ISRO performed 18 manoeuvres to avert collisions of its 53 satellites

The Government-run Indian space agency ISRO has a total of 53 operational satellites circling the Earth. This includes 22 satellites in Low Earth Orbit (about 500-1000kms above the earth) and 31 satellites in Geosynchronous Earth Orbit(about 36,000kms above the Earth, ISRO has revealed. Typically, the satellites placed in Low Earth orbit are meant for Earth-imaging or experiments, while the satellites placed in Geosynchronous orbit are meant for weather observation, communication, navigation.

ISRO'sIndian Space Situational Awareness Report (ISSAR) for 2025 mentions that there is a growing congestion in Low Earth Orbit, owing to the exponential growth in the number of satellites being placed there and the mounting threat of space debris. The report mentions that the Combined Space Operations Center (CSpOC) of America's USSPACECOM had issued 1,50,000 close approach alerts, which warn operators when satellites and debris pass within a dangerously close distance. Such constant monitoring of space objects is vital for avoiding collisions that could create more debris, which could heighten the risk for safe operations in space. Space debris and satellites in Low earth orbit travel at speeds of 28,000kmph, which means even the smallest pieces of debris colliding with a large object can generate more debris.

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Based on these alerts, ISRO performed a total of 18 collision avoidance manoeuvres: 4 for satellites placed in Geosynchronous Earth Orbit, while 14 collision avoidance manoeuvres were performed for satellites in Low Earth orbit. The $1.2bn NASA-ISRO Synthetic Aperture Radar(NISAR) satellite was also among those that had to perform a collission avoidance manoeuvre, ISRO said.

As the name suggests, a collision avoidance manoeuvre is a planned trajectory adjustment, where the satellite fires its thrusters to adjust its orbit. Such manoeuvres are done when the probability of collision with debris or another satellite exceeds a safe threshold.

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Satellite operators also routinely perform orbit maintenance manoeuvres to counter the minor changes in a satellite's orbital path caused by natural factors such as atmospheric drag, gravity, among others. Wherever feasible, collision avoidance requirements were met by adjusting orbit maintenance manoeuvres to avoid exclusive collision avoidance manoeuvres, ISRO said. Manoeuvring satellites in space is a task that consumes the onboard fuel of the satellite. Given that satellites depend on the limited quantity of fuel in their onboard tanks, every manoeuvre proves costly and reduces the life of the satellite. This is because, satellites go defunct when they deplete their onboard fuel and lose manoeuvrability.

ISRO's report noted that the projected deployment of multiple large constellations indicates a scenario where active satellites may outnumber space debris within the current decade, and a consequent increase in the burden of space traffic coordination.

"Out of the 10,749 Starlink satellites(belonging to Elon Musk's firm), 9396 satellites were still in orbit and 1,353 satellites re-entered the Earth’s atmosphere by the end of 2025. In addition, constellations like HulianwangDigui, Kuiper, USA-NRO (National Reconnaissance Office) launched 136, 180, and 99 satellites in 2025, respectively," it was added.