Chinese Defence Today - Kh-31P / YJ-91 Anti-Radiation Missile

The Kh-31P (NATO codename: AS-17C Krypton-C) is the anti-radiation missile (ARM) developed by the Russian Zvezda Bureau. The missile was based on the supersonic Kh-31A (AS-17A) anti-ship missile designed by the same bureau. The PLA obtained an unknown number of the missile in the late 1990s, and has been developing a licensed copy under the designation YJ-91. Unconfirmed reports suggest that the PLA may also acquire Kh-31A to arm its Naval Air Force’s Su-30MK2 fighter and JH-7 fighter-bomber.

The PLAAF has been trying to obtain a “standoff” anti-radiation missile (ARM) since the early 1980s. Early attempt such as the YJ-5, based on the U.S. AGM-45 Shrike missiles captured in Vietnam, was not successful. During the mid-1990s, the PLA was able to gain access to some latest Russian military technologies, including the unfinished Kh-31P (AS-17C) ramjet-powered ARM project. China reportedly approached the Russian Zvezda Bureau for a possibly co-production of the Kh-31P, but the report was later denied by Zvezda Bureau.

Later an Internet source photo showing a Kh-31P missile in a Chinese factory at an unknown location was disclosed. Some source suggested the PLA may had obtained several non-flying examples of the Kh-31P for testing and reverse-engineering. The Chinese copy of the Kh-31P is reportedly known as YJ-91. The existence of such a development programme was indirectly confirmed by the citation of the missile designation in several Chinese publications.

During 2002~2004 the PLA purchased an unknown number (~200) of the Kh-31P missiles from Russia, possibly due to the delay in the YJ-91 development. These missiles are used to arm the Su-30MKK fighters. The Kh-31P provided the PLAAF with an advanced medium-range standoff anti-radiation strike capability, which was not previously possessed by the force.

The Kh-31P was originally developed for the Soviet Air Force specifically against the U.S. Patriot air defence missile system. The missile is capable of suppressing enemy air defence systems and make its early warning ‘blind’ by striking their radar. Zvezda Bureau is also developing an improved 200km-range model which can directly attack enemy AEW or AWACS systems.

The Kh-31P features a long slim cylinder body with a sharp nose, with four rocket boosters attached at the rear half of the missile. There are four clipped delta wings and four smaller tail surfaces of similar shape organised in cruciform configuration around the fuselage. Internally the L-112E radar seeker (D~F band) is in the nose with the guidance system, batteries and radio altimeter in the remainder of the front compartment, and the 87kg HE warhead immediately behind. A fuel tank, presumably with a kerosene-type fuel, occupies the area to the leading edges of the wing and the area almost to the rear edges is occupied by the ramjet. Much of the rear of the missile is occupied by a solid propellant booster through which runs the ramjet nozzle. Actuators are to be found below the tail surfaces.

The Kh-31 features a unique dual propulsion system designed by the Soyuz Design Bureau in Turayevo near Moscow. First the missile is accelerated by its solid-fuel rocket engine to a speed of Mach 1.8, then the engine is discarded and the interior of the missile is converted into the combustion chamber of the missile's jet engine. The latter accelerates the missile to a speed of almost Mach 4.5, while four air intake holes on the sides of the missile body open up.

Length: 5.21m
Diameter: 0.36m
Wingspan: 1.15m
Weight: 600KG
Warhead: 87Kg HE
Propulsion: Ramjet + integral solid rocket boosters
Max speed: Mach 4.5
Max effective range: 110km
Guidance: L-112E passive radar homing, D~F band