The network of downrange stations

The network consists of the following stations, listed in order:  Galliot,  Natal in Brazil, Ascension Island in the South Atlantic, Libreville in Gabon and Malindi in Kenya. Information is transmitted between the stations and various centres using the 'Systa Transport' telecommunications system.  All the systems are verified for redundancy, in order to guarantee maximum availability: it is vitally important that they maintain contact with the launcher and retain control of the abort chain at all times.

The Telemetry system on the Montagne des Pères consists of three sub-systems:

The Galliot station

The Galliot station itself is assigned to Ariane full time.  Surrounding the Stella 43 antenna, which receives the signal from Ariane 5 at a rate of 1 Megabit per second (or a million zeros or ones per second!), a mass of computing equipment records, transforms and sends the data to the SCET.

NB: each downrange station has identical equipment to the Galliot station.

The Telemetry Operating System

The Telemetry Operating System (SET) includes, in particular, the Ariane 5 Telemetry Data Centralisation and Exploitation System (SCET), a computer system which centralises the data from all the Telemetry stations, pre-processes them and then distributes them in real time (CVI) to Range Safety, Arianespace and Tracking and Location.

The satellite tracking station

The fully-automated, satellite tracking station, which uses the CNES 2 GHz network's Star 45 antenna and the KuK antenna, operates continuously as part of the Toulouse Space Centre's tracking network, performing positioning and station-keeping operations for certain satellites.  In addition, during launch operations it acts as a backup for the Galliot station, to ensure that the signal is received.

As most Ariane missions involve placing telecommunications satellites into geostationary transfer orbits (GTO), more than 95% of launches take place in an easterly direction.

Since the 1980s, CNES and ESA have been working to set up a network of stations dedicated to Ariane for this standard trajectory, stretching from Kourou to West Africa.  To achieve this, the Telemetry Technical Manager at CSG is also responsible for coordinating the technical implementation of a network of downrange stations.  On a routine basis he is on standby for Galliot in Kourou, where he is physically based, but also for Natal in Brazil, Ascension Island in the South Atlantic, Libreville in Gabon and Malindi in Kenya.  During launches, this transcontinental link is used to remain in constant contact with the launcher, with  station coverage overlapping wherever possible, so that the next antenna in the link acquires Ariane's signal as it appears over the horizon before the previous station has even lost contact.

As authorised by agreements between ESA and the relevant governments, CNES is responsible for operating the Telemetry equipment at the stations, through protocols agreed upon with third parties. These operating contracts are prepared and followed-up by the head of the CNES/CSG Measurement Acquisition Department, SDO/AM.

Though French is the official contract language for operations, in this melting-pot of agreements and contact persons, the technicians usually communicate with several languages: 'Franglais', Franco-Brazilian or whatever is required.

Solely devoted to Ariane, the Libreville station is the only one with a permanent staff consisting of CNES manager and a Telemetry Industrial Service Contract (ISC) technician.  They are required to be proficient in several areas, in order to maintain the equipment on the site.  For standard launch campaigns, a third ISC technician is seconded here to provide support for a three-week period, lasting from the preparation phase until the end of the mission.

Atypical launches

For safety reasons, CNES/CSG never undertakes launches towards the south, which would involve the launcher flying over Brazil.  For launches in a north-easterly or northerly direction, which place sun-synchronous satellites such as Spot or Helios into orbit, it is essential to find suitable stations beneath the launcher's trajectory which are compatible with Ariane 5 telemetry, and to sign agreements with the relevant overseas authorities.  For launches towards the north, which have already taken place, agreements have been signed with the Canadian Space Agency regarding use of Saint-Hubert on its east coast, and with the United States for Wallops Island, close to Florida and also on the east coast of the continent.  Agreements have also been negotiated regarding use of the South Point station in Hawaii and the Dongara station on the west coast of Australia, which was used for the Rosetta launch.  Four different Ariane 5 kits can be also transported where they are needed to provide the interface between local antennas and the Ariane 5 receiving systems.  However, this is a complex system which needs to be installed one step at a time, which requires considerable preparation time.  For the launches of Envisat and Helios, equipment had to be deployed as far away as Svalbard, a Norwegian archipelago in the Arctic Ocean.