Pressure on ISRO to produce winner, after 2 failures in 2010
The flight of the Geosynchronous Satellite Launch Vehicle (GSLV-D5) — at 4.18 p.m. on Sunday — from Sriharikota will be an acid test for India as it seeks to prove the design, realisation and sustained firing of its indigenously built cryogenic engine. There is pressure on the Indian Space Research Organisation (ISRO) to produce a winner because of two back-to-back failures of the GSLV flights in 2010 — the first, with an indigenous cryogenic engine, on April 15 and the next, with a Russian cryogenic engine, on December 25.
ISRO’s next GSLV flight, with an indigenous cryogenic engine, on August 19, 2013, was called off 75 minutes before lift-off: the liquid fuel from the rocket’s second stage had leaked, wetting the first stage and the four strap-on boosters around it. So ISRO dismantled the 49-metre tall vehicle, weighing 415 tonnes and built a refurbished GSLV-D5, with new first and second stages and four new strap-on booster motors. It has used a new propellant tank in the second stage, made of an aluminium alloy different from the one used in August.
Cryogenic engines are essential for rockets to put communication satellites, weighing more than two tonnes, into orbit.
The Chandrayaan-2 mission, scheduled for 2016, will use a GSLV with an indigenous cryogenic stage. ISRO has to produce two winners in a row with GSLVs with India-built cryogenic stages before it can confidently send up the Chandrayaan-2, which will deploy an India-made lander and rover on the moon.
So Sunday’s mission is a crucial one and expectations are, therefore, high from ISRO to deliver. The three-stage GSLV-D5 will put into orbit a 1982-kg communication satellite called GSAT-14.
“We have done our best,” K. Radhakrishnan, ISRO Chairman, said on Saturday evening from Sriharikota. “The countdown for the [GSLV-D5] flight began at 11.18 a.m. The rocket’s second stage has already been filled with the liquid fuel and oxidiser.” Fuel-filling for the four strap-on booster motors began after 6 p.m. “Things are progressing smoothly and the weather is fine,” he said.
M.C. Dathan, Director, Liquid Propulsion Systems Centre (LPSC), ISRO, said: “We have done everything humanly possible” to ensure the success of the mission. “We have drawn on all the expertise available,” he said. The LPSC at Mahendragiri, Tamil Nadu, is the architect of not only the cryogenic stage for this mission but also the second stage and the four strap-on motors. The second stage and the strap-on motors use liquid fuel.
The Launch Authorisation Board met on Friday and gave the green signal for the launch. “Everything is fine,” the LPSC Director said. The filling of the cryogenic propellants in the third, uppermost stage of the vehicle would begin around 1 p.m. on Sunday.
ISRO rocket engineers said cryogenic technology is extremely complex and difficult to master. It uses liquid oxygen at minus 183 degrees Centigrade and liquid hydrogen at minus 253 degrees Centigrade. An engineer said: “The turbo-pump in the cryogenic engine should supply the fuel to the combustion chamber at high pressure. This injection should take place with the right proportion of the fuel and the oxidiser. Then the fuel has to be ignited. This is unlike the liquid engine where you mix the propellants and they ignite spontaneously.” There were challenges involved in developing the insulation to keep the liquid oxygen and liquid hydrogen at their low temperatures. “They should not boil off.”
The combustion of the propellants in the cryogenic engine should be proper. Otherwise, liquid oxygen and liquid hydrogen will explode. “It is not enough if you start the combustion. You have to sustain it,” the rocket technologist said.
If the GSLV-D5 mission lasts about 17 minutes, the cryogenic engine itself will fire for a full twelve minutes. At the end of seventeen minutes, the rocket will put the GSAT-14 satellite into orbit. GSAT-14 will be used for telecasting, telecommunication, tele-medicine and tele-education.