On February 15, 2017, PSLV-C37, the 39th mission of the workhorse launch vehicle of ISRO, injected ISRO’s Cartosat-2 Series Satellite weighing 714 kg and two ISRO Nano-satellites namely INS-1A (8.4 kg) & INS-1B (9.7 kg) and 101 Nano-satellites, from six foreign countries into a Sun-Synchronous Orbit (SSO) at an orbit of 506 km above earth, with an inclination of 97.46°. The mass of nano-satellites varied from 1 to 10 kg. The total weight of all the 104 satellites carried on-board PSLV-C37 was 1378 kg.
The large number of satellites in this mission demanded adopting innovative approaches in satellite accommodation and mission design.
Apart from conventional satellite adapters, namely, Payload Adapter (PLA) and Multiple Satellite Adapter (MSA), six numbers of custom made adapters were newly configured and used to house the nano satellites. Some of these adapters allowed multi tier mounting of satellites and few of them were accommodated on the Vehicle Equipment Bay itself. This architecture enabled the optimal utilisation of the payload volume as well as capability.
Next requirement was managing safe separation of these large numbers of satellites within the constraints of limited visibility duration of ground stations and maintaining safe distance between the separated satellites over a longer period of time.
This was managed by designing a unique sequencing and timing for separating the satellites and with complex manoeuvering of PS4 stage to which satellites are attached. The separation sequence, direction and timing were finalised based on extensive study to ensure safe distance among the 105 objects (including PS4 stage) in orbit, which renders 5460 number of pairs.
The next major requirement was to ensure reaching separation command from launcher to respective satellites honoring the predefined sequence, which involves a complex electrical wiring scheme. Any error in the wiring may result in release of wrong satellite leading to undesirable situation of collision between them.
Another innovative feature in this mission was capturing all the separation events of vehicle stages and 104 satellites using a comprehensive video imaging system onboard.
Meticulous planning was done at launch complex, SDSC SHAR on assembling and handling of all sub systems and satellite preparation. Apart from launching SSO, sub GTO and multi orbit missions, PSLV has established once again as a workhorse vehicle to undertake very complex missions like PSLV-C37.
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