04/08/2021
(Auto-translated from French)
In the field of radiocommunications, engineers have always favored high points to install transmitters and receivers: going upwards allows very wide areas to be covered and thus reduces deployment costs. The conquest of space has created the possibility of placing transceivers on artificial satellites that fly over the Earth in outer space, and thus opened up new prospects for long-distance communications. It was in 1960 that the first “telecommunications satellite”, Echo I, a simple reflector, was launched. Its successors will, for their part, quickly embed receivers and transmitters capable of amplifying the received signal before retransmitting it. The projects of constellations of telecommunications satellites do not date from yesterday.
Extract:
The 2010s: non-geostationary constellations
In June 2013, the first four satellites of the O3b constellation were launched. O3b is the acronym for “other 3 billion”, in reference to the three billion inhabitants of the planet who do not yet have an internet. It is a constellation in medium orbit at an altitude of 8,000 km in the equatorial plane, operating in the Ka band. Today, twenty satellites built by Thalès Alenia Space are in orbit and others have been ordered.
OneWeb, for its part, is a constellation project of around 600 satellites in low orbit at an altitude of 1,200 km, in Ku-band for links with end-users and in Ka-band for links with gateway stations. It currently has 110 satellites in orbit built by a joint company between Airbus and OneWeb.
The American giant Starlink of the company SpaceX has, meanwhile, already deployed 1,152 satellites and eventually plans 12,000 satellites.
Amazon is also considering the deployment of 3,236 satellites as part of its Kuiper project.
In February 2021, Thalès Alenia Space was selected to build the constellation of 298 satellites of the Canadian Telesat.
Finally, the European Commission announced a project for a European sovereign constellation to strengthen the strategic autonomy of the European Union. In December 2020, it selected a consortium made up of Airbus, Arianespace, Eutelsat, Hispasat, OHB, Orange, SES, Telespazio and Thalès Alenia Space to study the design, development and launch of an independent European space system. communications.
Efficient operation
Satellites communicate on the one hand with gateways, which provide interconnection with terrestrial networks and, on the other hand, with smaller end-user terminals in private homes or businesses. As with terrestrial microwave systems which operate in the same frequency bands, the width of the transmission cone is very narrow, just a few degrees. This strong directivity of the antennas makes it possible to share the frequency bands between several constellations of satellites, with geostationary satellite networks as well as with terrestrial networks.
The complexity of satellites and associated ground equipment varies from one constellation to another. Some operate like conventional satellites, retransmitting signals received from a user directly to a gateway. Others are more sophisticated and provide on-board signal processing, as well as inter-satellite links. These inter-satellite links make it possible to deploy a real mesh network in space, and communications no longer need to pass through certain territories. However, all of the data exchanged between users and satellites must be brought down to Earth: constellations, like high-capacity geostationary satellites, need many gateway stations to ensure this flow.
Some of the frequencies of these constellations have been declared by France to the ITU . This is the case for the frequencies of the Globalstar constellation, part of the frequencies of OneWeb and O3b. Other French rights registered by ANFR at the ITU could prove to be of interest for future constellation projects. For its part, ARCEP issues authorizations for operators, as it has just done for terminals and gateways in the Starlink / SpaceX constellation in France.
In terms of constellation, some are already seeing further. Thus, the European Space Agency is studying a constellation of satellites around the Moon in order to develop communication and radio navigation capabilities within the framework of the Moonlight project and to facilitate future missions to the Moon.
Read the complete article at: https://www.anfr.fr/toutes-les-actualites/actualites/les-constellations-de-satellites-de-telecommunications-des-origines-a-nos-jours/