North Korea's rapidly advancing ICBM capabilities pose a growing threat to the United States and its allies, according to experts who say it will become increasingly difficult to destroy Pyongyang's missiles prior to launch with preemptive strikes.
In the latest development, North Korea suggested Tuesday it is preparing to launch an intercontinental ballistic missile on a normal trajectory similar to what would be used in a real attack, rather than on the less threatening lofted trajectory of previous tests.
North Korea successfully launched a Hwasong-17 ICBM in November, according to its state media KCNA. The ICBM, like other ballistic missiles, was fired into space on a lofted trajectory before falling into the waters between North Korea and Japan.
Facing criticism that the ICBM's capabilities "cannot be proven by a lofted-angle launch alone," Kim Yo Jong, North Korean leader Kim Jong Un's influential sister, said the missile must be fired "at a normal angle" to demonstrate that it could target the U.S.
"I'll give an easy answer to that," she said. "We can try it soon and once you see it, you'll know."
The remark came after North Korea said it tested a "high-thrust solid-fuel motor" on December 15 that would lead to "the development of another new-type strategic weapon system."
"This test is likely an incremental step towards the goal of fielding a solid-fuel ICBM," said Ian Williams, deputy director of the Missile Defense Project at the Center for Strategic and International Studies (CSIS).
"We've seen North Korea expanding its use of solid-fuel engines for its missile forces for some time, and it has just been a matter of time before we saw it apply this technology to longer-range missiles," continued Williams.
Because solid fuel can be uploaded to a missile long before launching, using solid fuel saves preparation time, making the missile less vulnerable to attacks while sitting on a launch pad.
"Solid-fuel missiles have shorter preparation time prior to launch compared to liquid-fuel missiles, making destroying them prior to launch (left of launch) more challenging," said Williams.
The Hwasong-17 ICMB launched in November is believed capable of traveling up to 15,000 kilometers, more than far enough to cover the entire U.S. territory. If the solid-fuel engine is merged with a nuclear-tipped Hwasong-17 ICBM, it would become a formidable weapon.
"As North Korea shifts to solid-propellent ICBMs, its nuclear force will become harder to target and more survivable," said Jeffrey Lewis, director of East Asia Nonproliferation Project at the Middlebury Institute of International Studies at Monterey in California.
Experts said the U.S. needs to bolster its ability to intercept a solid-fueled ICBM after it is fired as trying to preempt it prior to launch becomes increasingly difficult. The task is especially difficult if many missiles are fired at one time.
The U.S. needs to "develop, test and deploy other means of interception in addition to its limited ground-based interceptors," including "interceptions from space," said Riki Ellison, chairman and founder of Missile Defense Advocacy Alliance.
Intercepting missiles after their launches is referred to as "right of launch" missile defense. Traditional U.S. right of launch missile defenses include ground-based midcourse defense (GMD); the Aegis sea-based midcourse defense; the THAAD, which is designed to counter short- to long-range missiles; and the Patriot surface-to-air missile defense, said Williams.
Williams added the U.S. has been modernizing its GMD system to destroy complex missiles as well as developing new satellites with enhanced missile-tracking capabilities.
Potential first strike danger
The test of a solid-fueled engine following the launch of the Hwasong-17 ICBM is alarming, said Evans Revere, a former State Department official with extensive experience negotiating with North Korea.
He noted that the regime has codified a law giving itself the right to use preemptive nuclear strikes against threats seen as imminent, even if it is not attacked.
"Seen in this context, the development of this new engine may indicate that North Korea seeks to develop an easily transportable, easily concealable, high-capability ICBM that could be used to carry out a nuclear first strike against the United States or its allies," Revere said. "If this is North Korea's intention, then we are heading into an even more dangerous era in which the risks posed by Pyongyang will rise dramatically."
At the same time, a solid-fueled ICBM, along with efforts to develop submarine-launched solid-fuel ballistic missiles, indicates North Korea is trying to "develop a more sophisticated and survivable nuclear weapons arsenal that can be used to conduct a second strike in the event of a conflict," Revere added.
A second strike refers to a retaliatory strike in response to an attack or a first strike.
Ken Gause, an expert on North Korean leadership and the director of strategy, policy, plans, and programs division special projects at CNA, said more advanced tests including an ICBM launch on a normal trajectory could be on the way as North Korea responds to the deployment of U.S. strategic assets to South Korea.
As a deterrent show of force following the test of what North Korea claimed as its first spy satellite on Sunday, the U.S. sent nuclear-capable B-52 bombers and F-22 stealth fighter jets to conduct joint exercises with South Korea's F-35 and F-15 warplanes near Jeju Island, according to South Korea's military on Tuesday.
South Korea said what North Korea tested on Sunday were two medium-range ballistic missiles.