How Inmarsat Works

Inmarsat owns and operates three constellations of communication satellites and a total of 12 spacecraft. Together they form the backbone of the world’s most versatile, reliable, commercial satellite communications network.

Flying in geosynchronous orbit 35,786km (22,236 miles) above the Earth, the satellites are positioned in nine orbital locations to give seamless global coverage.


Inmarsat launched the world’s first global mobile satellite communications system to enable merchant ships to stay in touch or call for help in an emergency.

Today they own and operate a total of 12 spacecraft flying in geostationary orbit 35,786km (22,236 miles) above the Earth. And we remain a pioneer in space communications and the industry leader with the planned launch of Global Xpress worldwide in 2015 and the development of our unique S-band aviation network across Europe.

Inmarsat-5 and Global Xpress

We are launching the world’s first global Ka-band mobile satellite system, delivering high-speed broadband to compact user terminals at up to 50Mbps.

We call this pioneering network Global Xpress.

Global Xpress will be delivered through our next-generation Inmarsat-5 (I-5) satellites, built by US manufacturer Boeing and based on its powerful 702HP platform.

The first Global Xpress satellite – I-5 F1 – entered commercial service on 1 July 2014, serving Europe, the Middle East, Africa and Asia. The second satellite successfully launched from the Baikonur Cosmodorome in Kazakhstan on 1 February. Following the successful launch of the third satellite in the constellation (I-5 F3), scheduled for late August, Inmarsat will progress towards global commercial service introduction of GX services by the end of 2015.

Alphasat and the award-winning I-4 series

With the launch of Alphasat in July 2013, Inmarsat became the commercial operator of one of the most technically advanced communications satellites ever flown into space.

The size of a London double-decker bus and with a total mass of more than 6.6 tonnes at launch, Alphasat is the largest European telecommunications satellite ever built.

Alphasat now supplements our ground-breaking Inmarsat-4 (I-4) series, which in 2010 was awarded the Royal Academy of Engineering’s prestigious MacRobert Award for innovation after all three I-4s established the world’s first global 3G network.

The Inmarsat-4 fleet are expected to support our L-band services without the need for replacement until the early-2020s.

The I-3 satellites: workhorses of the L-band fleet

The Inmarsat-3s – the first generation to use spot-beam technology – were launched between April 1996 and February 1998.

All five Inmarsat-3 satellites are currently in service. They were developed by prime contractor Lockheed Martin and payload provider Matra Marconi Space.

With an end-of-life power rating of 2,800W, each I-3 can deliver an EIRP (radiated power) of up to 48dBW, and can dynamically reallocate both RF power and bandwidth among a global beam and five spot beams, allowing greater reuse of the available spectrum.

Each I-3 also carries a navigation transponder designed to enhance the accuracy, availability and integrity of the GPS and Glonass satellite navigation systems.

The Inmarsat-3s are expected to remain in operation, providing communication and safety services in the L-band, until around 2018.


Inmarsat-2: first off the launchpad

Our first wholly owned satellites, the Inmarsat-2s, were built by an international consortium led by British Aerospace. They were launched in 1990-2 and, despite a planned design lifespan of 10 years, our final I-2 satellite continued in active service until December 2014, more than two decades later.

The design of the Inmarsat-2, a three-axis-stabilised spacecraft, was based on the Eurostar platform. Each satellite had a 1.3 tonnes launch mass, reducing to an initial 0.8 tonnes in orbit. Initial power rating was 1,200W.


Inmarsat Global Xpress: Changing the Future for Us All – Short

Inmarsat Global Xpress™ – our new superfast satellite network

Inmarsat-5 F3 satellite launch highlights