Andy Nativi
St. Louis
Enhanced electronic warfare systems drive U.S. Navy to improve F/A-18E/F sensor suite
Printed headline: Bug Eyes
The U.S. Navy wants to upgrade its F/A-18E/Fs with an infrared search-and-track system out of concern that increasingly sophisticated electronic jamming systems could thwart the fighter's radar system, leaving pilots "blinded" in air-to-air combat.
Although the service has been upgrading the fighter's radar, and the latest version (the APG-79 with active electronically scanned array) should have enhanced ability to nullify hostile jamming, Navy officials are worried about the proliferation of X-band electronic countermeasures systems, which could degrade radar performance. In particular, China's expansive spending on electronic warfare equipment is being carefully monitored. The service fears this build-up could compromise their own freedom to operate in the Pacific.
The addition of an infrared search-and-track system (IRST)--already standard on many Russian and western European fighters--would provide "spectral diversity" to the Navy. Even if the radar is jammed, a pilot would still be able to spot targets using the IR sensor. Also, the new subsystem could augment the radar by helping to detect hard-to-see targets, such as low- and slow-flying cruise missiles. Spotting such weapons can be a challenge for radars due to ground clutter, but missile engine exhaust plumes should be clearly visibly with the IRST.
The service is planning to field 150 of the new device on F/A-18E/F Block 2s in Fiscal Year 2012-13. Start-up development funds of $157.7 million are in the budget request now before Congress.
F/A-18 prime contractor Boeing has chosen Lockheed Martin to provide the sensor. A first prototype is set to be tested on a Super Hornet early next year through a company-funded risk reduction and capabilities demo effort. Enhanced versions of the AAS-42 electronics and optical units used on the F-14 (already available on South Korea's F-15K) will be repackaged in a modified 480-gal. fuel tank. The equipment will also feature an off-the-shelf thermal control unit.
Boeing opted for a podded solution to save money. "Originally, we considered integrating the IRST into the aircraft fuselage, on the upper nose, or on the gunbay doors, but these solutions required significant structural, electrical and cooling system modifications and, in both cases, called for relocating existing antennas," says Chris D. Wedewer, Boeing's F/A-18E/F IRST program manager. "We also investigated the possibility of putting an IRST pod on the right fuselage station, opposite the fuselage-mounted Raytheon [Advanced Targeting Forward-Looking Infrared] targeting pod, but this option came with too many operational limitations in terms of field of view," in particular when weapons are being carried, he adds.
Those limitations drove the decision to place the sensor on the centerline weapon station, traditionally the spot for the fuel tank. Since a fuel tank has already been cleared for that station, using such a device to house the IRST was seen as the next logical step. The IRST will also function as a fuel tank, with a part of a pod still able to accommodate 330 gal., Wedewer notes.
The main change to the external fuel tank will be to the front section, which will house the IRST. A fixed window will be installed, as well as a ram-air intake to provide air flow for the environment control system. The demonstrator system will provide a large air "scoop," but the operational version is supposed to be more streamlined.
One design challenge will be adjusting for weight-distribution center-of-gravity constraints. With most of the IRST hardware in the nose-section of the pod, that will not be easy and designers, as a fallback, are considering simply adding ballast in the rear section of the device to restore equilibrium. On the aircraft side, the installation addition of the IRST should be a non-issue if the F/A-18E/Fs have Advanced Mission Computers; a software upgrade is required, though.
Keeping the cost down--to around $2.5 million per pod--creates operational drawbacks, however. There are field-of-regard restrictions with this installation, which is why fighters generally have IRSR mounted on the radome. Such an installation may come in the future, Wedewer says. On the other hand, using a pod provides flexibility because they can be distributed among fleet users as needed. Initially, pods will likely be deployed with squadrons still flying the older APG-73 radar, which provides fewer counter-countermeasures capabilities than the newer model.
Pilots will have a choice of opting for the radar to cue the IRST or vice versa. A key advantage of IRST is that it remains passive, and by cross-cueing the two sensors a pilot can minimize use of the radar to just before firing a missile.
The IRST uses a long-wave sensor, operating in the 8-12-micron range for maximum detection. The device will provide targeting quality data, although not an imaging capability.