Infrared sensors, missiles gaining ground
The U.S. Navy expects to award contracts soon for a longer-range version of the 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 Super Hornet with a infra-red search and track (IRST) system. The two systems are complementary, improving the ability of Navy fighters to operate in what a 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—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'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.
The threat that is driving Block III and IRST has not been identified, but China analyst Richard Fisher of the International Assessment and Strategy Center points to Chinese advances in X-band active, electronically scanned array (AESA) radars, which are able to be used as very powerful jammers. A large group of incoming aircraft jamming at megawatt power levels could make radar use challenging, he says.
Other air forces are farther down this road. “The U.K. went with IRST, Meteor and Asraam (AIM-132 Advanced-Short-Range AAM) on Typhoon for this very reason (intense jamming),” comments a British industry executive and former RAF fighter planner. MBDA's Asraam is not unlike the Block III concept. Its Raytheon-designed seeker is related to that of the AIM-9X, and it has a considerably larger motor.
The performance of the Typhoon's Pirate IRST has increased due to better processing and software since it entered service in 2007, says aengineer. The service-entry standard was “pretty raw.” Better processing exploits the fact that the IRST is extremely agile, capable of performing complex tailored scans, because its steering mirror is much lighter than a radar dish. It can scan faster than an AESA, in some cases, because it does not transmit. “The angular and thermal accuracy provides the processor with enough data to analyze the core and the edges” of objects in the field of view, the engineer says. “It's like a fingerprint.”
This is key to IRST performance, because as a passive system it provides no time-based range data, and has been historically susceptible to false alarms from stars, cloud reflections and ground targets. Better processing and fbriast scanning also make it possible to use geometrical techniques for range measurement.
The updated Pirate is believed to have shown its ability to detect theat significant ranges in 2010, when four of the stealth fighters were deployed to Lakenheath AFB in the U.K., according to European industry sources. Selex leads the EuroFirst consortium that produces Pirate, and its Skyward-G for the JAS 39E uses similar technology.
The Super Hornet IRST mates a new processor to the sensor of the AAS-42, which was developed in the 1980s for the Grumman F-14D. It has already been supplied to exportoperators, including South Korea and Singapore, and is under contract for Saudi Arabia's new and upgraded F-15s.