A satellite success

Published : May 09, 2003 00:00 IST

With the successful launch of the multi-purpose INSAT-3A, the indigenous space segment capacity has been augmented significantly.

THE heaviest satellite so far in the INSAT system, INSAT-3A, is already in its designated slot at 93.5oE in the geosynchronous circular orbit 36,000 km above the Equator. The satellite - the third in the INSAT 3 series, after INSAT-3B and 3C was launched in the early hours (0422 hr Indian Standard Time) of April 10 aboard the European launcher Ariane 5 along with the satellite Galaxy-12 of PanAmSat. A day's delay was caused by a glitch in the ground telemetry tests. At the launch pad, tests revealed that the power of the telemetry signals from one of the two transmitters on INSAT-3A was falling below nominal levels. The problem could not be resolved immediately and the launch was called off three hours before the closure of the 41-min. launch window on April 9.

Later, it was found that the problem, which was identified as temperature-dependent effects on the charging of one of the capacitors in the transmitter, could be fixed easily. The launch was rescheduled for the next day. Ariane 5 launched the two satellites aboard flawlessly. The 11th commercial launch of Ariane 5 was particularly important, after the failure of the improved, more powerful version of Ariane 5 in December last.

Unlike its predecessors in the INSAT 3 series, 3A is a multi-purpose satellite. It can be used for communications, television broadcasting and meteorological services, including data relay and satellite-aided search and rescue (SAS&R) services under the international COSPAR-SARSAT programme for distress alert and location. It carries 25 transponders - 12 in the normal C-band frequency, six in the extended-C (XC) band, a frequency pioneered by the Indian Space Research Organisation (ISRO), and six in the Ku-band, and one in the S-band for SAS&R. In addition, there is an ultra-high frequency data-relay transponder (DRT), which uses the XC-band for downlink.

Nine of the 12 C-band transponders provide coverage to a large area in the neighbourhood region (with an Edge-of-Coverage or EOC beam power of 38 decibelWatt (dBW) - ideally suited for television broadcast - and the remaining three have India coverage beams (with an EOC beam power of 37 dBW). The XC-band and Ku-band transponders have India coverage beams with an EOC power of 37 dBW and 47.5 dBW respectively. The power of the Ku transponders on INSAT-3A is about 2 dBW higher than that of the ones aboard INSAT-3B. Although foreign satellites over the Indian region have more beam power, scientists at the ISRO feel that INSAT-3A's capacity is more than adequate for Very Small Aperture Terminal (VSAT) operators. However, VSAT operators demand a minimum of 50 dBW. Higher power in Ku-band reduces the loss of power in the atmosphere, particularly during the monsoon.

The meteorological payload aboard INSAT-3A has a Very High Resolution Radiometer (VHRR), which provides cloud images. The VHRR has a 2-km resolution in the visible band and an 8-km resolution in the infrared (IR) and water vapour bands. The satellite has a Charge Couple Device (CCD) camera with a resolution of 1 km, operating in the visible, near-IR and short-wavelength IR bands. Even if the VHRR fails, as it happened with INSAT-2E, the CCD image can provide adequate atmospheric details for meteorological services, although specialised software is required for image reconstruction.

The INSAT 3 series consists of five satellites, 3A to 3E. The total sanctioned cost for all the satellites, their launch services and their insurance cover is Rs.2,887.63 crores. The amount includes the charges for short-term leasing of transponders in order to augment the INSAT system capacity. The original sanctioned amount for the INSAT 3 system was Rs.2,429.12 crores. The hike may be partly accounted for by the charges for leased capacity. Since 2001, ISRO has leased 10 transponders from Thaicom-3 satellite, and might continue to do so till the end of the year. The ballpark market rate for leasing a transponder is $1 million a year. The average cost of a satellite is around Rs.150 crores, the average launch cost about Rs.275 crores and the insurance charge per satellite is about Rs.70 crores.

The order in which the satellites are launched - 3B, 3C, 3A, 3E and 3D may be perplexing. While the alphabetic order was preserved in the original plan, the launch of INSAT-3B was advanced to precede INSAT-3A in order to cater to the immediate requirements of XC capacity, which was depleted owing to the failure of INSAT-2D. Launched in June 1997, INSAT-2D became inoperable since October 4, 1997, owing to total power loss. Although the loss of 12 C-band transponders and 6 XC-band transponders was partially offset by the acquisition of an in-orbit satellite, Arabsat-1C (designated as INSAT-2DT), the absence of XC-band on INSAT-2DT meant that the requirements of business organisations, corporate networks and other closed user groups (CUGs) such as the National Stock Exchange (NSE) and the Reserve Bank of India that rely on VSAT communications, could be met only by launching INSAT-3B ahead of INSAT-3A. INSAT-2E, which was launched in April 1999, did not have XC transponders.

The launch of INSAT-3A did not follow INSAT-3B as originally planned, because of problems associated with the met payload aboard INSAT-2E. The changes, as recommended by a review committee, involved improving the servo motor to provide greater thermal stability to the VHRR scan assembly. Since 3A, unlike 3B and 3C, carries a VHRR, the failure of 2E's VHRR resulted in 3C being launched ahead of 3A, pending a review of the met payload by the committee.

The immediate needs of the India Meteorological Department (IMD) were met by receiving data from the European Meteosat under an agreement with the European Space Agency (ESA). The space segment for meteorological services was augmented in September last with the launch of a dedicated meteorological satellite, METSAT (now re-christened Kalpana-1 in memory of Kalpana Chawla), by the Polar Satellite Launch Vehicle (PSLV). METSAT incorporated changes recommended by the review committee in the met payload.

The failure of INSAT-2E was related to problems with the scan board assembly of the VHRR owing to thermal variations. The met payload aboard INSAT-3A is identical to that on METSAT.

ABOUT 30 minutes after lift-off, the 2,950-kg INSAT-3A, measuring 2 metres x 1.77 metres x 2.8 metres, was placed in the elliptical Geosynchronous Transfer Orbit (GTO) of 859.3 km perigee (the nearest point from the earth) and 36,055 km apogee (the farthest point) with an inclination (to the equatorial plane) of 1.99o. The accuracy of the deployment can be judged from the target figures for these parameters, which are 860 km (3 km), 36,057 km (160 km) and 2o (0.05o) respectively. The satellite was raised to the geosynchronous orbit through three planned firings of the 440 Liquid Apogee Motors (LAM) on board, giving the satellite the requisite velocity increments. These orbit-raising LAM firings, lasting 73 minutes 42 seconds, 53 minutes and three minutes 41 seconds on April 11, 12 and 14 respectively, were performed by commanding the satellite from the Master Control Facility (MCF) at Hassan in Karnataka.

Significantly, the perigee achieved in this launch is the highest for an INSAT launch. In the earlier launches of INSAT satellites by Ariane, namely 3B by Ariane 5 on March 22, 2000, and 3C by a dedicated Ariane 4 launch on January 24, 2002, the perigees were 560 km and 570 km respectively. While these were significantly higher than the perigees in the region of 200-300 km achieved by nominal Ariane 4 launches, a perigee of 860 km is a big jump and should have saved considerable fuel during the LAM firings and extended the satellite's life beyond the designated 12 years. (INSAT-3C was originally scheduled to be launched by Ariane 5 but because of its failure in July 2001 and its subsequent grounding, it was launched by Ariane 4 in a higher-than-nominal perigee.) At the time of its injection into the GTO, INSAT-3A had 1,603 kg of propellant. After orbit-raising operations, the satellite is stated to have 505 kg of propellant.

On April 16, the last of the main deployment operations that precede the necessary performance checks on the satellite before it can be declared operational, were carried out. These include procedures such as 3-axis stabilisation, followed by the deployment of the solar sail and boom on the north face of the satellite. The stabilisation is achieved through on-board momentum wheels whose speeds of 4,500 revolutions per minute provide the required gyroscopic stiffness for a three-axis stabilised configuration of the satellite. In this mode, the satellite will be locked to the Earth continuously through on-board optical sensors and will maintain a fixed and stable earthward attitude. In the fully deployed state, the satellite measures 24.4m in the N-S direction and 8.5m in the E-W direction.

The solar sail and boom is uniquely characteristic of the multipurpose communications and meteorological satellites in the INSAT system. They provide the necessary counteracting moment to balance the tilting force owing to solar radiation pressure on the satellite's asymmetric solar array, which generates power. The solar array on the south face and the antennae that stick out like ears on the west and east faces respectively of the satellite, were deployed on April 15. The sun-tracking solar panel has a total area of 26.6 sq m and is designed to generate 3.1 kW of power in orbit.

The reason for an asymmetric solar array - it extends only from the south face - is the met payload that carries the important VHRR instrument. The cooler for the VHRR sits on the north face and an unimpeded field of view for it is essential for efficient cooling. Therefore the solar array cannot be configured to be symmetric about the body of the satellite. The VHRR on the 1,050-kg METSAT does not have a solar sail and boom. In this case, the tilting force due to the asymmetric solar array is countered by a magnetic torquer. It is reliably learnt that INSAT-3D, the dedicated meteorological satellite to be launched in 2005, will have a magnetic torquer instead of a sail and a boom. In terms of technology, INSAT-3D will be a much heavier satellite (and hence will have a larger solar array) as compared to METSAT and the torquer would be a more difficult proposition.

The significance of INSAT-3A is twofold. One, it is the first INSAT-3 satellite carrying a met payload. Two, it significantly augments the indigenous space segment capacity for communications. Indeed, with the launch of INSAT-2E later this year or early next year, the total communications capacity on the INSAT system would nearly double (see table). As per the guidelines of the Satcom policy of 1997, after accommodating the transponder capacity required by the government, chiefly the Department of Telecommunications and the Ministry of Information and Broadcasting, there should be enough capacity to bring private users, mainly television channels, who have been riding on foreign satellites, on to the INSAT platform.

According to ISRO sources, this would be seen following the launch of INSAT-3A itself. There are about 15 foreign satellites with footprints over the Indian region, but very few NSS-703, Intelsat-704, Europestar I, PAS-10, Thaicom-3 and Asiasat-3 are being used by Indian television channel operators. INSAT-3A should be in a position to offer transponders to some of these channels and to new ones. Since television channels are allowed to negotiate directly with foreign satellites - as opposed to VSAT operators on whose behalf ISRO has been mandated to negotiate - unless ISRO is pro-active, cuts down red-tape and offers competitive transponder charges, even new operators might prefer to ride on foreign satellites.

While from the perspective of VSAT operators - who prefer to use Ku band rather than XC because of easy availability of imported reliable hardware, which are cheaper than XC equipment - the launch of INSAT-3A, which carries six Ku transponders, should be a welcome development. However, there seem to be several contentious issues, most importantly the issue of power, which could prevent this potential capacity from being used up immediately even though the VSAT segment is growing at the rate of about 30 per cent annually. B. G. Bhalla, secretary of the VSAT Service Providers Association (VSPA), said that at present there are 24,000 VSATs all over the country.

According to Bhalla, there is a 4-5 dBW difference in radiated power between INSAT and foreign satellites. Consequently, even though foreign Ku transponders are 1.8 times costlier as compared to INSAT transponders, VSAT operators prefer the former. Also, imported Ku hardware apparently supports a higher bit rate. Thus, Bhalla feels that foreign ku transponders bring down the overall operational costs. "However, we are caught in a Catch-22 situation because, as per policy, only ISRO is allowed to negotiate with a satellite operator on our behalf. If there is capacity on indigenous satellite, this will not happen," says Bhalla. Indeed, he feels that given the policy guideline, even the three or four operators who are currently using foreign Ku transponders may be required to move to INSAT-3A. ISRO sources say that the reason for such a guideline is that they are able to negotiate a better price. But Bhalla says: "If we negotiate in bulk we can land a much cheaper price than ISRO can. If television channels and ISPs [Internet service providers] are allowed to do so, why not us? Moreover, here we are forced to take one full transponder even if we need only a quarter transponder at any given time. ISRO is mature enough to be able to compete in the market."

The next generation of ISRO communication satellites, namely the INSAT-4 (A to G) series, are expected to have more powerful Ku transponders and XC transponders. According to analysts, about 300 transponders (for communications alone) would be needed by the year 2007. ISRO has estimated that 250 INSAT transponders (in all bands) would be available by then. But this is not borne out by ISRO's own satellite launch schedule, according to which, at best, only up to INSAT-4D would have been launched. By then INSAT-2E would have nearly reached the end of its life, and the total number of transponders would be around 200. Clearly, the crunch in INSAT's space segment for communications is likely to continue.

The first private Indian satellite, Agrani, to be launched by ASC Enterprises of Subhash Chandra, is slated to have 24 C-band and 14 Ku-band transponders, which may offset the crunch to some extent. The upshot, therefore, is that if ISRO does not have shorter satellite turn-around times, it should bring in innovations and put pragmatic policy instruments in place. Otherwise, it will lose potential customers to foreign satellite operators who are waiting to pick up the growing demand for transponders.

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