Chennai, April 18 (IANS) The 54.5-hour countdown for the April 20 launch of the PSLV rocket, which will put India's Resourcesat-2 and two other satellites into orbit, started early Monday in Sriharikota, the rocket port in Andhra Pradesh.

 
 "The 54.5-hour countdown started at 3.42 a.m. Monday," S. Satish, director for publications and public relations, Indian Space Research Organisation (ISRO), told IANS. Sriharikota is around 80 km from here.
 
 The Polar Satellite Launch Vehicle (PSLV) is expected to blast off Wednesday at 10.12 a.m. and will carry a total luggage of 1,404 kg.
 
 This comprises three satellites - the 1,206 kg Resourcesat-2, the 92 kg joint Indo-Russian nano-satellite Youthsat for stellar and atmospheric studies, and a 106 kg microsatellite X-sat for imaging applications, built by the Singapore-based Nanyang Technological University.
 
 The 44-metre tall PSLV is a four-stage rocket powered by solid and liquid propellants alternatively. The first and third stage engines are fired by solid propellant and the second and fourth stages are fired by liquid propellant.
 
 The Indian remote sensing satellite Resourcesat-2 was originally scheduled for a launch in January this year but got postponed to February and then to April.
 
 Remote sensing satellites send back pictures and other data for use. India has the largest constellation of remote sensing satellites in the world providing imagery in a variety of spatial resolutions, from better than a metre ranging up to 500 metres, and is a major player in vending such data in the global market.