POEM-4 was the spent fourth stage of PSLV-C60, turned into an orbital laboratory that carried 24 experiments after releasing the SpaDeX satellites on 30 December 2024. It re-entered over the Indian Ocean on 4 April 2025.
Re-entered Earth's atmosphere on 4 April 2025, according to the public satellite catalogue.
After the two SpaDeX satellites separated at about 475 km, the PS4 stage was restarted to drop to a near-circular orbit of about 350 km at 55.2° inclination. Leftover propellant was then vented to reduce the risk of an accidental break-up, and control passed to the POEM avionics, which held it steady in three axes.
POEM-4 hosted 24 payloads: 14 from ISRO and the Department of Space and 10 from non-government groups. They tested space robotics, seed germination and bacterial growth in microgravity, green propulsion, laser ignition of pyro devices, amateur radio and new sensors. A start-up also uploaded and ran an AI model in orbit. All the payloads completed their planned experiments.
The platform itself tested a mission computer built on ISRO's Indian-made 32-bit Vikram3201 processor and a nano star sensor. Reaction wheels and cold-gas thrusters extended its life by at least 45 days compared with earlier POEMs. It completed 1,000 orbits on 4 March 2025.
ISRO and the US Space Command tracked POEM-4 as its orbit shrank to about 174 × 165 km. It re-entered and fell into the Indian Ocean at 02:33 UTC (08:03 IST) on 4 April 2025. ISRO presents such planned, tracked re-entries as part of its effort to limit space debris.