- North Korea launched another intercontinental ballistic missile on Friday. ICBMs travel in a wide arc and can strike a target thousands of miles away with nuclear weapons. The missiles are similar in construction to rockets that launch people into space. The US and other countries have yet to master technologies that can stop ICBMs.
After years of failed efforts, North Korea successfully launched its first intercontinental ballistic missile on July 4. And now the country seems to have completed a second ICBM test, US officials said on Friday.
Initial estimates indicate that the recent missile could have the longest range of any that North Korea has tested so far. Japan’s chief cabinet secretary told Reuters that it flew for 45 minutes, longer than the 39-minute flight of the ICBM tested earlier this month.
Japanese public broadcaster NHK reported that the missile flew more than 1,800 miles above the Earth’s surface on a lofted trajectory, suggesting a tremendous range.
ICBMs can do exactly what their name implies: deliver a weapon, like a nuclear warhead or nerve agents, to another continent.
Unlike other military missiles, ICBMs are feared for their long range. They can fly more than 3,420 miles (5,500 kilometers), according to an article that John Pike, an expert on national security and expert, wrote for the Federation of American Scientists.
"ICBMs create a problem because they enable a country to break out of a regional context and move toward potential global impact," Pike, who now directs GlobalSecurity.org, wrote in 1998. "Regardless of the origin of a conflict, a country may involve the entire world simply by threatening to spread the war with an ICBM."
How ICBMs work
All ICBMs are large rockets with space for a payload on top. They're typically smaller than rockets that launch satellites and people into space, but structurally, the missiles aren't too different - which is why militaries pay close attention to countries that develop human-spaceflight programs.
Most ICBMs don't enter Earth's orbit. Instead, they travel in high, arc-like paths, similar to the way a football flies when chucked far downfield by a quarterback. The difference is that an ICBM "football" touches outer space, can strike a target from thousands of miles away, and is capable of destroying entire cities.
On Friday, North Korea launched its missile into a very high arc, and Japan's NHK reported it may have landed in Japan's exclusive economic zone. But if the missile had been pointed in a more forward direction, it could have traveled much farther.
Given the information that's been reported so far, Jeffrey Lewis, the publisher of Arms Control Wonk, estimated that the missile could have a range of 6,200 miles. That reach would put almost all of the continental US in range. Experts suggested that the first ICBM North Korea tested could go as far as 4,160 miles - a range that touches western Canada and most of Alaska.
Some ICBMs burn solid fuel, while others use liquid fuel or a combination of both, but the goal is to generate enough lift and thrust to deliver a bomb to a target as quickly as possible.
The US military maintains an aging arsenal of Minuteman III missiles, which can travel at top speeds of about 15,000 mph, according to the FAS. That's nearly 20 times the speed of sound, and it allows Minuteman IIIs to strike a target within about 30 minutes from more than 6,000 miles away, accurate to within hundreds of feet.
Rockets in flight
To reach such speeds and strike with such precision, ICBMs typically have three (or sometimes four) separate rocket motors, also called stages. This is because smaller rocket motors are easier to make than one big motor, according to Pike.
The lower, first-stage rocket is sometimes called a booster. Boosters are the largest part of rockets and do most of the heavy lifting. (ICBMs weigh as much as a few school buses, mostly because of the large amounts of rocket fuel they carry.)
Once the booster has used up its fuel dozens of miles above Earth, it detaches, and the second-stage rocket motor ignites. The same process happens with any subsequent stages.
During flight, ICBMs use several tricks to stay on course, though most adjustments happen during boosting, Pike said. Flight computers can monitor a rocket's trajectory and use whirring gyroscopes to help nudge and tweak the missile's direction. Some ICBMs also use cameras to look at constellations of stars while flying high above the cloud tops, constantly feeding that information into the flight computer to adjust the missile's path.
At each stage of flight, the missile and its payload move faster and faster, though they coast for some stretches to ensure an accurate strike. All the while, Earth's gravity pulls the weapon back toward the ground on a "ballistic" trajectory. By the time the last stage has burned out, all that remains is for the payload - a nuclear warhead, chemical weapon, or biological weapon - to deploy.
The Minuteman III can carry up to three nuclear warheads at once, but today, the missiles carry just one because of international arms control agreements. More-advanced ICBMs can carry even more nuclear warheads. Before the US military's Peacekeeper missile went out of service in 2005, for instance, it could be armed with up to 10 warheads - each of which could hit a different target.
Warheads often look like black cones because they're designed to withstand the searing heat caused by reentering our planet's atmosphere at incredible speeds. Some materials gradually burn away, like the heat shields on the Apollo moon mission capsules, or block the heat, like the ceramic tiles that lined the bottom of NASA's space shuttles.
After a warhead finishes plowing through the atmosphere, it keeps falling until it reaches the target. Some warheads can deploy parachutes to slow down further and precisely release chemical or biological agents, Pike said.
Nuclear warheads detonate automatically once they reach their targets, either above the ground (to destroy a large military complex or city) or upon hitting the earth (to destroy underground bunkers and missile silos). Some warheads can also be exploded dozens of miles overhead to generate a widespread, fearsome, electronics-destroying effect called electromagnetic pulse, or EMP.
Can ICBMs be stopped?
North Korea's reported feats have heightened global tensions and fears of nuclear conflict, particularly between the US and North Korea, but also with nearby nations such as China.
ICBMs are particularly scary because of how difficult it is to stop them after launch.
Such missiles are small, fast-moving targets, so hitting one with a countermeasure is like trying to shoot down a bullet with another bullet - while moving at more than 10,000 mph. What's more, many countries, including the US, use nuclear weapons that can't be stopped after launch, even if they were sent in error or unjustified malice.
The US has spent many billions of dollars to develop technologies that can intercept and destroy ICBMs. But progress since the Cold War has been slow and expensive. In May, the US Missile Defense Agency successfully tested such a system, called the Ground-based Midcourse Defense missile shield. It destroyed a mock ICBM in mid-flight over the Pacific Ocean.
However, many experts believe the test did not prove that the US could stop a North Korean nuclear attack.
"It is not even close to demonstrating that the system works in a real-world setting," Laura Grego, a physicist at the Union of Concerned Scientists, wrote in a two-part series shortly before the test. "The GMD system is still far from being able to provide reliable protection from a real-world missile threat."