ISRO’s ‘zero orbital debris’ milestone & the space debris crisis | Explained Premium

The Hindu explores the growing issue of space debris, and how a recent mission by ISRO was able to achieve a zero debris target

The story so far: The Indian Space Research Organisation (ISRO) has said its PSLV-C58/XPoSat mission has practically left zero debris in earth’s orbit. The space agency explained that the last stage of the Polar Satellite Launch vehicle (PSLV) used in the mission was transformed into a kind of orbital station — called the PSLV Orbital Experimental Module-3 (POEM-3) — before it was left to re-enter the earth’s atmosphere instead of floating in orbit once its mission was completed.

ISRO said that after it completed the primary mission of injecting all satellites into their target orbits, the fourth stage of the PSLV was transformed into the POEM-3. It was subsequently de-orbited from 650 kilometres to 350 kilometres, rendering it more susceptible to being pulled towards the earth and burning up in the atmosphere. ISRO also said it “passivated the stage,” meaning dumped its fuel, to avoid an explosion that could have flung small pieces of debris into orbit.

Developed by the Vikram Sarabhai Space Centre (VSSC) as an inexpensive space platform, POEM uses the spent fourth stage of a PSLV rocket as an orbital platform. Used for the first time in the PSLV-C53 mission in June 2022, ISRO had POEM orbit the earth as a stabilised platform to perform in-orbit scientific experiments with various payloads.

POEM is powered by solar panels mounted on the fuel tank of the rocket’s fourth stage and a lithium-ion (Li-ion) battery. It has a dedicated navigation, guidance, and control (NGC) system to stabilise its altitude along with helium control thrusters. The NGC system has four Sun sensors, a magnetometer, and gyroscopes, and talks to ISRO’s NavIC satellite constellation for navigation. POEM also has a telecommand system to communicate with the ground station.

ISRO first demonstrated the reuse of the spent fourth stage of its rocket in its PSLV C-44 mission in 2019. After satellites were injected in the target orbits, the fourth stage, carrying a student payload called Kalamsat-V2, was moved to a higher circular orbit of 443 km and stayed there, allowing the payload to make observations.

ISRO launched the PSLV C-58 mission from the Satish Dhawan Space Centre in Sriharikota on January 1, 2024. After deploying the XpoSat satellite in its desired orbit of 650 km, the fourth stage, now called POEM-3, was lowered to a 350-km high circular orbit. The lower a satellite is in orbit around the earth, the more drag it experiences and the more energy it needs to expend to stay in orbit.

POEM-3 featured nine payloads: two each from VSSC and Bellatrix Aerospace Pvt Ltd, one each from the start-ups TakeMe2Space, Inspecity Space Labs Pvt Ltd., Dhruva Space, and from LBS Institute of Technology, KJ Somaiya Institute of Technology, and ISRO’s Physics Research Laboratory, Ahmedabad.