In its seventh flight conducted today (September 12, 2002) from Satish Dhawan Space Centre, SHAR, Sriharikota, ISRO’s Polar Satellite Launch Vehicle, PSLV, successfully launched India’s first exclusive Meteorological satellite, METSAT, into a Geo-synchronous Transfer Orbit (GTO). This is the first time that PSLV is being used to launch a satellite into GTO; in all its previous flights, PSLV was used to place Indian Remote Sensing satellites and other auxiliary payloads in Polar orbits.

METSAT is now orbiting the Earth in GTO with a perigee (nearest point to Earth) of 218 km and an apogee (farthest point to Earth) of 34,700 km with an orbital inclination of 17.7 deg. with respect to the equator. The orbital period now is 10.5 hours.

PSLV-C4 lifted off from Sriharikota at 3.53 pm with the ignition of the core first stage and four strap-on motors. The remaining two strap-on motors of the first stage were ignited at 25 sec after lift-off. The major phases of the flight included the ignition of the second, third and fourth stages and their smooth separation after burn-out, separation of payload fairing after the vehicle had cleared the dense atmosphere and the injection of the METSAT into the GTO. The total flight duration from PSLV-C4 lift-off to METSAT separation from the fourth stage of PSLV in GTO was 1211 seconds (about 20 minutes).

The major changes made in PSLV since its previous launch in October 2001 included the improvements in the performance of the third stage solid propellant motor by optimising the motor case and propellant loading. Also, the propellant in the fourth stage liquid propellant motor had been increased from 2 tonne to 2.5 tonne. Besides, PSLV-C4 employed a carbon fibre composite payload adopter. All these have resulted in substantial payload advantage.

The vehicle trajectory was modified for the flight of PSLV-C4 to inject the METSAT into a Geosynchronous Transfer Orbit of 250 km perigee and 36,000 km apogee with an inclination of 18 degree with respect to the equator.

About PSLV

PSLV was initially designed for launching 900 kg Indian Remote Sensing Satellites (IRS) into a 900 km polar sun synchronous orbit. Since its first launch in 1993, it has been successively improved to enhance its capability.

In its PSLV-C4 configuration, the 44.4 metre tall, 295 tonne PSLV has four stages using solid and liquid propulsion systems alternately. The first stage is one of the largest solid propellant boosters in the world and carries 138 tonne of Hydroxyl Terminated Poly Butadiene (HTPB) based propellant. It has a diameter of 2.8 m. The motor case is made of maraging steel. The booster develops a maximum thrust of about 4,628 kilo Newtons (kN). Six strap-on motors, four of which are ignited on the ground, augment the first stage thrust. Each of these solid propellant strap-on motors carries nine tonne of HTPB propellant and produces 662 kN thrust.

The second stage employs the Vikas engine which carries 40 tonne of liquid propellant — Unsymmetrical Di-Methyl Hydrazine (UDMH) as fuel and Nitrogen Tetroxide (N2O4) as oxidiser. It generates a maximum thrust of about 725 kN.

The third stage uses 7.6 tonne of HTPB-based solid propellant and produces a maximum thrust of 260 kN. Its motor case is made of polyaramide fibre composite. The fourth and the terminal stage of PSLV has a twin engine configuration using liquid propellant. With a propellant loading of 2.5 tonne (Mono-methyl hydrazine and Mixed Oxides of Nitrogen), each of these engines generates a maximum thrust of 7.4 kN.

The 3.2 m diameter metallic bulbous payload fairing of PSLV protects the spacecraft during the atmospheric regime of the flight.

PSLV flight control system includes: a) First stage; Secondary Injection Thrust Vector Control (SITVC) for pitch and yaw, liquid propellant thrusters for roll with SITVC in two strap-on motors for roll control augmentation, b) Second stage; Engine gimbal for pitch and yaw and, hot gas reaction control for roll, c) Third stage; flex nozzle for pitch and yaw and liquid propellant thrusters in pulse mode for roll control, d) Fourth stage; Engine gimbal for pitch, yaw and roll, and, liquid propellant thrusters in pulse mode for control during the coast phase.

The inertial navigation system in the equipment bay, which is located on top of the fourth stage, guides the vehicle from lift-off to spacecraft injection into orbit. The vehicle is provided with instrumentation to monitor the vehicle performance during the flight supported by S-band PCM telemetry. C-band transponders cater to the tracking requirement. The ground based radar tracking system provides real-time information for flight safety.

PSLV employs a large number of auxiliary systems for stage separation, heat-shield separation and jettisoning, etc.


METSAT, launched by PSLV-C4 this afternoon, is the first exclusive meteorological satellite built by ISRO. So far, meteorological services had been combined with telecommunication and television services in the INSAT system. METSAT will be a precursor to the future INSAT system that will have separate satellites for meteorology and telecommunication & broadcasting services. This will enable larger capacity to be built into INSAT satellites, both in terms of transponders and their radiated power, without the design constraints imposed by meteorological instruments.

For meteorological observation, METSAT carries a Very High Resolution Radiometer (VHRR) capable of imaging the Earth in the visible, thermal infrared and water vapour bands. It also carries a Data Relay Transponder (DRT) for collecting data from unattended meteorological platforms. METSAT will relay the data sent by these platforms to the Meteorological Data Utilisation Centre at New Delhi. Such platforms have been installed all over the country.

At the time of its launch, METSAT weighed 1055 kg including about 560 kg of propellant. The propellant carried by METSAT is mainly required to raise the satellite from the Geosynchronous Transfer Orbit to its final Geostationary orbit. METSAT will be located at 74 deg East longitude.

METSAT has been designed using a new spacecraft bus employing lightweight structural elements like Carbon Fibre Reinforced Plastic (CFRP). The satellite has a solar array generating 550 watts of power.

Solar Array Deployment

METSAT’s solar array was automatically deployed immediately after its injection into Geosynchronous Transfer Orbit (GTO) by PSLV-C4. The successful deployment of the array as well as the general health of the satellite were monitored by a ground station of the ISRO Telemetry, Tracking and Command network (ISTRAC) located on the Indonesian island of Biak. The Master Control Facility (MCF) at Hassan in Karnataka has taken control of METSAT for all its post launch operations. Ground stations at Lake Cowichan (Canada), Fucino (Italy) and Beijing (China) are supporting MCF in monitoring the health of the satellite and its orbit raising operations.

In the coming days, METSAT’s orbit will be raised from its present elliptical Geosynchronous Transfer Orbit to the final Geostationary Orbit by firing the satellite’s Liquid Apogee Motor. The first orbit raising operation is planned on September 13, 2002, by commanding from MCF. The satellite will be commissioned into service after the completion of orbit raising operations and positioning it in its designated orbital slot of 74 East longitude as well as the in-orbit testing of all the onboard systems.

The Vikram Sarabhai Space Centre, Thiruvananthapuram, designed and developed PSLV. The inertial systems for the vehicle were developed by the ISRO Inertial Systems Unit at Thiruvananthapuram. The Liquid Propulsion Systems Centre also at Thiruvananthapuram developed the Liquid propulsion stages for the second and fourth stages of PSLV as well as the reaction control systems. Satish Dhawan Space Centre, SHAR processed solid motors and carried out launch operations. ISTRAC provides Telemetry, Tracking and Command support.

METSAT was developed by ISRO Satellite Centre, Bangalore. The Meteorological payloads were developed by Space Applications Centre, Ahmedabad. Master Control Facility at Hassan is responsible for all post launch operations on the satellite. Several industries and academic institutions were involved in today’s PSLV-C4/METSAT Mission.

The successful launch of METSAT into Geosynchronous Transfer Orbit has proved the versatility of PSLV to launch both Polar and Geostationary satellites. Together with GSLV, it will enable India to launch communication and meteorology and remote sensing satellites of different weight classes. The exclusive meteorological satellite, METSAT, once commissioned, is expected to vastly improve the meteorological services being provided by INSAT systems.