What is a hypersonic missile?
A hypersonic missile flies at speeds of Mach 5 and higher, which is five times the speed of sound (3836 mph), or roughly 1 mile per second. According to reports, Russia’s upcoming Kh-47M2 Kinzhal air-launched ballistic missile is allegedly capable of reaching Mach 10 speeds (7672 mph) and distances 1200 miles.
The Tomahawk cruise missile, the United States Navy and Royal Navy’s go-to long-range missile system, is supersonic, flying at 550 mph and covering a maximum distance of 1500 miles.
Can Radar Detect Hypersonic Missiles?
Yes, radars can detect hypersonic missiles, and hypersonic missiles are not “invisible” on radar. They aren’t even low-visibility; they’re just as easy/hard to track as supersonic or subsonic cruise missiles.
Because they will be flying at greater heights than slower cruise missiles, they will be trackable at further distances from the ground. They will also produce enormous InfraRed signatures, making them easier to detect and track than slower missiles.
In general, cruise missiles are difficult to detect from the ground; however, you must track them from the air. If you don’t have aerial detection (e.g., the E-2D of the United States) that can see and target them at long range, there may not be enough time to perform an interception once ground systems detect and track them.
The term “hypersonic missiles” refers to two different types of weapons. The first is a Hypersonic Glide Vehicle (HGV), and the second is a Hypersonic Cruise Missile (HCM). There’s also a class of hypersonic weapon known as a Ballistic Missile.
All of these technologies were considered in the 1950s and 1960s, and the Ballistic Missile (BM) was chosen as the best option. The others remained in research but were not developed for mass production. The Aero-Ballistic Missile (A-B), which is one variant of the ballistic missile is becoming more prevalent today, has some parallels to other hypersonic weapons in terms of speed of flight.
A ballistic missile fired from an airplane is known as an Aero-Ballistic Missile. Like other ballistic missiles, it can have a depressed flight path (i.e., not just ballistic since it may flatten out). The BMs’ range decreases when their flight path is flattened. In common with hypersonic missiles, the Aero-Ballistic is maneuverable.
The flexibility of missiles allows the path they fly to vary significantly from what was planned shortly after launch. This is significant for longer-range missiles, in which data from a detected launch is used to instruct radar where to search for the missile later in its journey.
Let’s begin with hypersonic missiles on radar. The curvature of the earth limits the usefulness of radar, which can only see out to the horizon. With radar, the higher you go, the longer you’re visible.
The higher the altitude, the less friction there is. Lower friction has a number of benefits, including greater range. The second benefit is improved maneuverability at high speeds. A third advantage is a reduction in heat that makes the missile easier to construct and harder to detect with Infrared sensors.
The goal is to travel as high as possible, but this makes you vulnerable to long-range radar tracking. Flattening the trajectory of a ballistic (including A-B) missile reduces the amount of time it can be detected by radar. An HGV flies at the outer limit of the atmosphere, so it doesn’t arch into space like a BM. As a result, for an extended period of time than a BM, its radar return is hidden by the curvature of the earth.
Both A-B and HGV capabilities allows for missiles to maneuver, thus radar may not be looking in the correct location. The recent North Korean test of what they said was an HGV but was more likely a MaRV (a method to add some agility to a ballistic missile warhead) demonstrated this by flying a J shaped flight profile.
In actual combat, it would appear as if they fired a missile into the sea, but it would then travel down the South Korean coast and strike a target in the south of the country. So, if your radar is on the border between the two countries looking north, you won’t see the missile that is now flying from the east.
What makes a hypersonic missile more difficult to detect and track by radar is not its stealthiness, but rather the combination of employing the earth as a radar blind spot and maneuvering unpredictably.
Note that HCMs were not mentioned thus far. Because they fly at such a low altitude and are highly maneuverable, Cruise Missiles are already extremely difficult to detect on radar. The missiles in a US cruise missile strike are programmed to approach the target from every angle simultaneously.
They fly patterns that utilize mountains, hills, and other natural features to block radar signals. Even without terrain elements to further protect them, they fly low enough that ground-based radar can’t detect them until they are within about 30–40 kilometers. A HCM can’t fly as low or be as nimble! As a result of friction and shortened reaction time to changing terrain or obstructions, HCM must fly considerably higher than a subsonic cruise missile and are easier to discover and track by radar.
Finally, there’s a concept known as Plasma Stealth (a cloud of ionized gas) that deflects radar waves. This isn’t just limited to hypersonic missiles; it’s been tested on planes as well. Even the 1960s SR-71 employed a little amount of plasma stealth (via a fuel additive). Russia says that it uses plasma stealth around its hypersonic missiles to reduce their radar cross section.
Although it is difficult to assess the effectiveness of plasma stealth, the available evidence suggests that it does not reduce RCS enough for contemporary radars to be able to detect and track a target effectively. While plasma stealth may be one of the ways radar detection has been reduced, the lower trajectory and agility are far more significant factors.