Putin's 'invincible' missile has a very common problem

• Putin has touted Russian hypersonic weapons like the Zircon missile as impossible to defend against.
• Zircon in particular is powerful but there are limits on what it can do, a Western expert says.

Russia's Zircon hypersonic missile can do two things: fly at almost 7,000 mph, which makes it very hard to shoot down, or hit a moving ship. But it can't do both.

That's the conclusion of a British expert who says that the Zircon is a powerful weapon with major limitations.

"The operational deployment of the Zircon is an important development, but one whose significance should not be exaggerated," according to Sidharth Kaushal, a naval warfare expert at the Royal United Services Institute, a British defense think tank.

President Vladimir Putin has touted Russia's hypersonic weapons as being "invincible." Russian officials claim the 3M22 Zircon can travel at Mach 9, or about 6,900 mph, which may be too fast for current tactical anti-missile defenses.

But Putin's rhetoric can't change the laws of physics. The problem is that objects traveling at hypersonic speeds — Mach 5 and beyond — ionize the air around them, creating a sheath of plasma around the object that blocks radar signals.

Yet radar is precisely how many guided missiles home in on their targets. Once the missile arrives near a designated point, an active radar seeker in the nose switches on, scans the area, and locks on target. Similar problems affect other high-speed missiles, like China's anti-ship ballistic missiles.

"Because the missile's plasma layer precludes the use of active radar and other onboard sensors to track a target vessel in the terminal phase, the missile likely has to slow down to well short of hypersonic speeds in order to track mobile targets," Kaushal wrote.

Against targets that are fixed, like buildings on land, it's not necessary to slow down. But when hunting ships, the Zircon would probably have to slow down to supersonic speed to use its radar. If that's the case, then as it nears the target, the Zircon would not be moving any faster than earlier Russian anti-ship missiles such as the P-800 Oniks, which has a speed of about Mach 2.5, or 1,900 mph.

Supersonic missiles can be intercepted by shipboard defenses such as the US Navy's SeaRAM gun/missile system.

In addition, when the Zircon is launched, a rocket boosts it to high altitude and supersonic speed, which is necessary for the Zircon's scramjet engine to kick in and reach hypersonic velocity. The disadvantage is that unlike supersonic anti-ship missiles that can skim just above the water to avoid radar detection, the Zircon will have to stay at an altitude of about 12 miles until it gets relatively close to the target. Flying higher for longer makes it more visible to radar.

"The missile can either be hypersonic or low observable but not both in tandem," wrote Kaushal.

The Zircon should not be underestimated. A destroyer, for example, might not detect a missile until it gets to within about 15 miles, according to Kaushal. "From this point, assuming the missile is a Zircon flying at speeds of Mach 5–6, the vessel would have 15 seconds to react."

Yet Kaushal is skeptical about Russian claims that the Zircon is really operational.

The weapon was developed remarkably quickly compared to previous Russian missiles. "Furthermore, there appear to be no reported test failures, which is irregular for a new missile, especially one as complex as a hypersonic cruise missile," Kaushal noted.

The Zircon has a reported range of about 621 miles, but this is contingent on the missile being accurately guided toward the target zone: Its on-board radar can only scan a limited area, and even an aircraft carrier is a small object to spot in a big ocean. Russia also has limited maritime surveillance and detection capabilities beyond its coastal waters.

"While not much is known about the navigation system of the Zircon, the risk of plasma blackout would seem to necessitate very precise inertial guidance" as guidance from GPS or from its Russian counterpart, GLONASS, "cannot be reliably assumed," Kaushal told Insider.

Nonetheless, the Zircon may end up giving many Russian warships a hypersonic attack capability. The weapon is about 26 feet to 32 feet long, meaning it is small enough to be fitted onto smaller warships such as Admiral Gorshkov-class frigates and submarines like the Yasen-class boats that worry NATO commanders.

"It is pretty big even by cruise-missile standards," Kaushal told Insider. "That said, most vessels in the Russian fleet are being equipped to carry cruise missiles, so that is definitely a design principle for even the smaller elements of the fleet."

Michael Peck is a defense writer whose work has appeared in Forbes, Defense News, Foreign Policy magazine, and other publications. He holds a master's in political science. Follow him on Twitter and LinkedIn.