BEIJING, WASHINGTON—The appearance of a test airframe for the Mitsubishi Heavy Industries (MHI) ASM-3 this month shows that the Japanese have worked through at least five configurations for the supersonic anti-ship missile.
Instability in the integrated-rocket-ramjet design suggests difficulty in development apart from officially acknowledged inadequacy in range.
Two major variations in configurations were envisioned in 2009, just before the program was launched. Two more have been seen in photographs and an official drawing, and now there is one more.
Further, the newly revealed configuration may not be that of the production weapon.
Deputy Defense Minister Yamamoto Tomohiro published a photo of the test airframe—possibly, but not necessarily, a complete missile—after a visit to MHI’s Komaki Minami Plant at Nagoya on July 14. Obviously an air-to-surface weapon using integrated rocket-ramjet propulsion, it was accompanied by an “ASM-3” placard to remove any doubt as to its identity.
Unpainted, it was clearly not a production round.
Originally scheduled to be developed in 2003-10, the ASM-3 program was deferred to 2010-16. Last year, when it had not entered service, then Defense Minister Iwaya Takeshi said it needed to be modified for more range, because of the improved reach of naval air defense systems of “some countries” (one of which was presumably China).
The original version reportedly had a range of less than 200 km (120 mi.); the new one will be able to fly more than 400 km, the Mainichi newspaper says.
Designs have varied externally in at least five respects: there have been two body lengths, two inlet shapes, varying positions of the inlets relative to length, and differing fin sizes; and fairings running along the body have been present or not. The body may also have two different diameters. Different designs also seem to have different sizes of cross sections for ramjet inlet boxes.
The test airframe that Yamamoto revealed had the short body, aft-swept, two-dimensional inlets in a mid-length position, and fairings. And, if there are two diameters, which is difficult to judge from photographs, the test airframe had the fatter one.
The inlet shape seen on July 14 was foreshadowed in an official 2009 illustration of a missile which (the ministry implied then) would be the operational system, appearing before 2020. But that one had the long body.
Two other ASM-3 configurations have previously been seen in photographs; both had only forward-swept inlets of three-dimensional, pen-nib form. One of those missile configurations, apparently the earliest, had the long body and no fairings. Another had the short body with fairings. Another design, shown in a 2009 drawing, was similar, but its inlet positions were different.
The purpose of the fairings is unknown. They could carry fuel lines or electrical or signaling wires. Designers will normally try to minimize drag by burying such features inside a missile’s cylindrical body.
A long body would hold more fuel, consistent with greater range—yet now, after the government has said more range is needed, it displays a short body design (but perhaps a fat one). There is no guarantee that this is the currently intended production configuration.
Integrated rocket-ramjet propulsion is used for all versions that have been seen. The ASM-3 first accelerates under the power of a solid-propellant rocket in its rear. When that burns out, covers over the inlets come off and the ramjet takes over, burning liquid fuel. Ramjet exhaust goes through the rocket’s nozzle, first passing through the space formerly occupied by the rocket propellant.
The ASM-3 is supposed to arm the MHI F-2 strike fighter, which now carries the subsonic ASM-2 anti-ship missile. When the supersonic missile was judged last year as not ready for service, the F-2 was not ready to accept it, anyway: the fighter needed a new mission computer, which was still under development.
The government has not said when the ASM-3 will be ready nor when the F-2 will be ready for it.
Meanwhile, Japan is buying the Kongsberg JSM subsonic but stealthy missile for strikes against surface targets, including ships, by Lockheed Martin F-35A Lightnings.