As per ISRO press release a 53 hours countdown has started in preparedness and checkout of rocket and other subsystems for the launch of GSAT 12 using a PSLV rocket in flight PSLV C17.
The Launch Authorisation Board (LAB) for PSLV-C17/GSAT-12 mission, which met on July 12, 2011 at Satish Dhawan Space Centre - SHAR, Sriharikota has cleared the launch of PSLV-C17 at 16:48 hrs (IST) on Friday, July 15, 2011.
The 53 hour countdown commenced at 11:48 hours on July 13, 2011. During the Countdown, propellant-filling operations of the liquid propellant second stage (PS2) and fourth stage (PS4) of the launch vehicle will be carried out. Mandatory checks on the launch vehicle and spacecraft including charging of batteries and pressurisation of propellant tanks will be performed. Readiness of various ground systems such as tracking radar systems and communication networks will also be checked.
PSLV-C17 will launch GSAT-12 satellite into a sub-Geosynchronous Transfer Orbit of 284 km perigee and an apogee of 21,000 km. GSAT-12 communication satellite weighing 1410 kg with 12 Ext-C Band transponders will augment the communication services in the country.
We give details about what is a countdown and what things are involved in this activity in our education blog shortly.
A brochure released by ISRO giving some information about this flight can be found here