MECHANICAL MODULAR OPEN SYSTEMS ARCHITECTURES
Raytheon has enterprisewide technology networks established to communicate and coordinate technology needs and developments across the company. These networks help ensure discriminating technologies are available to our system solutions that, in turn, provide our customers with the highest performance capability at the lowest possible cost.
One particular technology network is the Mechanical, Materials, and Structures (MMS) Technology Network (MMSTN) that focuses primarily on electronics packaging, advanced structures, emerging materials, and thermal management. This article discusses industry shifts toward open standards designs and how these shifts change and exert influence on the MMS technology domain.
OPEN STANDARDS AND ARCHITECTURE FOR COMPUTING SYSTEMS
Raytheon produces computing hardware and also adapts other vendors’ hardware for use in areas such as communications, cyber, electronic warfare, radar, surveillance and weapons. Many of the computing systems Raytheon builds on these platforms are considered embedded — systems designed to perform specific functions within a larger system. Recently, there has been a shift in customer requirements towards using embedded computing systems with modular open systems architectures. This is due in large part to the 2017 National Defense Authorization Act (NDAA) requiring all major defense acquisition programs receiving Milestone A or B approval after January 1, 2019 to be designed and developed with a Modular Open System Approach (MOSA) to the maximum extent practicable.1
MOSA divides systems into modules connected through well-defined interfaces. This enables customers to minimize “vendor lock” ,2 increase competition, maximize interchangeability, and facilitate technology refresh whereby pieces of a system are upgraded to improve or augment capabilities without replacing the entire system. Open architectures, generally agreed to reduce cost and spur innovation through open competition3, may also come at the expense of performance and reliability.4
Open architecture is commonly misunderstood as a systems engineering philosophy that impacts only systems engineers and system architects. However, architecture is “the fundamental organization of a system5” embodied in its modules and interfaces, including mechanical, electrical, and software interfaces. An open architecture will follow defined standards for these interfaces, often down to the module level, impacting the MMSTN engineering disciplines.
The VITA6 Standards Organization is responsible for developing and defining key open standards specifications for embedded computing systems and modules. VITA 48, commonly known as VPX-REDI,7 establishes the latest mechanical formats and interfaces between the computing module and the chassis. Within the VITA 48 framework are standards for different cooling schemes, including standard air cooling (VITA 48.1), conduction cooling (VITA 48.2), air flow through cooling (VITA 48.5), and air flow by cooling (VITA 48.7). The relative thermal performance of each of these is presented in Figure 1.
Air flow by (AFB) cooling techniques employ convective cooling across the board surface by placing it in an airstream. Air flow through (AFT) and liquid flow through (LFT) techniques plumb the cooling fluid into a finned heat exchanger frame, conductively cooling the board to the heat exchanger. As shown in Figure 1, LFT cooling achieves superior thermal performance compared to alternative methods. It can also support high altitude operation. While conduction cooled applications may suffice in many current ruggedized processing module applications, liquid cooling will be necessary to transfer the heat dissipated by state-of-the-art processor solutions in the near future.
In response to interest from Raytheon and others, VITA formed a new working group in early 2015, chaired by Raytheon, to write the standard on liquid-flow-through VPX-REDI (VITA 48.4). Participation in a standards working group gave Raytheon and other members early access to the new standard and lessons learned, and provided them an opportunity to steer requirements and help drive the pace of the standard development milestones to meet program needs. The VITA 48.4 standard was ANSI (American National Standards Institute) ratified in 2018 and is available for use by any VITA member.
Open standards specify external mechanical requirements, such as mounting, outline, and interfaces. Internal components, for example circuit card assembly (CCA) and heat exchanger, are mostly customizable. An example of a customized internal component that still supports external open standards is the Raytheon developed Enhanced Package Integrated Coldplate (EPIC),8 Figure 2. EPIC is a thin (less than 2mm in thickness) flexible microchannel heat exchanger that can directly couple to the processor lid or die without the need for silicone based conforming gap filler materials. The mechanical flexibility enables EPIC to bring the coolant closer to the heat source, rejecting nearly twice as much heat from a processor as other state-of-the-art cooling solutions (pyrolytic graphite, heat pipes, etc.), extending the thermal limit of embedded computing processors well into the future.
More specific to United States military products, the Sensor Open Systems Architecture (SOSA)TM Consortium9 is developing consensus-based, open technical standards specifying a reference architecture primarily aimed at Command, Control, Communications, Computers, Intelligence, Surveillance and Reconnaissance (C4ISR) sensor systems, including electro-optical and infrared (EO/IR), radar, signals intelligence (SIGINT), communications, and electronic warfare systems. The hardware working group within SOSA “specifies relevant existing standards and, as necessary, develops new standards to achieve modularity, interoperability, and scalability within a chassis” for all subsystems within a sensor product.10 SOSA is about two years old and is in the early stages of identifying and adopting relevant standards that extend to the entire sensor system.11 Future sensor pursuits will require conformance with SOSA standards that extend beyond embedded computing to other subsystems and interfaces within the sensor system, the radar antenna for example.
– Chris Koontz
1 National Defense Authorization Act for Fiscal Year 2017. Sec. 805 Subsection 2446a “Requirement for modular open system approach in major defense acquisition programs; definitions.” PUBLIC LAW 114–328—DEC. 23, 2016.
2 “Vendor lock,” also known as vendor lock-in, refers to a situation where a product architecture is customized or otherwise protected by intellectual property rights to the point where all upgrades must be performed by the original developer to avoid substantial switching costs
3 Baldwin, C. and Clark, K. “Managing in an Age of Modularity.” Harvard Business SchoolTM Publishing, 1997.
4 Christensen, C., Raynor, M. The Innovator’s Solution. Harvard Business School Publishing, 2003, p 133.
5 ISO/IEC 42010 – IEEE® Std 1471-2000 “Systems and software engineering — Recommended practice for architectural description of software-intensive systems.”
6 VME (Virtual Module Europa) International Trade Association.
7 VPX (ANSI/VITA standard 46.0), REDI (Ruggedized Enhanced Design Implementation).
8 US Patents 8,368,208 and 9,553,038.
9 Raytheon Space and Airborne Systems is a sponsor-level member in the SOSA Consortium.
10 “Sensor Open Systems Architecture: SOSA Overview.” The Open Group. opengroup.org. January 30, 2018.
11 McHale, John. “Sensor Open Systems Architecture (SOSA), an Overview.” Military Embedded Systems. March 17, 2017.