Alphasat I-XL (Inmarsat XL)

Alphasat I-XL [ESA]

Alphasat will be the satellite using the Alphabus proto-flight platform, achieving in-orbit validation of the platform through a commercial operator.

Alphasat I-XL (or Inmarsat XL) will feature a new generation digital signal processor for the payload, and a 12-meter aperture antenna reflector. The spacecraft will have a launch mass of more than 6,000 kg at launch, an electrical power of 12 kW. Planned for launch in 2012, Alphasat I-XL has a design lifetime of 15 years.

Inmarsat intends to fly an extended L- band payload, in parallel to and supporting its existing world-leading global mobile satellite services. This Inmarsat mission definition is based around multimedia mobile services already provided by the current Inmarsat-4 satellites through Broadband Global Area Network (GAN)

The satellite will be positioned at 25 degrees east, with its coverage centred over Africa and providing additional coverage to Europe, the Middle-East and parts of Asia.

Implementation of this Geo-mobile application will use the Alphabus platform design in a configuration that requires a 90 degree change to the satellite flight orientation to improve accommodation of the feed/reflector configuration and allow the embarkation of a large deployable reflector. Both of these capabilities will be offered as options in the Alphabus portfolio.

In addition, Alphasat will embark three ESA-provided technology demonstration payloads:

• An advanced laser communication terminal to demonstrate LEO to GEO communication links at 2 Gbit/s,
• Two Q/V-band communication experiments to assess the feasibility of these bands for future commercial applications,
• An advanced startracker with active pixel detector,
• An environment effects facility to monitor the GEO radiation environment and its effects on electronic components and sensors.

The Alphasat programme meets the diverse but mutually compatible goals of all the parties, such as the first flight and in-orbit verification of Alphabus and the implementation of an advanced L-band operational payload, which will supplement the existing Inmarsat satellite constellation and offer the opportunity for new and advanced services.

The contract was signed in November 2007 with a launch targeted by 2013.