Unmanned aerial systems (UAS) have long since proved their worth as critical intelligence-gathering assets. But can they assure data transmission all the time? Are they secure from enemy attack? What happens when an enemy has access to weapons that can shoot down UAS or otherwise deny operations in certain areas? 
Since missions are often covert operations, information about UAS loss rates is sketchy. In the past, they were used in areas where air superiority had been gained. Uncontested by enemy air defenses, UAS were exposed to ground fire only when flying low—during takeoff and landing, to gain a better view of targets, or dropping below the cloud base on rainy days. 
While generally safe from enemy fire at high altitude, UAS are susceptible to electronic attacks on their command and control links or electro-optical (EO) systems. 

Brazil equipped its Elbit Hermes 900 UAS with the Skyeye multi-payload system to provide persistent surveillance of wide areas. Skyeye operates with the standard Compass EO/IR payload. Credit: Brazilian Air Force

Lack of air supremacy can be devastating. For example, the U.S. Air Force, the largest UAS operator in the world, has lost 14 General Atomics Reaper and Predator aircraft since January 2014, on missions over Afghanistan, Syria, Yemen, Libya and Central Africa. Some losses were attributed to enemy action, although the Pentagon declines comment. 
In recent years, Iran has increased its UAS awareness and integrated combat platforms in all major training exercises, so ground forces and air-defense units can practice shoot-down skills. In 2014, Iran reportedly downed an Israeli Hermes 450 UAS flying near its uranium enrichment center in Natanz. The Iranians have repeatedly contested incursions of U.S. platforms into its airspace. The most notable was the loss of a Lockheed MartinRQ-170 Sentinel over eastern Iran in 2011, which was attributed to electronic or cyberattack. Iran has also downed or captured a Boeing Insitu ScanEagle UAS operated by the U.S. Navy. Iranian jets attempted several times to fire at USAF Predators over the Persian Gulf, but were chased away by fighter escorts.
The Iranians also have lost quite a few UAS, deployed in support of Iranian and Iraqi forces fighting the Islamic State in Iraq. Since 2006, Israel faced incursions by Hezbollah from Lebanon, trying to fly Iranian-made armed UAS over land or the Mediterranean, to hit strategic targets in Israel.  

The Sparrow miniature multi-rotor UAS from Torquing Group has 14 acoustic sonars providing a safety bubble around it to enable safe flights in dangerous areas. Credit: Noam Eshel/AW&ST

At first, the Israeli air force (IAF) intercepted these with fighter jets. In recent years ground-based air-defense assets have been used. The IAF has shot down a number of Iranian-made Lebanese and Syrian UAS since 2006. Israeli-operated Patriot missiles recently shot down enemy UAS over the Golan Heights as they turned toward Israel. Patriot missiles also downed UAS over the eastern Mediterranean that had been launched from Gaza.
Syria is another example of counter-UAS warfare, since coalition forces face ad-hoc defenses. UAS that sometimes operate without support are vulnerable to enemy fire. In recent months Syria has shot down a number of aircraft over its territory, among them a U.S. Predator, an undisclosed Turkish platform and one that supported an Israeli air strike but has not been identified. 
In eastern Ukraine, both sides claimed to have downed UAS. Last year, the Russians said they used electronic countermeasures to down an allegedly U.S.-operated IAI/Northrop Grumman Hunter RQ-5B. The Russians did not substantiate the claim and the Pentagon denies it operated such a vehicle over Crimea. 

The U.S. Army has evaluated Boeing’s High-Energy Laser for C-RAM and C-UAV missions. Credit: Boeing/Eric Shindelbower

While current counter-UAS (C-UAS) capabilities are based on existing assets, new systems becoming available improve the ability of ground forces to deny UAS operations. 
Modern tactical radars that deploy with ground forces enable detection and early warning. For example, the AN/MPQ-64 Sentinel from ThalesRaytheon and Giraffe AMB radar from Saab are available with enhanced C-UAV capability, as part of the counter-rocket, artillery and mortar (C-RAM) upgrade that improves radar tracking of high- and low-velocity targets in the cluttered environment above the horizon. RADA’s Multi-mission Hemispheric Radar provides such capabilities in a small package suitable for deployment with tactical forces. And Russia’s NNIIRT has developed vehicle-mounted phased-array 3-D radar (1L121E) to detect UAS and guided weapons. Company sources say the radar operates on the move to provide target data for other air-defense assets. 
Being alerted to the presence of a UAS is one thing, but denying it from completing its mission is another. The most basic form of attack is GPS jamming, although this is likely to affect only the simplest aircraft. More advanced platforms employ navigation systems enabling the UAS to sense an attack and switch to inertial guidance. An anti-jamming GPS device could also render simple jamming ineffective. 

The Army operates hundreds of AAI RQ-7B Shadow 200 UAS, configured to carry multiple payloads in the payload bay as well as under wing. Some have been upgraded to carry miniature weapons, such as Raytheon’s STM or Textron’s Fury. Credit: Noam Eshel/AW&ST

Since UAS effectiveness depends on maintaining an active data link with the user, disrupting the link is a valid countermeasure. Such a capability was developed by SRC working with the U.S. Army, combining the company’s AN/TPQ-50 radar with the AN/ULQ-35 Duke electronic warfare jammer to disrupt UAS data links. Cyberattacks also exploit UAS dependence on external communications and control. 
The U.S. Army is seeking to field an air-defense system dedicated to C-RAM and C-UAV missions. The truck-mounted system will be part of the Indirect Fire Protection Capability Increment 2 Intercept Program of Record, to improve protection for rapid deployment forces on contingencies beyond 2020. The interceptor missiles that could be deployed with such a system range from the Miniature Hit-to-Kill missile from Lockheed Martin to the combat- proven Tamir, the interceptor developed for Israel’s Iron Dome C-RAM system. 
The Army-funded HEL-MD (high-energy laser-mobile demonstrator) from Boeing has defeated mortars and UAS using a 10-kw off-the-shelf laser. Rheinmetall demonstrated the ability to combine several laser beams on a single target, which develops sufficient power to destroy UAS and cruise missiles (AW&ST March 30-April 12, p. DTI 6). In 2013, the company demonstrated a successful engagement of three UAVs, using high-energy laser effectors. Even without high power, laser beams can be used against EO systems, either to dazzle sensors or burn through optics. 
To evaluate such capabilities the U.S. Defense Advanced Research Projects Agency will conduct a “High-Energy Laser Rodeo” at White Sands Missile Range, New Mexico, Nov. 15. The event will open the door for laser weapon system developers outside official Defense Department programs to demonstrate their capabilities. 
As ground forces improve C-UAV capabilities, aircraft must evolve to provide needed data. One way of doing this is with standoff capabilities similar to those used by piloted aircraft against surface-to-air missiles. UAS are limited in payload—only larger medium-altitude long-endurance versions such as the General Atomics Reaper and Predator, IAIHeron TP and Heron I or Elbit Hermes 900 carry payloads that effectively perform standoff missions. IAI recently tested a standoff payload, the M-19HD, on a Heron I. With up to seven different sensors, including large-aperture, high-zoom cameras and thermal imagers, it engaged in persistent surveillance at long range. 
The opposite trend is reducing the size and cost of UAS to enable deployment by tactical elements, where countermeasures aren’t available. Two platforms developed in Israel, the ThunderB from BlueBird and Orbiter 3 from Aeronautics, represent different approaches. Powered by an internal combustion engine, ThunderB carries a 3-kg (6.6-lb.) payload on a 20-hr. mission. Orbiter 3, powered by an electric motor, is a flying wing that deploys a 5-kg payload for seven hours. Both are designed for tactical forces at brigade level and below. They are typically equipped with payloads of 1.5-3 kg, and reportedly provide the same data collection capability as much heavier systems operating at high altitude. 
Employing integral micro-UAS on the front lines would make warfighters less dependent on larger UAS support from high command levels. These miniature tactical systems rely on winged or flying-wing platforms, such as the AeroVironment RQ-11 Raven and Wasp, IAI Birdeye and Elbit Skylark. Pocket-sized versions employ rotary wing or small multi-rotor platforms for missions. British forces in Afghanistan have used the Black Hornet nano-UAS to gain situational awareness for force protection. Black Hornet is effectively a “flying camera,” intuitively controlled by the user at a range of a few hundred meters. 
Sparrow and Firecast miniature multi-rotor vehicles from Torquing Group are fully autonomous UAS, even in complex urban terrain, and enable multiple UAVs to operate in synch with each other. In fact, Sparrow’s operation system allows one vehicle to operate autonomously for 20-40 min., or several to swarm. Each Sparrow carries 200 grams (14 oz.) of payload that is not limited to EO.