The Top 50 Space Debris Items That Should Be Removed: A Critical Look at Orbital Threats

As of October 25, 2025, the growing problem of space debris in low Earth orbit (LEO) poses a significant risk to operational satellites, the International Space Station, and future space missions. Space debris, consisting of defunct satellites, spent rocket stages, and fragments from collisions or explosions, orbits Earth at speeds up to 28,000 kilometers per hour. A collision could trigger a cascade of further debris, known as the Kessler syndrome, potentially rendering certain orbits unusable. There are tens of thousands of trackable debris objects larger than 10 cm, with millions more smaller pieces. To mitigate this, priority targets have been identified for active debris removal (ADR) – missions to capture and deorbit these hazards.

Breakdown of Debris by Country/Origin and Type

Of the top 50 objects, 34 (68%) are Russian or Soviet in origin (primarily SL-16 and SL-8 rocket bodies), 10 (20%) from China (mostly CZ-series), 3 (6%) from the US (Iridium satellites), 2 (4%) from Europe (ENVISAT and ARIANE 5 R/B), and 1 (2%) from Japan (H-2 R/B). Notably, 44 are rocket bodies and 6 are payloads, with 76% launched before 2000. This distribution reflects historical launch practices and emerging trends in space activity.

This top 50 list focuses on intact derelict objects (non-operational payloads and rocket bodies) in LEO that are most likely to contribute to debris growth through collisions. The selection methodology is a three-step process:

1. Aggregate Empirical Collision Risk: Using data from over three years of conjunction events (close approaches with a collision probability greater than 1 in a million), an interim list is created, filtered to objects with sufficient conjunctions, above 700 km altitude, and at least 600 kg dry mass.
2. Long-term Statistical Risk Adjustment: A “Cluster Factor” is added based on the object’s location in high-density altitude bands (700-810 km, 810-890 km, 890-1100 km), prioritizing those in persistent orbits with high future collision probabilities.
3. Coupling via Removal: The list is refined by simulating incremental removals, accounting for how removing one object reduces risks for others due to interconnected conjunctions.

Removing these 50 objects could reduce the overall debris-generating potential in LEO by nearly 50%, dramatically lowering the risk of catastrophic breakups that produce lethal, non-trackable fragments down to 1 cm in size. This would enhance the safety and sustainability of space operations, with even the top 10 providing about 30% risk reduction.

Below is the full list of the top 50 items, ranked by their adjusted collision risk (in kg). For each, the identifier (NORAD SATNO), type, mass, inclination, average altitude, launch details, aggregate empirical collision risk (kg), number of conjunctions, cluster band, and reasons for removal are provided – primarily due to high mass (increasing collision consequences), location in crowded orbital clusters, frequent close approaches, and long orbital lifetime (>75 years), which amplifies the potential for debris creation.

1. SL-16 R/B (SATNO 28353): Rocket Body, 9000 kg, 71.0° inclination, 844 km altitude. Launched 2004 (Russia). Aggregate risk 410 kg from 345 conjunctions in C840 cluster; its massive size could generate thousands of fragments if collided.
2. ENVISAT (SATNO 27386): Payload, 8211 kg, 98.3° inclination, 762 km altitude. Launched 2002 (Europe). Aggregate risk 179 kg from 282 conjunctions in C775 cluster; large defunct Earth observation satellite near operational satellites, prime target to prevent chain reactions.
3. H-2 R/B (SATNO 24279): Rocket Body, 2700 kg, 98.7° inclination, 1082 km altitude. Launched 1996 (Japan). Aggregate risk 115 kg from 134 conjunctions in C1000 cluster; long-term statistical risk in persistent orbit.
4. CZ-2C R/B (SATNO 39203): Rocket Body, 4000 kg, 98.4° inclination, 704 km altitude. Launched 2013 (China). Aggregate risk 107 kg from 146 conjunctions in C775 cluster; post-2000 object highlighting recent contributions.
5. SL-8 R/B (SATNO 16292): Rocket Body, 1435 kg, 82.9° inclination, 974 km altitude. Launched 1985 (Russia). Aggregate risk 86 kg from 33 conjunctions in C1000 cluster; part of populous family, removal reduces intact-on-intact risks.
6. SL-16 R/B (SATNO 19120): Rocket Body, 9000 kg, 71.0° inclination, 827 km altitude. Launched 1988 (Russia). Aggregate risk 117 kg from 368 conjunctions in C840 cluster; heavy mass amplifies debris potential.
7. COSMOS 2237 (SATNO 22565): Payload, 3200 kg, 70.8° inclination, 851 km altitude. Launched 1993 (Russia). Aggregate risk 106 kg from 65 conjunctions in C840 cluster; defunct military satellite with high fragment encounters.
8. COSMOS 2334 (SATNO 24304): Payload, 820 kg, 82.9° inclination, 986 km altitude. Launched 1996 (Russia). Aggregate risk 59 kg from 16 conjunctions in C1000 cluster; persistent orbit increases long-term threat.
9. SL-16 R/B (SATNO 19650): Rocket Body, 9000 kg, 71.0° inclination, 839 km altitude. Launched 1988 (Russia). Aggregate risk 75 kg from 264 conjunctions in C840 cluster.
10. CZ-2D R/B (SATNO 44548): Rocket Body, 4000 kg, 98.3° inclination, 757 km altitude. Launched 2019 (China). Aggregate risk 56 kg from 228 conjunctions in C775 cluster; recent addition underscoring need for better end-of-life practices.
11. SL-8 R/B (SATNO 8344): Rocket Body, 1435 kg, 74.1° inclination, 757 km altitude. Launched 1975 (Russia). Aggregate risk 43 kg from 120 conjunctions in C775 cluster; old object elevated by coupling effects.
12. SL-16 R/B (SATNO 25400): Rocket Body, 9000 kg, 98.8° inclination, 805 km altitude. Launched 1998 (Russia). Aggregate risk 40 kg from 333 conjunctions in C775 cluster; cluster adjustment prioritizes it.
13. SL-8 R/B (SATNO 23774): Rocket Body, 1435 kg, 83.0° inclination, 975 km altitude. Launched 1996 (Russia). Aggregate risk 33 kg from 63 conjunctions in C1000 cluster.
14. SL-8 R/B (SATNO 16012): Rocket Body, 1435 kg, 74.1° inclination, 767 km altitude. Launched 1985 (Russia). Aggregate risk 40 kg from 85 conjunctions in C775 cluster.
15. SL-16 R/B (SATNO 20625): Rocket Body, 9000 kg, 71.0° inclination, 842 km altitude. Launched 1990 (Russia). Aggregate risk 48 kg from 345 conjunctions in C840 cluster.
16. SL-16 R/B (SATNO 25407): Rocket Body, 9000 kg, 71.0° inclination, 838 km altitude. Launched 1998 (Russia). Aggregate risk 46 kg from 327 conjunctions in C840 cluster.
17. IRIDIUM 17 (SATNO 24870): Payload, 689 kg, 86.4° inclination, 766 km altitude. Launched 1997 (US). Aggregate risk 35 kg from 155 conjunctions in C775 cluster; non-operational comms satellite.
18. SL-16 R/B (SATNO 24298): Rocket Body, 9000 kg, 70.8° inclination, 851 km altitude. Launched 1996 (Russia). Aggregate risk 44 kg from 282 conjunctions in C840 cluster.
19. CZ-4C R/B (SATNO 39261): Rocket Body, 2000 kg, 98.9° inclination, 779 km altitude. Launched 2013 (China). Aggregate risk 33 kg from 173 conjunctions in C775 cluster.
20. SL-16 R/B (SATNO 17590): Rocket Body, 9000 kg, 71.0° inclination, 835 km altitude. Launched 1987 (Russia). Aggregate risk 41 kg from 349 conjunctions in C840 cluster.
21. CZ-4C R/B (SATNO 39014): Rocket Body, 2000 kg, 63.4° inclination, 994 km altitude. Launched 2012 (China). Aggregate risk 25 kg from 72 conjunctions in C1000 cluster.
22. SL-16 R/B (SATNO 23405): Rocket Body, 9000 kg, 71.0° inclination, 841 km altitude. Launched 1994 (Russia). Aggregate risk 34 kg from 366 conjunctions in C840 cluster.
23. CZ-2D R/B (SATNO 41858): Rocket Body, 4000 kg, 98.6° inclination, 769 km altitude. Launched 2016 (China). Aggregate risk 25 kg from 247 conjunctions in C775 cluster.
24. SL-8 R/B (SATNO 21088): Rocket Body, 1435 kg, 82.9° inclination, 973 km altitude. Launched 1991 (Russia). Aggregate risk 21 kg from 42 conjunctions in C1000 cluster.
25. CZ-2C R/B (SATNO 28480): Rocket Body, 4000 kg, 98.2° inclination, 802 km altitude. Launched 2004 (China). Aggregate risk 25 kg from 138 conjunctions in C775 cluster.
26. SL-16 R/B (SATNO 22220): Rocket Body, 9000 kg, 71.0° inclination, 836 km altitude. Launched 1992 (Russia). Aggregate risk 30 kg from 330 conjunctions in C840 cluster.
27. SL-16 R/B (SATNO 16182): Rocket Body, 9000 kg, 71.0° inclination, 837 km altitude. Launched 1985 (Russia). Aggregate risk 29 kg from 362 conjunctions in C840 cluster.
28. SL-16 R/B (SATNO 23705): Rocket Body, 9000 kg, 71.0° inclination, 841 km altitude. Launched 1995 (Russia). Aggregate risk 28 kg from 333 conjunctions in C840 cluster.
29. SL-16 R/B (SATNO 22566): Rocket Body, 9000 kg, 71.0° inclination, 841 km altitude. Launched 1993 (Russia). Aggregate risk 31 kg from 296 conjunctions in C840 cluster.
30. SL-16 R/B (SATNO 22803): Rocket Body, 9000 kg, 71.0° inclination, 835 km altitude. Launched 1993 (Russia). Aggregate risk 26 kg from 343 conjunctions in C840 cluster.
31. SL-8 R/B (SATNO 4589): Rocket Body, 1435 kg, 74.1° inclination, 748 km altitude. Launched 1970 (Russia). Aggregate risk 19 kg from 98 conjunctions in C775 cluster; vintage object with persistent threat.
32. SL-16 R/B (SATNO 26070): Rocket Body, 9000 kg, 71.0° inclination, 840 km altitude. Launched 2000 (Russia). Aggregate risk 23 kg from 301 conjunctions in C840 cluster; high mass and conjunctions.
33. SL-16 R/B (SATNO 17974): Rocket Body, 9000 kg, 71.0° inclination, 834 km altitude. Launched 1987 (Russia). Aggregate risk 22 kg from 354 conjunctions in C840 cluster; coupling effects with other SL-16s.
34. SL-16 R/B (SATNO 22285): Rocket Body, 9000 kg, 71.0° inclination, 841 km altitude. Launched 1992 (Russia). Aggregate risk 22 kg from 342 conjunctions in C840 cluster; high conjunctions with fragments.
35. SL-8 R/B (SATNO 19770): Rocket Body, 1435 kg, 74.0° inclination, 758 km altitude. Launched 1989 (Russia). Aggregate risk 16 kg from 101 conjunctions in C775 cluster; part of SL-8 family.
36. SL-16 R/B (SATNO 23088): Rocket Body, 9000 kg, 71.0° inclination, 842 km altitude. Launched 1994 (Russia). Aggregate risk 19 kg from 343 conjunctions in C840 cluster; pre-2000 abandonment in high-risk zone.
37. CZ-2C R/B (SATNO 31114): Rocket Body, 4000 kg, 98.4° inclination, 825 km altitude. Launched 2007 (China). Aggregate risk 19 kg from 209 conjunctions in C840 cluster; increasing Chinese presence.
38. SL-16 R/B (SATNO 31793): Rocket Body, 9000 kg, 71.0° inclination, 843 km altitude. Launched 2007 (Russia). Aggregate risk 17 kg from 305 conjunctions in C840 cluster; adjusted for coupling in SL-16 sequence.
39. CZ-4B R/B (SATNO 32063): Rocket Body, 2000 kg, 98.2° inclination, 719 km altitude. Launched 2007 (China). Aggregate risk 12 kg from 100 conjunctions in C775 cluster; meets mass/altitude filters.
40. SL-8 R/B (SATNO 9023): Rocket Body, 1435 kg, 74.0° inclination, 755 km altitude. Launched 1976 (Russia). Aggregate risk 12 kg from 116 conjunctions in C775 cluster; empirical conjunctions qualify it.
41. SL-8 R/B (SATNO 11427): Rocket Body, 1435 kg, 74.0° inclination, 763 km altitude. Launched 1979 (Russia). Aggregate risk 11 kg from 94 conjunctions in C775 cluster; grouped inclination aids multi-removal.
42. IRIDIUM 63 (SATNO 25286): Payload, 689 kg, 86.4° inclination, 770 km altitude. Launched 1998 (US). Aggregate risk 9 kg from 153 conjunctions in C775 cluster; one of few US additions.
43. SL-8 R/B (SATNO 13649): Rocket Body, 1435 kg, 74.0° inclination, 764 km altitude. Launched 1982 (Russia). Aggregate risk 9 kg from 85 conjunctions in C775 cluster; aggregate risk in lower band.
44. IRIDIUM 29 (SATNO 24944): Payload, 689 kg, 86.4° inclination, 770 km altitude. Launched 1997 (US). Aggregate risk 9 kg from 172 conjunctions in C775 cluster; empirical risk from close approaches.
45. SL-8 R/B (SATNO 10142): Rocket Body, 1435 kg, 83.0° inclination, 968 km altitude. Launched 1977 (Russia). Aggregate risk 7 kg from 39 conjunctions in C1000 cluster; high cluster factor.
46. SL-8 R/B (SATNO 5707): Rocket Body, 1435 kg, 74.0° inclination, 758 km altitude. Launched 1971 (Russia). Aggregate risk 8 kg from 117 conjunctions in C775 cluster; early 1970s deposition.
47. CZ-2C R/B (SATNO 43610): Rocket Body, 4000 kg, 98.7° inclination, 706 km altitude. Launched 2018 (China). Aggregate risk 8 kg from 147 conjunctions in C775 cluster; recent addition just above threshold.
48. SL-3 R/B (SATNO 12457): Rocket Body, 1100 kg, 81.3° inclination, 868 km altitude. Launched 1981 (Russia). Aggregate risk ~8 kg (estimated) from ~100 conjunctions in C840 cluster; statistical risk in band.
49. ARIANE 5 R/B (SATNO 27387): Rocket Body, 2575 kg, 98.8° inclination, 770 km altitude. Launched 2002 (Europe). Aggregate risk ~7 kg from ~150 conjunctions in C775 cluster; linked to ENVISAT launch, coupling effects make it a priority for removal to reduce risks in crowded band.
50. CZ-6A R/B (SATNO 54236): Rocket Body, 5800 kg, 98.8° inclination, 862 km altitude. Launched 2022 (China). Aggregate risk ~6 kg from ~200 conjunctions in C840 cluster; from major breakup event generating 800+ fragments, urgent due to recent debris contribution and potential for further collisions.

Ongoing Challenges and Trends

Since January 1, 2024, 26 rocket bodies have been abandoned in LEO with orbital lifetimes exceeding 25 years – violating international guidelines. Of these, 21 are from China, each averaging over 4 metric tons, linked to megaconstellation deployments like Guowang and Thousand Sails. Projections indicate that China could add over 100 such bodies in the coming years if trends continue, as noted by Darren McKnight: “In the next few years, if they continue the same trend, they’re going to leave well over 100 rocket bodies over the 25-year rule… The trend is not good.” This acceleration occurs despite global improvements, with the US and Europe routinely deorbiting stages.

Pathways to Solutions: Emerging ADR Technologies

Key advancements include Astroscale’s ELSA-M, set for a 2026 launch, which is capable of removing multiple “prepared” satellites in one mission using magnetic docking. The European Space Agency’s passivation and deorbiting technologies are highlighted in their 2025 Space Environment Report. Other innovations encompass laser-based removal systems, autonomous remediation robots, and quantum optimization for multi-target mission planning. The space debris removal sector is projected to reach USD 1.6 billion in 2025.

In summary, this list is dominated by Russian SL-16 and SL-8 rocket bodies (over half), reflecting historical launch practices, with growing Chinese contributions from CZ-series rockets. Payloads like ENVISAT and Iridium satellites add variety, but the focus is on massive, persistent objects in key clusters. Prioritizing their removal through international ADR efforts is essential to safeguard the orbital environment for generations to come. As space activity intensifies with mega-constellations like Starlink, acting now could prevent an irreversible tipping point.

References

1. Top 50 List for 2025 by Darren McKnight, Erin Dale, Joe Cassady, Andy Ratcliffe, Satomi Kawamoto, Alessandro Rossi, and Dmitriy Grishko. Presented at the 76th International Astronautical Congress, Sydney, Australia, 2025.
2. Removing these 50 objects from orbit would cut danger from space junk in half by Eric Berger. Ars Technica, October 3, 2025.
3. ESA Space Environment Report 2025 by European Space Agency. Published April 1, 2025.
4. Astroscale’s New Patent Transforms Space Debris Removal by Astroscale. Published July 29, 2025.