In partnership with the U.S. Air Force, Raytheon Missile Systems is developing a new version of its combat-proven AGM-88 high-speed anti-radiation missile (HARM), which significantly increases its combat versatility and effectiveness, while making it more applicable to modern rules of warfare. Known as the HARM destruction of enemy air defenses attack module, or HDAM, the new system adds a GPS receiver and fiberoptic gyro inertial measurement unit (IMU) to the existing missile.

HARM first went into action in 1986, fired from U.S. Navy F/A-18 Hornets against Libyan targets. Since then, more than 20,000 have been built and more than 4,000 have been fired in combat. The changing nature of today’s warfare has placed increasing constraints and demands on the use of anti-radiation missiles such as the HARM, and the HDAM takes these into account.

“All Western air forces are getting smaller, so aircraft attrition is more critical than ever,” Raytheon’s HARM growth manager, Michael Vigue, explained to AIN. “As a consequence, SEAD [suppression of enemy air defenses] protection is more of a priority. At the same time, the nature of warfare has changed from global war to regional conflicts in which the anti-radiation environment is more complicated than ever. There are tight rules of engagement and a need to keep collateral damage to a minimum. There are a mess of Eastern and Western systems out there, operating together. It’s become a nightmare for the pilots.”

To answer these questions, the U.S. Air Force issued a requirement for a smarter anti-radiation missile, leading to a codevelopment program with Raytheon based on a low-cost, low-risk upgrade of the HARM. “The Air Force established the parameters for the HDAM, the main one being to leverage the system without losing any of the HARM’s existing strengths,” said Vigue. “That was paramount. Sometimes when new developments are applied to systems some of the old capability is lost, but in this case it was vital that did not happen.”

HARM is a modular weapon, comprising four main components: guidance section, warhead, control section and rocket motor. This design allows new developments to be applied to one of the components with lower development costs and with lower technical risks than creating an all-new weapon. HDAM is a prime example as it upgrades only the control section and leaves the other three untouched. The new section comprises a navigation set, flight control board, GPS antenna and power supply.

Adding GPS/IMU significantly enhances the weapon’s capabilities in a number of important ways. It is highly accurate, so the HARM no longer is considered a suppression weapon. It can be targeted much more specifically as the guidance system can be programmed to attack radars only within a specified zone. Standard HARM missiles have highly sensitive seekers and will target radars over a wide area.

The GPS system geographically constrains the target hunt, so the missile will not attack radars outside that area. Conversely, the missile can be programmed with a zone of exclusion to avoid specific areas, greatly reducing the chances of collateral damage. In an anti-radar engagement, the HDAM uses the seeker as the primary sensor, aided by GPS. However, with the radar seeker function turned off, the HDAM can be used as a point-to-point weapon against non-emitting targets, using GPS coordinates alone. This last attribute could open up a new world for the HARM, as it is one of only a very few supersonic long-range strike weapons currently available.

HDAM was tested in the U.S. last year against representative threat arrays in three firings–on June 20, July 21 and November 28. The tests were so successful that further trials were deemed unnecessary. HDAM is ready for delivery and a Pentagon contract for kit upgrades is believed to be imminent. Meanwhile, Raytheon is looking to expand exports of the missile and a number of countries are interested.

The company acts as the depot for the AGM-88 system and has a replacement exchange in kind (REIK) agreement with the U.S. Air Force. Under this deal–also in place for the Maverick and Sidewinder weapons–Raytheon takes existing missiles from Air Force stock and reworks them for international customers, providing the missiles with a “tip-to-tail” warranty. For the HARM, the refurbishment process typically takes 12 months. In return, the Air Force receives credit for new Raytheon products. The system allows new users to acquire weapons at reduced cost, while allowing the USAF to maintain the currency of its own inventory.

The HDAM kit is also available for export, subject, of course, to State Department approval. Under the REIK deal, an HDAM missile could be ready for export in about 18 months.

HDAM is one of a number of ongoing developments for the HARM family. Several customers have inquired about changes to various modules, such as new warhead or seeker options, to suit new tasks for the weapon.