A purpose-built radar system will scan low Earth orbit for dangerous debris objects

The central aim of SST is to provide an independent ability to acquire prompt and precise information regarding objects orbiting the Earth. Using this data, a wide range of services will be provided – such as warning of potential collisions between these objects or alerting when and where debris re-enters the Earth's atmosphere. This data will be stored in a catalogue and made available to SSA customers across Europe.

During the 2009-12 Preparatory Phase, there are two main roles for the SST: To define the future full SST system and to launch precursor services that serve as a test-bed and demonstrator for future development.

About SST

The infrastructure required to provide these capabilities is referred to as the 'SST segment'. It comprises surveillance and tracking sensors – which could be radar or optical – to acquire the raw data, which is then processed to correlate (or link) each object with ones already seen, or to indicate a new object if this has not been seen before.

Between 2009 and 2012, the SST Segment will obtain data by using currently existing sensors. When the full SSA programme is initiated, dedicated systems, with capabilities matching the needs of the service, will be developed and deployed.

The SSA-SST Space Surveillance Test and Validation Centre (SSTC) is located at ESA/ESAC, Spain.

SST Segment

Three main elements are required to ensure that the SST Segment can meet critical customer requirements and provide reliable operational services.

Zimmerwald SMall Aperture Robotic Telescope (ZimSMART)

A data catalogue

The core of the SST Segment is the catalogue; this contains information on everything that has been detected in orbit. In order to produce this catalogue, it is necessary to: reconstruct an orbit from the data that is produced by the sensors (orbit determination); check to see if this object has already been seen and is already in the catalogue (correlation); and monitor the data in the catalogue so that sensors can be tasked to update the information when needed.

A network of sensors to accurately detect objects orbiting the Earth

These sensors are usually either optical or radar systems. They are divided into two groups: surveillance or tracking.

1. Surveillance sensors perform the routine task of ensuring that data in the tracking catalogue is accurate and up-to-date. They typically 'stare' across an area of the sky and register objects passing through their field of view. They can observe multiple objects simultaneously and continually add to the quality of the data in the catalogue.
2. Tracking sensors are used when very high-precision data are needed about a specific object. This happens, for example, if it is predicted that this object will collide with an operational satellite. The highest quality of data is then needed to improve these predictions and assist the satellite operators to plan any necessary avoidance manoeuvres - or confirm that no manoeuvre is necessary. Some sensors can perform just one of these tasks, while others are able to have dual roles within the full system.

A system of governance and data management

This will ensure that the right people receive correct information in a timely fashion. Good data management also means that warnings are given as quickly as possible.

SST team

The SST team is based at ESA's Space Surveillance Test and Validation Centre (SSTC) and comprises experts dedicated to the creation of the initial precursor services as well as the definition of the full SST system.

In addition, the SST team is supported by specialists and industrial support personnel working at ESA establishments and industry across Europe.

The team is managed by Emmet Fletcher, from the UK, an engineer experienced in the space surveillance field. "The creation of an independent space surveillance and tracking capability is crucial to helping secure Europe's spaceborne assets. Even though it is a challenging project, we have a very motivated team and invaluable support from colleagues across the Agency and across Europe," says Fletcher.

Precursor services overview

Even before the full SST Segment is built, ESA's Space Surveillance Test and Validation Centre will deliver a valuable range of 'precursor' surveillance services to satellite operators/customers, utilising data from a number of existing European and international sources.

TIRA radardome at FGAN, Wachtberg, Germany

From 2009, these precursor services will comprise:

• The creation of a prototype catalogue of orbiting objects
• Critical collision avoidance services for satellite operators
• Tracking campaigns, both routine and on-demand in case of an identified collision risk
• The prediction and warning of uncontrolled re-entry events

Contributions from ESA Member States

The SST precursor services will take advantage of the numerous resources that exist across Europe. For data acquisition, data from radar and optical systems will be tasked to obtain both routine and ad-hoc data of both satellites and debris. These sensors are provided by national space agencies, European defence ministries, academia and private entities.

Control room at ESA's Optical Ground Station, Tenerife

On the engineering and scientific side, the SST precursor services will make use of contributions from European centres of expertise to ensure that the current store of knowledge is drawn upon where possible.

Since Space Surveillance is a global concern, the SSTC also works closely with our international partners. ESA has a long history of technical cooperation with agencies outside of Europe, The availability of international channels – such as the data provided by the US Air Force – greatly adds to the SSTC capabilities.

SSA also includes an upgrade to ESA's Space Debris Telescope at the Optical Ground Station, Tenerife, Spain. This upgrade will enhance the acquisition of data on objects in the geostationary ring and at Medium Earth Orbit (MEO) altitudes.

Facilities and infrastructure

Space Surveillance Test and Validation Centre (SSTC), ESA/ESAC

Starting in 2009, the SSTC became the focal point for all developments regarding the initial set of SST services to be offered in the precursor programme. The centre's activities include the prototyping of analytical software and operational tools and ensuring the development of data management procedure.

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