Countdown for the launch of PSLV-C32 to place India's sixth navigational satellite IRNSS-1F in the orbit started at Satish Dhawan Space Centre in Sriharikota this morning. ISRO's workhorse PSLV-C32 will lift off at 4 PM on Thursday. <br/><br/>ISRO sources said, Mission Readiness Review committee and the Launch Authorisation Board met at Sriharikota yesterday evening and cleared the 54 and half hour countdown which started at 9:30 AM today. The sources said, during the countdown, propellant filling operations would be taken up in the four stage vehicle.