With solar-powered final stage, ISRO gears up for first three-orbital mission

India's Polar Satellite Launch Vehicle (PSLV), in its 47th mission (PSLV-C45), will launch EMISAT, the primary satellite and 28 international customer satellites from Satish Dhawan Space Centre (SDSC) SHAR, Sriharikota.

“The launch is tentatively scheduled at 9.30 am on April 1 from the second launch pad, subjected to weather conditions,” ISRO said on Saturday.

The 436-kg EMISAT, based on ISRO's Indian Mini Satellite-2 (IMS-2) bus platform, is intended for electromagnetic spectrum measurement. EMISAT is an Electronic Intelligence Satellite of the Defence Research Development Organisation (DRDO), while 28 foreign satellites from four countries – Lithuania, Spain, Switzerland and the USA, which will be launched under commercial arrangements.

Apart from the satellites, it will also carry three experimental payloads. The mission was earlier planned on March 21, but was delayed mainly to ensure internal system readiness for a perfect launch. It is the first three-orbit mission for ISRO and first use of solar panel in fourth stage engine (PS4).

Though the workhorse launch vehicle of ISRO has several firsts to its credit, including injecting more than 100 satellites in space and placing them in two different orbits and switching off and switching on the PS-4 (fourth stage) in a single mission, this is the first time that PS-4 would be brought down to lower orbits to inject the satellites in three different orbits.

The PS4 orbital platform is envisaged to provide a microgravity environment for research organisations and academic institutes to perform experiments.

“In this mission, the PS4 hosts three payloads, Automatic Identification System (AIS) from ISRO, Automatic Packet Repeating System (APRS) from AMSAT (Radio Amateur Satellite Corporation), India and Advanced Retarding Potential Analyser for Ionospheric Studies (ARIS) from Indian Institute of Space Science and technology (IIST),” ISRO said.

The primary satellite, EMISAT will be injected into a 749 km orbit with an inclination of 98.376 deg, followed by two fourth stage restarts to achieve a 504 km orbit, where all foreign satellites – 24 from USA, two from Lithuania, one each from Spain and Switzerland--will be injected.

Totally weighing 220 kg, the foreign satellites included 25 3U type, two 6U type and one 2U type nano satellites. “Subsequently, the fourth stage is restarted again to achieve a 485 km orbit, to serve as an orbital platform to carry out space borne experimentation,” it said.

ISRO said AIS is for Maritime satellite applications capturing messages transmitted from ships, the APRS assists amateur radio operators in tracking and monitoring position data, while ARIS is for the structural and compositional studies of ionosphere.