Site: The Centre National d'Etudes Spatiales (CNES) - French Space Agency Toulouse Space Center
18, Avenue Edouard Belin
31055 Toulouse Cedex - France

Date Visited: September 11, 1997

WTEC: K. Bhasin (author), J. Pelton



The Centre National d'Etudes Spatiales (CNES) is a French public institution which was founded in 1961. Even though it is a French government agency, it reflects an industrial and commercial nature. CNES has created commercial companies based on its investment in space technologies. It is a shareholder in eight public-limited companies. These companies have turnover of nearly 7,000 million frames (MF) (approximately $1.2 billion). CNES' 1996 budget was close to 12,046 MF. It carries out its operations by participation in European Space Agency (ESA) programs (28%), national programs to maintain industrial competitiveness (22%), and maintaining advance R&D facilities (20%). It also provides access to space with the Ariane program (ESA), marketed by Arianespace (A CNES subsidiary) (30%). The panel visited CNES' Toulouse Space Center where the radiocommunications program is managed. Toulouse Space Center was founded in 1968 and is located in the nearby Technology Park and contains the major part of the CNES workforce. Within the radiocommunication program, the following major activities are conducted:

More detailed discussion of these activities is presented below:



The STENTOR Program is a technological program to prepare future generations of telecommunications satellites. The STENTOR satellite, which will be launched in early 2000, enables several advanced satellite payload and communication technologies to be validated in orbit. These are active antennas, thermal control, microwave components, lithium-ion batteries, and plasma propulsion. The participants are CNES, France Telecom, and Delegation Generale pour l'Armement (DGA). The estimated cost is $500 million. Notable is the industry contribution to its development, which will reach close to 25%.

The program is headed by a joint committee representing France Telecom, CNES and DGA. The state project team (France Telecom, CNES and DGA) is in charge of all technical and financial aspects, with CNES as project manager, and awards the qualification.

An integrated industrial team bringing together Matra Marconi Space (MMS), Aerospatiale, and Alcatel acts as joint prime contractor, under the authority of an industrial steering committee. Several equipment items are being developed by Belgian and German companies, supported by national government funding.

The main objectives of the STENTOR program are: (1) to coordinate activities ranging from R&D to the production and ground qualification of competitive equipment whose performance will have been proven in orbit, (2) to favor the most promising developments of a subsystem and/or complete system level in order to make the technological leaps necessary to keep up and improve competitiveness, (3) to conduct in-orbit experiments to characterize the actual performance of new equipment items and sub-assemblies and to evaluate operational improvements like autonomous station keeping, (4) to demonstrate new and/or enhanced services in orbit.

The STENTOR satellite has a mass of approximately 2,000 kg. It will be placed in a geostationary orbit near the Telecom-2 satellites. Of a total power of 2,500 W, at 2 years, 1,000 W will be allocated to the payload, both night and day. STENTOR will carry enough fuel for positioning, followed by 2 years in orbit to ensure the redundancy of the plasma propulsion system for this same period, necessary for intensive experimentation. The quantity of xenon required for plasma propulsion will be sufficient for nine years in orbit.

The Ku-band payload will be used to experiment with all the new functionality permitted by the technologies developed (flexibility, linearity, reconfiguration).

CNES will be responsible for satellite positioning and station keeping from the Toulouse Space Center. Station keeping over the 9 year period will be subject to arrangements enabling the satellite to be monitored during normal working hours. The first two years will be mainly dedicated to technology and system experimentation and to excercising different payload operating scenarios. It is planned to demonstrate new telecommunications services. The next seven years will serve to characterize aging and evaluate the stability of performance. They will be used especially to demonstrate new telecommunications services. STENTOR is a 3-axis stabilized satellite. The primary structure is basically that of Aerospatiale's Spacebus 3000.

The major advanced technologies which will be tested on the STENTOR are as follows:

The chemical and plasma propulsion subsystem, of conventional design, includes a 400 N apogee engine and 10 N thrusters used for positioning and east/west station keeping. The design of the following elements has been modified to improve both safety and performance: the 400 N apogee engine, the 10 N platinum rhodium motors, the helium tank and the pressure regulators. The plasma propulsion subsystem will be used to control the inclination and eccentricity for north/south station keeping. This subsystem includes in particular two plates of two plasma thrusters, a wound carbon Xenon tank with a titanium liner and a pressure regulator. The detailed design of the thrusters is based on a Russian concept. This completely new subsystem offers a high specific impulse leading to a significant reduction in mass due to the fuel savings.

The thermal control subsystem uses several capillary pumped fluid loops:

The electrical power supply is provided by a 2.5 kW solar array using gallium arsenide solar cells on germanium (GaAs/Ge), a totally new lithium-ion battery developed in conjunction with electric vehicles, and an electronic power switching regulator. The regulator and more especially the lithium-ion battery meet significant mass reduction objectives.

Attitude control: pitch is controlled by an onboard kinetic, momentum device, and roll and yaw by a solar sail. Attitude is determined using a standard earth sensor and precise Sun sensors. A highly advanced static earth sensor is also flown. Furthermore, a new generation GPS receiver will be flown on an experimental basis. It will provide the estimated orbit and spacecraft position once on station, allowing investigations into autonomous station keeping over a period of several months. A complementary orbit determination experiment will be carried out during the transfer phase.

The onboard processing handles all data exchanges aboard the satellite, carries out all data processing except that specific to the payload and controls ground/satellite exchanges. The technical solutions (1553 bus, dual computer assembly, ADA standard language, CCSDS protocol, monitoring and hierarchy-based reconfiguration device) and associated equipment have been developed for Eurostar 3000.

A switching matrix is used to connect the antenna and transponder directly in the case of the active antenna and via high-performance linear TWTAs (70%) in the case of the two passive antennas.

The TM/TC subsystem ensures the Ku-band link with control stations on the ground. A new receiver has been developed, as has a planar array directional antenna for station keeping operations. During positioning, global coverage is ensured by two antennas and the telemetry signal amplified by a power amplifier in the payload.

The communication payload: the Ku-band payload will have three transponders: (1) a very wide band transponder based on MMIC technology. The transponder enables data communication over a wide band, i.e., at high transmission rates, (2) a transponder using intermediate frequency conversion (IF < 1.5 GHz) and surface acoustic wave filters. It includes three channels with selectable bandwidth (36 or 72 MHz), (3) a digital television transponder which can multiplex onboard up to twelve TV programs to DVB-S standard and MPEG-2 format. This enables local broadcasters to access the satellite using small terminals. The extra high frequency (EHF) payload has been developed for propagation experiments. It includes a two-channel transponder and two-beacon transmitter. The antenna ensures coverage of metropolitan France and French Guiana both for transmission and reception.

Antenna technologies:

  1. A transmitting active antenna

    This is a reconfigurable multibeam antenna with 48 radiating subarrays powered by 48 SSPAs. It provides three fully independent, reconfigurable spots. It is fitted with a calibration assembly. The coverage is such that any zone visible on earth may be reached, though it can also operate in beam hopping mode.

  2. An ultra-lightweight reflecting antenna (2.4 m diameter)

    Of an extremely advanced technological design, this antenna with its deployable reflector has a very high gain. The deployment mechanism and reflector are being developed as part of the fertilization aspect of STENTOR. Numerous important European towns lie within the area covered by the antenna's polar diagram.

  3. A conventional steerable spot antenna

    The narrow beam (1.8 degrees) may be directed along two different axes and towards any visible point on earth.

The STENTOR satellite also flies a radiation monitor (COMRAD) designed to measure the radiation in both geostationary and transfer orbits and to characterize the behavior of electronic parts (memory, processors, FPGAs, ASICs etc) subject to this environment. Finally, the satellite is fitted with sensors to measure the characteristics of the plasma generated by the plasma propulsion and the effects on satellite materials in general and the solar cells in particular.

Navigation Program

CNES has been planning a complementary system for navigation to GPS (U.S. program) to improve the availability and precision of navigation signals. Several plans and programs are being developed. The first generation system, GNSS-1 (Global Navigation Satellite System) will provide navigational services over both oceans and continents. The objective is to improve the efficiency and value costs of air transport.

The use of geostationary satellites as a complement to the GPS constellation is an idea which emerged through cooperation between CNES and the DGAC, both of which have been working on the project for several years now. It has now become the reference solution on the international scene within the International Civil Aviation Organization (ICAO).

The program, known as GNSS 1 (1st generation Global Navigation Satellite System) could be prolonged later on by a second generation system, GNSS 2, in which navigation signals would be produced by a constellation of civil satellites (independent of GPS). Such a system would meet the desire for independence expressed by civilian users with respect to defense-based systems such as GPS (U.S.) or Glonass (Russia). Looking ahead, demand for such a system is likely to skyrocket with the extension to maritime and particularly land-based applications.

In order to step up the pace of development on the European segment, DGAC and CNES have decided to jointly develop the first stage, which will be a French contribution in kind to the program developed within the framework of ESA (for which France is the main contributor, at 45%). After an invitation to tender, Thomson was selected to be the prime contractor and leader of a European industrial consortium also including French companies Syseca and Sextant. Work began on 19 December 1995.

Taking into account CNES's experience in the area and the French contribution in kind to the program, ESA accepted CNES's invitation to host the ESA project team at the Toulouse Space Center. This team has been in place since February 1996. It includes, other than the ESA personnel, engineers from CNES and from the main civil aviation agencies in the countries concerned with the program.

Frequency Management Program

The highest authority for frequency management in France is the National Agency for Radiocommunication Frequencies (ANFR). Under this authority several agencies are responsible for managing the part of spectrum for which they have been designated as the responsible body. CNES Frequency Bureau is responsible for managing the Space Science Frequencies (e.g., 2 GHz S-band) for space operations, space communication networks and space research. Its main objectives are: (1) notifying the ANFR of the space networks using those frequencies, (2) managing the notification process (responses to administrations that could be affected by a new space science networks), (3) responding to any administration that is notifying a network that could affect a French space network, (4) as a technical body, organizing and managing coordination of its networks, (5) regulatory support to space projects.

CNES must refer every time to the ANFR, which will be the focal point in notifying space networks to the ITU-R, receive and send mail to the various administrations, and sign any coordination agreements.

The CNES Frequency Bureau coordinates the efforts of the French space science community in studies made within international working groups, in particular in preparing for the World Radiocommunication Conference. It has the support of other departments where experts may be sent to various international groups (e.g., WP 7C, WP 4A).

The main bodies where CNES Frequency Bureau is active are CEPT (the chairman of both groups dealing with the preparation of WRC-97 were from CNES), ITU-R, with the view to participate to all SG where sharing difficulties with other services are foreseen, and SFCG.

The CNES Frequency Bureau represented the interests of the French and European space science community in the preparation of WRC-97. France and CEPT have designated coordinators for all the various items of the WRC-97 agenda; European coordinators are by default French coordinators as well.


CNES Toulouse Space Center is a major national as well as international hub of the French Space Agency in the development of its space program. The CNES radio communications program is based on a close working relationship with the industry to develop and demonstrate advanced space communication technologies and applications as shown by the STENTOR program. In addition to its participation in ESA, this program pro-actively advances the French space communications industry.


CNES. 1996. Annual Report.

Published: December 1998; WTEC Hyper-Librarian