What is CNES doing ?

The "Space Debris and Space Surveillance" Unit

This activity is spread over the different departments, depending on the skills required by the Deputy Director of the Toulouse Space Centre (CST) who coordinates the different technical centres. From a technical and operational point of view, the unit undertakes studies using mathematical models to determine such factors as flux and the resistance of materials in orbit, trajectory, predicted atmospheric re-entry and other risks.

The CST is currently operating and tracking seventeen spacecraft that are either CNES satellites or satellites entrusted to CNES, by the Defence Ministry for example. The work also involves regulatory aspects and international relations. For this purpose, the team works with the Inter-Agency Space Debris Coordination Committee (IADC) and the United Nations. It contributes to the drafting of technical regulations and the development of ISO standards to be incorporated in the Space Act. The objective is to lay down a set of rules to combat the proliferation of debris, particularly by listing rules to help manufacturers avoid any risk.

How do these studies contribute to mission analysis?

The studies are a specific aspect of the analysis and aim to provide answers to the questions "What shall we do at the end of its lifetime and what are the associated risks?" and "What is the risk of collision with other objects?" The launcher has only a short orbital lifetime and therefore does not offer much risk of collision, but the situation is quite different for satellites that keep their stations for many years.

Predicting collisions

The first stage is to analyse the data provided by the American Space Surveillance Network, which catalogues and tracks debris larger than 10 cm in low Earth orbit and larger than 1 m in geostationary orbit. These data are not very precise but they nonetheless allow an initial estimate. The second stage, if a dangerous object is identified, is to request radar readings for better measurement of the debris’s trajectory and orbit. Although the military resources commissioned by the French Defence Procurement Agency provide some information, it would be preferable to have other measurements to complement them.

The CSG’s radar stations have been suggested as a possible complementary source, but currently they neither have the capability nor are sufficiently numerous to participate in such operations.

Orbit Computation Centre (COO)

Observation, detection and verification are the missions of the Orbit Computation Centre (COO), located on the campus of CNES Toulouse where it tracks the trajectories of waste material through Space. Six engineers take turns 24 hours a day verifying and giving seven-day forecasts of anything ‘up there’ that could intercept the orbits of Helios, Spot and the other vital satellites for which they are responsible. Last year the team issued 344 alerts, a dozen of which were classified ‘potential hazards’. Only two confirmed risks justified avoidance manoeuvres. All this requires the finest imaginable calculations and an intense use of probability theory. It begins with a data-acquisition phase with the help of Graves, a large radar-based network adapted for Space surveillance, run by the French Air Force. The task is especially difficult because the data is for a resolution of one kilometre. When the risk of a collision is one in a thousand, alerts are issued and observation stations are brought into play at Monge and Brest, as well as Germany’s Tracking and Imaging RAdar (TIRA). [Source L'Express – 25 March 2009].