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.
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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
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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?
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GOALKEEPER IN ACTION during recent trials. The 7-harrel gatling gun fires 30mm shells at the rate of 4200 per minute.
JANUARY 1989
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