European Union

The Space Surveillance and Tracking (SST) Segment is the part of ESA’s Space Situational Awareness (SSA) programme that focuses on detecting, cataloguing, and predicting the orbits of objects in Earth orbit, particularly space debris and operational satellites. Its mission is to support collision avoidance, re‑entry predictions, and fragmentation detection using ground and potentially space‑based sensors.

 

-An SST system combines data from various sensors—such as radars, optical telescopes, and laser‑ranging stations—to detect debris and catalogue objects in orbit. The objective is to keep an up‑to‑date list of object positions and trajectories so their motion can be predicted.

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-Once objects are detected, SST performs orbit determination and correlation (checking whether an observation matches an existing object in the catalogue) and updates object data over time to improve predictions. 

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-From the maintained object catalogue, the SST segment offers essential services:

• Conjunction predictions: issuing warnings of close approaches between spacecraft and debris.

• Fragmentation detection: identifying when an object has broken up and assessing the resulting debris field.

• Re‑entry prediction: estimating when and where objects will re‑enter Earth’s atmosphere. 

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SST segment’s software ecosystem:

• Backend processing: Observations ➝ orbit calculations ➝ database entries.

• Observation planning: Scheduling what and when to observe.

• Front‑end services: Tools for re‑entry prediction, fragmentation analysis, conjunction warnings, and catalogue queries

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-Because space surveillance is a global concern, ESA’s SST also works with international partners and participates in standardization efforts (e.g., with the Consultative Committee for Space Data Systems and European standardization bodies

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-ESA’s early SSA (2009–2016) deployed prototype SST systems and defined the concept of an “Expert Centre”—a central node coordinating multiple sensor networks.

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-The SST segment relates closely to the EU Space Surveillance and Tracking (EU SST) capability, established under the EU Space Programme to provide operational SST services such as collision avoidance, re‑entry analysis, and fragmentation analysis.

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-EU SST uses a network of ground‑based sensors from multiple member states and provides services to operators in Europe and globally.

-SST systems like ESA’s contribute to broader Space Traffic Management (STM) goals by improving global knowledge of object motion and reducing collision risk. They complement SSA efforts in other regions (e.g., U.S. Space Force Space Surveillance Network and similar European initiatives).

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-ESA has adopted a Zero Debris policy that goes beyond existing international guidelines by aiming to significantly limit the production of debris in Earth and lunar orbits by 2030 and ensure that ESA‑associated missions leave “zero debris” behind. This approach guides both mission design and operations and shapes technology development for sustainability. 

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-Key objectives:

• Preventing the release and proliferation of new debris.

• Controlling break‑up risk and system failures.

• Reducing collision risk between operating satellites and debris.

• Improving the clearance of orbital regions after mission end.

• Assuring safe re‑entry for decommissioned objects.

• Minimizing negative effects on astronomy and observation from space objects.

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-ESA Space Debris Mitigation Policy (2023): defines organizational responsibilities and overall mitigation goals.

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-ESSB‑ST‑U‑007 – Space Debris Mitigation Requirements — the core standard specifying technical mitigation requirements (updated in 2025 + references international best practices).

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-ESSB‑HB‑U‑002 – Compliance Verification Guidelines — helps engineers and programme managers check that mitigation requirements are properly met.

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-ISO 24113:2023 – Space debris mitigation requirements.

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-ECSS‑U‑AS‑10C Rev.2 — European Cooperation on Space Standardization’s adoption of the ISO standard.

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-ESA’s mitigation standard (ESSB‑ST‑U‑007)

A. End‑of‑Life Disposal

• Low‑Earth Orbit (LEO) objects must be disposed within five years after mission end (down from 25 years in older international norms).

• Disposal plans must achieve a ≥90% probability of success (and even higher for very large constellations).

• Long‑lived objects must be equipped with interfaces that allow active debris removal in case of mission failure.

B. Collision Avoidance & Space Traffic Coordination

• Builds on best practices for automating conjunction assessment and response actions.

• Defines thresholds for collision probability at which operators must maneuver spacecraft.

• Encourages coordination across operators to enhance shared understanding of traffic risks.

C. Constellation Requirements

• Specific controls on constellation deployment and disposal to limit cumulative collision risk and prevent multiple objects from being left in protected orbits.

D. Lunar & High‑Altitude Considerations

• Emerging requirements address debris mitigation in lunar orbits and GNSS altitudes, expanding the sustainability focus beyond LEO and GEO. 

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According to a non‑legally binding, collaborative document focused on achieving a Zero Debris future in Earth orbit by 2030.

1. Intended as a global initiative for the space community, building on existing debris mitigation norms and expanding them into measurable, community‑defined targets.

2. Signatories commit to shared principles and specific goals related to preventing, mitigating, and remediating space debris.

3. It’s a community‑driven strategy to influence industry and government behavior, not enforce legal obligations.