YDH-28

The YDH-28 (Formal designation: 28식 대함 유도탄 / 二八式對艦誘導彈, i-pal-sik daeham yudotan, "Type 28 anti-ship missile;" Short designation 유대함-28 Yudaeham-ipal "YDH-28") is a type of subsonic anti-ship missile developed in Menghe during the early 2000s. It is intended as a heavier, longer-range counterpart to the YDH-26, and it can be fired from the Mark 41 Vertical Launching System or from specialized vertical launch tubes on submarines. It also has a land-attack cruise missile variant, designated SY-28.

Development

In 1996, the Menghean Navy commissioned a study evaluating the advantages of supersonic and subsonic missiles for anti-ship missions. Previous development work under the Democratic People's Republic of Menghe had focused on heavy supersonic missiles like the YDH-23, and while the subsonic YDH-24 represented a major improvement over the YDH-22, it was still regarded as a disappointing weapon. Though the MoND's naval doctrine staff still favored heavy supersonic missiles, the theoretical study concluded that intermediate-range subsonic missiles could deliver the same warhead at a greater range on a smaller airframe, with similar resistance to jamming and more difficult detection. Contemporary experience supported these findings: The YDH-25, licensed from Letnia, had a range of 120 kilometers in a lo-lo trajectory, only slightly more than the small YDH-26 was projected to achieve. Another deciding factor came in 1999, when Menghe and Tír Glas began negotiations on a production license for the Mark 41 Vertical Launching System. Though the license was not approved until 2001, and the first Menghean ships carrying Mk 41 modules did not go to sea until 2005, the possibility of a domestic or foreign vertical launch system revealed the need for a compact, vertically-launched, long-range anti-ship missile.

The YDH-28 was developed in parallel with the lighter, shorter-ranged YDH-26, and was intended to complement it, not replace it. While the YDH-26 was designed by the Buksŏng Industries Group, formerly Institute 92, the YDH-28 was designed by the Navy Development Arsenal. It incorporated some components and experience from Buksŏng, but most development was conducted by the Menghean Navy as an in-house endeavor. The missile entered production in 2007, first for surface ship VLS, with deliveries of the submarine-launched variant beginning in 2009.

Design

For easier manufacture, upgrading, and modification, the YDH-28 is composed of four modular sections: the guidance unit, the warhead, the fuel and wing section, and the propulsion section. On variants of the missile not launched from fixed-wing aircraft, there is also a thrust-vectoring solid-fuel booster on the rear of the missile which propels it to flight speed and angles it onto the correct trajectory. Each section can be replaced with a section of the same type in an armory, and new variants of the missile with a modified module of any type can be easily introduced.

On anti-ship models of the missile, the main guidance unit consists of a high-powered active radar seeker in the nose. This is complemented by an advanced infrared homing camera in a streamlined pod which hangs below the fuselage. On air-launched missiles this pod is permanently fixed in place, while on all other variants it is stored inside the guidance head and extends downward after launch. This allows the missile to be fired out of 533mm torpedo tubes and vertical launch canisters. All variants have a fold-out blade antenna on top of the guidance unit, for transmitting targeting information between missiles or between the missile and a ship or aircraft.

The next segment contains the missile's warhead. Anti-ship models use a cylindrical warhead with recessed metal grooves cut into the outer sides; when the warhead detonates, these radiate outward as explosively formed penetrators, increasing the probability of damage to fuel lines, electrical wiring, engines, electronics, and weapon systems beyond the impact point. A variant with a single 500mm forward-facing shaped charge was tested, but never deployed.

The body of the missile contains liquid fuel for the turbojet engine. It also houses the main wing surfaces, both of which fold into the missile body in an overlapping layout before launch. Hinged, spring-loaded panels hold covers over the wing storage slots before launch, and after the wings extend these covers fold back over the empty slots, reducing air resistance. All anti-ship models of the missile have a range of 700 kilometers, though extended-range versions of the SY-28 land-attack missile exist.

Cruise propulsion is provided by a turbojet engine in the rear fuselage module. Air is drawn in through a recessed intake in the bottom of the missile body. A fold-down scoop-type intake was considered in development, but tests found that the current design achieved adequate airflow with fewer moving parts. In storage the intake is covered by a watertight plate, which blows off with the help of exploding bolts when the missile transitions from the solid-fuel booster to the cruising engine.

Flight trajectory

One of the interesting features of the YDH-28 is its smart programming. Each missile can be programmed to follow a custom trajectory after launch, approaching the target on a different axis from the launch platform to avoid detection or evading the locations of known screen ships. The shipboard user interface, also present on bombers (though not strike aircraft) assists in setting up trajectories so that missiles on different courses arrive on target at the same time, overwhelming the enemy's missile interception capabilities. By default, the YDH-28 follows a sea skimming trajectory for the entire flight, and if it passes over land it can enter a terrain-following radar mode to fly low over hills and mountains. The terrain-following radar also reduces the probability of colliding with rogue waves and aids navigation in rough seas.

Once a group of missiles is 50 kilometers from the designated target area, one missile climbs to an altitude of 100 meters and begins scanning for targets. Using its onboard datalink, it transmits the number and location of targets to the other missiles in the area, a useful feature when engaging ships which were detected in an area of uncertainty or which moved after the launch coordinates were generated. If the "spotting" missile is destroyed, another climbs to take its place. In a jamming-free environment, the networked missiles allocate targets among themselves, assigning multiple missiles to large radar contacts (carriers, cargo ships). The launch platform can also pre-program target selection parameters. In a high-jamming or high-EMCON environment, each missile randomly selects a target, with selection weighted toward large targets.

With targets allocated, the "spotting" missile drops to sea-skimming altitude, and groups of missiles fan out to approach from multiple angles at the same time. During the final approach, the missiles carry out pseudo-random evasive maneuvers to avoid gunfire and surface-to-air missiles. The high-powered radar seekers are designed to burn through jamming by ship-based antennas and jamming decoys, and the imaging-infrared seeker cross-references targets to further improve jamming resistance. If a missile does overshoot its target due to countermeasures, it circles back to re-engage from the other side.

SY-28

The SY-28 (Formal designation: 28식 순항 유도탄 / 二八式巡航誘導彈, i-pal-sik sunhang yudotan, "Type 28 cruise missile;" Short designation 순유-28 Sunyu-ipal "SY-28") is a land-attack cruise missile based on the YDH-28 airframe. It uses the same missile body, turbojet engine, and launch interface as the YDH-28, but with a different warhead module and guidance system. Rather than active radar homing, the SY-28 relies on a combination of inertial guidance, satellite guidance, and terrain contour matching, and can follow a pre-programmed indirect course to the target, including low-altitude terrain-following to avoid detection. Like the YDH-28, the missile's datalink can also transmit targeting information to a nearby friendly ship or aircraft, useful for assessing strike damage from preceding missiles.

See also

• YDH-24
• YDH-26