Communication Satellite GSAT-12 Reached its Home in a Circular Geo-synchronous Orbit

India's communication satellite GSAT-12, which was put in orbit on 15 July 2011, reached its home in a circular geo-synchronous orbit at an altitude of 36,000 km on 18 July 2011. The Polar Satellite Launch Vehicle (PSLV-C17) of the Indian Space Research Organisation (ISRO), which lifted off from the space station at Sriharikota on 15 July 2011, put the 1,410 kg GSAT-12 in a sub geo-synchronous transfer orbit (sub-GTO) with an apogee of 21,020 km and a perigee of 284 km.

GSAT-12 was launched to be useful in tele-education, tele-medicine, disaster management support, telephone services along with 12 extended C-band transponders.

Challenges of the GSAT-12 operation
After GSAT-12 was put in a sub-GTO (sub geo-synchronous transfer orbit), the liquid apogee motor (LAM) on board was fired once each day from July 16 to July 19 2011 to circularise the orbit at an altitude of 36,000 km. On July 16 and July 17, commands were given from the Master Control Facility (MCF) at Hassan in Karnataka to the LAM to take the satellite's apogee from 21,020 km to 36,000 km when the satellite was at its perigee. Similarly, the commands to the LAM to fire to take the perigee from 284 km to 36,000 km were given on July 18 and July 19 when the satellite was at its apogee.

What is Apogee and Perigee?
Apogee and perigee refer to the distance from the Earth to the moon.
•    Apogee is the furthest point from the earth.
•    Perigee is the closest point to the earth and it is in this stage that the moon appears larger.