SRIHARIKOTA: The Indian Space Research Organisation on Monday placed Defence Research Development Organisation-developed electronic intelligence satellite Emisat and 28 foreign satellites in orbits. Emisat, weighing 436kg, is meant for helping the military locate hostile radars.PSLV-C45 — carrying Emisat, 28 foreign satellites and three scientific instruments — lifted off from the second launch pad at Satish Dhawan Space Centre in Sriharikota at 9.27am. Around 17 minutes after lift-off, PSLV placed Emisat in an orbit in a 753.6km altitude.In next 1.5 hours, the launch vehicle’s fourth and final stage — PS4 — restarted and shut down twice, as the rocket manoeuvred to a 504km orbit. Around two hours after the mission started, the PS4 placed 28 foreign satellites — belonging to the US, Lithuania, Spain and Switzerland – in their orbits.It was the Polar Satellite Launch Vehicle’s 47th flight and was one of the longest missions of the launch vehicle around the Earth, lasting nearly three hours. The previous longest mission was that of PSLV-C40 in January 2018 which lasted two hours and 21 minutes.The launch has many ‘firsts’ to its credit — PSLV used a new variant with four strap-on boosters with each carrying 12.2 tonne of propellent for lift-off, and the rocket moved to three different orbits with the PS4 being restarted four times.The four-stage rocket’s final and fourth stage will stay alive for the next six months along with three scientific instruments that will collect data and relay them to the ground station.Isro chairman K Sivan congratulated the team for the success of the mission. He said, "We may attempt 30 missions before the end of this year. They include the launch of Risat, Cartosat 3 and Chandarayaan-2.”Since all the satellites are in their orbits, the mission’s primary goal has been achieved. However, for Isro scientists, it is far from over. As the top Isro scientists congratulated one another for PSLV’s success, engineers stayed glued to their systems as PS4 heads to the third and final orbit plunging from a 508km elliptical orbit to a 485km circular orbit after the thrusters of the stage were restarted and shut down twice.Isro used a multiple-burn technology where the engine shut down and restarted multiple times within a short period of time allowing the rocket to course to the next orbit with the payloads.Isro has already demonstrated multiple burn technology in at least four previous PSLV launches -- PSLV C-35 in September 2016, PSLV-C34 in June 2016 and PSLV-C29 in December 2015 and PSLV-C40 in January 2018.Piggybacking on the fourth stage are three scientific instruments made by three laboratories for three different applications -- an automatic identification system (AIS) developed by Isro for maritime applications, an automatic packet repeating system (APRS) developed by AMSAT or Radio Amateur Satellite Corporation, India, to assist amateur radio operators and an Advanced Retarding Potential Analyser for Ionospheric Studies (ARIS) made by the Indian Institute of Space Science and Technology (IIST) for atmospheric studies.The PS4 stage will remain as an orbital platform, circling the Earth, for the instruments to collect data and relay them to the ground station for the next six months. According to Isro officials, the stage is powered by solar panels.This is the second time that Isro is converting PS4 as a satellite-like orbital platform. On January 24, PSLV-C44 carried a student satellite in its PS4 which was alive for several hours — powered by batteries — helping the payload conduct microgravity tests.Read this report in Bengali