In this interview with The Diplomat, Mauro Gilli, senior researcher in military technology and international security at the Swiss Federal Institute of Technology, discusses the risks associated with the potential sale of the F-35 Lighting II to countries operating high-tech Russian-made weapons systems such as the Russian-made Almaz-Antei S-400 Triumf air defense system (NATO reporting name: SA-21 Growler). He is the co-author of “Why China Has Not Caught Up Yet: Military-Technological Superiority and the Limits of Imitation, Reverse Engineering and Cyber Espionage,” published in the academic journal International Security.
The Diplomat: First of all, what is radar and what is stealth?
Gilli: Radar is the acronym for Radio Detection And Ranging: it is a system that permits the detection of an object, such as an aircraft or a ship. It emits electro-magnetic pulses and captures their echo when they bounce back from “hitting” the surface of an object. Stealth technology (also known as “Low Observable”) is a set of features aimed at reducing an object’s observability to enemy sensors such as radar, infrared, and others. Radar is clearly the most insidious enemy sensor, given that it permits very long-range detection, and thus provides time for other systems such as surface-to-air missiles or interceptors to be employed against an incoming aircraft. Accordingly, stealth technology aims at defeating first and foremost enemy radars. By reducing the observability of an aircraft to enemy sensors, stealth reduces significantly the range at which such an aircraft can be detected – an F-35 for instance can be detected by the Russian S-400 only when it is about 40 km away, too late given that the F-35 carries weapons that can strike both aerial and ground targets at a much longer range.Enjoying this article? Click here to subscribe for full access. Just $5 a month.
In very simple terms, how do radar and stealth work?
Detection is about distinguishing an object from the background. Stealth is about accomplishing the very opposite: making an object indistinguishable from the background – camouflaging it. In very simple terms, we can make an analogy between radar detection and visual detection. If I look up in the sky trying to look for an object, I might not detect anything because the sky is vast while object of interest is going to be very small, especially at long range. Accordingly, distinguishing the object from sky will be very difficult, especially when one considers clouds, sunlight, birds, smoke, etc. But my chances of detection increase significantly if I narrow down the area of the sky I have to look at; if I manage to cancel the background disturbances; or if I know what I am looking for and I manage to make it stand out in comparison to the background.
Can you explain the last two points more in detail?
Over a light blue background, like the sky, a light blue object will not stand out, and hence it will be difficult to detect. But if we manage to change the light blue background into white, the light blue object will stand out much more, thus raising our chances of detecting it. Similarly, if we manage to change the color of the object form light blue to black, it will stand out more, both over a light blue background and even more over a white background, thus raising further our chances of detecting the object. This is essentially what radar systems try to accomplish. Long-range radars help identify the area of the sky where there might be an incoming aircraft. Then, short-range radars will focus on that area trying to cancel background disturbances while trying to illuminate the incoming aircraft. Stealth technology tries to accomplish the very opposite: concealing an aircraft with the surrounding background. It does so by deflecting away rather than reflecting incoming radar waves (through their smoothened shape, by shielding the engine duct and nozzle, etc.) and by absorbing them (through special coating called in fact radar-absorbing material).
How is this related to the sale of the F-35 aircraft to countries such as Turkey or, perhaps less realistically, India?
To use the previous analogy, by possessing both the F-35 as well as the S-400, Turkey or India could figure out how to change the color of the F-35 from light blue to black, and in part how to change the color of the background from light blue to white. To put it more precisely, stealth technology is aimed at reducing the observability to radars operating at specific angles and at specific frequencies. By modulating the frequencies and angles of operations of multiple S-400 systems, one could find the weak spots of the F-35 and, more important, its unique radar returns. By feeding such data into signal processing software, the chances of detection increases markedly – one country would be able to more accurately ignore false positives and more carefully avoid false negative. In other words, if you know what you are looking for, you can more easily find it.
Do you mean that concerns about the sales of the F-35 to India or Turkey would be justified?
In general, yes. We have entered a new era of great power rivalry, and two main rivalries are emerging: The U.S. and its allies on one side, and Russia, China, and their (very few) allies on the other. The radar system India and Turkey want to buy, the S-400, is produced by Russia and employed by both Russia and China. In other words, India and Turkey are buying the very radar system the F-35 is intended to defeat.
So access to the F-35 could help Russia and China.
Essentially, this is the concern of the U.S. government. Obviously, in conflict a multitude of factors play a role – electronic warfare, decoys, counterintelligence, and operation planning are all very important. But given that stealth creates an element of surprise, the U.S. government does not want to run the risk of losing such an important advantage. This is important also for conventional deterrence: the concern that the F-35 can be detected more easily or at much longer ranges would significantly weaken the U.S. vis-à-vis Russia and/or China from a psychological point of view.
What do we know about the capabilities of the S-400? Also, how is modern air defense structured to mitigate the risk of successful sorties by stealth fighters?
The S-400 is one of the most advanced air-defense systems in the world. In part, this is the product of the massive investments in radar technology that the Soviet Union made in the last phase of the Cold War. Yet, against U.S. stealth aircraft its very remarkable capabilities might still not be enough. A couple of years ago, Aviation Week & Space Technology gathered public available data and calculated that the S-400 can allegedly detect an approaching F-22 at only 21 km distance (13 mi) and an approaching F-35 at 34 km (21 mi). The problem is that both aircraft carry air-to-ground missiles with much longer range (64 km, 40 mi). A recent report by the Swedish Defense Research Agency has cast doubt on some of the capabilities of the S-400, primarily with regard to its missile range.
Shifting to how integrated air defense systems work, search radars (i.e., long-range, but imprecise) help cue fire-control radars (short-range, but more precise) over a given area where an aircraft is supposed to be approaching. Fire-control radars need to have the time to track and engage an incoming aircraft. This is why the range of detection is important. If a fire-control radar detects an incoming aircraft only very late, it might not have enough time to either track or to engage it.
In response to the U.S. decision on the F-35, Turkey unveiled its stealth aircraft project at the Paris Air Show. What do you think about it?
A lot of what Turkey said at the Paris Air Show seems domestic propaganda. Everything can happen, but the claim that the Turkish stealth fighter will be operative by 2025, that it will be the best in Europe, and that other countries will buy it… This is simply unrealistic. China has been working on its stealth aircraft for 20 years, during which its economy and defense budgets increased at an astonishing rate. And yet, its J-20 is still in development. In the best case, Turkey will field an aircraft with some frontal signature reduction and it will call it a fifth-generation aircraft. Even if it succeeded (and it is a big if, given the massive investments required), it is going to be hard to sell it abroad. China and Russia would have no reasons to buy a stealth aircraft from Turkey, given that they are working on their indigenous programs and given that Turkey is still a NATO country. For the same reason, NATO countries would have no incentives to buy a stealth aircraft from a country that was kicked out of the F-35 program because it operates the anti-air defense system produced by Russia.
Do you think India will fare any better if it tried to launch a fifth-generation stealth fighter?
India is an interesting country in that it has accomplished a lot of impressive results with advanced commercial and military technologies, last but not least its anti-satellite test in March. I have no doubt India will be able to put its pool of highly talented engineers to good use. This said, developing jet fighters entails a myriad of never-ending and very idiosyncratic problems, each of which can have catastrophic consequences. For jet fighters supposed to reduce observability to enemy sensors, the margin of error is even smaller. As I have argued in a recent article, there are no shortcuts to the development of stealth fighters: the whole process requires a lot of effort and hence time. Countries need to develop an advanced aerospace industrial base, which entails accumulating hands-on experience at each level of the design, development, and production stage – from the engineers working on the aircraft design and features to the specialized workers applying stealth coating. Moreover, a country needs to do testing and testing and more testing until everything works perfectly. In this sense, if India decides to pursue an indigenous stealth program, it can learn a lot from the problems China has encountered and the mistakes it has made over the past years.
Will the importance of stealth aircraft decline or rise on the future battlefield?
A lot of technological advances will inevitably degrade the advantage of current stealth aircraft. Some are already happening, like the employment of more powerful and accurate sensors (such as gallium nitride, for which in fact there are some spy-movie like stories). In practical terms, this is will not be the end of stealth: it means that the range at which current stealth aircraft can be detected will increase. In turn, these dynamics will very likely lead to further advances in military aviation, some of which are already taking place. The first is the pursuit of sixth-generation aircraft. From the designs that have been shown so far, we can infer that their goal is to minimize even further radar reflections (flying-wing shape, lack of vertical fins, etc.). The second is the pursuit of superior speed – that’s the hypersonic race that has received so much attention. For example, the SR-71 Blackbird could be detected by Soviet air-defense systems, but they could not engage it – at Mach 3, it was just too fast. The third reaction to the improvements in sensors will be the integration of stealth aircraft like the F-35 with forward unmanned sensors and shooters. In other words, manned stealth aircraft will move backward with respect to the theater of operation, while unmanned aircraft will operate closer to enemy anti-air defense systems or aerial platform (as discussed in a CBSA report, from page 43 onward).