2. Lure of Space
Human beings have irresistible urge to travel and explore. They are inherently curious and want to enrich their knowledge. They are also adventuresome. Consequently, they are eager to go to the farthest corners of the Earth, the deepest reaches of oceans and climb the highest mountain peaks, accepting the risks involved, if any. Driven by similar spirit of curiosity and thirst for knowledge, they want to explore the other planets in our solar system and peer into deep space to discover the secrets of the universe.
2.1 Enabling Elevations
The adventures of climbing high mountain peaks and riding balloons to high altitudes are exhilarating to everybody. But to scientists and engineers the bird’s eye-view of the Earth from high altitudes also presents a whole lot of wondrous applications and possibilities. From very high altitudes, one sees in one view large areas of the Earth. For example, from a mountain one kilometer high one can see up to a distance of about 112 km on a clear day. From a platform at a height of 36,000 km nearly one-third area of Earth is visible. As we shall discuss shortly, space systems engineers can harness the ability to obtain synoptic view of large parts of Earth for high value applications of remote sensing and communication, by utilizing versatile hovering platforms at the desired altitudes. It was such visions, which lead mankind to devise suitable transportation systems to send objects into space.
How does one reach high altitudes and establish useful viewing platforms? Balloons can climb to about 40 km and stay afloat for several hours. Although, airplanes chew up any distance at great speeds, they can overcome height only to a limited extent. The reason is that, in order to propel itself, an airplane needs to burn the onboard fuel and to be able to do so it needs to draw copious quantities of air, the oxidizer, from the surrounding atmosphere. So, the height to which an airplane can climb is limited to the height up to which the atmosphere is palpable, which is just about 15 km. Further, only those objects, which possess enough speed to counteract long enough the pull of the gravity, can hover in space. Only rockets can climb to any height, even beyond the atmosphere and into Space, since they carry on board both the fuel and the oxidizer. A rocket system can also impart high enough speeds to man made objects to sustain them as satellites of Earth for periods ranging from a few hours to several years.
2.2 Beginnings of Space Era
During World War II, rockets were developed as ballistic missiles to hurl bombs at enemy territories. They began to be utilized for peaceful purposes of Space research as sounding rockets from early 1950s. The Space research programs envisaged during the International Geophysical Year beginning in 1957 prompted Russia and the United States of America, USA, to announce their plans to put artificial satellites in Earth orbits for space research [Reference 9]. Russia succeeded in launching World’s first man-made satellite SPUTNIK-I, on 4th October 1957. For three weeks, the satellite sent radio signals as it circled the Earth every 96 minutes. Thereafter, the satellite began to spiral back and eventually fell from orbit into the atmosphere after 92 days. The USA launched its first satellite EXPLORER 1 on 1st February 1958. Many other nations in Asia and Europe, including India, entered Space research and launched their satellites [References 9 and 10]. Table 2.1 lists the first satellites of the different successful countries, their weights and orbital perigee/ apogee values, the names of the satellite launch vehicles and the heritage as well as the infrastructure in that country, which supported the launch vehicle.
Table 2.1 First satellites of Different countries
| Date | Country | Satellite | Mass, kg | Orbit Perigee/Apogee, km | Launch vehicle | Heritage and supporting Infrastructure |
| 4 October 1957 | USSR | Sputnik 1 | 84 | 227 / 945 | R –7 Family | World’s first ICBM |
| 1 February 1958 | USA | Explorer 1 | 5 | 347 / 1859 | Jupiter C | US Army Redstone Ballistic Missiles |
| 26 November 1965 | France | Asterix 1 | 42 | 527 /1697 | Diamant | Missile Industry |
| 11 February 1970 | Japan | Osumi 5 | 12 | 323 / 2440 | Lamda-4s-5 | Aviation, Electronics and Heavy Industry |
| 24 April 1970 | China | Mao 1 | 173 | 434 / 2162 | CZ - 1 | Missile Program |
| 28 October 1971 | UK | Black Knight 1 | 66 | 531 / 1403 | Black Arrow | Missile Program;
UK has since
abandoned its launch
vehicle program |
| 24 Decenber 1979 | Europe | CAT | 1602 | 125 / 14,047 | Ariane 1 | Aviation, Electronics
and Heavy Industry |
| 18 July 1980 | India | Rohini
S - 1 | 40 class | 307 / 921 | SLV-3 | Limited Aviation and
Heavy Industry |
| 19 September 1988 | Israel | Ofeq 1 | 155 | 250 / 1149 | Shavit | Missile and Aviation
Industry |
Thus began the Space Era. In the first 40 years, more than 4100 satellites, majority of them built by Russia and the USA, have been launched successfully. The satellites have been used for research in Space sciences, weather observations, remote sensing of the diverse land conditions on Earth, long distance and intercontinental telecommunication, TV broadcasting, Navigation and several other revolutionary applications. The satellites are in a variety of orbits, such as, Low Earth Orbits (LEO), simple Polar Orbits (PO), Sun-Synchronous Polar Orbits (SSPO), and Geo-Stationary Earth Orbits (GSO). Satellite borne telescopes have increased immensely the human knowledge in the field of Astronomy. For example, the Hubble Space Telescope has discovered many more billions of galaxies. Instrument probes have been sent to planets and into deep space even beyond the Solar System. Spectacular events of the Space Era include travel of human beings to Space to work there largely with earth-like ease. Man has even made return trips to the Moon and is considering manned exploration of the Mars.
2.3 Versatility of Satellites
The Space era has brought together a multitude of advanced and powerful technologies and employed them in space systems. Consequently, even a common class of modern satellites can carry a versatile set of systems. Some of them are listed in the following:
· Compact solar and other types of on-board electric power systems,
· Automatic orientation and pointing systems,
· Automatic internal temperature control systems,
· Sophisticated instruments for remote sensing and in-situ
measurements,
· Signal amplification and relaying equipment (Transponders),
· Orbit maintaining propulsion systems, and
· Systems for communication and data transfer between Earth and satellites.
Thus, satellites can act as long sustaining, and self-contained multi-function platforms providing limitless possibilities to peer into Space as well as gaze at Earth, like the legendary Sanjay of the epic "Mahabharat", who through "divya dristi" could listen to and see far away events.
2.4 Unprecedented Opportunities
Observation of radiation in different bands of the electromagnetic spectrum is the basic means of astrophysical study of deep space. Prior to the Space Era, Earth based optical telescopes and radio antennae were the main instruments, which collected the radiation. However, scientists have known that Earth based observations do not reveal all the secrets of the universe, because, some bands of the radiation reaching Earth are greatly modified and even totally absorbed by Earth’s atmosphere. Further, the radiation reaching Earth from far away cosmic bodies is of such low level that its detection is made difficult by the presence of noise caused by human activities and processes in the atmosphere. In order to overcome these limitations of the observations made from Earth, it is indispensable to establish observation platforms above the atmosphere. As sounding rockets can rise above the atmosphere, even in their brief sojourn they have enabled discoveries of a large number of sources of X-rays and gamma-ray bursts in deep space. Satellites, with their versatile capabilities and long sojourns, are even more productive and have enabled gigantic strides in unraveling the secrets of the universe. For example, the satellite borne Hubble Space Telescope has discovered many billions of previously unknown galaxies, as already mentioned.
2.5 Harnessing Space Technology for Concrete Benefits
Using the satellite as a viewing platform, one can observe the desired area of the Earth, as already mentioned. A camera onboard a satellite at about 1000 km height can photograph in one snap hundreds of square km area of Earth with a linear resolution of about 1 m. If the satellite is in a polar orbit it can photograph the whole of Earth in about 20 days. An aircraft borne camera, on the other hand, would take years to complete the same task. Photographing the Earth yields invaluable information on soil conditions, water bodies, crops, forest cover, land usage and a host of other parameters on Earth. So, the conditions on Earth can be monitored and cataloged with incredible speed from Space.
Observation of the earth, its atmosphere and the plasma enveloping it from a satellite is known as Satellite Remote Sensing. Observing an area of Earth in various narrow bands of the electromagnetic spectrum reveals a variety of characteristics of the area, such as, its temperature, moisture content, chemical composition, biomass composition. With the advances in optics, electronics and computers the acquisition, transmission and interpretation of satellite remote sensing data have become increasingly more accurate, detailed and fast. This has lead to quantitative interpretation of the remote sensing pictures rapidly and economically. The pictures contain such economically significant data as, extent and quality of surface water bodies, location of ground water and mineral deposits, health of the agriculture crop at different stages of growth and their final yield, quality and extent of forest cover, weather forecast, and locations of schools of fish. They also enable the survey of drought or flood affected areas, polluted water bodies, blighted crops and denuded forests [Reference 11]. So, the synergy of satellite remote sensing, data acquisition and interpretation has become a very powerful system for reaping unprecedented economic benefits in the areas listed above. These techniques are also extremely useful in detecting natural disasters and threats to environment. As a result, satellite remote sensing has become the backbone of the processes of survey, management and harnessing of national natural resources. For these reasons, space technology attracts us to venture into Space for observing Earth, to comprehend it's bounties as well as to detect the scourges of human inflicted pollution, ecological degradation and natural disasters, and to take timely corrective actions.
A satellite platform can be used not only for remote sensing; it can also be used for receiving and forwarding signals from one place to another on Earth. In this application, a satellite borne transponder replaces a repeater mounted on a tall tower on Earth. The height of a satellite can be hundreds or thousands of kilometers, whereas the height of relay towers, being physical structures on Earth, can be only a few tens of meters. Communication transponders mounted on one space platform at 36000 km, i.e., in geo-synchronous orbit, can substitute for thousands of terrestrial repeater towers and thus expand rapidly the network for audio and video communication. The communication coverage of a satellite in the geo-synchronous orbit is nearly one third of the Earth, as already mentioned. A constellation of three such satellites, placed equilaterally, can support a communication facility covering nearly the whole of the Earth. Only, the Polar Regions are not covered adequately by such a constellation. A satellite in equatorial orbit about 36000 km above Earth has got the very useful property of being Geo-stationary, such that the ground based antenna communicating with a satellite in GSO (Geo-stationary Orbit) has to be pointed only to a fixed object, avoiding the significant expenditure of mechanized automatic pointing. This property reduces significantly the cost of the ground segment of the satellite-based communication and broadcasting systems. This highly useful characteristic is perhaps the greatest economic motivation at present for taking to space, as may be seen from the huge share (about 80%) of communication satellites among the new satellites placed in space.
It is noteworthy that, the geo-stationary orbit is a relatively limited real estate and is already crowded. As a result, alternative satellite communication (SATCOM) systems have been conceived. A constellation of communication satellites in lower earth orbits, so deployed that all points on Earth are visible all the time to at least one of its satellites, constitute the alternative system. Because of this property, the constellation can connect any point on Earth to any other point on Earth.
In brief, the various motivations to venture into space are:
1. Discovering new sources of knowledge and materials, and whetting appetite for travel to uncharted territories, and
2. Establishing platform in space to take advantage of their vast terra view and set up facilities for Remote Sensing, satellite communications, and deep space observation.
2.6 Focuses in India
Peering into space does help advance the frontiers of knowledge and challenges human ingenuity and perseverance. It also brings tremendous prestige to the country(s) undertaking successfully such ventures. Further, human space travel is a good boost to the adventurous spirit and therefore arouses unparalleled interest among all classes of public. However, at the present juncture mere peering into Space and travel to it yield little concrete economic or developmental benefits to the less developed part of the world. On the other hand, as pointed out earlier, looking earthward and harnessing of satellites for remote sensing and communication purposes has tremendous potential for boosting the economic infrastructure, utterly lacking in the less developed part of the world, in highly cost and time effective manner. Specifically, space-borne systems have immense potential to augment some of the basic services of vital importance to a country, such as, those for weather observation, mass communication, telecommunication, remote sensing.
India the land of natural plentitude got reduced to a land of material poverty and squalor due to its horrendous acts of omissions in harnessing contemporary science and technology. As the country is blessed with an abundance of natural resources, their scientifically planned and prudent utilization is a key to the well being of the populace. A comprehensive cataloging of the natural resources, monitoring their utilization and planning their further sustainable utilization did not exist and called for urgent massive development of a geographical information database. Remote sensing from space and cataloging of the data were the obvious routes to follow.
Since, agriculture is basic to the food security of the burgeoning population, improving the productivity of Indian Agriculture is a national necessity. One of the critical inputs is an accurate and timely forecast of monsoon. In the 1960s India did not possess a state of art weather observation and forecasting system befitting its continental size. As a result, the agricultural economy of the country, heavily dependent on rain fed irrigation, suffered grievously for want of timely inputs of weather and rainfall forecasts.
The density of telecommunication is at once a measure of the economic status of the country and of the factors promoting the rate of growth of its economy. Increasing it spurs the growth. In 1960s, the telecommunication, and mass communication systems in the country were in an anemic state. They barely existed. The telephone density was less than one in a thousand. The strong correlation between phone density and rate of growth of the economy in developing countries is well known [References 39 and 40]. So, low phone density resulted naturally in low growth rate of the economy. To improve phone density and TV coverage by terrestrial networks, for removing serious bottlenecks in the growth of the economy, required unaffordable massive investments and unacceptably prolonged schedules. In this context, serious considerations of the various alternative technologies were not only timely but also urgent. A comprehensive satellite communication segment to augment the telecommunication infrastructure was thus an urgent necessity.
Development communication, to cause development and to deliver the development messages requires a wide spread network of radio and television broadcasting. The television coverage was confined to farmers in the vicinity of the national capital. As the country had rudimentary facilities in this essential field, the national priorities for their overdue massive augmentation by employing satellite broadcasting system were self-evident.
Thus, there was clear need for launching a comprehensive space program in the country, with focus on Remote Sensing and Communication applications of space technology [References 1, 12 and 13]. The Indian remote sensing satellites in SSPO in the IRS series providing unprecedented wealth of data about Earth, and the Indian multi purpose satellites in the INSAT series in the GSO enabling revolutionary communication coverage are the results of this focus.
2.7 Timely Recognition of Opportunities
In timely recognition of these needs and the pointed relevance of space technology to fulfill them, India decided whole heartedly at the beginning of the space era, i.e., in early 1960’s to harness space science and technology in these fields and catalyze an all round development of the economy of the country.
Incidentally, the actual revolutionary growth of these services, since achieved in the country through harnessing of space technology and their beneficial impact on the all round economic development of the country are too self evident to require any further explanation. For example, the tele-density in India was below 0.5 per hundred persons at the time of independence, remained in that range till 1988, but jumped to 1 per hundred in 1993 and has galloped to 8 per hundred in 2004. The products of satellite remote sensing are used extensively, yielding unprecedented speed and productivity in land use, soil and water conservation, harvest cataloging, and a multitude of such services at grass root levels. One notes with gratification that only with the backbone of satellite based wide band data, media and telecommunication and Internet networks being in place, the incremental contribution of the terrestrial systems to augment these services has been possible. Today, India is able to march in step with the developed world in the emerging fields of Information Technology, Digital pervasiveness, and Bio-informatics. With seamless connectivity with the rest of the world, India is poised to step ahead of even the developed world to emerge as the brain trust of humanity.
2.8 Path of Self Reliance
The impact of the Space program of India would have been marginal, had the country decided to depend only on the risk free buy and operate mode, employed in many other fields of engineering and technology, such as, civil aviation, basic electronics, computers, a variety of chemicals and metallurgical plants.
Taking note of the existence of its vast reservoir of poorly utilized scientific and technical manpower, India decided boldly to take the unorthodox route and engage actively in achieving self reliance in the field of Space Science and Technology, rather than depend upon the buy-and-operate mode, unlike some other developing countries. India recognized that only through self-reliance the most up to date space technology would be available to the country at affordable prices. Nonetheless, in the spirit of collaboration with the rest of the world in the emerging scientific and technical fields of interest to the country, India accepted friendly offers of other countries to participate in their programs, aiming to develop the satellite based Television, Communications and Remote Sensing systems and their applications, as also in research in Meteorology and the Physics of upper atmosphere and ionosphere. The path breaking projects like Satellite Instructional Television Experiment, SITE, Satellite Television Experiment Project, STEP, and Ariane Passenger Payload Experiment, APPLE, were some of the initiatives in this category.
Under the SITE scheme, some 1800 villages located in the remotest and the most backward regions of the country received television receivers for direct from satellite television signals, even before such receivers were installed in their provincial capitals. This momentous event demonstrated that space technology and its fruits can be taken first where they are needed the most for development. It showed that the benefits of space technology do not have to trickle down from the most developed to the least developed, unlike those of terrestrial systems. SITE also demonstrated the integrating influence on the whole country, by a single satellite television broadcast from the ramparts of Red Fort at Delhi on the Independence Day. The STEP prepared the country for satellite communication system and resolved doubts about its coverage and dependability.
2.9 Recognition of Imperatives of Self Reliance
The decision to engage proactively and achieve self-reliance enjoined vigorous pursuit of indigenous research and development in the entire spectrum of space science and technology, namely, space science, applications, satellites and space launch vehicles. Under this approach, India launched a comprehensive program of developing Indian personnel, through internal self-learning as well as through opportunities available abroad. The scope of learning included the various aspects of operations of space systems, their design and development processes and manufacturing know-how. Concurrently, in order to meet the demands of the envisaged space program, the country began to set up the infra structure to undertake research and development in the multidisciplinary and sophisticated fields, which were in the emerging phase at that time even in advanced countries.
Significantly, the founding fathers of the space program of the country took a conscious decision to utilize to the utmost the existing industrial and R&D infrastructure in the Country, which could contribute directly and even remotely to the program. This decision, at one stroke, reduced the quantum of incremental investments to be made specifically for the envisaged space program and increased the utilization of investments already made by the country.
2.10 Tailoring of Space Missions
The priorities of the country, sketched above, necessitated deployment of the remote sensing and communication satellites and their application payloads. The program planners discovered that to serve these two applications effectively, two different series of satellites would need to be established in two different types of orbits. This is the rationale for the series of Indian Remote Sensing Satellites (IRS) in polar orbit, and the series of Indian National satellites (INSAT) for weather observation and communication in the geo-stationary orbit (GSO). The chosen themes of remote sensing dictated the definitions of the on-board cameras, their observational wavelength band and resolution, pictorial swath size and resolution, data rate, onboard propulsion and electric power and the corresponding satellite mass, configuration and their suitable orbit. In the same manner, the requirements of meteorological remote sensing and satellite communication dictated the definition of the Indian National Satellite, INSAT, the series of multi purpose communication satellites in GSO. So, the application payloads of INSAT comprised, (i) Very High Resolution Radiometer, VHRR, for observing cloud cover and wind profile, (ii) a system for regular collection and relay of meteorological, hydrological and oceanographic observation data from unattended remote platforms at inaccessible places on land and water, and (iii) transponders in the S -, C -, and extended C – bands, to start with, for telecommunication and broadcasting services. It goes without saying that a commensurate network of ground stations forms part of the infrastructure to provide these space services.
Logically, the needs of the IRS series of satellites determined the specifications of the Polar Satellite Launch Vehicle (PSLV). Further, the definition of the Geo-stationary Satellite Launch Vehicle, GSLV, matched the needs of the INSAT series.
As the application component of the space program evolved and the space services were put into systematic operation, the number of satellites in service increased and the up gradation of their payloads took place and so were those of the performance specifications of PSLV and GSLV.
