How to Distinguish Between Space Launch Vehicles and Ballistic Missiles? [Reading Science]

A photo capturing the launch scene of an intercontinental ballistic missile (ICBM) provided by the U.S. Air Force.
[Photo by AP/Yonhap News]

[Asia Economy Reporter Kim Jong-hwa] As the world is on high alert to prevent the spread of the novel coronavirus infection (COVID-19), North Korea has unexpectedly launched multiple rocket launchers (MRLs), drawing criticism in diplomatic circles.

On the 9th, the Joint Chiefs of Staff announced that North Korea launched several types of short-range projectiles toward the northeast over the East Sea from the Seondeok area in South Hamgyong Province at around 7:36 a.m. Japan responded sensitively.

Japanese Defense Minister Taro Kono stated at a press conference that among the multiple projectiles launched by North Korea at that time, at least two were short-range ballistic missiles. He claimed that both MRLs and short-range ballistic missiles were launched together. However, it is unclear whether ballistic missiles were actually included. The official announcement from the Joint Chiefs of Staff referred only to MRLs.

But how did Japan determine that ballistic missiles were launched? Honestly, if North Korea claims they were space launch vehicles, isn't there no way to prove otherwise? And how do they distinguish between space launch vehicles and intercontinental ballistic missiles (ICBMs), which are very similar?

The criterion for distinguishing space launch vehicles from ballistic missiles is the 'launch angle.' Here, the launch angle refers not to the posture angle of the launch vehicle standing upright but to the flight trajectory angle. All space launch vehicles are launched vertically, so the initial launch angle is 90 degrees.

However, since the ultimate goal of a space launch vehicle is to carry satellites and place them into a specific orbit outside the Earth, the launch angle gradually changes. Therefore, even if launched vertically at first, as it approaches the designated orbit, the vehicle's angle decreases and eventually flies close to 0 degrees.

Ballistic missiles are also launched vertically from the ground. However, ballistic missiles tilt their angle by about 23 degrees when they go into space, and at this point, due to gravity, they begin to fall back to the ground. Thus, by tracking and analyzing the rocket's trajectory after launch, it is possible to determine whether it is a space launch vehicle or a ballistic missile. Also, by calculating the launch angle and flight distance, the actual target point can be identified.

For example, if you hear news that North Korea launched a missile at a high angle and it flew 4,000 km, it means it could actually fly farther. The reason the U.S. reacts sensitively to flight distances is that if launched at a normal angle rather than a high angle, the missile can fly two to three times farther. This is why it is believed that North Korea's ICBMs can reach U.S. territories including Guam and even the U.S. mainland.

For ballistic missiles, the launch angle, i.e., the flight trajectory angle, is very important. North Korea also calculates so that experimental projectiles land precisely in international waters of the East Sea or East China Sea before launching them at a high angle. Equally important as the flight trajectory angle is the launch azimuth. Especially for South Korea, where air traffic routes are busy and diplomatic relations with neighboring countries must be considered, special attention is paid to the launch azimuth.

Naroho launch scene.
Photo by Naro Space Center

South Korea sets the launch azimuth to 170 degrees when launching the Naro space launch vehicle, which is not a ballistic missile. When launching space launch vehicles, 0 degrees is usually set as north, 90 degrees as east, and 180 degrees as south. Since the Naro Space Center is located near Japan, Taiwan, China, and the Philippines, it is launched in the 170-degree direction to avoid dangerous areas and ensure safe flight.

In this case, the direction of the space launch vehicle in flight must be adjusted. After leaving the dangerous area, it flies on a normal orbit. Although this plan is very inefficient, it is an unavoidable choice to prevent conflicts with neighboring countries and reduce risks. South Korea cannot show power like the U.S. or China, nor can it act recklessly like North Korea.

Space launch vehicles are launched vertically into the sky, but from the moment they maintain horizontal flight in space, their angle and direction are continuously calculated and adjusted according to the influences occurring moment by moment. We must not forget that placing a single satellite into Earth's orbit requires not only the manufacturing of the launch vehicle but also tremendous efforts by scientists in controlling the flight process.