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A successful launch

Print edition : Feb 02, 2002 T+T-

The launch of INSAT-3C on January 24 signifies an important stage in the evolution of India's space technology programme.

ON January 24, after a last-minute hitch, INSAT-3C, the second in the INSAT-3 series of satellites built by the Indian Space Research Organisation (ISRO), was launched successfully by the Ariane 4 launch vehicle of Arianespace at 23:47 hrs Greenwich Mean Time (5-17 a.m. Indian Standard Time).

Twenty-one minutes after lift-off, the satellite was injected into the elliptical Geosynchronous Transfer Orbit (GTO) from where a sequence of manoeuvres would bring it to its designated slot at 740E in the circular geosynchronous or geostationary orbit (GSO) 36,000 km above the equator.

A computer glitch at the launch pad delayed the lift-off, which was originally scheduled for 4-23 a.m., by 11 seconds. However, since a launch window of 66 minutes had been provided for, the launch was put on hold, so that the problem could be sorted out within that 66-minute time latitude.

Immediate investigations revealed that the snag occurred owing to the erroneous interpretation of data by one of the two main countdown computers at the launch pad, which concluded that a valve was open.

The two count-down computers have different sets of systems on the launch pad and on the rocket. While one computer is responsible for monitoring the status of the fluids and the propellants on board, the other controls the electrical processes such as initialisation of the launch programme, activation of the engine steering systems and the transfer of power from ground supplies to on-board powerpacks. The two computers also check on each other's work to ensure that there are no mistakes. It was during such a cross-check operation that a computer error was detected.

The hold was lifted 12 minutes before the 66-minute launch window time ended. The count-down clock was reset to T minus 6 minutes and the count-down restarted at 23:41 hrs GMT. Twenty-one minutes after a perfect lift-off of Ariane's Flight 147, the 2,750-kg satellite separated from the third stage of the rocket, Ariane 42L - the designation 2L referring to the Ariane 4 configuration with two liquid engine strap-ons - and was injected into the GTO measuring 570 km x 35,954 km at an inclination of 3.990 in a three-axis stabilised mode. Half an hour later, at 05:47 hrs IST, the Master Control Facility (MCF) at Hassan in Karnataka received the first telemetry signal from the satellite.

According to MCF Director M.Y.S. Prasad, ISRO is perhaps the only space agency that gives such a wide launch window to the launch contractor. "With technical people involved with the project available on hand at the launch site, coupled with the capability to optimise the time that is required to calibrate the on-board gyros achieved from past experience, ISRO is able to give this flexibility to Arianespace. Any other customer would have pushed the launch to the next day," Prasad said. The launch costs paid to Arianespace is approximately $77 million.

According to Prasad, the initial health checks on the satellite indicate that its performance is normal. One of the first operations carried out on the satellite by telecommands from the MCF was the orientation of the outermost panel of the stowed solar panel on the south side of the satellite towards the sun in order to generate the electricity required by the satellite during its GTO phase. Then, the earth-viewing phase was oriented towards the earth and the on-board gyros, which maintain the attitude of the satellite, was calibrated.

The satellite, which is primarily being monitored and controlled from the MCF, also utilised INMARSAT's ground stations in Beijing, Fucino in Italy, and Lake Cowichan in Canada in its initial phase of operation. The satellite's orbit is determined precisely using the combined ranging data obtained by ISRO's network of Telemetry Tracking and Command (TTC) stations.

The accuracy of performance of the launch vehicle can be judged by comparing the planned orbital parameters for the GTO with those achieved. The planned orbital parameters were 570 km perigee, 35,952 km apogee (plus/minus 150 km) and an inclination of 40 (plus/minus 0.060).

INSAT-3C is the eighth Indian satellite to be launched by an Ariane launcher, the first being the experimental Apple satellite, launched way back in June 1981 aboard Ariane 1. Flight 147 was the 108th flight of the rocket Ariane 4, its 66th consecutive successful launch and the 13th mission of the Ariane 42L configuration.

After eight more launches, the workhorse Ariane 4, which has had six variant configurations depending upon the combinations of solid and liquid strap-ons, is likely to be phased out. It will be replaced by the more powerful Ariane 5, whose failed launch in July 2001 deferred the scheduled launch of INSAT-3C in August. According to Arianespace, the latest launch of INSAT-3C marks the last launch of the configuration Ariane 42L.

This time, a dedicated launch resulted in a more optimal GTO injection of the satellite. Instead of the usual perigee of 200 km, the perigee at injection this time was 570 km. This, according to Prasad, resulted in a velocity advantage of about 40-50 metres per second (m/sec) for the subsequent orbit-raising manoeuvres, the first of which was performed on January 25, the second on January 26 and the third on January 28, allowing the satellite to enter the drift orbit.

Orbit-raising manoeuvres are carried out by firing in stages, the 440 Newton liquid thrusters aboard, called the Liquid Apogee Motor (LAM). Although normally three LAM firings are carried out, this time four had been planned. According to Prasad, this was done to achieve an optimum drift velocity so that station acquisition (at 740E) is achieved in the shortest possible time. The firings, Prasad explained, depended on the injection parameters and the station acquisition requirements.

The first LAM firing (LAMF-1) lasted 3,548 seconds and increased the satellite's velocity by 625 m/sec. LAMF-2 lasted 1,790 seconds and increased the velocity by 384 m/sec. LAMF-3 was on January 28. The fourth firing will be planned after studying the satellite's orbit parameters. LAMF-4 will enable station acquisition and subsequent operations such as solar array, antenna deployment and checking of the payloads. The satellite should be ready for operations by February end, Prasad said.

The satellite carries at least 1.5 tonnes of the propellant monomethyl hydrazine (MMH) along with mixed oxides of nitrogen (MON-3) to carry out orbit-raising operations, for station-keeping as well as controlling in-orbit attitudes. The fuel levels on board will sustain the satellite's functions for at least 12 years. However, fuel saving does not result in any substantive increase in the satellite's life.

The main body of INSAT-3C has the shape of a cuboid measuring 2.1 m x 1.2 m x 2.8 m. Since the satellite does not have a meterogical payload, its solar panels extend symmetrically, in which position the satellite measures 15.5 m in length. The solar panels will generate 2.75 kW (kilo watts) of power. Even during eclipses, two 60 ampere-hour (Ah) nickel-hydrogen (Ni-H) batteries will support the entire payload operations.

Like its predecessors, INSAT is a three-axis stabilised spacecraft using momentum/reaction wheels, earth sensors, sun sensors, inertial reference units and magnetic torquers. It has two deployable antennae and three fixed antennae that carry out various transmitting and receiving operations.

Subsequently, INSAT-3C will be co-located with INSAT-1D, which was launched in July 1990 and parked at 83E. When INSAT-2E was launched, it was moved to 740E and is being currently used only for acquiring some meteorological imagery. The other INSAT satellites are INSAT-2C and INSAT-2B, co-located at 93.50E, INSAT-2E and INSAT-3B at 830E, INSAT-2A at 480E and INSAT-2DT (acquired from Arabsat) at 550E.

INSAT-3C carries 30 C-band transponders (24 in normal C and six in extended-C), two S-band transponders for broadcasting and one transponder for mobile satellite service (Frontline, January 18) operating in S-band uplink and C-band downlink. Thus a total of 111 INSAT transponders will be up in the sky. But, 30 of these, including 10 aboard INSAT-2B that have already been taken out of operation and 20 aboard INSAT-2C, which is nearing the end of its life, will soon be vacated. So, only 80-odd transponders will be available for operational use until they are augmented with the launch of INSAT-3A later this year.

INSAT-3C, which will cover both C and S bands across the country, will significantly augment the telecommunication services in the country, particularly VSAT operations.