RF Systems Collaborative Systems Engineering Approach to Power Supply Design Helps Win Major Satellite Communications Contract
Raytheon's win of the $1 billion Advanced Extremely High Frequency Navy Multiband Terminal (NMT) was recently upheld by a U.S. Government Accountability Office review, which cited the "technically superior" power system as a significant factor in its decision. This article describes how the power system development team's collaborative systems engineering approach was key to creating this winning design.
The NMT is the next-generation Navy satellite communications (SATCOM) terminal for ship, shore and submarine communications. Our customer, the Communications Program Office (PMW 170) — which reports to the Navy's Program Executive Office for Command, Control, Communications, Computers and Intelligence (PEO C4I) — is responsible for radio, terminal and antenna integration. NMT is part of the overall PMW 170 strategy to provide a fourfold increase in naval data-rate capacity over protected satellite communication links. This increased bandwidth will help the Navy accelerate current communication functions and meet future communication needs.
Seeking a Superior Design
The team's goal was to provide a stable system that would, in a military environment, supply power to nine different multiband terminal and antenna configurations. Each of the three platforms — ship, shore and submarine — has different delivered-power requirements that can vary as much as five times from platform to platform. To meet these divergent power needs, the team determined that the most cost-effective solution would be a common, scalable product that would provide the right amount of power for each configuration.
First Things First
Early requirements definition was critical to the success of the team's "systems approach" to design. This up-front understanding of requirements enabled the team to knowledgeably manage the engineering trade-offs that emerged later during the development.
The team also recognized that diverse stakeholder insights would be needed to create a power supply that not only met requirements, but met them exceptionally well. Therefore, requirements management was made a collaborative activity that included lessons learned from fielded Navy systems, feedback from Navy vessel tours and crew discussions, early supplier involvement (based on their capabilities and experience), and guidance from Navy logistics support personnel who had broad experience with a range of products.
The team's culture of information-sharing and knowledge-based decision making, which was supported by the Navy and Raytheon management, enabled systems knowledge to be incorporated into early concept reviews. This was crucial for all subsequent design work, allowing the inevitable trade-offs that occurred during hardware development — on space, weight, power and cost — to be made based on comprehensive stakeholder knowledge. All stakeholders were informed of design trade-offs through ongoing informal communications and formal design reviews.
Innovative Solutions to Unique Challenges
Providing quality shipboard power is a challenge unique to military vessels, where powerful electric motors and communications equipment draw current from the same power bus. Motors turning on and off almost always affect collocated equipment sharing the same power connection. (This unique shipboard power quality is defined in Mil-Std-1399-300B, "Electric Power, Alternating Current.")
The challenge was to create a Raytheon solution for this demanding power environment, and then package that solution in an affordable design. The result is a power system architecture that isolates load fluctuations from the prime power events by using a step-down transformer and feeding three separate power-factor correction (PFC) modules, one for each power input phase. The step-down transformer reduces or eliminates over-voltage transients on the prime power line before they reach the power-conversion electronics. The three PFC modules, developed by our partner, Advanced Conversion Technology, Inc., keep the voltage and current in-phase across all of the operating load conditions. As a result, the NMT operates as a well-behaved power consumer. This architecture ensures that the prime power delivered to collocated equipment on the same power line is not distorted. System performance is thereby maintained across a power range of greater than 5:1 to support the nine different configurations.
Once this well-behaved input was established, the next task was to store power locally to accommodate power drops resulting from automatic bus transfers and under-voltage conditions. This was done via energy storage capacitors. A current-sharing arrangement between the PFCs and the energy storage capacitors permits sharing across the three prime-input power phases. This arrangement provides some immunity to partial or total loss of a single prime-power phase.
The team then focused on powering the different electronics loads and antennas. Three different communication electronics sets support Q, X and Ka transmissions, as well as five different antenna types for ship, shore and submarine; all nine different installed configurations are supported. The power system solution is a common, modular supply with a 28VDC and a 280VDC output capable of powering either an antenna–transmitter assembly or circuit cards in electronics chassis.
The control of this power system benefited from valuable user-community, human-factors and safety-engineering inputs. The control panel, which provides power system status to help reduce errors and improve operational safety, was designed to be easily read by users of different heights, and at different angles. Additional status and monitoring electronics are available for system diagnosis of both the power system and all of the different loads powered by the system.
Overall, the NMT power system technology supports NoDoubt™ mission performance by providing a solid foundation for a stable, reliable, warfighter communications system.
