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ARTIST'S IMPRESSION OF the M-Class Frigate which is currently under consideration for the Australian and New Zealand navies. Twelve new frigates will be built eight for Australia and four for New Zealand. := i~,1#,< - f T -~/ ':!?:!~--- ~-----·-----------.. ,,,. .,_, _, GOALKEEPER last ditch antimissile defence Naval ships are extremely vulnerable to missile attack, as the Falklands and the Iran/Iraq wars have shown. The Phalanx gatling gun system was devised to combat missiles hut it has been surpassed by the Dutch-designed Goalkeeper system. Goalkeeper is being considered for the new Anzac frigates to he built in Australia. By LEO SIMPSON A ship under missile attack is in deep trouble. It has only a few seconds to identify the threat and then take drastic defensive action. If more than one missile is launched within a short time, it is in even deeper trouble. What to do? The days have long since passed when naval seamen had the ability to identify a threat and then take action to repel the attack. These days computers are used to monitor the air, identify friends and foes and to fire the weapons. The Goalkeeper is a last ditch defensive system against missiles. If the ship's medium and short range missiles have not been able to repel attacks, the Goalkeeper is intended to shoot missiles to pieces 4 SILICON CHIP before they hit the ship. The gun itself is a 7-barrel gatling gun which fires 30mm tungsten-capped shells at the rate of 4200 per minute or 70 shells a second. Muzzle velocity is 1150 metres per second. A brief burst of fire lasting only two or three seconds is enough to destroy any incoming missile after which the Goalkeeper system switches to track the next identified "threat" in readiness to destroy it too. Goalkeeper was developed by the Signaal Division of Philips and is completely autonomous. It allows incoming missiles to come quite close before it destroys them; a process which would be quite unnerving for any observer. And it has a sound unlike any other gunfire; a shattering roar at 70Hz. What was wrong with Phalanx? Phalanx is an anti-missile system fitted to some of Australia's naval ships but, as demonstrated in recent conflicts, it is not infallible. It too is a gatling gun (ie, a multiple barrel machine gun) firing 20mm "penetrators" made from depleted uranium (to make them very heavy). The problem for any anti-missile system is that it must search out and identify threatening airborne objects and then, having identified a particular threat, it must lock onto it until it is either destroyed or moves away. It then must lock onto the next threat and repeat the process. A particular weakness of the Phalanx system is that its radar system cannot do two jobs at one time. When it is tracking a particular object it cannot search the sky for other threats. Goalkeeper copes with that problem by having two radar systems. One is a search radar. It is a linear array "tube" which rotates rapidly at 60 revolutions per minute to quickly identify moving targets. It is powered by a travelling wave tube (TWT). The TWT gives a high power output for penetration thrciugh the most difficult weather conditions and it also allows great flexibility in operating frequency and pulse repetition frequency to counteract jamming. In conjunction with its weapons control computers, Goalkeeper's search radar can keep track of up to 30 objects in the sky. Having identified all the flying objects in the sky out to a distance of 30km or more, the Goalkeeper's computer gives them all a priority in terms of the threat they represent. Each object's distance, speed and direction is taken into consideration. Having assessed which object is the most threatening, the Goalkeeper's tracking radar then locks onto it. The tracking radar uses a 1-metre parabolic dish with dual feedhorns so that it operates in two frequency bands. One feedhorn gives a very narrow "pencil" beam for very accurate tracking at low altitudes. The latter is important when tracking sea-skimming antiship missiles because conventional radar can become confused between the target and its reflection off the surface of the sea. By continuously comparing the return signals from the two frequency bands (I and K-bands ), the tracking radar can track fast moving objects with very small radar cross-sections; eg, small missiles and shells. The galling gun The gun itself is a GAU-8/7 gatling gun made by General Electric and originally used on the US Air Force A-10 attack aircraft. For use in the Goalkeeper system it has been adapted to a naval gun mount and integrated with the two radar systems just described. The tracking radar and the gatling gun are mounted so that they track together. The total rotating assembly, comprising the gun, radar systems, turret, ammunition drum and other paraphernalia, weighs more than 6 tonnes. It is rotated and elevated electrically with DC motors. Maximum rate of rotation of the gun mount is one revolution per second. Accelerating such a heavy mass with the motors causes a peak electrical load of 90kVA which is supplied by nickel cadmium batteries. Naturally the slewing of the gun is restricted so that it does not shoot off parts of the ship and the barrel elevation can be varied between - 20° and + 80° with respect to the ship's deck. The computer system automatically compensates for pitch, roll, yaw and heave and flexing of the ship's deck due to heavy sea movement. While the gun has a very high firing rate of 4200 rounds/minute, its ammunition feed-and-storage drum (a belt system) only takes a total of 1190 rounds. This might not seem like much but it only takes a 2 or 3-second burst to destroy a missile. This means that about 6 or more missiles can be engaged and destroyed. After that, it takes about 25 minutes to reload the ammunition drum. How will it perform under real battle conditions? That has yet to be determined although the system has been extensively tested in the North Sea by the Netherlands Navy. Presently, the US navy is using an old hulk with a Goalkeeper system mounted on it. Missiles and shells are being fired at it to prove the system. No doubt it works well in such tests but what features will be produced by the missile manufacturers to beat it? ~ GOALKEEPER IN ACTION during recent trials. The 7-harrel gatling gun fires 30mm shells at the rate of 4200 per minute. JANUARY 1989 5