• The Indian Space Research Organisation (ISRO) announced that the upper stage of PSLV-C37 rocket, which launched a record number of 104 satellites more than seven years ago, has re-entered the Earth’s atmosphere as predicted.

• PSLV-C37 was launched on February 15, 2017 with Cartosat-2D as the main payload along with another 103 satellites as co-passengers. 

• 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 470 x 494 km size. It was regularly tracked and its orbital altitude slowly decayed, primarily due to atmospheric drag effects.

• 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 the atmosphere in October first week. The re-entry occurred on October 6. 

• 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.

What is a Satellite Launching System?

• India’s space research organisation, ISRO, initiated the development of launch vehicles in the early 1970s to enable the country to independently place satellites into orbit.  

• Satellite Launch Vehicle-3 (SLV-3) was India’s first experimental satellite launch vehicle, which was an all solid, four stage vehicle weighing 17 tonnes with a height of 22m and capable of placing 40 kg class payloads in Low Earth Orbit (LEO).

• SLV-3 was successfully launched on July 18, 1980 from Sriharikota Range (SHAR), when Rohini satellite, RS-1, was placed in orbit, thereby making India the sixth member of an exclusive club of space-faring nations • The Augmented Satellite Launch Vehicle (ASLV) Program was designed to augment the payload capacity to 150 kg, thrice that of SLV-3, for Low Earth Orbits (LEO). 

• While building upon the experience gained from the SLV-3 missions, ASLV proved to be a low cost intermediate vehicle to demonstrate and validate critical technologies that would be needed for the future launch vehicles like strap-on technology, inertial navigation, bulbous heat shield, vertical integration and closed loop guidance.

Major Milestones: PSLV and GSLV

The operationalisation of Polar Satellite Launch Vehicle (PSLV) and Geosynchronous Satellite Launch Vehicle (GSLV) brought India to the forefront of launch vehicle technology.

PSLV: Known for its reliability and precision, PSLV became the workhorse of ISRO, launching satellites into polar orbits and even interplanetary missions like Mars Orbiter Mission (Mangalyaan). 

GSLV: With the ability to launch satellites into geosynchronous orbits, GSLV expanded India’s capacity to launch heavier payloads. It also enabled India to enter the global satellite launch market. 

(The author is a trainer for Civil Services aspirants.)