Space Debris & ISRO's Collision Avoidance Manoeuvres: An NDA Science Explainer

On 5 August 2026, the Department of Space told Parliament that satellites in Low Earth Orbit (below 2,000 km) face the highest collision risk, that 20 of India's 22 active LEO satellites are in that higher-risk category, and that ISRO executed 20 Collision Avoidance Manoeuvres (CAMs) in 2025 and 9 so far in 2026. For an NDA aspirant this is an excellent space science topic — orbital mechanics, an environmental problem in a new domain, and international law, all in one.

The news in one frame

The essentials:

• Risk zone: Low Earth Orbit, below 2,000 km altitude, where the space-object population is densest.
• India's exposure: 20 of 22 active Indian satellites in LEO are at higher risk.
• Action: 20 CAMs executed in 2025; 9 so far in 2026.
• Policy: a framework on State liability for third-party damage caused by Indian space objects, formulated by IN-SPACe, is under consideration.
• International engagement: India participates in the Inter-Agency Space Debris Coordination Committee (IADC), the UN Working Group on Long-Term Sustainability (UN-LTS), the Expert Group on Space Situational Awareness, and space-traffic-management and debris working groups of the IAA and the IAF.
• Contribution: ISRO provided substantial technical input to the revised IADC space-debris mitigation guidelines.

What space debris is, and why a 1 cm fragment matters

Start with the physics, which is the examinable core:

• Space debris (orbital debris) is any human-made object in orbit that no longer serves a purpose: spent rocket upper stages, dead satellites, fragments from explosions and collisions, discarded hardware, even paint flakes and frozen propellant droplets.
• The danger is not mass but speed. In LEO an object travels at roughly 7 to 8 km per second — around 28,000 km/h. A head-on encounter can approach a relative velocity of 15 km/s.
• Kinetic energy scales with the square of velocity, so a fragment just 1 centimetre across carries the destructive energy of a small exploding device. Shielding can stop objects below about 1 cm; anything larger must be avoided, not absorbed.
• Orbital lifetime depends on altitude. Below roughly 400-500 km, residual atmospheric drag pulls debris down within years and it burns up on re-entry. Above about 800 km, drag is negligible and debris can persist for centuries.
• Kessler syndrome — proposed by Donald Kessler — is the runaway scenario in which collisions produce fragments that cause further collisions, until a debris belt makes certain orbits unusable. It is the reason mitigation is urgent rather than optional.

This applied physics is exactly what the NDA GAT science notes build.

The orbit regimes

A reliable classification question:

A geostationary satellite has an orbital period of exactly 24 hours and appears fixed over one point; a geosynchronous satellite matches Earth's rotation period but need not stay over one spot. At end of life, GEO satellites are moved to a graveyard orbit a few hundred kilometres higher, while LEO satellites are deorbited to burn up — the "25-year rule", now being tightened.

How a collision avoidance manoeuvre works

The operational chain:

1. Track — ground radars and optical telescopes catalogue objects. India's Project NETRA (Network for Space Object Tracking and Analysis) builds this capability, and IS4OM — ISRO System for Safe and Sustainable Space Operations, at Bengaluru — is the dedicated control centre.
2. Predict — orbits are propagated forward to compute a conjunction: the predicted miss distance and the probability of collision.
3. Decide — if the probability crosses a threshold, a manoeuvre is planned.
4. Manoeuvre — the satellite fires thrusters to change velocity slightly, shifting its orbit enough to miss. Every CAM spends propellant, which directly shortens the satellite's working life — the real cost of debris.
5. Verify — the new orbit is confirmed and the satellite resumes its mission.

Mitigation measures beyond avoidance: passivating spent stages by venting leftover fuel and discharging batteries so they cannot explode; deorbiting at end of life; design for demise so components burn up fully; and India's stated goal of debris-free space missions by 2030.

These themes recur in the NDA daily current affairs.

The law of outer space

Round out with the treaty set — high-yield and often mismatched:

• Outer Space Treaty, 1967 — the foundation. Space is the province of all mankind; no national appropriation of celestial bodies; no weapons of mass destruction in orbit or on celestial bodies; States bear international responsibility for national activities, including those of private entities.
• Rescue Agreement, 1968 — assistance to and return of astronauts and space objects.
• Liability Convention, 1972 — the launching State is absolutely liable for damage caused on the surface of the Earth or to aircraft in flight, and liable on a fault basis for damage in outer space.
• Registration Convention, 1975 — space objects must be registered with the UN.
• Moon Agreement, 1979 — the least ratified of the five.
• UNOOSA — the UN Office for Outer Space Affairs, based in Vienna, servicing COPUOS, the Committee on the Peaceful Uses of Outer Space.
• India's domestic layer: the Indian Space Policy 2023, with IN-SPACe as the single-window authoriser and regulator for non-government entities, NSIL as the commercial arm and ISRO as the R&D agency.

The revision hook: LEO = below ~2,000 km, densest and riskiest; 20 of India's 22 active LEO satellites at higher risk; ISRO did 20 CAMs in 2025 and 9 in 2026; orbital speed ~7-8 km/s, so a 1 cm fragment is destructive; Kessler syndrome = collision cascade; MEO for navigation, GEO at 35,786 km for communication, polar/sun-synchronous ~600-800 km for imaging; graveyard orbit for GEO, deorbit for LEO; Project NETRA and IS4OM (Bengaluru) track objects; debris-free missions target 2030; Outer Space Treaty 1967 (no appropriation, no WMD, State responsibility), Liability Convention 1972 (launching State — absolute on Earth, fault-based in space), Registration Convention 1975; UNOOSA/COPUOS at Vienna; IN-SPACe regulates, NSIL commercialises.

Why it matters

For the essay/interview and bigger picture:

• Everyday dependence: navigation, weather forecasting, disaster warning, broadcasting, banking timestamps and military reconnaissance all ride on satellites. Losing an orbital band is not an abstract loss.
• A commons problem: orbit is a shared resource that no one owns and everyone can degrade — the classic tragedy of the commons, now above our heads.
• Strategic stakes: debris-generating events, including anti-satellite tests, endanger every user's assets, which is why mitigation norms are also a security conversation.

Exam relevance in one paragraph

For NDA GAT, retain: Low Earth Orbit, below about 2,000 kilometres, is the most congested and collision-prone region of space, and of India's 22 active LEO satellites 20 are at higher risk, prompting ISRO to execute 20 Collision Avoidance Manoeuvres in 2025 and 9 so far in 2026; objects in LEO travel at roughly 7 to 8 kilometres per second, so even a one-centimetre fragment carries destructive energy, and the runaway collision cascade first described by Donald Kessler is known as the Kessler syndrome; debris above about 800 kilometres can persist for centuries because atmospheric drag is negligible, whereas below 400-500 kilometres it re-enters within years; India tracks objects through Project NETRA and the IS4OM centre at Bengaluru, participates in the Inter-Agency Space Debris Coordination Committee and UN long-term-sustainability work, and targets debris-free space missions by 2030, while a framework on third-party liability formulated by IN-SPACe is under consideration; in law, the Outer Space Treaty of 1967 bars national appropriation and weapons of mass destruction and fixes State responsibility, the Liability Convention of 1972 makes the launching State absolutely liable for damage on Earth or to aircraft and liable on fault for damage in space, and the Registration Convention of 1975 requires registration with the UN, all serviced by UNOOSA and COPUOS at Vienna; orbits run LEO for remote sensing, MEO for navigation and geostationary orbit at 35,786 kilometres for communication. For the essay, frame it as keeping orbit usable for the next generation.

🎯 Practice MCQs

Q1. Low Earth Orbit extends up to an altitude of about: (a) 2,000 km (b) 200 km (c) 35,786 km (d) 100 km → (a) — about 2,000 km.

Q2. Typical orbital speed in LEO is roughly: (a) 7-8 km/s (b) 1 km/s (c) 100 km/s (d) 0.5 km/s → (a) — about 28,000 km/h.

Q3. ISRO executed how many collision avoidance manoeuvres in 2025? (a) 20 (b) 2 (c) 100 (d) 9 → (a) — 20 (9 so far in 2026).

Q4. The runaway collision-cascade scenario is called the: (a) Kessler syndrome (b) Coriolis effect (c) Doppler shift (d) Chandrasekhar limit → (a) — the Kessler syndrome.

Q5. A geostationary satellite orbits at an altitude of about: (a) 35,786 km (b) 2,000 km (c) 800 km (d) 400 km → (a) — over the equator.

Q6. Navigation satellites such as GPS typically occupy: (a) Medium Earth Orbit (b) LEO (c) GEO (d) polar orbit → (a) — MEO.

Q7. Sun-synchronous orbits are used mainly for: (a) remote sensing with consistent lighting (b) television broadcast (c) deep-space probes (d) manned flight → (a) — Earth imaging.

Q8. India's space-object tracking project is: (a) Project NETRA (b) Project Arrow (c) Project Tiger (d) Project Varsha → (a) — Network for Space Object Tracking and Analysis.

Q9. ISRO's dedicated space-situational-awareness control centre is: (a) IS4OM, Bengaluru (b) VSSC, Thiruvananthapuram (c) SDSC, Sriharikota (d) SAC, Ahmedabad → (a) — IS4OM.

Q10. Retired geostationary satellites are moved to a: (a) graveyard orbit (b) polar orbit (c) transfer orbit (d) parking orbit at 400 km → (a) — a higher disposal orbit.

Q11. The foundational treaty of space law is the: (a) Outer Space Treaty, 1967 (b) Moon Agreement, 1979 (c) Registration Convention, 1975 (d) Rescue Agreement, 1968 → (a) — the 1967 Treaty.

Q12. Under the Liability Convention, 1972, liability for damage on Earth is: (a) absolute (b) fault-based (c) shared equally (d) non-existent → (a) — absolute (fault-based for damage in space).

Q13. UNOOSA is headquartered at: (a) Vienna (b) Geneva (c) New York (d) Paris → (a) — Vienna.

Q14. India's single-window authoriser for private space activity is: (a) IN-SPACe (b) NSIL (c) DRDO (d) TRAI → (a) — IN-SPACe (NSIL is the commercial arm).

Q15. "Passivation" of a spent rocket stage means: (a) venting fuel and discharging batteries to prevent explosion (b) painting it (c) refuelling it (d) parking it in GEO → (a) — removing stored energy.

📋 How this gets asked (PYQ pattern)

Space science is a reliable NDA sci-tech set. The reliable framings are orbit altitudes and their uses (LEO, MEO, GEO at 35,786 km), the Kessler syndrome, treaty-to-year matching (Outer Space 1967, Liability 1972, Registration 1975), and Indian body identification (ISRO, IN-SPACe, NSIL, NETRA). A common trap places navigation satellites in GEO (they are in MEO) or makes liability fault-based for damage on Earth (it is absolute). The fresh 2026 hook is the CAM count and the LEO risk figures — ideal for "which orbit / which treaty / which body" items. We reference the pattern, not any exact past question.

Preparing for NDA? Space science, orbits and international space law are high-yield GAT topics and strong SSB conversation on India's strategic capability. Follow our daily NDA current affairs and train with serving-officer faculty in the upcoming Cavalier courses in Delhi.

✍️ Written by Aditya Tiwari — Physics, space science & current-affairs faculty at The Cavalier. Reviewed by the Cavalier Faculty Desk. The Cavalier, founded by ex-Army officers, has trained NDA/CDS/SSB aspirants since 2001 (Facebook · YouTube).

Source: PIB / Department of Space, 5 August 2026. Facts cross-verified with independent sources.