25-hour countdown begins for 56th Mission of India’s 321-tonne PSLV rocket

The 25-hour countdown to the 56th flight of India's PSLV rocket began at 10:56 am Friday, as the 321-tonne rocket waits to blast off from India's spaceport at 11:56 am on Saturday. In what is dubbed as 'PSLV C-54/EOS-06' mission, the rocket designed and developed by Indian Space Agency ISRO will be carrying nine satellites. While the primary passenger is ISRO's own EOS-6 or Oceansat, the eight co-passengers will be small satellites, each of which weigh below 20 kg.

EOS-6 is the third-generation satellite in the Oceansat series. This is to provide continuity services of Oceansat-2 spacecraft with enhanced payload specifications as well as application areas.

This mission gains significance as it is among the longest to be undertaken by the PSLV rocket. From the time the rocket lifts off from the first launchpad of Satish Dhawan Space Centre in Sriharikota, it would take more than two hours and six minutes for the final satellite to separate from the rocket and get injected into orbit.

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Given that there are nine satellites to be ejected into orbit, the PSLV rocket will be performing two manoeuvres to change its orbit. According to ISRO, the first satellite EOS-6 will separate at an altitude of 742 km. Thereafter, the first orbit change will be performed by deploying the OCTs (Orbit Change Thrusters) and the rocket's final stage will be brought to a lower altitude of 708 km. At the end of the second orbit change, the rocket's final stage will be brought from 563 km altitude to 514 km.

Orbit changes are carried out because each satellite is meant for a particular purpose and the user/customer requires the satellite to be in a particular orbit at a specific altitude above the earth's surface, to perform its job suitably. Hence, the mission is planned in such a way that the respective satellites get placed in their designated orbits.

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The passenger satellites in this mission include 'BhutanSat', a satellite that India has built for Bhutan and their scientific community. In addition to this, there will be satellites designed and built by Indian startups - 'Anand' imaging satellite from Pixxel, two satellites 'Thybolt' from Dhruva Space and four 'Astrocast' satellites from an American firm will be riding as co-passengers, on a commercial basis. These companies are customers of ISRO's commercial arm NSIL or New Space India Limited.

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