High Altitude Attitudes

As the missions for unmanned aerial vehicles increase in complexity, the challenge for COTS suppliers is to create smaller embedded computing systems, says Dave Garcia.

Unmanned aerial vehicles, commonly referred to as UAV's, are defined as powered aerial vehicles sustained in flight by aerodynamic lift over most of their flight path and guided without an onboard crew. They may be expendable or recoverable and can fly autonomously or piloted remotely. UAVs, either remotely piloted or self-piloted, can carry cameras, sensors, communications equipment or other payloads for reconnaissance and intelligence-gathering missions, and more challenging roles are envisioned, including combat missions.

Today, UAVs take on more dangerous missions on the battlefield as they offer clear advantages over manned aircraft. One is safety, as take-off and landing are usually remote controlled. And once they're airborne, UAVs can stay aloft for days or weeks on end, following a predetermined path and guided by Global Positioning System satellites. More robust UAVs can cruise at heights considered too low for manned craft and with no lives at risk, and UAVs can enter extreme environments.

Lessons from recent combat experiences in Kosovo, Afghanistan and Iraq have shown that UAVs can provide vastly improved acquisition and more rapid dissemination of intelligence, surveillance and reconnaissance data. The benefits and promise offered by UAVs in reconnaissance, targeting and attack have captured the attention of senior officials in the Department of Defense (DoD), members of Congress and the public alike.

UAVs range in size from handheld to runway-operated aircraft whose payload weight capabilities range from a few pounds to 2000 pounds. The Department of Defense built up its arsenal of UAVs in the late 1980s and 90s in close range (50 kilometres), short range (200 kilometers), and endurance categories (anything beyond). The close and short-range categories have since been combined, and later, a shipboard category was defined. Close and short-range vehicles are now classified as tactical UAVs, which include 50 to 1000 lb. deployable air vehicles, followed by the endurance category, which is capable of extended duration flights, typically 24 hours or greater.

Other UAVs include the Vertical Takeoff & Landing (VTOL), which is self-explanatory and typically rotary wing; Man Portable, which is light enough to be backpacked by an individual and launched by a hand-throwing or sling-shot mechanism, but larger than micro air vehicles; Optionally Piloted Vehicle (OPV), which is capable of manned or unmanned flight operations and typically an adaptation of a general aviation aircraft; and Micro Air Vehicle (MAV), which is defined as having no dimension larger than 15 cm (6 in.).

UAVs are getting smaller and lighter, and they need to fly further and further away from the command center. On top of this, the demand for UAVs is increasing. Because time-to-market is so important, the military has begun to purchase basic commercial-off-the-shelf (COTS) systems and adapt the configurations to meet application-specific requirements. This makes good sense, as many UAVs require very similar computing platforms and high-speed I/O, and there's no need to start from scratch for each and every system. As the missions for UAVs increase in complexity, the challenge for COTS suppliers will be the creation of more capable, smaller embedded computing systems.

A COTS-based approach also facilitates a move away from legacy systems toward newer technologies that transmit and receive data much faster, are more powerful, take up less space, and weigh less. A quad-redundant system, if based on legacy 6U VME bus, for example, requires computers that weigh 40 lbs. eachæthat's a total of 160 lbs. A version based on a 3U cPCI system can weigh as little as 9.6 lbs. and requires 50 percent less power and half the space. And because the system is based on COTS, it can be delivered to the market in half the time for much less money.

Basic systems that include a single-board computer (SBC), data bus, analogue and discrete I/O, power supply, and ample spares to accommodate growth are a prime solution for UAVs. To that end, SBS Technologies offers the Advanced Mission Computer (AMC-cPCI 3000 Series), which consists of three compartments, one containing the CompactPCI card slots, the second containing the power supply, and the third containing the external I/O connections. It is based on a 3U cPCI COTS computing platform and comes with a 500 MHz PowerPC based CM4 SBC, and proven real-time operating systems such as Wind River's VxWorks and Green Hills' Integrity. It easily integrates with other CompactPCI and PMC modules.

The key to making COTS work for the military is building systems around open-standard interfaces to allow developers to capitalise on technology insertion; that is, to upgrade individual modules while maintaining backplane compatibility.

The technology insertion can usually be done without paying for the design of new modules, as long as the module and associated software adheres to industry standard bus interfaces, form factors, operating systems, and application programming interfaces (APIs). This enables system upgrades and performance increases without reengineering. In fact, SBS offers an engineering development unit (EDU) that enables software developers to write code before the rugged version is completed, rapidly reducing overall development time and speeding time-to-market.

To deal with exposure to harsh and unfriendly environments, military COTS vendors offer rugged versions of commercial products. They also take care to understand the thermal and mechanical characteristics of their boards. Other ways to make the system rugged include routing external I/O signals through the backplane to the PCB interconnect and the D38999 series front panel connectors. For cooling, the COTS mission computer system removes heat primarily through thermal conduction. By careful component selection, placement, and thermal conductivity between the CompactPCI modules and the chassis, the system can operate at temperatures up to +85° degrees C.

Designers can use a mission computer such as the AMC-cPCI 3000 Series as a starting point for UAV development, adding a graphics board, discrete I/O, or high-speed serial interfaces as required. Integration services ranging from shock, vibration, thermal modeling and analysis, board level integration, software development, and qualification are also available to speed the development process.

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