System Development & Applications (2010)

Inmarstat 4 Spacecraft

In the for-profit sector, SSPI honors Inmarsat as the creative innovator and EADS Astrium as systems engineer and project manager for the complex, multi-year effort to develop and launch the Inmarsat-4 system of spacecraft.  Serving about 98% of the global population, the I-4 satellites use onboard processors to adapt to changes in traffic across the globe, and can generate nearly 256 spot beams for users on earth while dynamically allocating bandwidth based on demand.  Beams are also electronically steered for optimal pointing and performance independently from the satellite itself or its reflector.  Like their predecessors, the I-4s are equipped with a single global beam that covers up to one-third of the earth's surface.  Each satellite also generates 19 wide spot-beams that provide continuous coverage across the same region for Inmarsat's existing high-end services.  One unique feature is the ability to generate beams of variable size to adjust the performance of the link with user terminals of different size and capability.  The narrow spot-beam capability is new to the Inmarsat-4s, and 228 of these narrow spot-beams form the backbone of Inmarsat's satellite network.  

The six-ton I-4 spacecraft are among the largest commercial communications satellites ever launched.  Their size made it a significant engineering challenge to design the large L-Band feed, 12-meter antenna reflector and payload digital processor while fitting the satellites into a launch vehicle.  The main technical challenges faced in developing the Inmarsat-4 were design and manufacture of the digital processor, plasma propulsion system, payload engineering and system engineering by EADS Astrium in the UK and France; the L-band reflector by Astro Space (Northrup Grumman, USA); and the L-band feed by EMS (now MDA, Canada).    

While the key enabler for the Inmarsat-4 project was the payload digital processor, other novel feats of spacecraft engineering were needed to accommodate the demanding payload.  The massive digital processors, each weighing 85 kg and dissipating close to 1,000 W of power, had to be located on internal floors of the spacecraft rather than external radiating walls. The thermal engineering required the use of advanced loop heat pipes crossing the satellite floors and acting as a high conductivity path to external radiating surfaces.   

Electrical propulsion systems that expel ionized gas at high velocity are nearly five times more efficient than traditional chemical propulsion.  They present wide-ranging challenges to design, however, because of the need to avoid negative interactions and interference between propulsion and telecommunications.  The successful design solution achieved by EADS Astrium kept the spacecraft within the design limits of the available launch vehicles.


Satellite Users Interference Reduction Group and WBU-ISOG

In the non-profit sector, SSPI honors the Satellite Users Interference Reduction Group (SUIRG) and the World Broadcasting Union – International Satellite Operations Group (WBU-ISOG) for leadership over many years in the effort to reduce the impact of satellite radio frequency interference (RFI).  Interference in the satellite network disrupts transmission, reduces quality of service and threatens the economic fundamentals of the world’s most successful space business.  Conservative estimates for a fleet of only three satellites put the cost of RFI at $2 million per year from reduced capabilities and additional labor and services.  From its founding in 2003, SUIRG has been dedicated to identifying the major factors in satellite RFI, developing policies and techniques to reduce it, and creating collaboration within the satellite industry in order to act.  SUIRG has surveyed the industry in order to establish a baseline for interference measurement, tested interference from WiMax devices, and developed recommendations for access and uplink procedures and a universal carrier ID system for faster identification of interference sources.  This work has dovetailed with that of WBU-ISOG, whose Rogue Carriers Working Group has won the support of equipment manufacturers, satellite operators and end-users since 1992 to include a WBU-ISOG Carrier ID standard in all new video encoder models and, where possible, in software upgrades for older models.  It also meshed with efforts by the Global VSAT Forum, which developed a training program for VSAT installation and activation by operators to reduce errors in satellite access.  Other industry associations – including CASBAA, SIA and WTA – have contributed their support in educating the industry about the importance of reducing RFI.  More recently, the major global and regional satellite operators, led by Intelsat and SES, have put their commitment and resources behind this global effort.  Emerging results include an RFI-mitigation partnership among 13 satellite operators, the formation of a Space Data Association that will automatically collect and house interference data from the satellite operators and an RFI Alert Network managed by SUIRG that will help operators identify interfering signals.

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