GENERAL

What is EU SST?

EU SST stands for European Union Space Surveillance and Tracking. An SST system is a network of ground-based and space-based sensors capable of surveying and tracking space objects, together with processing capabilities aiming to provide data, information and services on space objects that orbit around the Earth.

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How is the industry involved in EU SST?

EU SST fosters the competitiveness, efficiency and innovation capacity of the European space industry and research institutions by means of open tenders, following the principle of "best value for money".

Therefore, the European industry and research institutions are involved in activities such as data provision, functioning of Operations Centres, development of services, and R&D. Currently, around 80% of the total funding of EU SST is used for this purpose.

More information on the R&D activities performed within EU SST can be found here.

Does EU SST cooperate with other space agencies or SSA initiatives?

The SST Cooperation, composed by the Member States of the SST Partnership and EUSPA, does cooperate with international organisations, space agencies, and other SSA initiatives. There are also links between the Member States of the SST Partnership and the European Space Agency (ESA), as those Member States are also members of ESA, although ESA is not involved in EU SST.

In addition, EU SST contributes to global burden-sharing and international cooperation in the SSA domain, in particular with the United States of America.

If I have a general enquiry or request for information, how can I contact EU SST?

For enquiries or requests for information regarding EU SST, you can contact the EU SST Front Desk. The contact details are available here.

SENSOR, PROCESSING AND SERVICE FUNCTIONS

Which level of coverage do the EU SST sensors have?

EU SST aims at having full coverage of the GEO and MEO regions for objects larger than 35 cm by 2023. For the LEO region, EU SST aims at covering almost 100% of objects larger than 50 cm and approximately 20% of the objects larger than 7 cm.

EU SST seeks to increase its autonomy at all orbital regimes. To this end, its sensors network is under continuous upgrade and expansion, which improves the EU SST coverage and orbital information accuracy and timeliness.

What is the Processing function? Who is in charge of it?

While there is processing of data across all three functions of EU SST, the role of the Processing function is to collect, store and share all measurements from the sensors contributing to EU SST through the EU SST Database and to use this data to generate the EU SST Catalogue in the future.

The German SSA Centre (GSSAC) is responsible for the EU SST Processing function, in particular for the development, maintenance and operation of both the EU SST Database and the future EU SST Catalogue.

COLLISION AVOIDANCE SERVICE

Which are the criteria used to consider a close approach and provide the Collision Avoidance (CA) service?

The EU SST CA service establishes three levels of risky events:

  • High Interest event (HIE), with ALERT level (the highest level of risk – a mitigation action will be recommended if the risk is in the near future);
  • Interest event, with WARNING level (medium to low level of risk – a mitigation action may be required if the risk increases);
  • Information event, with INFO level (low level of risk).

The criteria and thresholds to define each level of risk are based on time to close approach, Scaled Probability of Collision (PoC), and/or geometry (radial and total miss distances). The thresholds used to provide the service are defined in the Service Configuration Document agreed between the user and EU SST. They are defined by the user in coordination with the responsible OC, tailored to each user’s needs and considerations.

For a more comprehensive explanation of the criteria used in the CA service, please refer to the EU SST Service Portfolio, publicly available here.

How many close approaches are detected for EU satellites?

In the first semester of 2021, more than 7,000 close approaches were detected in the three orbital regimes. Out of this number, nearly 190 were considered High Interest Events. Those are events with a high level of risk that require to be further analysed and monitored and that trigger all the mechanisms to activate the EU SST contributing sensors to obtain more accurate data.

Regarding orbital regimes, most of the HIE happened in LEO (nearly 140), followed by the GEO events (40) and the MEO ones (10) where for the first time a Galileo spacecraft made a collision avoidance manoeuvre. More details about the support of EU SST to Galileo can be found here.

RE-ENTRY ANALYSIS SERVICE

How often do space objects re-enter the Earth?

As of January 2025, a total of 5,884 payloads, 4,279 rocket bodies and 22,213 pieces of orbital debris have re-entered into the Earth’s atmosphere1. Since the beginning of the Space Age, this corresponds to an average of one intact object (either payload or upper stage) re-entry every 2.5 days, and one piece of debris re-entry every 26.5 hours.

EU SST monitors the re-entry of rocket bodies and other large objects.

 

  1. Kelso, T.S., 2025. Celestrak SATCAT, accessed on 19 February 2025 at https://celestrak.com/pub/satcat.csv.