Site: Matra-Marconi Space (MMS)
31 rue des Cosmonautes
Z.I. du Palays
31007 Toulouse Cedex
Date Visited: June 25, 1992
Report Author: V. Chan
See Matra Marconi Space U.K. Ltd. site visit report for background information. MMS employs a staff of 2,000 in France.
The major communications R&D program of MMS-Toulouse is SILEX. The total cost will be 150 MAU (approximately $150 million) for two packages, one on SPOT and the other on ARTEMIS. The SPOT-4 package is due to launch in 1995, with ARTEMIS launch scheduled for one year later. The project has been in Phase C/D (flight package design and development) since December 1990. It will demonstrate a LEO-GEO link for which it will act as terminals. The packages are designed for five to ten years of in-orbit life-time, and the GEO package has provisions to downlink to the Canary Islands. The SILEX project employs 200 persons, with 70 at MMS.
The rationale for this expensive development program is the belief that continuous world-wide growth of data exchange needs will require in the near future a significant modification to the present structure of communication networks. In particular, the use of ISLs will become essential in order to match future traffic demand.
A LEO-GEO link would relieve the constraints of low-earth orbiter connectivity. The total visibility duration is increased; the use of the on-board resources such as sensors without recorders is allowed and the expansion of the ground segment, that would otherwise be required to be spread all over the world, can also be reduced.
A GEO-GEO link allows a ground station to have direct access, via a relay satellite, to spacecraft not in its field-of-view. Regional and domestic networks and services (e.g., telephony, TV, business data) can then be interconnected and their coverage extended to significantly improve their service and reach.
It is believed that optical ISLs will ultimately be better than RF links because of the antenna size, mass and volume advantages of optics. In addition, there are other advantages such as reduced interference with other systems, lower power consumption, and better growth potential.
The SILEX package will weigh 128 kg on the SPOT and 140 kg on ARTEMIS (interface plates excluded). It takes two minutes to acquire over a seven milliradian uncertainty. A beacon is used for this function. It combines sixteen 0.5 W lasers to obtain an 8 W output. Acquisition is performed by means of a 288 x 384 array of Thomson CSF charge-coupled devices (CCDs). The forward GEO-LEO link rate is 2 Mbits/sec and the backward (LEO-GEO) link is 50 Mbits/sec. The package is designed to have autonomous control, i.e., operation of the system does not require fine intervention from the ground.
The bench design is rigid (first vibrational mode is at 130 Hz). The tracking system uses a 14 x 14 CCD array, with 0.2 microradian error. The telescope size is 25 cm and the overall wavefront quality is one-tenth of a wavelength. It will track to within one degree and acquire to within 10 degrees of the sun. There were 13 pieces of equipment developed under 20 subcontracts (seven duplicate) during breadboard Phase B.
Future developments underway include a 500 Mbits/sec ISL using one dichroic filter and polarization combining to get 4 times operations with higher laser power.
In the future, MMS is looking to reduce weight by reducing or combining functions such as acquisition and tracking subsystems. They have also targeted goals to increase laser power to one watt, a one microradian beamwidth, a mass of 60 kg, and a transmission rate of 1 Gbits/sec using YAG and heterodyne detection. The target launch is SPOT-5.
As far as other R&D is concerned, they are also proposing a LAN for the space station with space-qualified 100 Mbits/sec Fiber Distributed Data Interface (FDDI) technology. They are waiting for decisions on COLUMBUS.
Other communication ideas under consideration include:
MMS is in a leading position among European aerospace companies. It reinvests a high percentage of its earnings in research and development. The staff seems to be well-trained. It has been selected as prime contractor for the SILEX program, the most important and most expensive communication satellite development currently funded by ESA. They will undoubtedly be the first to put up an optical ISL for commercial usage and will be in a commanding position globally if successful.