Inmarsat's Alphasat satellite is being prepared for launch at the European spaceport in French Guiana, South America.
The spacecraft – the largest European telecommunications satellite ever built – is currently in the payload preparation facility being fuelled with chemical propellant.
Once fully laden Alphasat will have a final mass of 6.6 metric tons.
The Alphasat mission was developed in the largest public-private partnership of its kind, involving Inmarsat and the European Space Agency (ESA).
It is the first spacecraft to use the high-power Alphabus platform – Europe's response to market demand for more broadcasting services.
Alphasat is one of two satellite passengers for Arianespace's next Ariane 5 launch, scheduled for lift-off on 25 July.
Once in orbit at 25° East, Alphasat will expand Inmarsat's global mobile telecommunications L-band network – delivering new capabilities in terms of performance and resource availability over Europe, the Middle East, Africa and parts of Asia.
It will provide 50 per cent more accessible spectrum, with double spectral efficiency and nearly 20 per cent more channels than an Inmarsat-4 satellite.
The 7-metre (23 ft) tall satellite has a solar array spanning nearly 40 metres (131ft) once deployed in orbit, generating more than 12 kW of power.
The support of the UK Space Agency, along with the UK's Regional Development Agencies for London, South East England and the East of England, was instrumental in the development of Alphasat's critical new payload technologies.
The payload was designed and built by Astrium in Portsmouth, England, with final assembly and testing taking place at the company's facility in Toulouse, France.
This Arianespace mission is designated Flight VA214 to signify the 214th launch of an Ariane-series vehicle from Kourou, French Guiana.