Iridium, Thuraya, Inmarsat – Satellitennetzwerk

Iridium — Satellite network

The Iridium network has the area code: +8816.

Iridium is a global satellite commu­ni­ca­tions system consisting of a total of 66 active and 6 reserve satel­lites, for a total of 72 satel­lites. Origi­nally, 77 satel­lites were planned; 77 is the atomic number for the chemical element iridium.

With Iridium NEXT, a new satellite network has been installed since December 2018, which allows data rates in the Iridium Certus service of up to 700 kbps, making internet and other digital services possible for special data terminals. Up to 1.4 Mbps is planned in a further expansion stage. Iridium Certus is available for use on land and at sea (maritime).

Iridium has been approved for the Global Maritime Distress and Safety System (GMDSS) as part of the innova­tions. However, GMDSS is so far (as of January 2022) only available for one maritime phone (LT-3100S), the GMDSS function for the maritime Certus terminals of the manufac­turers Thales, Intellian and Cobham is still pending.

The current phone models will continue to function on the NEXT network, but will continue to offer only 2.4 kbps data rates.

The main advantage of a satellite-based commu­ni­ca­tions system is that large areas can be covered without terres­trial stations. The terminals commu­nicate directly with the satel­lites. The satellite network is connected to the existing terres­trial telephone and internet network via several gateways (ground stations). Iridium devices can be used absolutely globally.

In the case of Iridium, the individual satel­lites are additionally connected to each other by inter-satellite links (ISLs). An active connection is mediated from satellite to satellite until one of these is within range of a gateway. The connection then finds its way into the terres­trial networks via this ground stations.

The trans­mission power of cell phones is limited for health reasons. To enable a connection to be estab­lished, the satel­lites must therefore be in a low earth orbit. The Iridium satel­lites orbit the earth at an altitude of about 780 km in six nearly polar orbits (orbital incli­nation = 86.4°), each with eleven functioning satel­lites and one reserve satellite per orbit. A satellite needs about 100 minutes to orbit the earth, and about 10 minutes from horizon to horizon. Due to the polar orbits, the coverage density at the poles is partic­u­larly high. Until today, Iridium is the only satellite network that guarantees coverage at both polar caps.

Commu­ni­cation with Iridium is possible from any location on Earth at any time, provided there is a clear view of the sky in all direc­tions. To ensure proper, uninter­rupted commu­ni­cation with Iridium, no object above an elevation angle of 8.2° should interfere with the view to the sky. At a location that does fit this rule, such as in a deep ravine, inter­rup­tions in commu­ni­cation may occur. Even shrubs, trees, house and cabin walls can interfere with Iridium commu­ni­ca­tions. In a very deep canyon, where there is an unrestricted view of the sky only at the zenith, no commu­ni­cation is possible for more than 120 minutes in the worst case, since no Iridium satellite comes into visual contact during this time. Due to the Earth’s rotation, an Iridium satellite is again at the zenith after about 120 minutes.

Although Iridium’s network coverage techni­cally permits worldwide use, Iridium satellite phones may not be imported or used in some countries for legal reasons (e.g., in 2021: India, Cuba, North Korea). Some countries allow the import, export and operation of Iridium satellite phones on their territory only under certain condi­tions. In some countries, there is a mandatory regis­tration of Iridium satellite phones (e.g., in 2021: Russia). Before operating, importing or exporting satellite phones, it must be clarified whether this is permitted and whether there is a mandatory registration.

About the history of Iridium

The idea for Iridium was born at Motorola in 1985. It was to enable worldwide voice and data trans­mission via satellite phones and PDAs. In 1988, the concept for it was finalized, and then in 1991, Iridium Inc. was founded to develop the system and put it into operation in September 1998. The construction of the satellite network cost 5 billion USD.

Already in August 2000 Iridium Inc. had to declare bankruptcy. The satel­lites should be steered into the earth’s atmos­phere in order to let them burn up purposefully.

On January 1, 2001, the Iridium system was taken over by the newly founded Iridium Satellite LLC and commercial opera­tions resumed on March 30, 2001. The satel­lites are operated and maintained by Boeing. The largest single customer, accounting with 20%, is the military, led by the U.S. Department of Defense. Other users include shipping companies, airlines, scien­tists and mining companies.

In 2004, planning began for a new satellite network called “Iridium NEXT.” In January 2017, the first rocket was launched, followed by three more in the same year. By December 2018, all satel­lites had been replaced and the new Iridium Certus service with data rates of up to 700 kbps was available.