Countdown begins at 11.48 a.m. on Wednesday
With the 53-hour countdown for the launch of the Polar Satellite Launch Vehicle (PSLV-C17) commencing at 11.48 a.m. on Wednesday, the stage is set for the rocket's lift-off from Sriharikota at 4.48 p.m. on Friday.
The PSLV-C17 will put in orbit communication satellite GSAT-12, which weighs 1,410 kg. It is a more powerful version of the standard PSLV, called PSLV-XL that will put the satellite in orbit after a 20-minute flight.
“The countdown is going on satisfactorily,” said P.S. Veeraraghavan, Director of Vikram Sarabhai Space Centre (VSSC) in Thiruvananthapuram, from Sriharikota on Wednesday. The launch window is between 4.48 p.m. and 5.08 p.m. “We will use the earliest opportunity” at 4.48 p.m. for the rocket's ignition, he said. The four-stage PSLV was built by the VSSC.
This is the second time that a powerful PSLV-XL version will lift off from the second launch pad at Sriharikota. It was earlier used to put Chandrayaan-1 into orbit on October 22, 2008. While the six strap-on booster motors of the standard version of the PSLV carry a total of nine tonnes of solid propellants, the strap-on motors in the XL version are powered by a total of 12 tonnes of fuel.
“This is [also] the second time that a PSLV is being used to put a satellite in a geo-synchronous transfer orbit (GTO),” said Mr. Veeraraghavan. It was earlier used on September 12, 2002 to put Kalpana, a weather satellite, in GTO.
Raising the apogee
In fact, the PSLV-C17 will put GSAT-12 in a sub-GTO with a perigee (nearest point to the earth) of 284 km and an apogee (farthest point from the earth) of 21,000 km. After it is put in a sub-GTO, commands will be given to the liquid apogee motor (LAM) on board the satellite to boost the apogee to 36,000 km. After it is done, commands will be given to boost the perigee from 284 km to 36,000 km.
“For the first time, in our communication satellites, we are raising the apogee from 21,000 km to 36,000 km in two stages. This is a crucial manoeuvre. To raise the apogee, you have to fire the LAM when the satellite is in its perigee. So the LAM firing is a challenge,” said a satellite technologist of the Indian Space Research Organisation (ISRO). The satellite will thus reach a circular geo-stationary orbit of 36,000 km.
Advanced mission computer
“A significant feature of the PSLV-C17,” said Mr. Veeraraghavan, “is that it will use an advanced mission computer with indigenous processors. The ISRO built the computer. We also built our own processors. The advanced mission computer will be used for navigation, guidance and controlling” the rocket. The ISRO earlier used imported processor chips in the PSLV missions. In the PSLV-C12 mission in 2009, it used one chain of imported processors and another chain of indigenous processors. “In this mission, both the prime and the redundant chains have indigenous processors,” Mr. Veeraraghavan said.
The GSAT-12, with 12 extended C-band transponders, will be used for tele-medicine, tele-education, telephone and various other communication purposes.
This is the 19th PSLV mission, out of which 17 have been successful in a row. The PSLV-C17 weighs 310 tonnes and is 44 metres tall.