ISRO to setup space tracking radar in Northeast, telescope in Ladakh

Indian Space agency ISRO is working on setting up facilities across the country to track space objects in Low Earth orbit (about 500-1000kms above the Earth) and potentially, even higher. This comes at a time when Low Earth Orbit is getting congested with satellites and space debris, and the risk of accidental collision is growing rapidly. "The establishment of an optical telescope at Hanle, Ladakh, is underway. Design and review of an indigenous phased array space object tracking radar was completed by a national-level expert committee in 2025. Efforts to establish an indigenously developed radar in the north-eastern part of India are underway. The Baker Nunn Schmidt Telescope (BNST), currently being refurbished at Nainital, under collaboration with ARIES, is also expected to enhance space object tracking capability in the near future," ISRO stated in the Indian Space Situational Awareness Report (ISSAR) for 2025.

At present, ISRO's Multi-Object Tracking Radar (MOTR) at the Satish Dhawan Space Centre in Sriharikota tracks space objects, including Indian rocket bodies and satellites. Multi Object Tracking Radar (MOTR) is an L-Band Active Phased Array Radar designed to track multiple objects. It is a long range tracking radar capable of tracking objects with a radar cross section of 0.25square meters, up to a range of 1000km.

By using radio waves and their reflections to estimate the position of objects, radars operate in both day and night conditions. Inaddition to radars, ISRO is also planning to install optical telescopes, which are only capable of night-time operations in regions with a clear, unobstructed view of the dark sky. This is why a high-altitude cold desert region such as Ladakh has been chosen for installation of telescope. These telescopes are meant to detect space objects(satellites) using sunlight that is reflected off them. A combination of radars and optical telescopes installed at various locations is essential for Space Situational Awareness(SSA), which is the is the process of tracking, monitoring, and predicting the positions of satellites and space debris in Earth’s orbit. This information helps ensure safe, sustainable space operations. It involves gathering data via ground-based sensors and telescopes to avoid collisions and assess risks to space assets.

Just like a person on the ground can see an overflying aircraft only for a minute or two, a tracking facility(radar or antenna) can see a satellite or debris only when it is within its range. Therefore, multiple tracking stations positioned at vantage locations across the globe are required to have near-complete coverage of objects in Earth's orbit.

The ever-increasing threat of collisions between space objects

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'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.

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. Based on these alerts, ISRO performed a total of 18 collision-avoidance manoeuvres: 4 for satellites in Geosynchronous Earth Orbit, and 14 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 collision 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.