COVER STORY

Looking ahead

To complement its technological strengths and remain an effective provider of national satellite communication services and a competitive player in the world space market, ISRO must evolve fresh strategies.

R. RAMACHANDRAN

WITH the successful launch of the multi-purpose satellite INSAT-2E - the last of the INSAT-2 series - and given the prospects of its successful operationalisation, the question is: where does the Indian Space Research Organisation (ISRO) go from here?

Like many of its predecessors, INSAT-2E combines telecommunications and meteorological payloads, the former primarily for Fixed Satellite Services (FSS) and Direct Broadcasting Services (DBS). It is claimed that INSAT-2E is the forerunner of the INSAT-3 series in terms of technology, but how does its conceptualisation fare, given the changing scenario in the world satellite business and the emerging telecommunication technologies and services?

Seven years ago, addressing the question of the kind of satellites that would be needed in the first quarter of the next century, Dr. Pramod Kale, a former Director of ISRO's Space Applications Centre in Ahmedabad, wrote in the Journal of Spacecraft Technology, an in-house publication of ISRO: "The communication requirements are growing day by day and so are the meteorological requirements. The multi-purpose, multi-user nature of INSAT-1 and INSAT-2 satellites cannot cater to all the growing needs. The time has come now to separate the meteorological requirements and communication requirements and cater to these requirements separately, by designing satellites specifically meant for these purposes."

INSAT-3B, which will be launched later this year.

INSAT-2C, which was launched in 1995, and INSAT-2D, which was launched in 1997 and subsequently abandoned, were dedicated communication satellites. But INSAT-2E has been configured as a multi-purpose satellite. The reason for not including a meteorological payload in 2C and 2D had less to do with techno-economic considerations than with the fact that sufficient space segment for meteorological operations was available on 1D, 2A and 2B satellites. Indeed, some ISRO scientists maintain that the multi-purpose payload is still cost-effective and point out that a dedicated American meteorological satellite like GOES, with a capability just about the same as that of INSAT-2E, cost more than twice as much as INSAT-2E.

There are reasons for this. Unlike in the case of telecommunications services, the user community in respect of meteorological services is small and not very diverse. Therefore, while it makes sense to have dedicated communication satellites the same cannot be said of meteorological satellites; the latter are thus rendered inefficient users of the "real estate" in space, as space technologists call it. Moreover, even a meteorological payload has to carry some telecommunications payload in order to transmit data. Therefore, further additions of the telecommunications payload lead to a cost benefit in terms of better use of the "real estate". The INSAT multipurpose satellite, as ISRO scientists point out, is a configuration that is optimised from this perspective.

According to these scientists, the concept of a multi-purpose satellite will be invoked in future designs as well. However, INSAT-3D has been configured as a dedicated meteorological satellite and ISRO has not spelt out the economics in this case. Perhaps the fact that it may be launched by the indigenous Geosynchronous Satellite Launch Vehicle (GSLV) will make it economically viable.

The Geostationary Satellite (GSAT) being configured at the ISRO Satellite Centre in Bangalore.

IN a multi-purpose satellite, there is a limitation in respect of the total power availability because the design allows for only a single solar array on its south face. Dedicated telecom satellites have symmetrically mounted arrays that generate more power. With the emerging space-based telecommunications technologies, there is an evident shift towards high-frequency bands such as Ku which require greater on-board power. High-power devices, such as the Travelling Wave Tube Amplifiers (TWTAs), occupy more space and entail higher heat generation and, consequently, require more efficient heat dissipation systems, which increase the overall satellite mass. Technological evolution has also led to concepts such as steerable on-board antennae, spot beams that provide higher radiated power over a small area and enable frequency re-use, beam switching and frequency hopping and selectable polarisations. Better electronic devices have also meant greater life in space and this has led to longer spacecraft missions; this in turn has necessitated larger quantities of on-board fuel, which add to the satellite's lift-off mass.

The economics of the above considerations favour a larger transponder capacity on the satellite for better utilisation of the "real estate", and this has resulted in a trend towards satellites of higher and higher mass. It is predicted that by 2005, nearly 50 per cent of the satellites launched will weigh in excess of 4,000 kg (see graph). In general, the weight of the payload delivered in the orbit as a fraction of the total spacecraft mass increases with the spacecraft's mass. The evolution of launchers such as the new Ariane 5 has complemented this trend. Ariane 5 is expected to have a carrying capacity of up to 10 tonnes by the turn of the century.

Besides the evolution in technologies for FSS, Mobile Satellite Services (MSS) have also grown over the years. Although a geostationary satellite can provide MSS to a limited extent within the geographical area of the footprint - as was done with dedicated transponders in specific frequency bands with INSAT-2C and 2D - the technological evolution towards global communication systems with portable equipment, as pioneered by INMARSAT, has led to the concept of Low Earth Orbiting (LEO) satellite constellations like Iridium, Globalstar and ICO. These systems are configured with tens of satellites, each with a few transponders and masses in the region of hundreds of kilograms. Thus, on the one hand there is a trend towards very heavy geostationary satellites and, on the other, there is the move towards small LEO satellites.

THE one-tonne-class INSAT-1 was used largely to prove a concept that had been evolved and to validate a system - with both space and ground segments - in operation. The two-tonne-class INSAT-2 system served to establish satellite-building capability, and if it lacked some of the emerging technological elements in its design and configuration, such as the Ku-band capability and spot beams, it was only to be expected considering the limited growth of space-based services in the country. But today the situation is vastly different. With a move towards an open skies policy, the trend is towards digital services, a convergence of computers and communications and the growth of value-added services such as Internet services. So, is the INSAT system geared to meeting these demands as the country moves into the next century?

In general, among the various considerations for designing a satellite configuration, the following are important: communication capacity demand, spread of the ground segment, communication transponder requirements and frequency bands to be used, on-orbit life and launch vehicle capability. In the Indian context, the first of these is driven by domestic policies, and till date the INSAT system has evolved largely to meet the demands of the Department of Telecommunications (DoT) and the Ministry of Information and Broadcasting (I&B). Given the limited technological perspective of these two organisations, the definition of the space segment of the INSAT system, in terms of technology, seems to have been limited by the definition of the ground segment requirements of DoT and I&B even though the technological capability exists within ISRO.

Take the case of the Ku frequency band for Very Small Aperture Terminal (VSAT) communications. While the world was moving towards the use of Ku-band, the INSAT system introduced, for the first time in the world, the upper extended band (UXC) for VSAT operations. Indeed, with lobbies of foreign suppliers of Ku-band systems working overtime, a controversy was generated about a decade ago in technical circles. Dr. N. Seshagiri, Director-General of the National Informatics Centre (NIC), used to criticise ISRO openly for not moving over to Ku.

The basic issue was not ISRO's capability in handling space systems in the Ku-band but an undefined demand in that region of the spectrum. Indeed, as if to prove a point, ISRO carried three Ku transponders each in INSAT-2C and 2D. However, as some ISRO scientists point out, the user agencies could not visualise services occupying more than two Ku transponders for the entire decade. In fact, the 3 Ku transponders on INSAT-2C, which were allocated to the DoT, remain unutilised. The failure of INSAT satellites which carried the UXC transponders has affected VSAT operators.

ISRO's initiative in introducing the UXC-band is a reflection of its technological innovation drive. When the INSAT-2 system was being defined, the International Telecommunications Union (ITU) released less than 300 MHz bandwidth each for uplink and downlink in the UXC region for VSAT communications. ISRO has in some sense pioneered the use of this band. It managed to get three slots in the geostationary orbit for using this band. Other countries, which moved in late, have got only one slot. ISRO saw an enormous potential in exploiting this band in the space segment for VSAT operations in the country on a dedicated basis.

The choice between the Ku-band and the UXC is essentially based on two considerations: power limitation and bandwidth limitation. For equivalent capacity, C/UXC transponders require typically one-fifth of the power that Ku transponders require because of the latter's higher frequency and the need to provide greater margins of attenuation in rain and propagational losses. But Ku offers virtually unlimited bandwidth. UXC, on the other hand, has only a 300 MHz bandwidth; given a 40 MHz bandwidth for each transponder, this means that only six transponders can be used from an orbital slot. In other words, while the Ku-band is power-limited, the UXC -band is bandwidth-limited. There are also equipment-related issues. Wavelengths at Ku being smaller, small dish antennae would suffice, whereas for UXC the antennae would be larger. The resultant cost difference for ground systems, however, is marginal, according to ISRO experts. Further, Ku systems were then available off the shelf whereas UXC systems had to be developed indigenously. The Ku -band is also free of interference and is easily coordinated, compared to UXC. For optimal use, all these factors have to be considered, depending on the service envisaged.

ISRO reasoned thus: if one got into UXC, instead of Ku, with three slots and with two co-located satellites carrying two UXC transponders in each, one would have 12 UXC transponders. On the other hand, as long as the C-band remains the mainstay band for communications, use of the Ku-band would require five times more power just for two Ku-band transponders; in addition, the entire spacecraft would have to be reconfigured with a separate set of antennae for the Ku-band and related on-board hardware. This would lead to a lot of extra satellite mass and extra volume for mounting the Ku hardware because of its dependence on the bulky TWTAs rather than the compact solid state power amplifiers (SSPAs).

The demand for VSAT communications has grown rapidly and far beyond the DoT's projections after the Government decided to allow private operators to use the satellite capacity for VSAT-based business networks. Until then VSATs were being used only for VSAT networks of government agencies, including the DoT. Today there are nearly 9,000 VSAT terminals. Even though the INSAT system has put in space as many as 24 UXC transponders, today there is a crunch on the availability of UXC transponders because of the failure of two satellites - 2A and 2D. The frequent failures of the Fujitsu-made SSPAs on the operational satellites have compounded the situation.

Even so, the problems would not have been so serious if the DoT had not placed restrictions on the use of the available UXC transponders. For example, until recently the DoT had disallowed the use of four UXC transponders by private networks because of problems of coordination and interference with the DoT's own network. It now turns out, as ISRO has demonstrated by gathering data (somewhat belatedly though), that there is no problem at all and these transponders can also be leased out to VSAT operators. Four UXC transponders can easily serve eight small VSAT networks with half a transponder capacity each. A network such as the National Stock Exchange, with 2000 terminals, would require two transponders.

THE problem can be traced to the manner in which transponder capacity is allocated by the INSAT Coordination Committee (ICC), which is subservient to the DoT and the I&B Ministry, without any technical evaluation and assessment of the demands made by the two agencies. At present, besides the requirements of the Defence Department, the ICC divides the transponder capacity entirely between the DoT and I&B Ministry based entirely on the demands made by the two.

This has led to inefficient use of transponder capacity by the two. Even for ordinary telephony, there is no assessment of how efficiently the satellite capacity is used. For example, improved technologies, like digital transmission, can make for more efficient use of the bandwidth and hence the transponder capacity.

Take, for example, the three Ku transponders on INSAT-2C (launched in 1995) which were allocated to the DoT for managing inter-trunk telecommunications traffic by linking Delhi, Bangalore and Sikandarabad. After three years, these links are yet to be established. Moreover, as ISRO pointed out recently, linking these cities through an optical fibre network is far more cost-effective and quicker. However, the DoT wants to go ahead with its plans, without any sense of urgency; as a result the Ku -bands on INSAT-2C are lying idle. In the case of Doordarshan, transponder capacities are often utilised for political ends - for example, for introducing regional services at the whims of Ministers. Unfortunately, the ICC does not seem to be overly concerned about how the bandwidth is utilised. It is learnt that even the projected demand of 134 transponders in the Ninth Plan period has been made arbitrarily.

Another undesirable feature is that transponder requirements of all other customers, such as private VSAT operators, are also coordinated by the DoT. All VSAT operators have to apply to the DoT, which leases out UXC transponders on payment of licence fees. This has led to a situation in which ISRO builds the satellite but the DoT makes money on the satellite transponders by leasing out capacity which it acquired by overstating its needs. Similarly, Doordarshan has leased the unutilised transponder allocated to it to the U.S. television company CNN for $1 million a year. Clearly, there is an urgent need to evolve a policy framework for transponder allocation and use because, besides having a bearing on efficient use of the spectrum, this also has technology implications for satellites that ISRO is designing.

Part of the blame rests with ISRO, which has not taken a proactive approach in making an independent assessment of the demand and developing the space segment accordingly. Even the initiative one saw when it introduced UXC seems to be lacking now. ISRO should have foreseen the rapidly growing VSAT demand in the country, planned for capacity utilisation of transponders and satellites and provided for contingency measures in case of satellite failures. With a new policy in respect of Internet Service Providers (ISP) in place, VSAT communications by ISPs is likely to grow significantly; but no assessment appears to have been made of the growth of this demand. Telecom experts say that VSAT communications is the only way to provide rural telephony (particularly in combination with Wireless in Local Loop (WLL) technology, as pointed out by Dr. S. Chandrashekar, a former ISRO scientist). This demand will also greatly increase in the near future. To meet all these requirements satellite capacity (in Ku or UXC) has to increase vastly and satellite designs have to be evolved accordingly.

* This is Arabsat-1C, the replacement satellite for INSAT-2D, which was abandoned following loss of power. In addition, seven C-band transponders have also been leased on the Thai satellite Thaicom. Note: Nine transponders in INSAT-2E (four in the normal C-band and five in the lower extended C-band) are to be leased to INTELSAT; therefore, INSAT-2E will augment the transponder capacity on the INSAT system only to the extent of five normal C-band transponders. The total availability of transponders on the INSAT system is at present less than the normative capacity of all the INSAT satellites that are currently operational; this is because of the failure of solid state power amplifiers (SSPAs) of the transponders that use the Fujitsu-made gallium-arsenide field effect transistors (GaAsFETs) in INSAT-2A,2B and 2C.INSAT-2E uses not SSPAs, but the more reliable and higher power Travelling Wave Tube Amplifiers(TWTAs) procured from the French company Thomson CSF.

UNFORTUNATELY, the INSAT-3 series of satellites, right up to 3E, seem to be only an extension of INSAT-2E. In terms of their size, mass, technology and number of transponders, they do not seem to be vastly different from the INSAT-2 series (see table) although the need is to provide far greater space segment capacity.

INSAT-3B, with its 12 UXC-band transponders, will be launched before INSAT-3A in order to solve the current crunch in UXC capacity. In terms of new technologies, only INSAT-3C has incorporated frequency re-use, thereby doubling the normal C-band capacity. None of them, however, has features like spot beams, although ISRO scientists say that spot beams may not be of particular relevance to a vast region like India. But the incorporation of such technologies may become important if ISRO wants to enter the global market in a bigger way, beyond its current agreement with INTELSAT.

Most important, having established an industrial base for manufacturing ground systems in the UXC-band, ISRO's next series of satellites do not seem to be geared to giving a push to the use of this band in a big way and consolidate the domestic industry. In fact, the parts relating to SATCOM in the new telecom policy (NTP) of 1999, announced in March, should give ISRO cause for worry. It allows users to avail themselves of transponder capacity from both domestic and foreign satellites, particularly for access to gateways for ISPs. Although this must be done "in consultation with ISRO": what that means administratively and operationally is not clear in the absence of a clear-cut policy for the allocation and leasing of INSAT transponders. The new policy also allows for the use of the Ku-band for communication purposes.

The two elements of the SATCOM policy could together upset ISRO's plans and satellite designs. Unless ISRO makes its own assessment of the growing demand for transponders and adopts a proactive approach, it may find itself unable to provide adequate space segment and may lose customers to foreign satellites. Private telecom operators, for whom use of VSATs is an option, may choose to use foreign satellites that offer the Ku -band unless ISRO makes an aggressive push for the use of the UXC-band, or equivalently, economics permitting, provide adequate Ku-band capacity. The NTP would seem to have accentuated the inadequacy of the INSAT-3 system.

From its configuration, the INSAT-3 series, with its lift-off mass in the two-tonne class like INSAT-2, seems to have been evolved with the limited perspective of the GSLV in mind and not to meet a growing communications demand. However, the irony is that the realisation of the GSLV in an operational mode is likely to take some years and all the satellites in the INSAT-3 series may have to be launched in a procured launch like Ariane. As ISRO, which doubtless has technological strengths, enters the new millennium, a retrospective look seems to suggest that there have been demand-supply mismatches, shortcomings in long-term programme planning and a failure to keep up with trends in satellite technology. These need to be addressed and a mid-course correction may be necessary to evolve fresh strategies that enable ISRO to remain effective as a provider of national satellite communication services and at the same time be a competitive player in the world space market.