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Raytheon develops over-the-shoulder AMRAAM


Flight testing of improved medium-range air-to-air missile gets under way

Raytheon will begin delivering a high off-boresight (HOBS) modification for the AIM-120 AMRAAM to allow the missile to take advantage of wide-angle radar and infrared (IR) sensor suites on the next generation of fighters. Meanwhile, flight testing has just started of the AIM-120 pre-planned product improvement (P3I) missile at the US Air Force's Eglin AFB test centre.

HOBS, unlike the AIM-120 P3I programme, requires no changes to the missile's hardware, but uses modified flight control software to permit increased manoeuvrability against targets to the side or potentially behind a fighter. HOBS has been developed using Raytheon funding, but the company has a contract to deliver the new operational flight programme to the US government later this year.

"As we progress to aircraft with greater situational awareness and 360° sensors on a system that allows you to develop information, it's our objective to look at providing the agility to target those people they detect," says Calvin Derck, Raytheon senior manager business development, air-to-air missiles.

AMRAAM was designed as an active-radar-guided missile, and can be launched before lock-on and use a number of other targeting cues. The Lockheed Martin F-35 Joint Strike Fighter will feature a distributed aperture IR system providing surround vision, while the Lockheed Martin/Boeing F-22 has growth provision for a side-looking radar array. AMRAAM could also be targeted using an off-board third party sensor.

An enhanced datalink is being considered as an extension to currently funded improvements. The P3I missile, which is due to enter service in 2004, has a new reduced- length guidance section, as well as faster commercial processors, which has freed up around 150mm (6in) in the forward body for system growth.

"We've looked at pushing the warhead forward and using the space to grow the motor 6in [150mm]. This would give you substantially more range in the area of 15-25%," says Derck.

Raytheon's preference is for a new dual-pulse rocket after considering options including a liquid fuel ramjet, variable flow ducted rocket and the Evolved Sea Sparrow's larger diameter solid fuel motor.