press club of india, Indian Tehalka News
Thirty years after Rakesh Sharma became the first Indian to venture into space, flying aboard a Soviet Soyuz spacecraft, an Indian crew capsule and rocket that could one day carry astronauts will get their first trial next week.
The experimental flight of the Geosynchronous Satellite Launch Vehicle (GSLV) Mark III, scheduled for next Thursday (Dec. 18), will send the unmanned crew module on a suborbital trajectory, with the latter splashing down in the Bay of Bengal about 21 minutes after the rocket lifts off from Sriharikota.
This flight would test the crew module’s re-entry characteristics, said K. Radhakrishnan, chairman of the Indian Space Research Organisation (ISRO). Recovery of the spacecraft from the ocean, carried out with the help of the Indian Coast Guard, would also be “an involved task.” Back in January 2007, ISRO had orbited a small 550-kg spacecraft, the Space Capsule Recovery Experiment (SRE-1), that carried out remote-controlled experiments in the microgravity conditions of space. After 12 days in orbit, the spacecraft was successfully brought back, landing in the Bay of Bengal with remarkable precision. This provided experience with re-entry, a prerequisite for manned spaceflight.
A project report prepared by ISRO envisaged carrying out a manned mission in about seven years at a cost of around Rs. 12,400 crore. Thus far, the Government has not cleared such a project.
However, since 2007, the Government had given Rs. 145 crore for the development of critical technologies needed for a manned mission, according to Dr. Radhakrishnan.
The 3.7-tonne crew module being tested next week will be the same size, shape and weight as the capsule that is being developed to accommodate up to three astronauts. It will be equipped with the heat-protecting tiles and parachute system of the manned version.
While a capsule in orbit around Earth will re-enter with a velocity of over 28,000 km per hour, next week’s test will see the GSLV Mark III leave the crew module at a height of about 125 km with a velocity of around 19,000 km per hour. The crew module carries sensors that will make measurements of over 200 parameters during the flight, including the temperature, pressure and stress experienced at various points in the structure. “This flight will give us tremendous confidence in our design and provide important inputs for proceeding with development of the manned capsule,” observed S. Unnikrishnan Nair, project director for the Human Spaceflight Programme.
After separation from the GSLV Mark III, six liquid-propellant thrusters on the crew module will be used to correct any perturbations that occur during separation and bring the capsule down at the correct angle for re-entry into the atmosphere.
Once re-entry starts at a height of about 80 km, the thrusters will cease to operate. As the crew module streaks through the atmosphere, the air around it heats up and the spacecraft slows down. The heat shield at its base will be exposed to temperatures of around 1,000 degrees Celsius, according to Mr. Nair. (In re-entry from orbit, the temperature could touch 1,600 degrees Celsius.)
At a height of about 15 km, with the capsule travelling at 839 km per hour, the complex process of deploying the parachutes begins.
The crew module carries two independent sets of parachutes, both of which are simultaneously deployed. First, the 2.5-metre diameter pilot parachutes come out, followed by the 6.5-metre drogue parachutes, which cut the capsule’s velocity down to 180 km per hour.
Then the main parachutes are deployed at a height of about 5 km. These parachutes, each 31 metres in diameter, are the largest ever made in the country and were developed by the Aerial Delivery Research & Development Establishment, an Agra-based national defence laboratory.
On splashdown, the main parachutes will be immediately detached from the crew module and a beacon giving its position activated. A fluorescent green dye will also be emitted to aid in locating the spacecraft.
In the coming test, the crew module could experience decelerations of up to 13 g, said Mr. Nair. But, in a mission with humans onboard, the capsule’s thrusters would continue to operate till parachute deployment began, adjusting the spacecraft’s orientation and trajectory, and keeping deceleration levels to less than 4 g. (One g being equivalent to the tug of Earth’s gravity.)
From : The Hindu