The upper stage of PSLV-37 which launched a record number of 104 satellites re-enters the Earth's atmosphere on 6 Oct 2024

PSLV-C37 was launched on 15 Feb 2017 with Cartosat-2D as the main payload along with another 103 satellites as co-passengers, namely INS-1A, INS- 1B, Al-Farabi 1, BGUSAT, DIDO-2, Nayif 1, PEASS, 88 Flock-3p satellites, and 8 Lemur-2 satellites. It created history as the first mission to launch 104 satellites with a single vehicle.

After injecting the satellites and passivation, the upper stage (PS4) was left at an orbit of approximately 470x 494 km size. It was regularly tracked by USSPACECOM as an object with NORAD id 42052 and its orbital altitude slowly decayed, primarily due to atmospheric drag effects, as shown below.

Since September 2024, IS4OM (ISRO System for Safe and Sustainable Space Operations Management) regularly monitored the orbital decay as part of its regular activities and predicted the re-entry into atmosphere in the first week of October 2024.

The orbit had decayed to a size of 134 x148 km, as of 6th the October, 12:45 UTC. As per US Space Command (USSPACECOM) prediction published in Space Track, the re-entry took place at 06 Oct 2024 15:49 UTC (+/-1 minute of uncertainty), while IS4OM prediction also showed that the re-entry would occur on 06 Oct 2024 at 15:48:25 UTC. The corresponding impact point is in North Atlantic Ocean.

The atmospheric re-entry of the rocket body within 8 years of its launch is fully compliant with the international debris mitigation guidelines, in particular, the guideline of Inter-Agency Space Debris coordination committee (IADC) that recommends limiting the post-mission orbital life of a defunct object in Low-Earth orbit (LEO) to 25 years.

This requirement was met by properly designing passivation sequence which lowered the orbit of PS4 after the injection of the payloads. At present, special initiatives are undertaken to ensure that the residual orbital lifetime of the PSLV upper stages is reduced to 5 years or even less by actively de-orbiting them to lower altitude orbits through engine re-starts, as in PSLV-C38, PSLV-40, PSLV-C43, PSLV-C56, and PSLV-C58 missions. Controlled re-entry of the upper stage is also envisaged for the disposal of the upper stage in future PSLV missions. As part of its longstanding commitment to preserve long term sustainability of outer space activities, ISRO will continue to implement proactive measures to meet the objectives of Debris Free Space Mission (DFSM) by the year 2030.

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