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NEW GENERATION IR AAMS IN DEVELOPMENT

On 22nd September Dr. Jacques S. Gansler, US Undersecretary of Defense for Acquisition and Technology, signed the Acquisition Decision Memorandum for the purchase of the first batch of Raytheon AIM-9X missiles, thus heralding the final countdown to operational deployment of the new Sidewinder. "This missile is urgently needed by our fighter jets," remarks Rear Admiral James Godwin of the US Navy, heaving a sigh of relief, for by his own admission the short-range air-to-air missiles currently at the disposal of the US forces are markedly inferior to those available to some opponents. "There are a number of guided missiles on the world market which perform better than the AIM-9M Sidewinder," he adds. Above all, the MiG-29's with their R-73 (AA-11 "Archer") are viewed as a significant threat.

The Americans themselves did not take this threat seriously for a long time, for after all the Vympel R-73 has been in service since as long ago as 1986. It was not until a full ten years later that the contract to develop the AIM-9X was awarded to Hughes (now a part of Raytheon). This weapon is intended to overcome the shortcomings of the previous Sidewinder, which is not manoeuvrable enough and is vulnerable to infrared countermeasures.

For cost reasons, the AIM-9X makes use of some components from the existing Sidewinder. These include the proximity fuse and the fragmentation warhead of the AIM-9M plus the Mk.76 model 71 solid-propellant rocket motor. The span of the small delta wings at the tip has, however, been significantly reduced to 35 cm, while the control surfaces at the rear are much smaller as well.

To deliver the required manoeuvrability, especially for extreme changes of direction immediately following launch, the AIM-9X has four vanes in the rocket nozzle which can deflect the thrust in any direction. This will enable the new Sidewinder to engage targets lateral to the direction of travel of the launch aircraft.

This off-boresight capability is viewed as essential to new short-range air-to-air guided missiles. Because fighter aircraft are verging on the limits of their agility due to limited crew toleration of g forces, the missiles must be made more manoeuvrable. Ideally the pilot will have a helmet-mounted display so that all he needs to do is to look the adversary. The missile seeker will follow every head movement so that firing "around the corner" will no longer be a problem.

This enticing scenario of course also requires the gimbal-mounted seeker to have a large squint angle, ideally +/-90-o. The AIM-9X's sensor is a large thermal imager array which operates in the medium wavelength range.

The acquired data is evaluated by a powerful electronic system which, for example, filters out background noise or flares emitted by the enemy aircraft. It also calculates the optimal trajectory, since once the rocket motor has burnt out after a few seconds, the missile must continue its flight using its own energy.

Data on the range of the AIM-9X is naturally classified, but evidently the tests carried out to date have been satisfactory. Since the first missile was test launched from an F-18C Hornet on 18 March 1999 over China Lake, California, 23 test flights have been completed. In ten of them drones like the QF-4 (unmanned Phantom) were attacked, in some cases under difficult conditions with countermeasures and a noisy ground background.

Rear Admiral James B. Godwin reflects on the results with satisfaction. "The AIM-9X satisfied or exceeded all the criteria necessary for release of serial production." Subject to the outcome of negotiations which were not yet complete at the time of going to press, Raytheon is to build 143 AIM-9X's in the first production batch, with delivery to the US Air Force and the US Navy commencing in the summer of 2002.

In the meantime testing will continue. It is planned to culminate in an exercise at the end of 2002, on the basis of which full rate production will be given the go-ahead. The US armed forces intend to procure around 10,000 AIM-9X missiles over a period of 18 years. The Navy hopes to have its F-18C/D's equipped with the new missile by April 2003, while first deployments with the Air Force's F-15C/D's are due in August 2003. Then of course the F-22 Raptor, the F-16 and the F-18E/F will also be fitted with the AIM-9X.

With this substantial order under its belt, Raytheon is already looking for export business for the new Sidewinder, supported by the Pentagon. "We are currently in discussions with around 10 countries," says AIM-9X Program Manager, Colonel Jim McClendon. The first international order could be signed within a year, he believes.

Meanwhile, the competition is far from asleep. As well as the Russian Vympel R-73, there are no fewer than four other air-to-air guided missiles on offer for the close-in aerial combat mission. The Israelis were the first to respond to the appearance of the R-73, developing the Rafael Python 4. This does not have thrust vectoring control, but instead the missile has 14 fins and control surfaces.

The precise seeker design of the Python 4 is not known, but it is assumed that it is highly resistant to IR countermeasures. The software which controls the trajectory is said to also be very sophisticated. Thus, even in the terminal stage of its approach to the target, the missile still has sufficient energy to counter evasive manoeuvres. The solid-propellant motor is evidently built so as to initially deliver the maximum thrust and then to transition to a longer phase of lower thrust.

The Python 4 is in service with the Israeli Air Force. To export the missile, Rafael signed an agreement with Lockheed Martin, enabling it to be manufactured in the USA as well.

Rafael's Python 4 was one of the contenders in the Australian competition. However, in February 1998 the RAAF finally decided on the Matra BAE Dynamics ASRAAM. This missile has a long history, having originally been conceived as a European/US collaborative development programme. But one by one all the other partners dropped out and the UK Ministry of Defence continued development as a purely national programme. In April 1992 British Aerospace was awarded a development contract worth #570 million (DM 2 billion).

ASRAAM (Advanced Short Range Air-to-Air Missile) has no aerofoils and only four small control surfaces at the rear. This enables it to achieve high speed, albeit probably at the expense of manoeuvrability. One advantage this missile has is the seeker, which was originally developed by Raytheon and is largely identical to the one on the AIM-9X. This has a resolution of 16,384 pixels (128 x 128 detector elements).

Flight testing began in June 1995 at Eglin AFB in Florida, and as of July Matra BAE Dynamics had reported 22 test launches. As is customary on British weapons programmes, the schedule has slipped somewhat. Entry into service, originally planned for the end of 1998, is now not expected before the end of the year. The Tornado F.3 will be the first aircraft to be equipped with the ASRAAM, followed by the Harrier and later by the Royal Air Force Eurofighters.

While the British took their courage in their hands and decided to pursue their own programme with the ASRAAM, Bodenseewerk (BGT) succeeded in winning several other European partners to work on development of its IRIS-T. In the spring of 1998 Greece, Italy, Norway, Sweden, Germany and Canada all signed an intergovernmental agreement on the development phase, which is to run to the end of 2002.

Although IRIS-T has the same diameter as a Sidewinder, none of its components come from the AIM-9. For example, the infrared guidance system was developed by BGT. It consists of several rows of detectors which scan the environment over a mirror. The +/-90-o angle of vision is ideally suited for target designation using a helmet-mounted sight. Digital data processing produces effective IR counter-countermeasures.

IRIS-T's large fins and its rear control surfaces should make it highly manoeuvrable. The control surfaces are mechanically coupled with thrust vectoring in the nozzle of the solid-propellant motor built by Fiat Avio and Nammo.

After the first test firing of an IRIS-T from the ground in March, the first airborne launch took place in mid-October. The main issue of interest here was to see how the missile would behave on release. The aim is to begin work on a pilot batch in 2002 and to ramp up to full production from the end of 2003.

Negotiation of the production contract is currently under way. The six nations participating in the programme could purchase as many as 4,000 missiles between them, with Germany and Sweden expected to be the biggest customers. They are looking to equip the Eurofighter and the JAS 39 Gripen, amongst other aircraft.

From page 88 of FLUG REVUE 12/2000