasonal aerosol. Dust, urban-industrial pollution and marine aerosols contributing as source in southern part of the country however, accurately assessing their concentrations, properties and duration requires satellite and ground-based measurements. MODIS level-2 data have been used to study the seasonal and geographical variation of AOT for different latitudes over Pakistan form 2005-06. The maximum value is in the range 0.9 – 1.0 at 26oN -34oN/ 60 oE -74oE during the monsoon season.

UV Insolation Monitoring in Asia - Pacific Region

Abstract
The depletion of the ozone shield over the Polar regions has raised many question such as climate and risks for humans and ecosystems resulting from enhanced UV radiations. The human exposure to UV radiation may result in many skin and eye disorders. A quantitative relation between the amount of UV radiation received and its adverse effects needs to be investigated. It is well known that even if the emission of ozone-depleting substances is halted immediately. The continuing depletion of the ozone layer will result in several thousands of extra cases of skin carcinoma. one of the important parameters to determine the extent of the climate change and the increase in UV radiation in the Asia-Pacific region is to monitor solar radiation (UV radiation) on a regional basis Minimum UV irradiation has been observed at Karachi (24.87ºN, 67.03ºE) during summer monsoon (July-Aug-Sep) with a cloud cover ranging from 90 to 100% UV-B perturbations have also shown antyicorrelation with total ozone. A satellite-based UV monitoring network could be useful to observe the distribution of the solar UV insulation over a large area and its seasonal dependence. the salient features of such programme could be the determination of seasonal trends and the variations in the distribution of solar UV radiation. Such a network would help arriving at representative models of UV radiation incidence and would enable the study of the temperature and dynamic behavior of the troposphere and stratosphere providing ground truth information for the calibration and verification of remote measurements using satellite, radar, lidars etc. ©1998 Elsevier Science Ltd. All rights reserved

Statistical Analysis of Wind Speed and Direction Obtained Through Satellite Based DCP Network

Abstract
Measurements of wind speed and direction made through a country wide satellite based network were analyzed to study the seasonal behaviors of wind patterns. The effect of surface temperature was also taken into consideration. since information on the wind statistics and the intensity of their fluctuation, being the primary feature of natural turbulent flows, are generally required. In particular, pollutants dispersion is governed by vertical and horizontal wind direction fluctuations. The large scatter observed low speed or non-neutral conditions was correlation less than 1 hr. It appears that the wind speed was the main factor affecting the variability of its standard deviation (SD,). The normalized total wind speed (at z-I0 m), standard deviation ở√ V is well approximated by 1.2 / V m/s for lower wind speeds (V < 5 m/s) and by Ởv /V = 0. 09 when V > 5 m/s. The wind direction standard deviation follows a similar law with Ởw = 8.00/ Vm/s for r V< 5 m/s and Ởw = 0.128 for higher wind. [/toggle] [toggle title="Satellite-based Study of Aerosol Optical Thickness and Cloud-Cover over Pakistan"] Abstract
This paper is based on aerosol data level-2 as obtained from Moderate Resolution Imaging Spectroradiometer (MODES) onboard Aqua and Terra satellites and cloud data of Automatic Picture Transmission (APT) onboard NOAA (12.15,16) satellites. These data were obtained at different lat/long over Pakistan for the period 2000-2003. Aerosol Optical Thickness (AOT) was studied for area covering 22-36ºN, 60-68ºE. The maximum value is in the range 0.2-0.6 at 22ºN60-68ºE over the Arabian Sea during the months of Apr-June. The reason is, during the northern hemisphere summer, pressure becomes low over Asia, where there is intense surface heating but remains quite high over the cool seas to the south. The moist equatorial air moves north under this pressure gradient, which decreases the optical thickness. As the air moves north, away from the equator the Coriolis force has more and more effect, so the winds are south and southwesterly over Pakistan. Similarly aerosol optical thickness at 31ºN, 60-80º E (in land over Pakistan) shows that it is in the range of 0.2-0 8. Like aerosols, clouds were also affect the weather, therefore, the APT cloud data for the period 2000-2003 were used to study over well distributed places of Pakistan, which implied that during this period the northern areas of Pakistan remained mast cloudy and the southern part of the country remained least cloudy in the winter and post monsoon seasons.

Seasonal study of aerosol shows that in monsoon season (June-Aug value o f AOT over the areas covering 22-31ºN 60-72ºE. is in the range 0.3-0.6 while in dry post monsoon (Sep-Nov) and cold winter season (Dec-Feb) it is mostly in the range U 7-0.8. The study of AOT at 36ºN, 60~75ºE (northern mountainous region; shows that most of the time it is in the range 0.2-0.4 in the mentioned seasons implying that the atmosphere was not perfectly transparent. Since aerosols act as Cloud Condensation Nuclei(CCN) so upper region of Pakistan remained mostly cloudy in the same period.

Prediction of Maximum Usable Frequency (MUF) / Optimum Traffic Frequency (FOT) for Single and Multi-Hop Circuits

Abstract
One of the main requirements of the High Frequency data users the world over is the prediction of Maximum Usable Frequency (MUF)/Optimum Traffic Frequency (FOT) for various single and multi-hop circuits. For every circuit there is a maximum radio frequency above which the signal will penetrate the ionosphere and be lost to space. One of the tasks of SUPARCO is to predict MUF/FOT (which is 85% of MUF) for nearly 216 national and international circuits, 2 months in advance, for various Defense/Civil establishments in the country. For the prediction of MUF, various characteristics i.e. stations’ separation, latitude, longitude, the time of day, season, sunspot numbers and CCIR coefficients for low and high solar activity are taken into account.

Long-Term Trends in Total Ozone over South Asia as Observed By Satellites (TOMS AND GOME)

Abstract
The breakdowns of stratospheric ozone by man made halogenated chemicals are known to be responsible for ozone depletion observed at poles and mid-latitudes. Total Ozone measurements from NASA ‘s Total Ozone Mapping Spectrometer (TOMS) and from Global Ozone Monitoring Experiment (GOME,) on Earth Resource Satellite (ERS-2,), for July 1995 to Dec.1997 and/or the year 2000 were used to determine the quantitative spatial and temporal resolution of ozone over the region. The study was also aimed at quantitative evaluation of ozone data derived from TOMS and GOME. Daily total ozone observations made by these satellites over South Asian region (Dhaka (23.450 N 90.290) Dehli (28.18º N, 77.30º E,) ,Karachi (24.53º N, 67020º E,), Tehran (35º N,51.03º E), Chitral (35º N, 71º E,) Lahore (31.34º N, 74.19º E,) and Quetta (31.12º N, 67.01º E,) . Long term trend estimates obtained from the linear regression analysis show significant positive ozone trend in the southern latitudes ranging from +15.6% to 15 % (Dhaka, Dehli and Karachi) over the study period However, the measurements for mid latitudes (Tehran, Chitral, Lahore and Quetta,) have shown significant negative trend of –I5% to —1.3 % in total ozone.

Long-Term Trends in Total Ozone over Pakistan Using TOMS Data 1978-98

Abstract
Ozone measurement from the American satellite, Nimbus 7 Total Ozone Mapping Spectrometer (TOMS), which operated from November 1978 through early May 1993. and later on data from the TOMS on-board the Russian Meteor 3 satellite till Dec, 1994 have been used to determine trends in total ozone over Pakistan. Both TOMS data records with spectral range 311-380 nm, and spectral resolution 1 nm, provide global measurements of total column of ozone on daily basis. Ozone data from 1995 onwards was obtained from Earth Probe and Japanese Advance Earth Observation Satellite (ADEOS) measurements, However, data gap existed for the period between mid 1994 to mid 1995, The reprocessed (version 7) daily total ozone observations made by these satellites over Pakistan (Karachi 240N, 670E, Lahore 310N, 74ºE, Quetta 31ºN, 670E, Chitral 35º N, 71º E) for the period from November 1978 till December 1998 have been used to investigate total ozone trends. Long term trend estimates obtained from the linear multiple regression analysis show no significant ozone trend in the south of the county (Karachi), However, the measurement for mid latitude (Lahore, Ouetta) northern region (Chitral 350N, 710E) have shown significant negative trend in ozone. The objective of this paper is to present the result of an analysis of the TOMS total ozone data over Pakistan.

Long-Term Trend in the Total Ozone over Asia using Satellites and Balloon Based Ozonesonde Data

Abstract
Global environmental issues. include ozone layer depletion, global warming, acid deposition, tropical deforestation, desertification, pollution problems in developing countries, its impacts and damages affect not only the countries that caused the problems but go beyond their national boundaries and reached a global scale. These problems are inter- related in a complicated manner. The loss of ozone high in the atmosphere as consequences of human activities is a serious global scale environmental problem. Total ozone measurements from Total Ozone Mapping Spectrometer onboard Nimbus 7 (NASA). Meteor 3 (Russian), and Earth Probe (NASA) from November 1978-2001 use to determine the quantitative spatial and a temporal resolution of ozone over the South Asia have been used to investigate total Ozone trends. Long- term trend estimates obtained from the linear multiple regression analysis show no significant Ozone trend in the Southern part of Asia However, the measurement for mid latitude and northern region have shown significant negative trend in ozone. Ozone profile are also measured using GPS based Radiosonde / Ozonesonde balloon sounding system. The flight were carried out at 25’ N and 66º E up to 30-35 Km altitude. In this study the tropospheric ozone formation, stratospheric ozone subsidence and its variation (Seasonal) near and above the ground, temperature and dynamic behavior of the troposphere and stratosphere are also discussed.

MECHANICAL ENGINEERING

Investigation into Microstructures of Maraging Steel 250 Weldments and Effect of Post-Weld Heat Treatments

Abstract
This study was undertaken to gain a better understanding of microstructures obtained by multipass gas tungsten arc welding in maraging steel grade 250. Metallography and microhardness measurements were carried out on sheet and welded joints in as-welded and post-weld aged conditions. It was found that there was a significant amount of reverted austenite formed on cell boundaries of weld metal after aging at 758-823 K for 3-5 h, and was stable at room temperature. Aging at higher temperatures led to an increase in the continuous network of patchy austenite along the cell boundaries. The reason for the above, in our opinion, is the concentrational heterogeneity which characterizes the microstructure of maraging steel welds. No reverted austenite was observed in as-welded specimens. Solution annealing at 1093 K for 1 h did not completely eliminate the chemical heterogeneity associated with weld structures. However, homogenizing at 1373 K produced homogenous structure that on subsequent aging produces austenite-free lath martensitic structure.

Failure Analysis of HAZ Cracking in Low C–CrMoV Steel Weldment

Abstract
This case study describes the failure analysis of steel nozzle in which cracking was observed after a circumferential welding process. The nozzle assembly was made from low C–CrMoV alloy steel that was subsequently single pass butt welded using gas tungsten arc welding. No cracks were found in visual inspection of the welds; however, X-ray radiography showed small discontinuous cracks on the surface in the area adjacent to weld bead, i.e. heat affected zone. The welding of nozzle parts made of same material was a routine process and this type of cracking did not occur in the past. Therefore, it became essential to determine the root cause of the failure. A detailed investigation including visual examination, nondestructive testing, optical microscopy, microhardness measurements and residual stress measurements were carried out to find out the primary cause of failure and to identify actions required to avoid its reoccurrence in future. Results of the investigation revealed that the principal cause of failure was the presence of coarse untempered martensite in the heat affected zone due to localized heating. The localized heating was caused by high welding heat input or low welding speed and resulted in the high transformation stresses. These transformation stresses combined with the thermal stresses and the constraint conditions to cause intergranular brittle fracture.

Evolution of microstructure and mechanical properties during quenching and tempering of ultrahigh strength 0.3C Si–Mn–Cr–Mo low alloy steel

Abstract
Effects of quenching and tempering treatments on the development of microstructure and mechanical properties of ultrahigh strength 0.3C Si–Mn–Cr–Mo low alloy steel were investigated. Samples were austenitized at 1123–1323 K for 2400 s and oil quenched (OQ) to produce mixed microstructures. Tempering was carried out at 473–773 K for 2–3 h. Phase transformation temperatures weremeasured using dilatometer. The microstructures werecharacterized using optical and scanning electron microscope. SEM–EDS analysis was carried out to determine the type and size of non-metallic inclusions. Volume percent of retained austenite was measured by X-ray diffraction technique. Hardness, tensile properties, and impact energies were also determined for all heat treated conditions. Fractography of impact specimens were done using stereomicroscope and SEM. The results showed that newly developed steel exhibited peak hardness, yield strength, and tensile strength of about 600 HV, 1760 MPa, and 1900 MPa, respectively, when OQ from 1203 K and tempered in between 473 and 573 K, combined with adequate ductility and impact toughness. Decrease in hardness andstrength was observed with increasing tempering temperature whereas the impact energy was stable up to 623 K, however, impact energy was found to decrease above 632 Kdue to temper martensite embrittlement.

Study of Crack Propagation behavior in the Integrally Stiffened Panel and Conventional Stiffened Panel

Abstract
The crack growth characteristics of the integrally stiffened panel and conventional stiffened panel based on fracture mechanics and finite element analysis are investigated. A fourteen-stringer stiffened panel is analyzed for a central skin crack propagating towards the adjacent stringers. Stress intensity factors and fatigue crack propagation rates of both types of the stiffened panels are then compared. The analyses result show that integral stiffening cause higher stress intensity factor than conventional stiffened panel as the crack tip passes through the stringer and the integrally stiffened panel has less damage tolerance capability than the riveted stiffened panel.

Study on Damage Tolerance Behavior of Integrally Stiffened Panel and Conventional Stiffened Panel

Abstract
The damage tolerance behavior of integrally and conventional stiffened panel is investigated based on the fracture mechanics and finite element analysis. The load bearing capability and crack growth characteristic of both types of the stiffened panels having same configuration subjected to distributed tensile load is examined in this paper. A fourteen-stringer stiffened panel is analyzed for a central skin crack propagating towards the adjacent stringers. Stress intensity factors and fatigue crack propagation rates of both types of the stiffened panels are then compared. The analysis results show that integral stiffening causes higher stress intensity factor than conventional stiffened panel as the crack tip passes through the stringer and the integrally stiffened panel has less load bearing capability than the riveted stiffened panel.

Mechanical Properties of Honeycomb Sandwich Panels of Aluminum and Glass Fiber Facings of Different Core Thickness from ASTM Standards

Abstract
The experiments were designed and performed to find the Material Properties of Honeycomb Sandwich Panels and to compare the difference in properties between Aluminum Facing Honeycomb Sandwich Panels and of Glass Fiber Facing Honeycomb Sandwich Panels. Another set of experiments were performed to find the Lamination Strength of Bond used for joining facing and core of honeycomb sandwich panels. Again the tests were performed on both of the facing types of Sandwich Panels.

Study on Damage Tolerance Behavior of Integrally Stiffened Panel

Abstract

SPACE SCIENCE


Monitoring Of Space Debris

Abstract
Space is commonly thought of as a vast emptiness. Stars, planets, asteroids and gaseous clouds are contained within this vast void. Within the part of space in the earth orbit there is a lot more stuff. Billions of pieces of old space ships, satellites rockets are right now orbiting the earth at speeds between about 20,000 and 25,000 miles per hour, at altitudes from hundreds of miles to many thousands of miles around and above the Earth. Cloud of debris rather than the millions of discrete items that exist now. Where pieces of debris collide with other pieces of debris, creating more pieces of debris. Which in turn collide with each other, creating still more debris. it is obvious , if small pieces of debris can cause damage, then larger pieces can cause even greater damage, when they collide with an other orbiting object. According to an estimate, United States tracks some 8,000 pieces of space debris greater in size than 4 inches (about 10 cm). It would be appropriate to form a network of observers to undertake such observations. In fact this would strengthen the existing network for orbiting objects. In order to make awareness of space debris and its hazardous effects. SUPARCO optically tracked the Russian Space Station MIR during its decay phase. Tracking was carried out using traditional low cost equipment. Orbits and look angles were calculated to determine time and direction of appearance, so as to locate and observe the MIR. To reduce the creation of new debris, efforts should be made to devise launch techniques.

Magnetic Storms at Karachi and Their Effects on Hf Radio Communication in the Country during the Solar Cycle (1989-2000)

Abstract
A total of 374 large magnetic storms (Kp/K>=5) occurring at Karachi during the solar cycle (1989-2000) have been studied. This study discusses a seasonal and annual frequency of occurrence of these magnetic storms. During magnetic storm, the most conspicuous effects noted are lowering of the critical frequency of F2 layer(foF2) and increase in absorption, due to which the range of usable frequencies is narrowed.

Geomagnetic Field Variation Monitoring at Karachi, Pakistan

Abstract
Magnetic storms occur when charged particles from the Sun collide with the Earth’s magnetic field. These storms vary in size and intensity. During the sunspot minimum, severe storms can occur. Generally, the storms affect at higher latitudes but severe magnetic storms affect at mid and even at low latitudes.

This study discusses the occurrence of two severe magnetic storms (K, 3-hourly local magnetic activity index =8) during 7-11 November, 2004 which affected HF Communication in various parts of Pakistan (lower mid latitudes) completely / partially. The magnetic storms were pursued of two X-class solar flares on 4th (the largest ever, with a size X45, more than twice as large as any previously recorded), and 10th November 2004 respectively. These solar flares were monitored / reported by SOHO, GOES10 and GOES12 satellites. Effects of these magnetic storms were monitored by an Automatic Magnetic Observatory System (AMOS-III) at Karachi, Pakistan. The first severe magnetic storm began at 1024 hrs (GMT) on 7th November with ranges (estimated) DX=444 g, DY=240 g and DZ=136 g while the second one began at 0750 hrs (GMT) on 9th November with ranges DX=370 g, DY=190 g and DZ=130 g. During magnetic storms, the ionospheric data, acquired by two digital sounders (DGS-256) at Karachi (24.95O N, 67.14O E) and Islamabad (33.75O N, 72.87O E) have been analyzed. Most prominent effects noted were total blanketing at night-times, F-layer stratification, increase in absorption, lowering of the critical frequencies of F layer (at Islamabad, it was below the lower limit of normal frequency range of the equipment) and enhancement in height (virtual height reaches up to 550 Km). These effects have been discussed in detail by comparing the frequency and height graphs during storm periods with the monthly medians of these ionospheric parameters.

Es Occurrences at Islamabad during 1989-97, on the Downleg of Solar Maximum (1989-90)

Abstract
Ionospheric data of Islamabad (33.75ºN, 72.87ºE) have been used to study the seasonal and annual Es occurrences, using the ionospheric Es parameters foEs, fbEs and total blanketing due to Es over the period 1989 – 97. It is observed that the seasonal % occurrences of Es (foEs), blanketing frequency (fbEs) and total blanketing due to Es are maximum in summer and minimum in winter both for day and night – time throughout the period 1987 – 1997. The % occurrence of the first two parameters is greater at night than during the day in all the seasons, while a reverse trend exits for the third parameter. Therefore, the radio communicators are liable to face problems in HF communication during the season of summer irrespective of the solar epoch, Moreover, they are liable to face more problems during day – time than at night. Best conditions for HF communication prevail in winter. The annual % occurrence of Es (foEs) and blanketing frequency (fbEs) both for day and night – time are observed to be overall in phase with the solar cycle, while that of the total blanketing due to Es overall in anti phase.

Correlation Between foEs at Islamabad and the Sunspot Numbers over the Solar Cycle (1986 – 97)

Abstract
Ionospheric data of Islamabad (33.75ºN, 72.87ºE) have been used to study the correlation between annual means of foEs and that of the Smoothed Sunspot Numbers (SSN) during the day and night-time over the solar cycle (1986-97). Also, the variations of seasonal means of foEs over this solar cycle have been studied. It is observed that the variations of annual means of foEs and SSN during the day-time are positively correlated over the period 1987-94, while they are overall negatively correlated at and near the solar minima (1986 & 1996). Moreover, the variations of annual means of foEs and SSN at night are also positively correlated over the period 1987-93, whereas negatively correlated at and near the solar minima (1986 & 1996). The comparison of the three seasons has shown that the maximum of seasonal means of foEs occurs in summer and the minimum in winter, both for day and night-time during the complete solar cycle.

Comparative Study of h’F at Islamabad during Solar Minimum (1996) and Solar Maximum (2000) Years

Abstract
For comparative study of h’F (virtual height of ionospheric F-layer) at Islamabad (33.75oN, 72.87oE) during Solar Minimum (1996) and Solar Maximum (2000) years, the seasonal and annual means of monthly medians of h’F are used. The h’F are determined by the ionograms recorded at Islamabad using the Digisonde DGS-256. The comparison shows that the seasonal means of h’F are greater during Solar Maximum (2000) than those during Solar Minimum (1996) in all the seasons both on day and night. During Solar Minimum (1996), the seasonal means of h’F are the highest in summer and the lowest in winter on day as well as at night. However, during Solar Maximum (2000), the seasonal means of h’F are found to be the highest in equinoxes and equal in winter and summer on daytime, whereas at night these are the highest in summer and the lowest in winter

Comparative Study of fmin at Multan during Solar Minimum (1996) and Solar Maximum (2000) Years

Abstract
The minimum frequency at which echoes are observed in vertical incidence soundings, fmin is dependent, amongst other terms, on the absorption present in the ionosphere and thus can be used as an absorption index. In practice, it is particularly useful to discover the large changes in absorption with time and position. For comparison of daytime fmin at Multan (30.20N, 71.50E) during Solar Minimum (1996) and Solar Maximum (2000) years, the seasonal and annual means of monthly medians of fmin are used for the study. For determining fmin the ionograms recorded at Multan by Panoramic Ionospheric Recorder-9 (PIR-9) have been used.

Effects of 08 October, 2005 Earthquake on the Geomagnetic Field at Karachi

Abstract
This study reveals that the ‘shallow focus’ major earthquake (M = 7.6) occurring at Muzaffarabad on 8 October, 2005 produced sharp level shifts of magnitude 70 – 75 nT in local F (Total Scalar Magnetic Field) and that of 80 – 90 nT in Z-component on 1 & 6 October, 2005, as pre -effects on the earth’s magnetic field. These sharp shifts in levels of local field F and Z-component restored back to its normal values after 4 hr 5 minutes on 1 Oct, 2005 and 2 hr 53 minutes on 6 Oct, 2005. Highly disturbed wave having amplitude 52nT and oscillation period 23hr 47 minutes in the field F was also observed about 3 days (4 & 5 October, 2005) before the occurrence of earthquake. Further, analysis of the amplitudes (0.5≤A1≤1 nT, 1.1≤A2≤5 nT, 5.1≤A3≤10 nT and A4>10 nT) of these aperiodic oscillations in F-plots for magnetically quite days (∑K ≤ 20) have shown that the appearance of amplitudes A1 and A4 in the F-plots decrease during October, 2005 i.e. month of earthquake and during September, 2005 i.e. one month before the event respectively. The mean monthly occurrence of A4 attained a lowest value of 1.3% in September, 2005, just a month before the earthquake. While the mean monthly percent occurrence of A1 attained a lowest value of 11.14% and that of A4 attained a highest value of 6.2% in October, 2005(i.e. the month of earthquake). This suggest that the sharp shifts in the levels of field F & its Z-Component as well as decrease in the % occurrence of A4 to 1.3 one month before the event must be the indications of the occurrence of the earthquake at Muzaffarabad. The critical variation in amplitudes A1 and A4 during the months before, after and the onset of major earthquake determines the precursors of the shallow type major earthquakes like the one happened at Muzaffarabad.

”Triggering

Abstract
It is observed that the large traveling ionospheric disturbances having period greater than 2 hours, LS TIDs (> 2h), can trigger the downward flux of electrons (1.36×108 to 2.08×109 e cm-2 sec-1 ) from protonosphere to ionosphere, producing the night-time enhancements (NEs) in foF2 at mid-latitudes around mid- night. This study is facilitated by deriving a formula for determining the downward flux of Protonospheric electrons.

Space Radiation Effects on Spacecraft Microelectronics

Abstract
One of the primary design considerations for a space mission is the survivability of its electronic systems in an ionizing radiation environment. The increasingly complex mission requirements of modern spacecraft for military, commercial and scientific applications have mandated the need for highly capable microelectronics. This trend has been accompanied by the need to provide affordable, lightweight, low volume and low power systems. Both these trends have resulted in the need to adopt commercial microelectronics for space missions as well as to examine emerging technologies. By their very nature, commercial technologies are constantly changing.

The effects of radiations on commercial device technologies have widely been discussed in literature. This paper summarizes these discussions to outline trends in different radiation effects with changing device technologies. A review on radiation response of very large scale integration (VLSI) devices will also be presented.

On the Cause of Forenoon and Postnoon Bite Outs in foF2

Abstract
A seasonal study of foF2 data of two Pakistani Ionospheric Stations viz : Karachi and Islamabad for the period from March 1982 to February 1983 shows that the percentage occurrence of the fore – noon & post – noon bite – outs traveling from a higher latitude to a lower one is maximum in winter and minimum in Summer. A reversed seasonal trend is observed for the bite – outs which traveled from lower to higher latitudes. The propagation of fore – noon and post – noon bite – outs from higher to lower latitudes and vice versa gives a clue that the possibility of their production by E x B drift may be ruled out and that a plausible cause of the bite – outs may be meridional wind (equatorward / poleward winds).

COMPUTER SCIENCE


Development of a knowledge based system for reactive scheduling in manufacturing cells

Abstract
This paper describes a Knowledge-Based Reactive Scheduling System (KBRSS) for Just-In-Time (JIT) manufacturing cells. The system can handle the predictive/static and reactive/ dynamic scheduling problem in a manufacturing cell. The approach taken in this scheduling system is to combine heuristic and rule-based system techniques, incorporating a number of knowledge rules which take into account the circumstances and constraints of the manufacturing cell. The system information is maintained on a conventional database i.e dBase III plus, which is interfaced to an expert system shell, ARENA. The KBRSS is illustrated with the help of an example.

An expert system for scheduling in just-in-time manufacturing cells

Abstract
This paper describes the design and application of a knowledge based system that assists scheduling in cellular manufacturing to create feasible and accurate schedules in static and dynamic (reactive) situations. The scheduling system works with the four manufacturing resource constraints of machines, tools, manpower and material through the development of rules in the knowledge base. These rules interact with the static and dynamic database of the manufacturing resources to ascertain their availability and then to sequence the various jobs. The sequencing can be carried out through various heuristic rules, (such as First-In-First-Out, Shortest Processing Time, Earliest Due Date, Critical Ratio and Management Priority) set by the user. The system has the ability to defer decision making to the system user if any constraint is violated. The resulting schedules are presented as Gantt charts which can be used as control tools. The system has been developed on a PC using proprietary Expert system shell called CRYSTAL.

Artificial Intelligence & Simulation Techniques

Abstract
This paper describes the experience gained from the theoretical study of Artificial Intelligence and simulation techniques and AI applications that combine features of Artificial Intelligence and simulation. Following topics have been discussed in this paper a) Artificial Intelligence (AI) & AI Techniques b) Simulation and simulation techniques c) AI Applications.

ELECTRONICS


Identifying Phase Noise in VCO and Methods to Minimize the Noise Floor

Abstract
This paper discusses the phase noise with reference to Leeson’s oscillator model, describes the noise generating mechanisms comprising of flicker FM noise, thermally induced and broadband noise and provides the designer with simplified key parameters that should be designed properly to achieve good phase noise performance. Design of customized VCO (Voltage Controlled Oscillator) running in the range of 1.5 GHz to 2.3 GHz with tuning sensitivity of 100 MHz/volts is presented which successfully proves the theoretical considerations developed.

Design & Analysis of An X-Band QPSK Modulator Using Direct Carrier Modulation Technique

Abstract
This paper presents the design & simulation of a QPSK Modulator (Quadrature Phase Shift Keying) based on Direct Carrier Modulation technique with a very simple circuitry. In this design, two double balanced mixers, Branch-line coupler & Wilkinson power combiner are used. The selection of a Double Balanced Mixer, being the main component of the design, is a critical issue. Specifications of mixer such as Conversion loss, Interport isolation etc are discussed. Branch-line coupler is used to produce in phase & quadrature signals & Wilkinson power combiner is used to combine the two modulated orthogonal signals at the output. These passive components are easy to fabricate, occupy reasonable area and provide satisfactory performance as compared to their counterparts. The simulated spectrum and static constellation diagrams of the modulator are presented. The circuit has been designed at 8.3 GHz X Band for 150Mbps bit rate

Indigenous Development of a C-band Solid State Power Amplifier

Abstract
Six (06) Watt Solid State Power Amplifier (SSPA) has been designed and developed with over all gain of 60 dB and gain flatness of ±0.7 dB at standard C-band (3.7 to 4.2GHz). Radial stubs have been inserted in Short Circuited Shunt Stub (SCSS) to solve problem of impedance pulling faced in using Internally Matched Transistors (IMTs). P1dB Compression Point, Gain Flatness over entire bandwidth and Intermodulation Products (IMs) of the SSPA have been tested and measured. Test results and the integration of the indigenously designed and developed SSPA are presented in this paper.

SPACE ELECTRONICS


Shaping of Satellite Footprint Contours for the Desired Geographical Coverage Using MathCAD®

Abstract
The prediction of footprints is the basic requirement for a satellite antenna design. A highly shaped beam is used to improve antenna gain over the prescribed area and to reduce interference outside the coverage area. Footprints are predicted from the knowledge of antenna far-field pattern. The shape of the resulting far field pattern can be controlled by variations in various geometrical parameters of the satellite antenna. In this paper the shaping of satellite footprint is presented by variations in the feed positions. Three sectoral feed horns are used to feed the 1.5m offset reflector. Three possible configurations of feed network are analyzed to predict the far field pattern for each configuration. The resulting far field pattern is then transformed to get footprints over the geographical map of Pakistan. The shape of the resulting footprint contour is altered by slight variation in the position of one of the feed horn.

Sensor Design Techniques and Constraints

Abstract
Most crucial part of remote sensing satellite is the sensor. Two main classes of sensors are passive and active. In active sensors, energy is generated form within the sensor system and beamed outward to illuminate the target. The energy reflected back from the target is picked up by the sensor. Cost of such systems is higher than passive sensor systems. In passive sensors electromagnetic radiation received comes from an external source such as Sun and the reflected energy is again picked up by the sensor. Passive sensors are sensitive to clouds and haze. Thematic Mapper of Landsat and HRV of SPOT lie in the category of passive sensors, while SAR is an example of active sensor used for earth observation.

The payload sensor(s) design is crucial in defining mission’s purpose. The sensor characteristics account for the entire payload’s mission and the other space segment elements are really in service to the payload. Sensor design should flow from measurement requirements and is best performed as an iterative process between designers and the science community within the constraints set by fundamental physics, the state of the technology, and cost. Trade-off studies assess instrument design alternatives that can produce the required measurements within the constraints set by fundamental physics, the state of the technology, and cost. Advancement in sensor technology continue to improve performance, cost, size, mass, and power parameters to suit mission objectives. Here we will discuss the image acquisition part of the sensor its design and constraints. The physics of diffraction is a key factor that constrains sensor design, other are size, mass and power requirements. Beside these there are some other constraints which are necessary to be considered for the selection of senor components, material and calibration technique, like temperature coefficients, effect of radiation, and vibration effects etc. Here different techniques/approaches and constraints regarding the design of electro-optical imaging system are discussed.

ENVIORNMENT


Particulate matter (PM2.5) concentration and source apportionment in Lahore

Abstract
The work reported in this paper was carried out to study the trends of PM2.5 (particles with an aerodynamic diameter of 2.5 µm or less) concentrations and source apportionment of PM2.5 monitored at an urban residential site in Lahore, Pakistan. PM2.5 aerosol samples were collected for 2 days in a week at 12 h interval in a day, both in dry and wet seasons, on ZefluorTM filter papers using Thermo-Electron Corporation Reference Ambient Air Sampler (RAAS). Total 310 samples were collected during the period under study, i.e., from November 2005 to December 2007. High PM2.5 loads were observed in winter, which were approximately 4 times greater than those observed in the summer, spring, fall and monsoon seasons in the yearlong measurements. Source apportionment was performed on short duration analysis results of November 2005 to March 2006 using Positive Matrix Factorization (PMF) model. The results derived from PMF model indicated that the major contributors to PM2.5 in Lahore are: soil/road dust, industrial emissions, vehicular emissions and secondary aerosols. It is, therefore, concluded that in addition to local vehicular and industrial emissions, the city is also affected from trans-boundary air pollutants particularly due to secondary aerosols (especially SO42-) during winter which increase PM2.5 concentrations manifold when relatively less mixing height exists. The sulfate particles also facilitate in haze/fog formation during calm highly humid conditions, thus reduce visibility and increase the incidents of respiratory diseases encountered in the city every year.

EARTH SCIENCE


Seismic Monitoring of Volcanoes using Satellite Based System

Abstract
Natural disaster is the result of abnormal natural phenomena acting on mankind. Terrestrial volcanism is among the most spectacular and fundamentally important surface phenomena of the dynamic tectonic activity of the Earths. Over ninety percent of volcanism is associated wit/s the seismic activities. The surface of the planet earth is broken into a number of lithospheric plates that move constantly relative to each other. Most of the world’s active volcanoes are located close to the boundaries between these plates, but volcanic activity also exists within the plates themselves, giving rise to intra-plate” volcanoes.

1Operating on a global scale, satellite based Argos system is an attractive possibility with its low weight, low cost, easy to-deploy platforms. Argos and remote sensing data to monitored 129 volcanoes in 20 countries. Remote sensing data is used to detect lithological differences, vegetation changes, altimetric variations after volcanic events, and the extent and growth of urban areas into endangered areas. Unattended Argos transmitters at remote sites can send data at the first sign of volcanic activity. Volcanologists around the world receive geological, geophysical and geochemical data in their location up to 20 times a day, for analysis. This paper, discussed how the permanent monitoring can help to mitigate the effects of an eruption. This paper also focuses on the seismicity studies and seismic tomography through teleseism arrival times

CLIMATE CHANGING


An Overview of the Impact of Global Warming on Water Resources and Adaptive Measures

Abstract
The study includes the impacts of global warming on hydrological process, vulnerability assessment using the results of climate models for water resources and adaptation measures. The study infers that 1.7 billion people presently live in countries that are water- stressed. Projected climate change would further decrease available water in many of these water-stressed countries, most of these being developing. Global warming generates high intensity rainfall with short duration, which affects runoff process. It also influences the groundwater resources. Due to sea level rise by global warming, the freshwater- seawater interface is shifted further inland and this shifting leads to a reduction in the volume of fresh groundwater resources. Most of fresh water is used to grow food; however, 60% of water used for irrigation is wasted.

The study also includes some adaptation measures (responsive / anticipatory) and viable suggestions to save the water resources especially below the surface. Emphasis is given on the anticipatory adaptation; to minimize the accumulation of Greenhouse Gases (GHGs) in the Earth’s atmosphere.

CHEMICAL ENGINEERING


Some studies on thermo-oxidative degradation of natural rubber

Abstract
Thermo-oxidative stability of polyisopreme (N.R.) unvulcanized has been examined by measurement of loss in weight on heating in air. Polyisopreme samples were heated at four different temperatures i.e. 260,280,300 & 320 0c for ten hours & percent volatilization and rates of volatilization were determined at each temperature. It has been found that above 2800c degradation proceeds rapidly. Activation energy based on rate of volatilization is 25Kcal/mol.

CONTROL SYSTEM


A Test Bed for Verifying Spacecraft Attitude Control System

Abstract
The design of satellite attitude control system has emerged as a benchmark control problem due to the highly non-linear nature of spacecraft rotational dynamics, limited actuation mechanisms available in space and a large number of parametric uncertainties in the plant model. The complete design of any attitude control system therefore involves modeling of the dynamics of the rigid body along with the mathematical modeling of the actuators and their impact on attitude dynamics. In this paper we develop and present complete 3-degrees of freedom, non-linear rotational model of the satellite. We also develop control laws based on gas thrusters as actuators. The control solution is based upon optimal control laws leading to control maneuvers being performed with an economy of fuel. A gas thruster’s inherent tendency to chatter is investigated and the performance of a proposed solution is evaluated. Out of the successful simulations, evolved a test bed consisting of nonlinear plant model, generalized actuator models, and a set of control laws typically employed in space missions. Within this test-bed different controller designs can be tested, rapidly prototyped and allowed to run in real time.

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