Small form factor and ultra-small form factor mission computer/network solutions meet expanding UAV requirements
As missions expand and the classes of different types of unmanned aerial vehicles (UAVs) become better defined, the commercial off-the-shelf (COTS) community can meet the new requirements with open architecture solutions that reduce design risk, lower costs, and speed time to deployment. UAV system designers can select solutions based on their application requirements, the line-replaceable unit- (LRU) or line-replaceable module (LRM)-based subsystem solution that best meets mission needs, payload capabilities, and the platform’s size, weight, and power (SWaP) limitations.
When it comes to UAV processor and networking applications, one size definitely does not fit all. The taxonomy of unmanned platforms continues to expand to meet a wider range of mission types and environments. These different classes of UAVs have varying operational requirements and sensor payload capacities. Moreover, the amount of onboard electronics that each type of UAV needs to interface, and how much sensor data it must process, will vary greatly between the size and the class of the UAV platform.
Today’s military UAVs include high-altitude/long-endurance (HALE)-type unmanned aerial systems (UASs) such as Northrop Grumman’s RQ-4 Global Hawk and the newer MQ-4C Triton aircraft. These UAVs have a wingspan similar to that of a Boeing 747 and a service altitude of approximately 60,000 feet. In the medium-altitude class of long-endurance (MALE) UAVs are found tactical platforms such as the General Atomics MQ-1 Predator and MQ-9 Reaper. For lower-altitude or shorter-range operations, smaller UAVs such as the Boeing Scan Eagle or Textron RQ-7 Shadow – with wingspans of 10 to 14 feet and operating ceilings of 15,000 feet – are the workhorses.
Meeting the needs of UAVs with COTS solutions
The good news is that SWaP-optimized COTS processing and network solutions designed to meet the needs of each of these three classes of UAV have evolved and matured in parallel. Until recently, these solutions have ranged from upgradeable 3U OpenVPX backplane-based LRM systems at the high end to compact, self-contained LRU systems built with rugged PC/104 or COM Express-based small form factor (SFF) technologies in the midrange. A new class of extremely compact LRUs, ultra-small form factor (USFF) systems, has also recently emerged that delivers unprecedented size and weight reduction without compromising network-management capabilities. These USFF systems are ideal for the smaller, low-altitude UAVs with the most pressing size and weight limiations..
For system designers – after taking into consideration their platform’s available space and weight limitations – choosing between the various classes of COTS mission computer and networking solutions for UAVs will typically involve tradeoffs in terms of thermal-management requirements and processing performance. For example, 3U OpenVPX chassis systems can support a wide range of cooling options, including natural convection, air-cooled, and liquid cooling methodologies. In comparison, the midrange SFF and USFF approaches, while significantly smaller and lighter, are limited to natural convection cooling. Due to its ability to cool higher temperatures, the 3U OpenVPX solution is also able to support hotter multiprocessor architectures, while SFF and USFF designs find their sweet spots best supported by mobile laptop-type class Intel Core i7 and low-power tablet-class ARM processors. Examples of these 3U OpenVPX systems are the Integrated Mission Management Computer (IMMC) systems deployed on Global Hawk and Triton. (See Table 1.)
The small form factor LRU approach
For those UAV applications where available space and weight preclude the use of the larger ATR-style chassis used by 3U OpenVPX systems, system designers have turned to SFF solutions. These rugged and compact “shoebox”-size COTS subsystems – frequently based on standard PCIe104 and COM Express modules – can deliver multicore fourth-generation Intel Core i7 processing and Cisco IOS network routing in five-pound LRUs that do not require fans or moving parts to handle thermal management. It is also now possible, with the use of software-based routers such as the Cisco Systems 5921 Embedded Services Router (ESR) software, to reduce weight by nearly 40 percent for applications that require both a mission computer and network router because both functions can be integrated into a single LRU without adding any additional weight. The combined router/mission computer approach also significantly reduces costs because the total system is priced lower than separate distributed processor and hardware router LRU system alternatives.
The emergence of ultra-small form factor COTS
For the most demanding space- and weight-sensitive UAV applications, the new class of USFF subsystems holds great promise. Some of these rugged “pocket-size” solutions take up only 10 cubic inches, weigh half a pound, and consume less than 5 W of power. The first products in this class have been aimed at addressing requirements for Ethernet switching. They are targeted for technology refresh to upgrade older platforms with modern Internet Protocol (IP)-based data networks, or for deployment on smaller UAVs to connect Ethernet-enabled embedded devices such as computers, cameras, sensors, and command-and-control equipment deployed at the network edge. These miniature network-switch systems are less than 10 percent of the size and 25 percent of the weight of the most recent comparable small form factor switch offerings yet are able to deliver fully managed Ethernet switching.
New connectors boost USFF
Helping to make this reduction in SWaP possible is the use of new connector types such as microminiature MIL-DTL-39999-like connectors for Gigabit Ethernet connectivity. For applications requiring 10/100 Ethernet shielded connectivity or when enhanced signal integrity is required, a rectangular connector fitted with Quadrax contacts can now be supported in an USFF LRU. The specialized Quadrax connector delivers superior electromagnetic shielding of Ethernet signals, with 100-ohm differential impedance matching for all Ethernet signals. Integrated electromagnetic (EMI)/power filtering handles power input voltage, spikes, surges, transients, and EMI/EMC compatibility for aircraft installations.
An example of the new class of miniature MIL-circular connector enabled USFF network switches is the Curtiss-Wright Parvus DuraNET 20-11 8-port GbE Ethernet switch subsystem (a six-port 10/100 Ethernet switch variant with Quadrax contacts is also available). (See Figure 1.) These rugged, miniaturized, carrier-grade Layer 2/Layer 3 switch solutions have precision time stamping (IEEE-1588v2), advanced Quality of Service, SNMPv3 management, and zeroization capabilities. When fitted with Quadrax contacts, the switch can provide enhanced protection against EMI generated by either the network switch or the other electronics onboard UAV platforms. This level of EMI isolation was recently required for several UAS platform installations where the mission of the UAS facilitates situational awareness for commanders to see, understand, and act decisively in time-critical situations. The network switch had to operate without being affected by or interfering with the platform’s noisy onboard communications equipment, to serve essentially as a flying cellphone tower.
Packaged in a fully sealed IP67 enclosure, these USFF LRUs have no moving parts, support extended temperature operation (-40 to +85 °C) and are resistant to high shock/vibration, humidity, altitude, and dust/water ingress. Designed for use in airborne platforms and ground vehicles with reduced SWaP requirements, these units support power input voltage, spikes, surges, transients, and EMI/EMC compatibility per MIL-STD-704F, MIL-STD-1275D, MIL-STD-461F, and RTCA/DO-160 for use in civil and military aircraft and ground-vehicle installations.
Curtiss-Wright Defense Solutions cwcdefense.com