Air traffic controllers tend to respond sharply whenever a drone appears near their airfield. At Germany’s most important airport in Frankfurt am Main, flight operations even had to be completely suspended for almost one hour in May 2019 due to a drone sighting. After all, even a small specimen can cause an aircraft to crash, for example if it gets into the engine. In the case of Frankfurt, the effects on air traffic remained modest, despite the economic damage, also at the expense of passengers. But it does not always turn out so smoothly: One incident at Europe’s seventh largest airport, London Gatwick, was particularly serious in December 2018. Two drones sighted over the tarmac paralyzed air traffic for three days in succession, around 1,000 flights were cancelled and 140,000 passengers grounded. The financial damage is estimated at 50 million pounds.
Thus far unregulated
In Germany, anyone can purchase a drone without taking a qualifying test. Their number is estimated to be at least 500,000, perhaps more than a million. More than three quarters of them are in private hands. The powerful cameras of the unmanned aerial vehicles (UAV) in particular are a reason for many to buy, as they offer private individuals the opportunity to take spectacular aerial photographs. Some of the drone pilots, however, are prepared to put people at risk just to be able to upload a sensational video on YouTube – for example of aircraft taking off and landing. Although there are clearly defined legal regulations for droning, such as restricted zones around sensitive areas as airports, the authorities lack the means to enforce these bans. And careless and reckless hobby pilots are not the only danger. Criminals and terrorists can also use drones specifically for punishable offences: from the smuggling of drugs and weapons over prison walls to attacks on different targets, many scenarios are conceivable.
Magic words: sensor fusion
As Head of Strategy at Rheinmetall Air Defence, Matthias Diem is concerned with effective methods of defence against these “non-cooperative drones.” The first step is detection. “With our expertise in military air defence, drone detection is basically not a major challenge,” Diem says. Rheinmetall offers a wide range of highly effective systems that can swiftly detect even small UAVs: from multi-mission short-range radar to the MSP600 multi-sensor platform and the FIRST infrared sensor. Rheinmetall’s high-resolution sensors will even detect whether a drone is carrying cargo or is armed.
All the sensor data then converges in the Rheinmetall Skymaster C2 (Command & Control) system – the Rheinmetall experts refer to this as sensor fusion: “We have to compare the situational map we receive from our sensors with the data from German Air Traffic Control (DFS) and determine which object located in the airspace has no business being there,” explains Diem. The Skymaster system is ideally suited for this purpose: it is directly connected to the UTM system (Unmanned Aircraft Traffic Management) of DFS and can create a comprehensive and complete situational map from the collected data. This enables the controller to quickly decide whether there is a threat or not.
Sensitive and effective
If the controller comes to this conclusion, the non-cooperative drone must be neutralized as quickly as possible. In principle, there are a whole range of effective agents available for this purpose – one also speaks of effectors. “The protection of civilian airports is the ultimate discipline, and here we operate in a highly complex and very sensitive environment,” says Diem. It’s not just the effectors that must not pose any danger to people; the non-cooperative drone must also be landed or, if necessary, crashed in as controlled a manner as possible. Firearms or lasers are practically out of the question due to the environment in which they are used.
Rheinmetall is currently relying mainly on two effectors in this area, which guarantee rapid neutralization and maximum safety for people and security for property. On the one hand, this is a so-called jammer. It uses an interference signal to block the radio link between the pilot and the drone. Depending on the drone model and its software, it either hovers, lands or crashes. There is also the possibility that the drone automatically returns to its starting point. The jammer is integrated into the Skymaster C2 system and has a range of around 2.5 kilometers, depending on the position of the remote control. But it also has its limits, as Diem explains: “The frequencies on which we can operate are heavily regulated by the authorities, because of course the jammer must not interfere with other radio signals at the airport. That limits our possibilities.”
Therefore, it is important to add at least one more effector to the jammer. In the case of the Rheinmetall solution, this is a hunting drone that literally grabs the target out of the sky. The hunter drone sits over the non-cooperative drone and launches a stable net over it at just the right moment. This brings its rotors to a standstill and the drone gets trapped in the net. “In this way, we can bring about a timely intervention and remove the drone from the danger zone,” explains Diem. The hunting drone is up and running quickly: “Once the incident arises, it only takes ten to 15 minutes for us to neutralize the ‘intruder,” explains Diem. A human pilot is nowadays sitting at the controls of the combat drone, but Diem outlines that this will not always remain the case: “We are working intensively on a fully automatic solution likely to materialize in one to two years. The combat drone has already demonstrated its skills in successful tests at the Manching Air Base under the auspices of the Bundeswehr and German Air Traffic Control. After interception, the Skymaster system also provides all the necessary data to assess whether the drone has been successfully stopped and the threat averted. This enables the air traffic controller to decide on the basis of reliable information whether flight operations can be resumed or not.