PC/104 and UASs: The beauty of the system
Good things really do come in small packages: It’s as though small, lightweight PC/104-based subsystems and Unmanned Aircraft Systems (UASs) for defense and aerospace applications were made for each other.
PC/104-based systems are handling processing and networking duties on many Unmanned Aircraft Systems (UASs) flying missions around the globe today: Several examples include serving as mission computers on the MQ-5B Hunter and acting as mobile network router systems on the Predator. In fact, you can find PC/104 technology flying today supporting the U.S. Navy, Air Force, Army, and Coast Guard aboard unmanned surface vehicles, unmanned helicopters, and unmanned fixed-wing aircraft.
One of the beauties of the PC/104 architecture is that when these cards are packaged within a rugged chassis, the system designer can access all the benefits of this well-established, widely used standard without actually having to deal directly with the modules themselves. When deployed in enclosures with standard interfaces, the user experiences a highly reliable, easily inserted or removed, compact, and cost-effective “black box” solution. What’s in the box matters only in that the solution delivers optimal performance in harsh environments with the most compact footprint.
PC/104-based boxes hit all the key sweet spots for UAS system integrators looking to add highly rugged and Size, Weight, and Power (SWaP)-optimized mission computers and networking nodes to their platforms (Figure 1).
When it comes to open-standard, broadly supported system architectures, PC/104 delivers all the high-demand requirements in a cost-effective small package that loads the benefits of proven COTS technology into an easily integrated Line-Replaceable Unit (LRU). That’s not to say that PC/104 is the answer for every situation, however. If the application requires flight- or safety-certified system hardware, or the function needs intensive levels of processing horsepower that requires multiple bigger and hotter processors, the integrator may instead want to consider a high-performance bus/backplane approach. In such cases, a Line-Replaceable Module (LRM) such as VPX may be a better option. A good rule of thumb is if the required module dissipates more than 100 W, PC/104 is not likely the best solution. Moreover, while it’s possible to pursue rigid design assurance certifications such as DO-254 or DO-178 with PC/104-based solutions, the associated cost and the need for detailed artifacts for each of the system’s components tend to argue for a custom solution rather than a COTS PC/104 design. However, PC/104 is hard to beat for the numerous types of mission computers and network switch applications that UASs require for onboard systems management and data communications.
Stability and flexibility
In recent years, as UASs have proliferated, it was only natural that PC/104 would find a place on these highly SWaP-constrained platforms. Starting with the module itself, the PC/104 story is one of stability and flexibility. The PC/104 form factor, regardless of which variant one considers – the newest-generation card types that feature PCI Express or the legacy cards built around the PCI/ISA bus – provides a consistent form factor, measuring roughly 3.6" x 3.8", that delivers an ideal small building block for systems design that has remained stable since it was first introduced in the early 1980s. Since then, PC/104 has been embraced as the go-to small-form-factor choice for building lightweight, low-power processing systems. Today there are more than 100 suppliers of PC/104 cards, providing system designers with countless options for mixing and matching Single Board Computer (SBC) and I/O module types. This well-established market ecosystem ensures longevity of support while keeping costs competitive.
Because of the large number of suppliers, system integrators can mix and match modules, virtually as easily as one would with Lego blocks, enabling users to configure the particular I/O their application requires without the higher cost of a backplane or the larger chassis required by 3U or 6U backplane-based designs.
Rugged without compromise
Another important feature of PC/104 cards is how rugged they are. In fact, because the modules have a very small surface area and their main connectors provide a very reliable connector from board-to-board, PC/104 offers a system building block that is inherently rugged for vibration and shock (Figure 2). Standard procedure at Curtiss-Wright for Parvus PC/104 solutions is to perform defense and environmental tests, including MIL-STD-810 and 461 EMI; newer systems are tested through DO-160 for environmental and EMI for commercial aerospace applications.
Processing on UASs
PC/104-based subsystems are frequently used today as mission computers on UASs, providing general-purpose PC functionality with a processor and traditional peripheral I/O devices, such as Ethernet, serial, analog, digital, and audio/video. Because each UAS platform will require specific communications interfaces depending on the types of payload they carry, the mission computers are modified to support the specific devices onboard the aircraft or vehicle, such as the 1553 bus; ARINC 429 databus; or synchronous, asynchronous, or digital I/O needed for the particular radios or avionics that the processor will communicate with.
These mission computers – typically located in front of the UAS’s network router and switches – gather information from the platform’s sensors and then share the data through the switches and routers.
Networking on UASs
Because UASs are essentially sensor platforms, PC/104 hardware is frequently used for adding Ethernet connectivity between the sensors and other computing devices onboard a UAS. This enables information gathered by the sensors or processed by the mission computers to be shared locally on a LAN. When a PC/104 Layer 3 router device is used, it enables an interlink to be established between the devices on the UAS and other platforms in the air, or to remote stations on the ground or at sea. For example, a UAS might have a tactical radio or satcom connection to the router, which then can relay data off the platform to provide situational awareness to the warfighter. In this fashion, every UAS or platform can become a node in the network, providing information that enables mission commanders and mission planners to make informed decisions on the battlefield.
PC/104 in the air: The MQ-5B Hunter
A good example of how PC/104 systems are deployed on UASs today is provided by the Hunter from Northrop Grumman. The MQ-5B Hunter UAS is currently being used by the U.S. Army to conduct battlefield surveillance using its multimission optronic payload. The UAS flies over the battlefield gathering reconnaissance, surveillance, target-acquisition, and battle-damage information in real time. It then relays the information via video link to commanders and soldiers on the ground.
The mission computer on the Hunter is a Curtiss-Wright Parvus DuraCOR 810 subsystem. The system integrates a low-power 1.4 GHz Intel CPU, together with a MIL-STD-704/1275 power supply in a rugged aluminum chassis that uses MIL-DTL-38999 connectors. Up to six spare PC/104-Plus slots are available for mission-specific I/O functionality. Weighing only 7.8 lb. (3.5 kg), this compact system measures only 10.60" (269.24 mm) x 5.30" (134.62 mm) x 5.30" (134.62 mm), including its connectors.
One of the growing trends the industry is seeing with UAS-deployed PC/104 systems is the growth of LRU functionality consolidation, as system integrators are looking to put more functionality than ever before into the same physical envelope. As semiconductor devices continue to reach higher levels of integration, it becomes increasingly viable to combine a number of separate functions that would have formerly required their own dedicated chassis into a single box.
With the mission profile of UASs continuing to evolve, PC/104 hardware – by its very nature small, lightweight, and low power – will continue to be a good host, providing a cost-effective, stable, and flexible means of deploying ever-greater amounts of processing and connectivity to support and protect warfighters.
Curtiss-Wright Defense Solutions