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Aviation History
1983
1983 - 0535.PDF
powered electric actuators. The antenna for the command-inertial datalink sits next to the rocket-motor nozzle looking aft. The missile will be delivered as an all-up round, fuelled and armed and ready to fire. Existing handling gear will be used, with self-test initiated once the weapon is on the aircraft. Amraam has three distinct guidance phases: command-inertial, autonomous inertial, and active terminal. Targets are detected by the aircraft fire control radar operating in track-while-scan mode. In the case of the F-18's Hughes APG-65 radar, the ten highest-priority targets— based on range and closing velocity—are kept on file, and the top eight are presented to the pilot on his radar display. When the pilot designates a target for attack, its position is automatically loaded into the missile's inertial reference unit. Up to the moment of launch the missile and aircraft share a common inertial reference. After launch only the aircraft knows the target's latest position. If the opponent is "benign" the missile will con tinue on inertial guidance until close enough to switch on its active radar seeker. If the target is manoeuvring, however, its position as stored in the missile's memory must be updated. This is achieved using the low-power sidelobes of the air craft fire control radar. The missile's inertial reference unit is provided with the latest target position once every "frame", or complete scan of the radar. Command-inertial midcourse guidance allows up to eight Amraams to be guided simultaneously to eight different targets, with the fire control radar continuing to scan to detect new targets. Time-to-go to active-radar switch-on is displayed to the pilot, allowing him to cease updating and FLIGHT International, 26 March 1983 Command-inertial .guidance -Autonomous range . Terminal • -=E3TJE^S53& Amraam relies on active-radar terminal guidance for beyond-uisual-range fire-and-forget capability to break off the attack once the missile has acquired its target. If at any point his opponent ceases to be able to manoeuvre outside the missile seeker "basket", the defender can stop updating, allowing the missile to continue on inertial guidance until within active-radar range. Amraam's X-band radar seeker has a choice of modes depending on the type of target. High pulse-repetition-frequency transmission is best for long-range, look up targets, and medium pulse-rate pulse- Doppler for look-down attacks. Home-on-jam The above modes are used when the target is "in clear". If the attacker is using self-screening electronic counter- measures the missile can be launched on to midcourse and terminal radar home-on- jam guidance. The missile is able to switch in and out of this mode several times during its flight. For short-range attacks, where the pilot acquires his target visually, Amraam can be fired along the aircraft boresight directly into active-radar mode. This provides launch-and-leave capability in close combat. Firing trials have demonstrated some of these modes. The first guided launch, from an F-16 on August 26,1981, scored a direct hit on a QF-102 target drone. The test demonstrated integration with the F-16's fire-control system, and the missile's active-radar terminal guidance. The second guided launch, from an F-15 on November 23, 1981, scored another direct hit against a QF-102. The engage ment was a look-down/shoot-down tail attack, with the F-15 at 6,000ft, Mach 0-75, closing on the QF-102 at 1,000ft, Mach 0-7. Cued by the F-15's radar and launched by its stores control system, the missile demonstrated inertial midcourse guidance, then acquired its target in ground clutter. The sixth and final prototype firing, late in 1982, demonstrated the weapon's ability to intercept a low-flying aircraft using self-screening electronic counter- measures. The missile was launched from an F-15 at 16,000, 20km from a QF-102 drone flying towards the F-15 at 400ft. Launched into command-inertial guidance, and switching to active radar to acquire then intercept the target, the missile passed within warhead lethal radius. At the time Hughes announced that the six prototype Amraams had scored two direct hits, one successful intercept (the sixth missile), a partial success when the missile completed its inertial phase but failed to lock on using its active radar seeker, and two failures. In each case the problems were clearly defined, says Hughes, and corrections were made in subsequent missiles. Amraam's shape is constrained by the space available on aircraft designed around the Sparrow F-14 Launcher F-15 Launcher access uplock forward and rear F-14 Cavity AIM-7F outline AMRAAM outline F/A-18 Gear doors F-15 Engine access (aft) F-15 Gear door (forward)
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