Why North Korea Launches Its Missiles In Lofted Trajectories?

trajectory paths

North Korea conducted its first test of the Hwasong-15 Intercontinental ballistic missile (ICBM) early Wednesday which puts all of US in striking range. The missile soared to an altitude ten times higher than the International Space Station.

The missile was fired at a high lofted trajectory, reaching an altitude or apogee of 4,475 kilometers and flew 950 km during a 53-minute flight before landing in Japanese waters as reported by Korean Central News Agency (KCNA)

Most of the North Korean long-range missiles use lofted trajectory, also called as high angle trajectory or high angle launching method.

Lofted Trajectory

When you throw a ball straight up (in lofted trajectory) it flies higher and lands back or falls almost at the same point it is thrown.

If you throw the same ball at an inclined 45° degrees angle (normal trajectory), this time it covers a longer distance.

lofted vs normal trajectory

Lofted trajectory is firing a missile almost vertical or straight up.

So firing a missile straight up, you will get your maximum altitude that way, but travel a relatively short distance from the missile launch site.

The latest test launch of Hwasong-15 in lofted trajectory reached apogee, or altitude of 4,500 kilometers, and traveled a distance of 960km.

Had the Hwasong-15 been fired at a shallower angle or in normal trajectory, it would have flown more than 13,000km.

Altitude/Apogee of various ICBMs in normal trajectory

U.S Minuteman III ICBM – Altitude/Apogee -1600km, Range -13,000km.

Russian TOPOL-M – Altitude/Apogee-1000km, Range -11,000km.

France M51 SLBM – Apogee -1000km, Range – (8,000Km to 10,000km).

Chinese DF-41 ICBM – Apogee – 1000km, Range – (14,000km to 15,000km).

Indian Agni 5 ICBM – Apogee – 800km, Range – (6000Km to 10,000Km).

Apogee/Altitude of ICBM in different trajectories

Lofted trajectory – greater than 2000km (4,500km for Hwasong-15)

Normal or minimum energy trajectory – (800km to 1200km)

Depressed trajectory – (95km to 300km).

Lofted high angle launching method 

1) Countries like US, Russia, China and India normally test long-range missiles over the ocean to its full range. North Korea can’t test missile for its full range because it is surrounded by states, and to avoid any escalated tensions that might occur from missiles flying into or over surrounding states, mainly Japan, they reduce the range of the missiles by launching it straight up.

2) Throw a ball high, it descends earth faster. So when you launch a missile vertical to higher altitudes, the warheads would come back to earth at greater speeds putting more stress on the warhead nose cone. This means you’re thoroughly testing warhead re-entry for speeds greater than one flown on a normal trajectory.

3) A lofted launch can also make the Re-entry vehicle (RV) descend more quickly during the terminal phase. Hwasong-15 reached an altitude of 4,500km and when the warhead descends to earth from that altitude, it accelerates down faster allowing missile defenses less time to intercept.

4) Lofted trajectories will produce the longest flight times for a given range. The Hwasong-15 flight took 53 minutes, whereas an ICBM, if flown on a normal trajectory, would complete its full flight in just 30 minutes.

Normal or Minimum Energy Trajectory 

ICBM’S reach altitudes of 800km to 1200km on normal trajectories. The most energy efficient trajectory for flying a ballistic missile over a given range carries it high above the atmosphere. The maximum range for a given missile is achieved by traveling on such a trajectory. For an ICBM if 30 minutes is the total ICBM travel time, then 20 min of the time (the longest part of the flight called Midcourse phase) occurs outside the earth’s atmosphere.

Depressed Trajectory

A depressed trajectory (95km-300km) is a non-optimal, lower and flatter trajectory which takes less time between launch and impact, but with a lower throw-weight. The main reason to choose a depressed trajectory is to evade anti-ballistic missile systems by reducing the time available to shoot down the missile or warhead.

Depressed trajectories stay close to the earth’s surface which can help missiles and re-entry vehicles avoid radar detection. By staying close to earth they are shielded from the view of distant radars due to the earth’s curvature. Also flying low complicates the ability of some space-based systems to engage the ballistic missile.

Missiles flown on a depressed trajectory can have significantly shorter flight paths and therefore shorter flight times, than those flown on a normal trajectory of the same range. But missiles and warheads on lofted or depressed trajectories require extra energy, and extra speed, to cover a given distance.

A depressed trajectory is normally used for submarine-launched ballistic missiles (SLBM’s) which could, in principle, be brought close to the waters of the enemy nation to launch underwater nukes from Ballistic missile submarines (SSBN).

Depressed trajectories will produce the lowest flight times, followed by the minimum energy trajectory, with lofted trajectories achieving the longest flight times for a given range.

By varying the missile payload or warhead weight, different trajectories (normal, depressed or lofted) can be selected. A missile carrying a lighter payload will reach longer ranges on the same amount of fuel.

 

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