Rezwan Ferdaus, a U.S. citizen and graduate of Northeastern University, was arrested by the Federal Bureau of Investigation (FBI) in 2011 for supporting al-Qaida and plotting to fly a motorized airplane – loaded with explosives and controlled by a global positioning system (GPS) – into the U.S. Capitol Building and the Pentagon. Though the FBI insists the public was “never in danger,” the threat of a terrorist attack via unmanned aircraft system (UAS) technology is increasing. If someone other than FBI undercover agents supplied explosives to Ferdaus, the story would have been very different.
A UAS (commonly known as “drones”) refers to an unmanned aerial vehicle (UAV) as well as the operating system controlling the UAV from the ground. According to a research firm report, published on 28 December 2016, total UAS sales surged to 2.2 million worldwide in 2016, and an estimated 3 million UAS will be produced and sold in 2017. The numbers are concerning, with continued and increased use of UAS by the Islamic State group (IS) abroad. The U.S. intelligence community speculates whether the United States is prepared to defend against a UAS terrorist attack on U.S. soil.
Defining the Threat
Following the online release of 13 volumes of the IS’s magazine Rumiya, the world has begun witnessing terrorist attacks inspired by instructions detailed in that magazine. Rumiya, used for IS propaganda and recruitment purposes, serves as a tutorial for conducting attacks – from knife-wielding to acquisition and use of the perfect vehicle for striking crowds. IS also promotes through its online platform UAS tutorials, including how to arm an attacker with explosives. A UAS attack reduces would-be terrorists’ limitations when using trucks and vehicles against hardened targets. The question is, “How prepared is the United States to defend against an object that is easily acquired without suspicion, inexpensive, portable, and provides those instructed – or inspired by the IS – a distinct tactical advantage?”
National Counterterrorism Center Director Nicholas Rasmussen told the U.S. Senate Committee on Homeland Security and Government Affairs in September 2017 that, “two years ago [a terrorist threat using UAS on U.S. soil] was not a problem, a year ago this was an emerging problem, now it’s a real problem.” At the same Senate Committee meeting, FBI Director Christopher Wray told members of the Senate Homeland Security and Government Affairs Committee that intelligence indicates a strong terrorist interest in using UAS technology.
Wray further commented that, “We’ve seen that overseas already with growing frequency. I think the expectation is that it’s coming here imminently. I think they are relatively easy to acquire, relatively easy to operate, and quite difficult to disrupt and monitor.” The accessibility and affordability of UAS make it an increased concern. The IS had been using UAS since early 2014 to gather intelligence on the battlefield and broadcast videos online to further its propaganda platform. Since 9/11, dozens of bombing attacks using UAS have occurred.
According to the Federal Aviation Administration (FAA), nearly 700,000 UAS were registered over the past year, as the FAA requires individuals owning UAS weighing more than 0.55 lbs. but less than 55 lbs. to register before operating the UAS outdoors. The growing “off the shelf” commercial UAS industry has made the technology easily accessible and affordable to millions worldwide. Commercial UAS offer ready-to-fly small UAS (SUAS) with high-quality live video transmission, GPS auto-return home, 3- to 4-km range, and 25-minute flight times out of the box for less than $1,000. High-end commercial UAS (~$3,000) can lift between 6.5-13 lbs. and, depending on payload, fly 18-35 minutes. Also, for less than $1,000, custom-built UAS designed for heavy lifting could easily exceed the capabilities of hobbyist and aerial photography UAS from parts sourced online.
In a January 2017 article, FAA Chief Administrator Michael Huerta estimated that 7 million UAS could be sold in the United States before 2020. Given the number sold and required to register to the FAA, there clearly is a gap of unknown possession of this technology making it harder for law enforcement to detect owners and locations. In addition, users can purchase components to assemble or buy the entire UAS unit online under complete anonymity.
Determining Implications & Countermeasures
Implications exist for utilizing this technology to conduct an explosive or biological attack on both hard and soft targets. IS is technologically savvy and directs likeminded people to either direct or inspire such attacks. Several reasons make this a more plausible threat now than ever before:
- Operators of this technology can be out of line of sight and miles away, allowing for more covert operations;
- UAS technology use can avoid the typical and conventional security measures in place to deter terrorist acts;
- Low relative costs allow for disposable technology;
- The devices are quiet, which slows reaction time and detection;
- Many UAVs are equipped with cameras, which is in line with the IS propaganda platform; and
- Minimal piloting skills are required to operate this technology.
Several countermeasures are needed to combat this imminent threat. In August 2017, the Pentagon approved a policy allowing U.S. military bases to disable or destroy UAS that pose a potential threat. In May 2017, the Trump Administration proposed legislation (not yet approved) to expand the power to track, monitor, and destroy UAS to “any member of the Armed Forces, a federal officer, employee, agent, or contractor, or any other individual that is designated by the head of a department or agency.” Law enforcement agencies and the intelligence community need systems in place that effectively detect and, when necessary, stop UAS from reaching their potential targets.
Technology has both good and nefarious uses. As UAS technology advances, the likelihood of IS (or those inspired by its ideology) using this technology becomes more likely. Beginning in February 2016, the FAA has researched UAS detection technology such as thermal cameras, as well as acoustic, radio, and radar technologies, to explore ways to best detect rogue UAS at airports. However, none of these technologies offer a “perfect” solution as they all have their limitations and many remain untested.
The first obstacle to overcome is detecting the presence of UAS operations and then accurately locating the UAV. The FAA is working with various private technology companies, government agencies, and universities to solve this problem.
Texas A&M in partnership with Gryphon Sensors developed an active UAS detection system comprised of ground-based sensors and radars, combining fixed sites that are being used at Griffiss International Airport in Rome, New York. This unmanned traffic management system dubbed Skylight, has been tested with cooperation from the New York state Governor Andrew M. Cuomo, who is investing as much as $30 million in state funding toward UAS detection, management, and innovation. The mobile version of the Skylight system resembles a news van with off-road and technological capabilities, highlighting a significant disparity between the cost to own and operate UAS (less than $3,000) and the cost to detect rogue UAS (hundreds of thousands to millions of dollars for research, development, and implementation).
The required equipment to defend against small, yet effective, delivery vehicles is complex to build, maintain, and operate. However, the development of mobile detection capabilities is important for deploying on short notice to locations where expensive fixed UAS detection and management systems are not yet implemented, or to supplement defenses while more robust, fixed sites are constructed. The need for effective, accurate UAS detection and management systems is critical to support military, law enforcement, humanitarian efforts, search and rescue missions, critical infrastructure such as power plants, and general property defense.
Once located, there are several approaches for denying undesired UAS operations: physical destruction (firearms), disabling the UAS (casting nets), disrupting the wireless control or jamming GPS signal receivers, or remotely hacking the flight control software. A UAS’s proximity to people or valuable resources determines the necessary actions.
If a suspect UAV is carrying potentially hazardous cargo, forcing down the UAS with kinetic measures may not be the most prudent solution. In this instance, a protocol manipulation system can passively detect and analyze radio frequency signals transmitting on unlicensed frequencies. With this information, the system can then exploit the weaknesses in the detect-control protocol to control the UAV. Combining this technology with a kinetic mechanism offers flexibility with a multitier defense system. For example, navigate the UAV to a safe location, then disable it. A potential problem with this system though is its use of common commercial UAS control protocols, which may not consider a wide variety of custom and open-source flight control solutions.
Signal jamming and directional radio frequency interference are two more methods of denying UAS operations. Jamming GPS/Global Navigation Satellite System (GLONASS) reception can force a UAV to land using built-in failsafe mechanisms. The failsafe mechanisms address contingencies such as loss of GPS/GLONASS satellite reception, loss of radio control link, and low battery. Loss of satellite navigation could degrade the UAV and its ability to automatically hover over a specific location, making the drone more difficult to control. Loss of the radio control link would likely cause the UAV to “return home,” where it autonomously returns to a predetermined location. Commercial drones often have several low-battery conditions that are intended to save inexperienced users from crashing their expensive equipment. A low battery may cause a UAV to “return home” if it has enough power. If the battery reaches a critical state where it does not have sufficient power to return home, it could trigger “auto-land,” where the UAV would simply land wherever it is. To land the UAV, a combination of sensors assesses altitude and position via barometric pressure, ultrasonic sensors, and optical flow sensors.
Identifying Caveats & Future Efforts
Denying GPS/GLONASS may not be effective for two reasons: (1) not all UAS rely on satellite navigation; and (2) a moderately skilled operator could successfully execute a mission using manual controls with visual navigation via live feed. Triggering only one of the failsafe mechanisms could cause the UAV to land in an undesirable location, so using a sequence of signal jamming techniques offers more solutions. Following is an example of an approach to multitier denial:
- Jam the radio control and video transmission links, causing the UAV to trigger the “return home” failsafe;
Once the UAV is determined to be a safe distance away,
Jam GPS/GLONASS, causing the UAV to stop the “return home” function and it will just hover (note: the UAV will drift with the wind);
One could then disable the UAV with kinetic means or force the UAV to run itself to a critical battery state, causing it to auto-land.
The potential drawbacks of any singular denial method highlight that a multitier defense strategy would stand a higher chance of success against a wider variety of UAS types and attack scenarios.
Advancement is needed in detection technology to deter these attacks and assist law enforcement, but it will not eliminate the threat or the likelihood that attacks will happen. Similar to the many lone-wolf threats that go undetected, it is likely the UAS threat will increase in probability given the relative ease for acquiring and operating, as well as the difficultly for disrupting and monitoring this evolving technology.
The views expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Air Force, the Department of Defense, or the U.S. government.