ISRO success stories

Print edition : April 28, 2001

The launch of the GSLV marks the beginning of a significant phase in launch vehicle technology development for the Indian Space Research Organisation, which already has an impressive record in the field of sophisticated satellite technology.

FROM building the first experimental satellite Aryabhata in 1975 to the world class operational Indian Remote Sensing (IRS) satellite series on the one hand and the third generation communication satellite INSAT-3 on the other, is indeed an impressive track record by any standards for the 30-year-old Indian Space Research Organisation (ISRO). It could well be argued that the development of launch vehicle technology, which began in the mid-1960s, has not achieved the same degree of success. Indeed, many, both within the organisation and without, believe that the launch vehicle front did not receive the same kind of focus as satellite development did, particularly after Satish Dhawan retired from ISRO in 1984. At a time when ISRO's launch vehicle development has reached an important phase with the launch of the Geosynchronous Satellite Launch Vehicle, it would be appropriate to put satellite technology development also in perspective.

At the launch of the first Rohini-75 rocket at Thumba, 1969.-

Vikram Sarabhai, the founder of the Indian space programme, had realised the potential of space communication systems in putting television to use as a mass education tool throughout the country. He visualised and suggested this as early as 1966-67, just three years after the first geosynchronous satellite, SYNCOM, was launched. In 1967 he initiated studies with a view to using space communication systems for operational television broadcasting. A joint study by ISRO and the National Aeronautics and Space Administration (NASA) of the United States was conducted in 1967 which recommended a hybrid system of direct broadcast by satellite combined with terrestrial TV transmitters as the most effective means of countrywide TV coverage. In 1968 a National Satellite Communication (NASCOM) study group was set up by the government. These studies and deliberations paved the way for the acceptance in 1969 by the government of the proposal to conduct the Satellite Instructional Television Experiment (SITE) with NASA's ATS-6 satellite. In 1969 studies were also conducted on the use of communication satellites for meteorological earth observations.

BASED on these studies and a joint study with the Massachusetts Institute of Technology (MIT) in 1970, ISRO evolved in the early 1970s the unique multipurpose nature of the INSAT system that included direct TV broadcasting, communications and meteorological observations and it was firmed up during 1975-77.

Aryabhata, India's first experimental satellite, 1975.-

The decision to undertake SITE before embarking on an operational system was taken primarily with the aim of gaining experience in the development, management and testing of a satellite-based instructional television system. SITE was successfully conducted during 1975-76. It was the earliest large-scale direct broadcasting experiment anywhere in the world and marked a milestone in the application of space technology for national missions, particularly in developing countries. After SITE had been on for nearly four months, in November 1975 the government accepted in principle the use of satellites for domestic communications. This led to the conceptualisation of the multipurpose INSAT system, the formal approval for which came in July 1977.

SITE was followed by the Satellite Telecommunication Experiments Project (STEP), a joint ISRO-Post and Telegraphs Department project using the Franco-German Symphonie satellite during 1977-79. Conceived as a sequel to SITE, STEP was for telecommunications what SITE was for TV. STEP was aimed to provide a system test of using geosynchronous satellites for domestic communications, enhance capabilities and experience in the design, manufacture, installation, operation and maintenance of various earth segment facilities and build up requisite indigenous competence for the proposed operational domestic satellite system, INSAT, for the country. Two transponders on Symphonie were used for these experiments on satellite communication, radio networking and TV transmission.

The first Indian launch vehicle SLV-3 in flight, 1980.-

While the INSAT system studies were going on, ISRO (along with the Department of Atomic Energy) took up and successfully executed a major indigenous venture of establishing an earth station at Arvi near Pune in 1972. Towards gaining experience to build India's own satellites and launch vehicles, ISRO initiated in the early 1970s two projects: the first Indian satellite project, Aryabhata, which was realised in 1975, and the first Indian launch vehicle, SLV-3, which was realised in 1980.

ARYABHATA, the first Indian satellite, was conceived with the primary aim of establishing indigenous capability in satellite technology. It enabled ISRO scientists and engineers to learn the basics of satellite technology in designing, building and operating the satellite. Taking advantage of the free launch opportunity provided by the erstwhile Soviet Union, this 360-kg, spin-stabilised satellite was launched on April 19, 1975, into a near circular orbit of 600 km.

PSLV D-2 lift-off, 1994.-

Soon after, in 1976-77 a similar opportunity was provided by the European Space Agency (ESA) on its developmental flights of the Ariane launcher. ESA had offered a free flight for any payload and India accepted the offer. This important opportunity was utilised to build indigenously a 672-kg state-of-the-art three-axis-stabilised (as against the spin-stabilised Aryabhata) geosynchronous communication satellite called APPLE - Ariane Passenger Payload Experiment - which was launched in June 1981. The satellite had only one communication transponder but the entire exercise of building a large three-axis stabilised satellite to operate in the geostationary orbit resulted in ISRO acquiring the necessary expertise that was to prove invaluable to build the indigenous second generation INSAT-2 series of satellites in the 1990s. Various subsystems were developed, such as the communication transponder, graphite fibre-reinforced plastic antenna reflector, earth sensors, momentum wheel, apogee kick motors and, most important, it provided the experience of operation of these subsystems in the environment of outer space. This laid the foundations for indigenous technology development necessary to put an operational INSAT system in place. Also, many experiments that could not be completed during STEP's time-frame were continued in the form of the APPLE Utilisation Programme, which provided valuable experience in space communication systems.

The INSAT system was conceived as an operational system with multipurpose and multiuser satellites as its mainstay. The INSAT-1 satellite series was designed by ISRO scientists and engineers but was built by an American company, Ford Aerospace. Even though experience to build geosynchronous satellites had been gained through APPLE, the decision to have the INSAT-1 series built by foreign companies was driven by the need to establish quickly an operational system so that satellite communication became an accepted technology by the user agencies in the country than wait until the ISRO attained the maturity to build operational satellites. Ford was chosen from among three bidders: Hughes Spacecraft and a European consortium were the other contenders. Only Ford offered to build a three-axis stabilised platform, necessary for meteorological cameras to work on a continuous basis, even though Ford too was executing the solar sail concept for the first time. Because of INSAT's unique multipurpose design, INSAT-1 used an asymmetrical solar array in order to ensure a clear field of view into cold space for the radiation cooler of the Very High Resolution Radiometer (VHRR) earth imaging instrument. The solar sail was deployed to offset the asymmetric solar pressure on the solar array. INSAT-1 satellites built by Ford Aerospace were launched from abroad through procured U.S. and French launches. In all, four INSAT-1 satellites - 1A, 1B, 1C and 1D - were launched of which two, 1A and 1C, failed.

ASLV D-2 mission, 1988.-

The one-tonne class INSAT-1 was used mainly to prove a concept that had been evolved and to validate a system - both space and ground segments - in operation as mentioned earlier. The next generation two-tonne class INSAT-2 system served to establish indigenous satellite building capability. The INSAT-2 series was thus fully designed and fabricated by ISRO with strong participation from Indian industry.

Five INSAT-2 satellites - 2A to 2E - have flown so far through procured launches aboard Ariane, of which 2A was retired early and 2D failed.

THE essential difference between the INSAT-1 and INSAT-2 series was an increase in the number of transponders and the introduction of new, extended C band frequencies for enhanced communication capabilities. After the launch of 2A and 2B, its communication capabilities were further enhanced in 2C and 2D by the introduction of Ku band as well (for the growing VSAT operators). However, these satellites which carried a Ku-band payload were dedicated communication satellites with no provision for a meteorological payload. (Incidentally, these were, therefore, symmetrical satellites without the solar sail.) 2E was again a multipurpose (asymmetrical) satellite carrying meteorological and communication payloads.

The lack of Ku band in all the INSAT-2 satellites, and likewise some of the emerging technologies such as spot beams, was essentially due to the limited growth of space-based services in the country so far. But in today's scenario of changed domestic policies the demand for communication capacity is growing at a phenomenal rate and, with the open skies policy, ISRO's strategies on the communications satellite front beyond the INSAT-2 series should have evolved from this perspective. But unfortunately, the INSAT-3 series of satellites, up to 3E whose details are available, seem to be only an extension of INSAT-2E. In terms of their size, mass, technologies and number of transponders, they do not seem to be greatly different from the INSAT-2 series, despite the emerging urgent need for greater space segment capacity on ISRO satellites. This need has only been accentuated by the New Telecom Policy (NTP) which allows private users to lease capacity on foreign satellites.

GSLV-1, 2001.-

Unfortunately, from its configuration INSAT-3 seems to have been arrived at with the limited perspective of the GSLV in mind and not to meet a growing communications demand. The first INSAT-3 satellite, INSAT-3B, was launched in March 2000 aboard Ariane. The next in the series is due this year. However, some flexibility has been incorporated in the INSAT-3 series. The configuration of each satellite in the series in terms of payloads is different, including a completely dedicated meteorological satellite. It is not clear how the techno-economic arguments, which dictated the multipurpose configurations in the INSAT-1 and INSAT-2 series, now make such dedicated configurations viable, considering that the government continues to remain the major user of the meteorological component of the INSAT space segment capacity.

Just as APPLE provided the necessary experience in operationalising a communications system on an end-to-end basis, the experimental satellites, Bhaskara-I and II, conceived around 1975, provided the necessary experience of conducting earth observation satellite missions which were to become the basis for the IRS series of satellites. Remote sensing applications were initiated in 1970 using sensors borne in balloons, aircraft and satellites. Several sensors including multispectral scanners and radiometers were also developed. Bhaskara-I and II, which were evolved from Aryabhata and carrying remote sensors in the visible, infrared and microwave region of the electromagnetic spectrum, paved the way for an end-to-end experimental satellite remote sensing programme. Bhaskara-I was launched in 1979 followed by Bhaskara-II in 1981.

The Bhaskara satellites had two-band TV payload for land application and a satellite microwave radiometer for oceanographic/atmospheric applications. Although the capabilities of the Bhaskara satellites were limited compared to contemporaneous earth observation systems, this programme, conducted between 1976 and 1982, provided valuable experience and insights into a number of aspects, such as sensor system definition and development, conceptualisation and implementation of a space platform, ground-based data reception and processing, data interpretation and utilisation which formed the basis for the polar orbiting IRS series of satellites.

The one-tonne class IRS-1A was launched in 1988 aboard the Soviet launcher Vostok and it carried two payloads employing Linear Imaging Self-Scanning Sensors (LISS) which operate in pushbroom scanning modes using Charge Coupled Device (CCD) arrays of 2,048 elements. The technologies employed in IRS-1A were certainly state-of-the-art, though the resolution achieved then (72.5m and 36.25 m) was below that of SPOT (20 m and 10 m). However, the resolution achieved in the IRS satellites today, after launching six more successfully, was the best available (3.5 m resolution) in the remote sensing business in the world until the IKONOS satellite of the U.S. was launched in 1999.

IRS-1C and 1D constituted the second generation remote sensing satellites carrying a multispectral camera having three bands in the visible, near infrared and middle infrared. It also carried a wide field multispectral sensor with a coarse spatial resolution but wide swath to improve temporal resolution. Data from these were the best ever high resolution data available to the user community in the world, until the advent of IKONOS. The subsequent remote-sensing satellites, IRS-P2 (no longer operational), P3 and P4 (Oceansat dedicated to ocean studies) have all been launched by the indigenous Polar Satellite Launch Vehicle (PSLV). The next IRS satellite, IRS-P5, is intended for cartographic applications, and hence called Cartosat, and IRS-P6, called Resourcesat, are scheduled to be launched in 2001-2002. Although the nominal design life of IRS satellites is three years, nearly all the IRS satellites have performed well beyond their design life up, to five years and more.

Besides communication and remote-sensing satellites, ISRO has also been evolving spacecraft platforms for near-earth orbit applications, particularly scientific experiments. In the 1980s when developmental launches of the Satellite Launch Vehicle SLV-3 were taking place they were used to place small 35 kg satellites, called Rohini, in near-earth circular/elliptical orbits. Three such Rohini satellites were launched in the three successful SLV-3 launches. With these successes it was realised that 150 kg class experimental satellites could be launched in near circular low earth orbits with the successful development of the Augmented Satellite Launch Vehicle (ASLV).

Such a mission could provide a platform with a low turnaround time, relatively inexpensive and autonomous capability to conduct space science experiments. This satellite series was called Stretched Rohini Satellite Series (SROSS). However, with the completion of the ASLV project in 1994, no such experimental platforms have been proposed. Perhaps economic considerations have prevented such proposals. But a capability has been built up in ISRO to design special space platforms for scientific experiments. Indeed, there is a proposal now for a dedicated satellite for X-ray astronomy called Astrosat but this is intended to be launched aboard one of the PSLV launches of the future.

The evolution of spacecraft technology in ISRO, from the 50 kg-class Rohini experimental satellites to 2-tonne INSAT-2 and 3 satellites, implies a corresponding evolution in the technologies of its various subsystems. What distinguishes technologies for spacecraft from their equivalent terrestrial applications is the need to ensure that the systems will perform unattended for long periods of time with a great degree of reliability in hostile environments of space. The other equally important consideration in building space systems is to make systems lightweight, low power-consuming and miniature. This calls for innovative engineering solutions and optimisation.

One parameter that points to growing sophistication in ISRO's satellite building capability is the following. From Aryabhata, with a structural mass of 30 per cent of the total satellite mass, to INSAT-2 with an estimated mass of just 9 per cent there has been a steady decrease in the structural mass fraction. This has been achieved essentially through the use of new materials such as carbon fibre-reinforced plastic, magnesium alloys, aluminium-lithium alloys and beryllium for components and honeycomb elements instead of solid elements. Similarly, the power needs of Indian satellites have gone from a few watts in Rohini to kilowatt range in INSAT-2. Also, mission lifespans have increased from a few months to 10 years. Power generation, storage and management technologies too have correspondingly evolved. While a Rohini satellite required only five watts of power, the INSAT-3 satellite requires 1.7 kW. The design life of the INSAT satellites themselves has steadily increased from seven years of the INSAT-1 to 10 years of the INSAT-3.

The importance of the 1100 cu m acoustic chamber at the National Aerospace Laboratories (NAL), set up in the 1980s, in achieving this cannot be underestimated. It has enabled testing of satellites for stresses under launch and in-orbit conditions. Random vibrational levels, acoustic environment simulations and other structural tests are now possible with actual fabricated satellites rather than model simulations or scaled down tests. This has helped bring down conservatism and minimise tolerance windows in the design of the spacecraft. This in turn has meant a greater payload fraction in the satellite.

With the increasing sophistication of satellite missions and diversity of mission objectives, the technological complexities of building satellites suited to mission goals too have increased. Over the 25 satellite launches that the ISRO has carried out in the last two and a half decades, the organisation has achieved a degree of sophistication that makes it an emerging competitor in the world space business. Indeed, some have argued that ISRO has attained such a stage in satellite building that this activity can be hived off as a separate corporate entity operating on commercial lines and let the organisation focus on evolving new spacecraft platforms for the future and strategies for the new millennium. Unfortunately, this vision is not evident at least as yet, and if ISRO wishes to survive in the global space segment market it would better begin to think and act differently. As an enormous storehouse of expertise and skill, ISRO should become an important revenue earner for the country before that expertise is lost out to foreign space operators.

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