Unmanned, Virtually Unlimited

By Jeff Rhodes Posted 6 April 2011

The Kettering Aerial Torpedo, the world’s first unmanned aerial vehicle, was a remarkable piece of technology. With a wingspan of nearly fifteen feet and a length of twelve and one-half feet, this UAV, known as the Bug, was guided toward its target by a system of pre-set internal controls. After flying more than seventy-five miles at speeds close to 120 mph, an electrical circuit closed automatically, shutting off the engine. The wings were then released, causing the vehicle to plunge to earth. The Bug’s 180-pound payload of high explosives detonated on impact with the ground. The date: 1918.

Unmanned aircraft have come a long way since then.

Over the years, several names have been applied to these aircraft—drones, RPVs—remotely piloted vehicles, or UAVs—unmanned aerial vehicles. Whatever the aircraft with no people on board were called, these systems were viewed, at best, as an adjunct to the combat forces of the United States. Today, the official term is Unmanned Aircraft Systems, or UAS, and these vehicles are critical, essential components of US operations around the globe.

But in many ways, today’s unmanned vehicles have come full circle. The ability to cover ground, whether measured by range or by endurance, is a defining characteristic. The exponential leap in computing power, advanced flight controls, and materials over the last twenty years have combined to allow even small unmanned systems to carry a useful payload.

Throughout its history, Lockheed Martin has been involved with unmanned aircraft, starting with the Bug, which was developed by legacy company Dayton-Wright. Four target drone designs were built during World War II. Two small remotely piloted vehicles, including one designed to loiter and then crash into radar sites, came in the early 1970s. The MQM-105 Aquila was developed in the late ’70s to serve as the Army’s first battlefield RPV, although it was ultimately canceled for budget and technical reasons.

The ramjet-powered, high-altitude D-21 reconnaissance drone was developed in the 1960s by the Skunk Works, the company’s advanced technology division. In the mid-1990s, the Skunk Works produced the RQ-3 DarkStar, which introduced autonomous operation and stealth into the unmanned world. DarkStar, designed to penetrate defended airspace, was to team with the larger Northrop Grumman RQ-4 Global Hawk in the high-altitude reconnaissance arena. However, budget constraints in the late 1990s forced the US Air Force to choose one platform. The service opted for Global Hawk’s longer endurance.

Today, the Skunk Works, based in Palmdale, California, is responsible for a number of unmanned vehicles that vary in size and mission with capabilities that range from hypersonic speeds to loitering quite literally for years.

Desert Hawk
In July 2002, only 127 days after contract signing, the first two Force Protection Airborne Surveillance System, or FPASS, vehicles and equipment were delivered to the US Air Force. Called Desert Hawk, this system is an airborne sentry that extends the vision of ground security forces protecting a forward base.

Each Desert Hawk system consists of six aircraft, a laptop computer, one remote video terminal, and a support kit. The aerial vehicle, which can be carried in a backpack, is made of a molded, Styrofoam-like material. It has a fifty-two inch wingspan and is thirty-four inches long. It is launched by a bungee cord. The more capable Desert Hawk III configuration is used by US and British forces today. This version has one-hour endurance and can carry a one-pound payload.

After Desert Hawk was fielded, the program transferred to Lockheed Martin Mission Systems and Sensors in Eagan, Minnesota. However, with the Eagan facility set to be closed by 2013, Desert Hawk will likely move back to the Skunk Works.

Stalker is a small UAS developed in response to a request from a US government customer to fill a national need. The vehicle had to have two-hour endurance, be easily maintained, operate on specific communications architecture, and have a zoomable electro-optical sensor or infrared camera. Development took eight weeks.

The vehicle, which has a wingspan of ten feet and is six feet long, weighs about sixteen pounds and has the ability to precisely drop a three-pound payload, such as rations, ammunition, or spare batteries. It is kept aloft by an advanced chemistry rechargeable battery. “Stalker is not detectable at its operational altitude of about 1,000 feet,” noted Tom Koonce, the Stalker program manager. “From the ground, it can’t be seen or heard. It can track people or cars or monitor a building with live video in real time.”

One Stalker system consists of four air vehicles made of composite materials, two briefcase-sized ground stations, a field support kit that includes spare batteries, a battery charger, a servo repair kit, and voltage converters. The air vehicles operate autonomously. “Duct tape is a repair tool,” said Koonce. “One aircraft fits in a box that is two feet by two feet by 5.5 feet. A design point was that the entire system could be checked through an airport and could fit in a Humvee.”

The imagery kit that is part of the ground station is basically a universal translator. It can take raw imagery and convert that information—which includes georeference data—to hard video that is usable in a variety of formats or that can be emailed over a secure Ethernet connection.

One major improvement to Stalker now being tested is a new type of fuel cell. “Propane is available cheaply all over the world,” noted Koonce. “Hydrogen fuel is not that plentiful.” The switch to a fuel cell has an additional benefit—longer endurance. In test flights, a Stalker has been flown for more than eight hours.

Stalker has been deployed for three years with hundreds of flights at all altitudes and in rugged terrain and extreme temperatures. A marine version of Stalker can land on the water and floats. The Skunk Works recently received US government approval to offer Stalker to Argentina, Brazil, Japan, the United Arab Emirates, and NATO.

The Falcon Hypersonic Technology Vehicle 2, or just HTV-2, is one of the first programs to attempt to develop technologies to demonstrate critical technologies that enable long-duration, maneuvering hypersonic flight.

Funded by the Defense Advanced Research Projects Agency, or DARPA, HTV-2 is a rocket-launched, maneuverable lifting body air vehicle that glides through the atmosphere at speeds above Mach 20, or roughly 15,220 mph.

There had been a number of research efforts—some dating back to the 1950s—to develop vehicles that operate in the low hypersonic range, or Mach 5 and above. However, there was no data available for the speeds where HTV-2 flies. Everything about this program had to be developed from scratch—the vehicle, the telemetry system, the flight and reaction control system. The talents of engineers and technicians at several Lockheed Martin companies were critical in the design and development of HTV-2. Even the Minotaur IV Lite booster, a modification of an existing booster, had never been used on a mission that went downrange within the atmosphere, rather than straight up and outside the atmosphere on a ballistic trajectory.

During the first test flight of HTV-2 on 22 April 2010, the vehicle, which looks somewhat like a cone split lengthwise, separated from the booster and flew as planned for nearly ten minutes at speeds ranging from Mach 20 down to Mach 10. It then encountered higher-than-predicted adverse yaw conditions that coupled into a roll, which exceeded available control capability. The vehicle, made of a heat shield consisting of hundreds of layers of composite material and a titanium internal structure, then did what it was designed to do in the event of an anomaly—safely and automatically terminate its flight by spiraling down into the Pacific Ocean.

“This was not a low-risk mission,” said Robert Wetherall, the Skunk Works HTV-2 program manager. “And nearly everything went according to plan. We learned so much and dramatically expanded the hypersonic database. It was ten minutes of hypersonic data we didn’t have. Everyone agreed the mission was a qualified success.”

After a six-month independent engineering review board investigation, DARPA’s findings concluded that “…no major changes to the HTV-2 vehicle are required to mitigate the first flight anomaly. Engineers will adjust the vehicle’s center of gravity, decrease the angle of attack flown, and use the onboard reaction control system to augment the vehicle flaps.”

Wetherall added, “The root cause of the anomaly was that our preflight predictions of the aerodynamics weren’t quite right. It’s hard to model eight degrees angle of attack at 150,000 feet while flying at Mach 20. We have gone back to the wind tunnel, improved the instrumentation and data collection and are now updating the aero database. We want to have the best possible chance to get downrange and complete the second flight.”

The second HTV-2 vehicle is now being completed, and the second flight is scheduled for August 2011. If everything goes according to plan, liftoff will come from Vandenberg AFB, California, and the vehicle will fly west to an area about eighty miles north of Kwajalein Atoll in less than thirty minutes. At the end of the flight, HTV-2 will plunge nose-first toward earth much like the Kettering Bug—only at a speed of about Mach 4.

The X-47B, the test vehicle for the US Navy’s Unmanned Combat Air System Demonstration, or UCAS-D, program, made its first flight from Edwards AFB, California, on 4 February 2011. UCAS-D is the Navy’s effort to design, develop, and integrate an autonomous, fighter-sized, high subsonic UAS on an aircraft carrier.

Skunk Works is a teammate-subcontractor to Northrop Grumman on the X-47B. The vehicle, which has folding wings, has a wingspan of sixty-two feet and a length of thirty-eight feet. It is stealthy in design, although to reduce cost and complexity for the demonstration program, many parts are not made of stealth materials. The Skunk Works workshare includes development and fabrication of the arresting hook, control surfaces, and edges, including the engine inlet lip. Skunk Works technicians will maintain these components during flight test and carrier operations. The arresting hook system was particularly challenging because it was a clean-sheet design concept. Design of the control surfaces and edges capitalized on Skunk Works expertise and experience.

After a series of envelope expansion flights at Edwards, the X-47B will be transported to NAS Patuxent River, Maryland, in September for additional testing including land-based catapult takeoffs and arrested landings. The demonstrator will then go to Lakehurst, New Jersey, for environmental testing and then back to Pax River. “In 2013, it will be hoisted aboard a carrier,” noted Paul Wieselmann, the program director for the Skunk Works part of the X-47B program. “Once at sea, it will be catapulted off. Thirty minutes later, it will come back and make a fully autonomous, arrested landing.”

The second X-47B demonstrator will have both a probe and a receptacle for aerial refueling and will be used in the Navy’s Autonomous Aerial Refueling, or AAR, project in 2014. AAR will demonstrate the ability of a UAS to approach a tanker, make contact, and refuel in midair by itself.

The Navy issued a Request for Information in May 2010 for the new Unmanned Carrier-Launched Airborne Surveillance and Strike, or UCLASS, program. UCLASS calls for the production of a combat-ready system with early operational capability in FY 2018.

The US Navy began looking for a vertical takeoff and landing, or VTOL, unmanned system in 1999. The Marine Corps later became interested in fielding a UAS with higher speeds that could keep up with the V-22 Osprey tiltrotor. The services today are developing near-term systems in the Fire Scout and Eagle Eye unmanned vehicles.

“Ultimately, the military is looking for one vehicle that has both VTOL capability and survivability,” said Kevin Lewelling, the program manager for a Skunk Works-sponsored research effort called VARIOUS, for VTOL Advanced Reconnaissance/Interdiction Organic Unmanned System.

“Around 2004, we started studies into a vehicle that could accomplish all the basic requirements,” noted Lewelling. “We were looking at several propulsion types that could enable a number of lift concepts. The engine is the heart and soul of a vehicle like this.”

An engine partner was found in Teledyne Turbine Engines, which had an in-house technology development effort underway for a convertible engine, or one that operates at higher power for VTOL operations and shifts to lower power output for efficient wingborne operation.

VARIOUS is a stealthy, sweptwing design that looks similar to an F-117. The design features two lift fans that produce eighty-five percent of the vertical lift, with the remaining fifteen percent of lift coming from a down-vectored engine nozzle, similar to the F-22. Once in wingborne flight, a part of the convertible engine is shut down, and the engine operates at lower power. The design has an internal payload bay that is eighty-two inches long, sixteen inches deep, and thirty inches wide that can be used for a number of purposes, including launching weapons, conducting surveillance/reconnaissance missions, or hauling high-value cargo.

“This UAS can take off and land on any air-capable ship, including littoral combat ships,” said Lewelling. “It will extend the reach of the fleet. The Navy can get planes into combat much more quickly than a carrier battle group can.”

In 2007, the team focused on testing a wind tunnel model, developing flight control law technology, and hover rig testing. But government research funding dried up in 2008.

“The government has several UAS programs that are not working like they should. The requirements for a VTOL UAS still exist. We’ve accomplished what we need to do to make sure the aircraft can fly and operate in all modes. Propulsion development will continue, and the engine will be ready when a formal VTOL UAS program starts,” concluded Lewelling. “In the meantime, we will decide whether to build a demonstrator on our own to prove its viability.”

RQ-170 Sentinel
On 4 December 2009, the US Air Force acknowledged, via a written statement, the existence of a low observable UAS built by the Skunk Works called the RQ-170 Sentinel.

The official statement says in part, “The RQ-170 provides reconnaissance and surveillance support to forward deployed Combat Forces. The fielding of the RQ-170 aligns with Secretary of Defense Robert M. Gates’ request for increased intelligence, surveillance, and reconnaissance (ISR) support to the Combatant Commanders and Air Force Chief of Staff Gen. Norton Schwartz’s vision for an increased USAF reliance on unmanned aircraft.”

The RQ-170 is operated by the 30th Reconnaissance Squadron at Tonopah Test Range, Nevada. The 30th RS is assigned to the 432nd Wing at Creech AFB, Nevada. To date, no photographs of the RQ-170 have been officially released.

“Our engineers say this project is as difficult to develop as the SR-71 was in the 1960s,” said Eric Hofstatter, the program director for the Integrated Sensor Is Structure, or ISIS, project. “But like the ‘Blackbird,’ ISIS will be a game-changer.”

ISIS began as a DARPA program in 2004. The concept is to place an ultralarge phased-array radar that can track moving air and ground targets day or night over a very large area from an altitude of 70,000 feet, remain motionless, and stay on station for as few as three years or as many as twelve. “The idea is that once ISIS is airborne, it won’t come down,” Hofstatter noted.

“From that altitude, it’s possible, for example, to see all of Iraq and Iran. The US Army, Navy, Air Force, and all the three-letter government agencies, such as the CIA, can use this capability. Customs could track everything moving in the Gulf of Mexico at one time,” added Hofstatter. “And it never blinks. There will be continuous data on who came, where they came from, and where they went.”

The ISIS demonstration system will be a 450-foot long, 150-foot diameter, solar- and fuel cell-powered airship. Its Raytheon-built dual band (UHF and X-Band) low-power radar will be housed in a pill-shaped structure the size of a six-story building inside the airship envelope. The radar will have an aperture close to 600 square meters in size.

Now in Phase III, the Skunk Works, with assistance from several other Lockheed Martin companies, will build the demonstrator airship. The demonstrator will be assembled at the historic airship dock in Akron, Ohio. In April 2013, the demonstrator will be flown to the Florida Keys for a ninety-day trial. “But we’re shooting for a year,” said Hofstatter. “Weather is really not an issue. The radar has very good weather prediction. Besides, the airship can be moved 100 miles away and still be able to see what it needs to see. It’s the same with self-defense. ISIS won’t be on the front lines. Even if it were close, it can see the bad guys coming from a long way off.”

The airship features an inflated fixed tail with movable control surfaces. The radar itself is located inside the airship to balance center of gravity and center of buoyancy, so the airship will be extremely stable. Solar cells covering much of the top surface will provide power during the day and charge the fuel cells that provide power at night. The envelope is made of a flexible composite laminate called Dyneema SK78, which is used to make sails for racing sailboats. This material is lightweight and resists damage. Even the sturdiest of the four grades of the laminate that will be used on the airship is only about the thickness of a sheet of waxed paper. Electric motors will turn the large maneuvering propellers.

“The potential value and the potential savings with ISIS are staggering. ISIS could have an 1,100-to-1 advantage over existing AWACS or JSTARS platforms,” said Hoffstatter. “And it will always be on station.”


Jeff Rhodes is the associate editor of Code One.