Upper stage of historic PSLV-37 mission re-enters Earth’s atmosphere eight years after launch: ISRO

The Indian Space Research Organisation (ISRO) informed that the upper stage of the Polar Satellite Launch Vehicle C-37 (PSLV C-37 mission) re-entered the Earth’s atmosphere on October 6.

The PSLV-C37 mission was launched on February 15, 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. The space agency created history as it was the first mission to launch 104 satellites with a single vehicle.

Then ISRO chairman A.S. Kiran Kumar speaks during a press conference after the successeful launch of a record 104 satellites on-board PSLV-C37/Cartosat2 Series from Sriharikota on February 15, 2017. | Photo Credit: File photo

After injecting the satellites and passivation, the upper stage (PS4) was left at an orbit of approximately 470x494 km.

“It was regularly tracked by US Space Command (USSPACECOM) as an object with NORAD id 42052. Its orbital altitude slowly decayed, primarily due to atmospheric drag effects,” ISRO informed on October 8.

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

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

The atmospheric re-entry of the rocket body within eight 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.

According to ISRO, this requirement was met by properly designing a passivation sequence, which lowered the orbit of PS4 after 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,” the ISRO stated.