U.S. Navy Follows U.K. Lead On Infrared Systems

By Bill Sweetman
Source: Aviation Week & Space Technology
July 08, 2013
Credit: Crown Copyright

The U.S. Navy expects to award contracts soon for a longer-range version of the AIM-9X Sidewinder, known as Block III. Not only will it be a major change to the AIM-9X—retaining only the seeker, optical target detector (laser fuze) and data link of the Block II weapon—but its development is starting before the Block II has finished operational tests.

The Block III is associated with the Navy's effort to fit the F/A-18E/F Super Hornet with a Lockheed Martin infra-red search and track (IRST) system. The two systems are complementary, improving the ability of Navy fighters to operate in what a Boeing engineer calls an “RF (radio frequency)-denied environment” that will challenge X-band systems such as fighter radars and the seeker of the AIM-120 Advanced Medium Range Air-to-Air Missile (Amraam).

With these developments, the U.S. Navy is following the lead of other air arms—notably, the Royal Air Force—in investing in non-RF sensors and weapons that work far outside the within-visual-range envelope. One key technology is better processing that has greatly improved the performance of IRST.

Competitive prototype contracts for the Block III missile's new warhead and body/motor will be issued this year and next, according to budget documents. The biggest change will be a larger, more powerful motor. The AIM-9X has the same 5-in.-dia. motor as the original AIM-9, and its improved performance over the older versions is a result of lower drag.

After competing the warhead and motor, the Navy expects to select a single Block III system design in fiscal 2015. That would lead to Milestone B approval and the start of engineering and manufacturing development in the second quarter of 2016, with developmental testing completed by the fourth quarter of 2018.

The Navy has not disclosed the Block III range target, but Raytheon's vice president for air warfare systems, Harry Schulte, says the goal “overlaps” the Amraam envelope. “It's more than a 10 percent impact,” he says. Boeing has also said that the Super Hornet IRST, tested on a Beech King Air this year, can achieve detection ranges compatible with Amraam.

Raytheon is studying options including a larger-diameter motor and pulsed motors, according to Schulte. Pulsed motors can provide a better optimized trajectory than a bigger motor, which can cause the missile to overspeed unless it flies a high, arcing trajectory. So far, however, there is no known operational pulsed motor in the U.S. The Israeli Rafael Stunner missile, under development for the David's Sling ballistic missile defense system and designed for simple adaptation into an AAM, has a three-pulse motor with boost, sustain and end-game stages.

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