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India Launches Remote Sensing Satellite.

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India Launches Remote Sensing Satellite.
India Launches Remote Sensing Satellite: Image credit: ISRO.

An Indian PSLV rocket blasted off today from the Satish Dhawan Space Center carrying the IRS-P6 remote sensing satellite into an 821 km high polar orbit. The rocket was launched even though the weather was poor with heavy rains – the wind, however, wasn’t a problem. IRS-P6 is the most advanced remote sensing satellite built by the Indian Space Research Organization (ISRO); it will primarily monitor natural resources, like water, agriculture, and gather land management data.

In its eighth flight conducted from Satish Dhawan Space Centre, (SDSC), SHAR, Sriharikota, today (October 17, 2003), ISRO's Polar satellite Launch Vehicle, PSLV-C5, successfully launched the Indian remote sensing satellite, RESOURCESAT-1 (IRS-P6) into a 821km high polar Sun Synchronous orbit (SSO). The 1,360 kg RESOURCESAT-1 is the most advanced and heaviest remote sensing satellite launched by ISRO so far. PSLV forms an important component of the end to end system created by ISRO for natural resource planning and management.

PSLV-C5 lifted off from SDSC, SHAR, Sriharikota at 10:22 am 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. After going through the planned flight events including the separation of the ground-lit strap-on motors, separation of air-lit strap-on motors and first stage, ignition of the second stage, separation of the payload fairing after the vehicle had cleared the dense atmosphere, second stage separation, third stage ignition, third stage separation, fourth stage ignition and fourth stage cut-off, RESOUCESAT-1 was systematically injected into orbit 1080 seconds after lift-off.

RESOURCESAT-1 was separated after suitable reorientation of the fourth stage-equipment bay combination to avoid any collision with the satellite. RESOURCESAT-1 has been placed in the polar Sun Synchronous orbit (SSO) at an altitude of 821 km with an inclination of 98.76 deg with respect to the equator.

About PSLV

It may be noted that PSLV was designed and developed by ISRO to place 1,000 kg class Indian remote sensing satellites into polar Sun-synchronous orbit (SSO). Since its first successful flight in October 1994, the capability of PSLV has been enhanced from 850 kg to the present 1,400 kg into 820 km Sun Synchronous Orbit. PSLV has also demonstrated multiple satellite launch capability. So far, it has launched seven Indian satellites as well as four small satellites for international customers.

The improvement in the payload capability of PSLV over successive flights has been achieved through several means - increase in the propellant loading of the first stage solid propellant motor and second and fourth stage liquid propellant motors, improvement in the performance of the third stage motor by optimizing motor case and enhanced propellant loading and employing a carbon composite payload adapter. The sequence of firing of the strap-on motors has also been changed from two ground-lit and four air-lit to the present four ground-lit and two air-lit sequence.

In the PSLV-C5, the metallic third stage adapter was replaced by the one built with carbon composites. Also, the liquid propellant second stage was operated at a higher chamber pressure for better performance.

In its present configuration, the 44.4 metre tall, 294 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) 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 4,762 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 solid propellant and produces 645 kN thrust.

The second stage employs indigenously built Vikas engine and carries 41.5 tonne of liquid propellant - UH25 as fuel and Nitrogen tetroxide (N2O4) as oxidiser. It generates a maximum thrust of about 800 kN.

The third stage uses 7.6 tonne of HTPB-based solid propellant and produces a maximum thrust of 246 kN. Its motor case is made of polyaramide fibre. 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 7.3 kN.

The 3.2 m diameter metallic bulbous payload fairing of PSLV is of isogrid construction and protects the spacecraft during the atmospheric regime of the flight. PSLV employs a large number of stage auxiliary systems for stage separation, payload fairing separation and jettisoning, etc.

PSLV control system includes: a) First stage; Secondary Injection Thrust Vector Control (SITVC) for pitch and yaw, reaction control thrusters for roll b) Second stage; Engine gimbal for pitch and yaw and, hot gas reaction control motor for roll control c) Third stage; flex nozzle for pitch and yaw and PS-4 RCS for roll control and d) Fourth stage; Engine gimbal for pitch, yaw and roll and, on-off RCS 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. S-band PCM telemetry and C-band transponders cater to this requirement. The tracking system provides real-time information for flight safety and for preliminary orbit determination once the satellite is injected into orbit.

The Vikram Sarabhai Space Centre (VSSC), Thiruvananthapuram, designed and developed PSLV. The ISRO Inertial Systems Unit (IISU) at Thiruvananthapuram developed the inertial systems for the vehicle. The Liquid Propulsion Systems Centre, also at Thiruvananthapuram, developed the liquid propulsion stages for the second and fourth stages of PSLV as well as reaction control systems. The Satish Dhawan Space Centre (SDSC), SHAR processed the solid motors and carried out launch operations. ISTRAC provided telemetry, tracking and command support.

With seven successive successful launches, PSLV has proved itself as a reliable vehicle for launching Indian remote sensing satellites. Besides, it has been used for launching a geo-synchronous satellite, KALPANA-1. ISRO has proposed to use PSLV for India's first unmanned mission to moon, Chandrayaan-1.

RESOURCESAT-1 carries three cameras as follows:

* A high resolution Linear Imaging Self Scanner (LISS-4) operating in three spectral bands in the Visible and Near Infrared Region (VNIR) with 5.8 metre spatial resolution and steerable up to + 26 deg across track to obtain stereoscopic imagery and achieve five day revisit capability

* A medium resolution LISS-3 operating in three spectral bands in VNIR and one in Short Wave Infrared (SWIR) band with 23.5 metre spatial resolution

* An Advanced Wide Field Sensor (AWiFS) operating in three spectral bands in VNIR and one band in SWIR with 56 metre spatial resolution.

RESOURCESAT-1 also carries a Solid State Recorder with a capacity of 120 Giga Bits to store the images taken by its cameras which can be read out later to the ground stations.

Soon after its injection into orbit, the solar panels on board RESOURCESAT-1 were deployed automatically to generate the necessary electrical power for the satellite. Further operations like three axis stabilisation are being carried out. The satellite health is being continuously monitored from the spacecraft Control Centre at Bangalore with the help of ISTRAC network of stations at Bangalore, Lucknow, Mauritius, Bearslake in Russia and Biak in Indonesia. Further operations on the satellite like orbit trimming, checking out the various subsystems and, finally, switching on the cameras will be carried out in the coming days.

With ISRO satellite Centre (ISAC), Bangalore, as the lead Centre, RESOURCESAT-1 was realised with major contributions from Space Applications Centre (SAC), Ahmedabad, Liquid Propulsion Systems Centre (LPSC) at Bangalore, and ISRO Inertial Systems Unit (IISU), Thiruvananthapuram. ISTRAC is responsible for initial and in-orbit operation of RESOURCESAT-1. The National Remote Sensing Agency 's (NRSA) Data Reception Station at Shadnagar near Hyderabad receives the data from RESOURCESAT-1.

Once commissioned, RESOURCESAT-1 will not only continue the services of IRS-1C and IRS-1D, but also enhance the remote sensing services by providing imageries with improved spatial resolution and additional spectral bands.

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