A Boeing-led team has demonstrated that a group of EA-18G Growler electronic attack aircraft, connected by a prototype data link, can track a moving ship accurately enough to guide a missile to it, without the help of radar.

In follow-on tests, proposed for next year, the Growlers would be linked to an F/A-18E/F Super Hornet fighter carrying an infrared search-and-track (IRST) system for long-range detection and tracking of airborne targets.

Along with the U.S. Navy's pursuit of a highly modified, longer-range Block III version of the Raytheon AIM-9X infrared-guided missile (AW&ST July 8, p. 26), the passive targeting program reflects rising concern about the use of advanced jamming technologies by potential adversaries. These use digital radio-frequency memory (DRFM) chips that can intercept, record and mimic incoming radar signals rapidly and accurately, providing very effective jamming.

DRFM technology has been in existence since the 1980s and is used in European fighter self-protection suites. However, with the development of low-cost solid-state RF technology for commercial communications, it is becoming much more accessible and being exported by Russia and other nations. In October 2012, for example, U.S. Navy F/A-18Es visiting Malaysia flew in formation with Malaysian air force Sukhoi Su-30MKMs that carried Knirti SAP-518 jamming pods, previously seen only on Russian Su-34s. The SAP-518 is a new, high-power system that is believed to use DRFMs.

In the Growler demonstration, conducted during the Navy's Fleet Experimentation 13 campaign out of NAS Patuxent River, Md., two EA-18Gs and an E-2D Advanced Hawkeye airborne early warning aircraft were fitted with an additional Harris Corp. processor running Rockwell Collins tactical network targeting technology (TTNT) software and a Northrop Grumman time-difference-of-arrival (TDOA) algorithm.

RF emitters aboard ships were detected by the passive electronic surveillance measures (ESM) aboard the aircraft (the Growler's Northrop Grumman ALQ-218 and the Lockheed Martin ALQ-217 on the E-2D). By comparing the difference between the times of arrival of the signals at each platform, the system could precisely geolocate the targets. The system can work with two platforms, but can resolve ambiguities faster with three.

The most important advance, according to Boeing's director of innovation and capability growth, Paul Summers, was to show that a target moving at 15 kt. could be located accurately “within the seeker bins for a variety of weapons.” The key to doing this is a multi-platform, low-latency, high-throughput data link that shares intercept data in near-real time. The demonstration also incorporated L-3 Communications' Network-Centric Collaborative Targeting data link so that target data could be sent to Air Force assets such as the RC-135 Rivet Joint.

The Navy is developing a range of “net-enabled” anti-surface-warfare (ASuW) weapons that are designed to receive target updates in flight and then identify and hit targets with radar or infrared sensors—Raytheon received a development contract in July for the latest of these, the AGM-154C-1 variant of the Joint Standoff Weapon.

“The beauty of the capability is the ability to [target] passively,” Summers adds. The attack can be carried out without using tracking radar, which may alert the target. Passive tracking is accurate at very long range, and the signals positively identify the target. An industry executive working on another net-enabled ASuW program notes that although emission control (restricting RF transmissions from ships) can in theory frustrate passive tracking, “in the real world, if you have Aegis-class ships, they transmit.” The Navy has allocated funds to incorporate networked passive ASuW targeting in operational Growlers and E-2Ds, with fielding planned in 2018.

A proposed demonstration next year will apply the same technology to air combat, in a program associated with Boeing's Advanced Super Hornet project. The goal is to add the TTNT data link and TDOA processor to a Super Hornet, using the fighter's passive sensors—high-gain ESM, using the APG-79 active, electronically scanned array radar, the ALR-67(V)3 defensive ESM and the in-development IRST—to add air-target data to the picture. The IRST provides very high bearing accuracy and its capability would be improved as a result of being cued by the RF sensors.

Combined with the AIM-9X Block III, passive air-to-air targeting would allow the Super Hornet to perform a radar-silent attack well beyond visual range, as well as bypass any adversary jamming.

The Swedish air force, with its long experience in data links, is believed to have a quiet air-to-air attack capability that was originally deployed with an upgraded version of the JAS 37 Viggen and is likely to be incorporated into the JAS 39C/D Gripen. It also requires two or more fighters with their radars working in passive mode and is used in conjunction with the AIM-120B missile. Summers notes that the Boeing team “has some knowledge of what other countries are doing.”