With the buildup toward a possible conflict in the Middle East and the continued concerns about homeland security, one of the key technologies to be deployed will be unmanned vehicles. Deployed on land and in the air, these unmanned vehicles will be used for all manner of surveillance, intelligence gathering, and even offensive missions. The most well known of these are Unmanned Aerial Vehicles (UAVs) and the still experimental, Unmanned Combat Aerial Vehicles (UCAVs), plus a host of ground and underwater vehicles. The distinction is also beginning to blur between a cruise missile, which can loiter over a target area before identifying and engaging its target, and UAVs in general.
UAVs come in all sizes, from small model aircraft fitted with a television camera for close-in surveillance in urban environments to very large aircraft like the Global Hawk, which can fly for more than 24 hours at very high altitude. One distinction of the larger UAVs and ground vehicles is that they can maneuver around their environment autonomously, requiring acute situational awareness, hence a lot of embedded processing power. This is not much of an issue in the air as it is unusual to encounter objects that cannot be classified easily and GPS can be used to determine position and altitude. Ground vehicles need much more information to navigate their environment successfully. In times of conflict there may not be roads to rely on, so the vehicle must be able to identify a path that it can dynamically traverse at a reasonable speed without hitting anything, falling over, or missing its objective. Sensors, which might be optical, infrared, or millimetric radar, must be stereoscopic to measure distance. Also, a wide field of view is required to preplan turns and other maneuvers. There is the possibility of other autonomous vehicles operating in the same space and the complexity of the compute task can be appreciated. This is a much more complex task than maintaining distance between you and the car in front of you on the freeway.
Small unmanned vehicles generally have minimal processing requirements, being controlled directly by an operator connected through an umbilical or high-speed video link. Onboard processing might be limited to assisted flight control or object avoidance. For example, it has been proposed that future helicopters will be able to control a swarm of these smaller UAVs to undertake relatively simple offensive missions in the battlefield without risk to the crew of the helicopter. As the size and mission complexity of the vehicle increases, so does the need for computing power and this is where VMEbus starts to fit.
Consider a future UCAV. Its mission is ultimately to replace a manned combat aircraft, probably still directed from an Airborne Warning and Control System (AWACS) aircraft. The end user’s expectation is that it will be smaller, lighter, more maneuverable, and, of course, much cheaper. This may or may not be reasonable, but if all things remain equal and a UCAV is expected to undertake the same mission as an F-16, but without a person at the controls, then how much is really going to be saved? The level of complexity will be the same, so the airframe might need to be just as large, with the need for a large heavy engine and lots of fuel.
Increased maneuverability is one issue to consider. Today’s combat aircraft are limited in their flight envelope by the person at the controls. A trained pilot can withstand around 9G before blacking out and losing consciousness, so this is typically the limit set for manned combat aircraft. There is no reason why this same artificial limit should be imposed on a UCAV. Why not go for 20G turns or even more? The limit will be set by the structural integrity of the aircraft and the equipment inside it. Conduction cooled VME cards are typically specified at 12G acceleration. That gives a comfortable margin over the 9G limit. To have a similar margin at 20G would mean aiming for 28G. To put this in perspective a 1.6-pound VME card will weigh 45 pounds at 28G and a 50-pound chassis with VME cards inside would weigh a staggering 1400 pounds.
So the way to get to reduced size, weight, and cost is not necessarily to duplicate an existing platform without the person, but to be radical with the avionics architecture so that more really does equal less.