Is there a way to shoot down drones?

American RQ- 170 unmanned reconnaissance plane captured by Iran

In the 1960s, China used Soviet-made S-75 (NATO code name Sam -2) air defense missiles to shoot down the American-made U-2 high-altitude reconnaissance plane. When answering a reporter's question, Foreign Minister Chen Yi replied humorously, "We stabbed it with a bamboo pole". On February 9, 65438, Iran claimed to have captured an American drone, which was later confirmed to be Lockheed RQ- 170 Sentinel. This is a bat-like jet stealth drone, which is said to have been deployed in the battle to kill bin Laden. Iran did not say that it was stabbed with a bamboo pole, but "hit" with electronic countermeasures against soft killing. Later, an Iranian engineer revealed that after interfering with the communication of the drone, when the drone switched to GPS automatic homing, it deceived the drone by forging GPS signals. The United States claimed that this was a mechanical failure and demanded that Iran return it. Of course, Iran directly refused, and it had to dismantle the captured "sentinel" to make Iranian drones.

Which is more credible, the Iranian version or the American version, is an ongoing debate. But drones will become an increasingly important factor in future air combat. How to shoot down the drone is a problem.

As the name implies, drones are unmanned aircraft. There are two kinds of drones: remote control and autonomous control. Remote-controlled drones are remotely controlled by ground operators. In fact, it is not unmanned driving, but someone is driving in the distance. Remote-controlled unmanned aerial vehicle (UAV) requires high communication guarantee, and it is easy to work normally because of interference. Autonomous control does not need human intervention, it will not work normally because of communication interference, and it is not limited by remote control distance, but it has high technical requirements. Compared with UAV in 1960s, the autonomous control level of modern UAV has been greatly improved. Take-off, landing, simple maneuvering and ensuring the track according to the routing point can all be completed autonomously, and the operator only needs to issue high-level task-based instructions without delving into complicated details.

There are two problems in shooting down drones, one is to find and lock, and the other is to strike. UAVs are usually smaller than manned aircraft. Saving the cockpit may not necessarily reduce the weight, but the use of drones is relatively simple, mainly used for reconnaissance, and some have the function of attacking the ground. The actual combat professional ground attack UAV is still in the early stage of scientific research, and the UAV used in air combat has not yet stepped out of the conceptual stage. Therefore, the UAV has low maneuverability and there is no requirement for the reinforcement of the fuselage; Modern mainstream drones do not exceed high subsonic speeds, so the requirements for engines and fuselage are further reduced; Unless it is a drone dedicated to electronic warfare, there is no requirement for electronic capabilities in Hangzhou. All these make the drone relatively light and compact. Contemporary UAVs, represented by American MQ- 1 Predator, have not adopted stealth design in large numbers, and are mainly used in environments without air and air defense threats from the other side. A new generation of UAV, represented by RQ- 170 Sentinel, adopts a lot of stealth technologies, such as tailless flying wing layout, air inlet on the back of the aircraft, flat nozzle with lower shield, etc. Tailless flying wing not only has small forward radar characteristics, but also minimizes lateral radar characteristics. The rear intake of a stealth drone like RQ- 170 Sentinel also uses a wave-absorbing grille. If the "mesh" of the grating is smaller than the radar wavelength, then the grating is equivalent to a complete radar wave plate, which can reflect the radar wave in a harmless direction and avoid entering the air inlet to form cavity reflection. If the flat nozzle with downward and backward shielding is adopted, both radar and infrared characteristics are effectively shielded, and the flat nozzle is also beneficial to disperse the jet, strengthen the mixing with the ambient air and further reduce the infrared characteristics. Such a high stealth drone also has strong survivability under the threat of the other side's relatively complete air superiority and air defense. Small, stealth drones are not easy to be found by conventional air defense systems, but generally speaking, the problem of finding and locking drones is similar to that of general anti-stealth, which is a big topic, so I won't digress here.

U.S. unmanned reconnaissance plane shot down by China.

Shooting down drones is another problem. Drones are also planes. This is a simple fact. If you can shoot down the plane, you can shoot down the drone. In the 1960s, the China Air Force repeatedly used the shoddy J -6 Air Canada to shoot down the invading American unmanned reconnaissance plane. At present, it is still the most direct tactic to shoot down drones directly with fighter planes. Air-to-air missiles and artillery are effective destructive weapons. However, the particularity of UAV makes soft kill attractive.

Remote-controlled UAV is vulnerable to electronic interference. Strong jamming or deception jamming can block the remote control channel and make the UAV out of control. In theory, enemy drones can use fake signals to lure landing or counterattack. In today's highly developed digital communication and encryption technology, it is technically difficult, but it is still possible to make the drone out of control. Technically, when the remote control fails, it can automatically switch to program control, that is, automatically fly to the next standby point according to the predetermined route point, or return directly. Navigation of routing points requires GPS or inertial navigation.

GPS provides accurate navigation data through precise satellite timing and constellation coordinates. GPS has military code and civil code, the encrypted military code is more accurate, and the unencrypted civil code is open to everyone. With the use of accurate maps, civil vehicle-mounted GPS can be used on known roads with an accuracy of meters, while military GPS can achieve an accuracy of meters or even higher in any case. Technically, it is possible to suppress the interference of GPS signals with airborne navigation system. The core of inertial navigation is gyro. Traditional mechanical gyroscopes are rarely used, while ring laser gyroscopes are widely used because of their high precision and low cost. The advantage of inertial navigation is that it is completely autonomous and does not need any external signals, so it is the main navigation means of nuclear submarines, and of course it is also widely used in aviation. Even in the GPS era, when the GPS signal is lost or seriously disturbed, inertial navigation can be used instead. But the gyro has drift deviation, and the longer the time, the greater the cumulative deviation. Usually, GPS signals are used for periodic correction and drift deviation is corrected at any time.

Even the disposable precision-guided ammunition like JDAM is equipped with a ring laser gyro, and it is inconceivable that the UAV is not equipped with a ring laser gyro, so even if it can successfully interfere with the remote control and GPS, it cannot force the UAV to get out of control. In theory, you can fake the GPS signal, cheat the drone or turn it on again. But not to mention the difficulty of forging GPS signals, typical navigation systems have Kalman filtering, which makes it easy to distinguish unreasonable mutations. Kalman filter theory was established in 1960s, which is a milestone of signal processing and automatic control technology, and created the theoretical framework of predictive correction method. Simply put, Kalman filter is to predict the future state with a mathematical model according to the recent past and current state, and then correct it with the measured value to ensure the accuracy of further prediction. The mathematical model can be established by theoretical calculation or empirical data, and the reasonable range of the difference between the measured value and the predicted value can also be established by statistical method. Beyond this reasonable range, it can be confirmed that the measured values are unreliable and should be discarded with a specified probability, so that signal processing and abnormal data discrimination go beyond the traditional realm of slapping the head and relying on experience. Of course, if the deviation of the forged signal increases gently enough, Kalman filtering can also be fooled. However, it is not easy to "pour" fake GPS signals into drones, and the same problem exists in jamming remote control signals.

Russian "parking lot" electronic warfare system

Simply put, jamming is to "inject" false signals or noise signals into the other antenna to replace or drown the real signals. Omni-directional antenna has no directivity and is insensitive to aircraft attitude, but its signal gain is low and it is susceptible to interference. The GPS signal comes from the zenith, and the remote control satellite communication signal also comes from the zenith. In order to improve signal gain and suppress clutter interference, UAV should use directional antenna with strong directivity and point to zenith. Directional antenna has a main lobe and a sidelobe. The main lobe points to the signal source, and the sidelobe is inevitable due to the physical characteristics of the antenna. The antenna with good directivity has a smaller sidelobe. For example, the main lobe is like the direction of the line of sight, and the side lobe is like the corner of the eye. For directional antenna, it is best to set the interference source in the same direction as the signal source, otherwise it will only enter the antenna through the sidelobe, but this requires higher power. It's like disturbing your vision through the corner of your eye. If the intensity of interference light source is low, it will not work. If the angle difference between interference and signal is too large, the interference effect will be greatly reduced. Therefore, if you can't set jamming satellites in orbit, you can only use high-altitude balloons or high-altitude planes to take the jammer to high altitude and jam the drone from a favorable angle. But this is very demanding. The flying height of the drone itself is high, and the height of high-altitude balloons or high-altitude aircraft is higher, so it needs to be close to the flight trajectory of the drone. It is not easy to deploy high-altitude balloons to a specified height and track them in time. It is better to attack the UAV directly with high-altitude aircraft jamming, so the practicability of high-altitude top-down jamming is very limited.

If you can't fool the drone with fake GPS or remote control signals, you can scare the drone with strong interference, and you can also use electromagnetic killing to acupuncture. This is the legendary electromagnetic pulse weapon. For a UAV covered with electronic equipment, disabling the electronic system is at least as effective as destroying the engine or fuselage with explosion.

High power microwave will damage radar and electronic system, which is a fact that theoretical physicists have long predicted. 1945 During the first nuclear test in June, Fermi ordered electromagnetic shielding of electronic instruments, but many measuring instruments were still saturated by electromagnetic impact. In the early 1960s, the United States conducted many nuclear tests in space, trying to establish the influence of the electromagnetic pulse generated by the nuclear explosion in space. But physicists underestimated the power of the electromagnetic pulse generated by the nuclear explosion in space, and several test instruments were saturated and could not get meaningful readings. After greatly expanding the measuring range of the instrument and making careful preparations,1On July 8, 1962, the United States conducted another space nuclear test code-named "Starfish" at an altitude of 400 kilometers above Johnston Island in the central Pacific Ocean. A thermonuclear weapon with the equivalent of 1450 tons produces a huge fireball in space like an artificial sun. Hawaii, which is 1450 kilometers away, can see a strong flash through the clouds. Space nuclear explosion has caused strong artificial auroras in near-earth space. The New Zealand Navy, far away in the South Pacific, is conducting anti-submarine exercises at night, and the bright night sky illuminates the sea, which is a spectacle. The powerful electromagnetic pulse generated by the "Starfish" nuclear explosion saturated the readings of almost all measuring instruments. At least 300 street lamps were damaged in Hawaii, many burglar alarms sounded, and the microwave relay station of the telephone company was damaged, resulting in the interruption of telephone communication between Culai Island and other islands in Hawaii. The electromagnetic pulse damaged the solar panels and circuits on the satellites, and the three satellites immediately failed. A month later, seven satellites failed, including Telstar, the first commercial communication satellite. The cumulative effect of residual radiation eventually led to the failure of nearly 65,438+0/3 satellites in low earth orbit. The Soviet Union also conducted a similar test in Kazakhstan, in which the No.1 184 test resulted in a strong pulse of underground long-distance cables, which led to a fire in a power plant in Karaganda.

Although the electromagnetic pulse generated by nuclear explosion is powerful, it is too earth-shattering to use. Andrei sakharov, a Soviet nuclear physicist, put forward the method of explosive magnetic flux compression in 195 1 before he became an alien molecule, which compressed the coil section or the number of coils in the magnetic field at the moment of explosion of high-energy explosives, resulting in "concentration" of cutting magnetic lines and magnetic flux, thus generating powerful electric pulses. Another method is to generate high-temperature and high-pressure plasma by explosion, which flows at high speed in a catheter with electrodes, or to generate powerful electric pulses by cutting magnetic field lines. The explosive compression method can only be used once, and the magnetic fluid method can be used many times. The explosive magnetic flux compression method has been used to generate megawatt instantaneous power, and the magnetic fluid method can also generate powerful electric pulses, which can be used to drive virtual cathode tubes or other microwave generators to generate microwave pulses and emit microwave energy to the target through directional antennas.

Electromagnetic attack, like shooting, can be as deadly as a sniper rifle, or it can be fired continuously like a submachine gun. Short pulse can make the energy highly concentrated and powerful enough to destroy the military electronic system or industrial power equipment strengthened by electromagnetism; Rapid shooting can effectively deal with dense targets, or make up after missing. After all, the directional antenna of electromagnetic attack weapons also has aiming problems, but the energy density should be reduced accordingly, which is suitable for dealing with unprotected targets such as unprotected office computers and civil lighting, and also has enough lethality for simple drones without electromagnetic reinforcement.

спн-2 Jamming Station of Russian "Yard" System

Electromagnetic attacks are particularly effective for drones. The more autonomous the UAV is, the more it relies on various radars. From navigation radar to fire control radar to radio altimeter, all kinds of antennas are used to receive weak electromagnetic echoes, which are essentially amplification devices of electromagnetic pulses, so they are particularly vulnerable to electromagnetic attacks. Even if there is no antenna, the long conductor itself is a good antenna, so electromagnetic attack is also very effective for the control cable of UAV. Circuit boards lacking electromagnetic shielding are also good targets for electromagnetic attacks. Being hit by a target is similar to being hit by lightning. According to the different energy received, the damage can range from signal error code, signal saturation, circuit components burning, until the equipment is hit by strong current, and then fire and explosion.

Where there is a spear, there must be a shield, and the shield of electromagnetic attack is electromagnetic shielding. The ground system can be shielded by a tight metal cover with good grounding, but it is not easy for UAV to achieve good shielding. When the plane flies in the air, the friction between the body and the air is easy to accumulate static electricity on the surface, which is easy to attract lightning strikes and amplify the effect of electromagnetic attacks. Lightning protection of aircraft has always been a problem. Although there are discharge needles, we still try to avoid walking in the minefield, but it is not easy to avoid electromagnetic attacks. Aircraft with metal fuselage can easily disperse the energy of lightning strike or electromagnetic attack through the conductive surface, and the rest can only be resisted by the structure of the fuselage. The UAV uses a lot of composite materials, which is not only light in weight, but also good in stealth. The problem is that the conductivity of composite materials is not good, and when lightning strike or electromagnetic attack occurs, it is impossible to quickly channel energy. About 20% of lightning strikes on airplanes cause radomes to be damaged, because radomes are usually made of FRP. In the process of obtaining FAA airworthiness certificate, Boeing 787 was delayed for a long time because it did not solve the lightning protection problem of composite fuselage. UAV uses a lot of composite materials, which may eventually become a fatal weakness, especially vulnerable to electromagnetic attacks.

For decades, electromagnetic attacks have been regarded as science fiction weapons, because weapons-grade explosive magnetic flux compression devices or explosive magnetic fluid devices have never passed the test. The specific development of electromagnetic attack weapons is a tight-lipped secret in all countries, but one of the basic requirements of the next generation of strategic bombers of the US Air Force is to have electromagnetic attack capability. The next-generation bomber was originally required to start using 20 18. Now it is impossible for the US defense expenditure to shrink sharply, but the technical preparations are ready. Boeing conducted its first electromagnetic attack missile test in May 20 1 1, and its technical verification will be completed in May 20 13. The missile body, guidance and propulsion are not too special, and the key technology lies in the non-nuclear electromagnetic pulse generation technology. The computer animation released by Boeing shows that an invisible cruise missile flies quietly in the dark. When it passed by, the lights in the building went out like a spell, and the office computer with flashing screen became waste after a puff of smoke. It is not difficult to imagine that using more powerful electromagnetic attack missile warheads as air defense attack weapons can make drones "fascinated". This may be the ultimate anti-UAV way.