Aerial drones have garnered a lot of attention (and controversy) for their ability to launch missile strikes for the U.S. military against enemies in Afghanistan, Pakistan and other hotspots. However, the Department of Defense is now cultivating another type of unmanned aerial vehicle (UAV) for use in combat planning, designed to soar high above the battlefield for so-called ISR (intelligence gathering, surveillance and reconnaissance) missions.
The STS-111 aircraft, which is still in prototype, is in essence a worm-like weather balloon that undulates through the Earth's lower atmosphere, guided by satellite or ground communications or programmed to operate autonomously. "It's really a communications platform that has the ability to provide ISR," says Dan Erdberg, vice president of operations for Sanswire Corp. in Aventura, Fla. Sanswire and Stuttgart, Germany-based TAO Technologies formed a new entity called Sanswire-TAO in June 2008 specifically to develop, market and sell a lineup of ISR UAVs (the STS-111 being their first).
The 33.8-meter long STS-111 is made up of four segments that form what Erdberg refers to as an "airchain" platform. The first segment consists of a bullet-shaped balloon filled with helium, making it lighter than air. The remaining three segments (connected by hinges) house a single, elongated balloon filled with a gaseous fuel made of mostly methane, making it neutrally buoyant (the balloon's mass equals the mass of the air it displaces).
All four segments are contained within a large vented bag that helps the segments move by allowing air to flow in and out. As the aircraft takes off, the gas in each of the balloons expands, forcing air out of the outer bag. At the same time a blower attached under the first segment sends air back into the outer bag. This constant flow of air into and out of the bag creates the motion that helps the STS-111 gain altitude. A small propeller affixed to the underside of the first segment provides thrust and steering.
When fully inflated the STS-111's widest point is 3.4 meters, and it can carry a payload (cameras and sensors, for example) of up to 9.1 kilograms over a distance of 2,800 kilometers. The aircraft is designed to carry out its missions at altitudes between 3,048 to 9,144 meters.
The Sanswire-TAO aircraft is different from other military drones in several ways, but the two most important are cost and flight duration. Whereas the STS-111 costs about $3 million to make, the Air Force's new "Gorgon Stare" UAV, essentially a Reaper drone fitted with wide-area surveillance sensors, costs about $15 million. And, while a fully loaded Reaper can stay in the air for a maximum of 14 hours, the STS-111 is designed to monitor enemy targets for up to two-and-a-half days before returning to base.