Peter La Franchi/ADELAIDE
Imagine an airborne gunnery system capable of firing 40mm grenades millions of rounds a minute against ground targets. Australian stock exchange-listed Metal Storm has unveiled concepts for such a futuristic-sounding system. It has also detailed a proposal to fit an advanced 25mm machine gun into theatre defence missiles as the basis of an alternative approach to engaging ballistic missiles outside the Earth's atmosphere.
The concepts are based on emerging multiple barrel, electronically controlled weapons technology that has gained the backing of the US Defence Advanced Research Projects Agency (DARPA). On 23 March, the agency announced $10.25 million multiyear funding for the technology to support the development of a combat rifle variant, and options to explore alternative applications such as a minefield clearance and a new type of ship-based close-in weapons systems.
Metal Storm says that the full list of options in the DARPA contract remain undisclosed. He says, however, that it is "highly possible" that the airborne gunnery system concept could attract DARPA funding in its own right.
Metal Storm was established in 1996. A partnering agreement with Science Applications International was sealed the following year as the focus for its development for military and civilian applications in the USA and Australia.
The company has repeatedly demonstrated rates of fire ranging between thousands to over 1 million rds/min over the past five years using prototype 9mm guns. The technology is based on fitting multiple rounds into a single barrel, with each round separated by propellant. The barrel itself is lined with capacitors linked to a computer-based weapons controller. When the computer sends a firing command to the barrel, the capacitor nearest the mouth discharges to ignite the propellant mass behind the first round, forcing it into flight.
The overpressure caused by the charge detonating expands the second round to prevent sympathetic detonations of further charges held in the barrel. The computer controller then initiates the firing sequence for the second charge in the barrel, with the process repeated for each round. Because the charges are electrically detonated, the time between the ignition of each charge can be programmed to rates of millionths of a second. Other than the projectile, there are no moving parts in the weapon to slow the rate of fire.
By linking large numbers of barrels together, the potential rates of fire can be dramatically increased, giving the ability to fire a wall of projectiles against unitary and wide area targets with an unprecedented level of control.
The system also allows for the application of a broad range of effects against a target by varying the rate of fire, modifying the firing pattern by using different barrels in different sequences and using different types of projectiles loaded into different barrels. A wider area of effect can also be achieved by splaying the barrels to spread the projectile pattern.
Grenade boxes
The proposed airborne ground-attack system is based around grenade boxes carried in a pod beneath a fighter in a pod, or integrated into the fuselage of a dedicated unmanned air vehicle (UAV). Each box would comprise one hundred 40mm barrels, each containing six air-burst grenades. Metal Storm proposes grouping the boxes into clusters of 12 to each aircraft, creating a single-pod weapon comprising 1,200 barrels and 7,200 grenades. The weapon would weigh 1,900kg (4,200lb).
According to Metal Storm managing director Mike O'Dwyer, the airborne weapon would be used in conjunction with an battlefield surveillance sensor such as the Northrop Grumman Longbow fire-control radar carried by the Boeing AH-64 Apache helicopter.
The AH-64/Longbow package, O'Dwyer says, would stand-off and designate the targets electronically, defining full flows and perimeters and allocating rates and densities of fire from a menu.
The targeting sensor/weapon combination should be thought of in terms akin to a computer laser printer head and a blank sheet of paper.
He imagines the aircraft carrying Metal Storm as the printer and the target as the page. The aircraft will operate "in the same way that your printer will operate, in a very precise manner, putting the right number of dots into the right area without you having to intervene once you have set it up. We have to know where the page is on the ground. It has to be identified. But if it is identified [by the AH-64/Longbow combination] and we set the printer up, then we can get the printer to operate," O'Dwyer says.
Typically, Longbow targeting information would be fed to two large, dedicated Metal Storm-equipped UAVs. The combined UAV payload would be 24 40mm splayed boxes, with 2,400 barrels and holding 14,400 grenades.
The page upon which capability would print, O'Dwyer says, would be an area of 354,000m² (3.8 million ft²), based on a single strike involving all 14,400 grenades fired at 5m (16ft) intervals. The time to fire the full payload of 14,400 grenades would be 0.02s, or a maximum rate of fire equivalent to 43 million rds/min. One side effect, O'Dwyer says, is that such a rate of fire would give a vertical acceleration to the wings that might exceed their structural integrity.
Concept demonstration
Few details have been released on timeframes for deployment of such a system. But O'Dwyer says design work leading to the fabrication of an airborne prototype is under way in the USA. Similarly, the development of 40mm grenade rounds is planned as part of a Metal Storm/Australian Defence Science and Technology Organisation concept demonstration programme expected to receive government funding in Australia's 2000/1 defence budget.
O'Dwyer also suggests that the airborne system could be used in civilian firefighting roles, with projectiles carrying fire-retardant dry chemicals, or foam-generating compounds.
The proposed theatre missile defence variant would involve a 25mm Metal Storm gun carrying 100 high-explosive fragmenting rounds in a gimbal mount in the nose of an interceptor missile, to allow for multiple attacks against a single target. While the concept has echoes of the "Brilliant Pebbles" fragmenting warhead concept explored by the USA, O'Dwyer says the intention would be to use the Metal Storm gun as part of an interceptor also capable of a direct kinetic-energy kill.
As the interceptor closes on the ballistic missile, the Metal Storm gun would open fire at 90m to create a stream of fragments 150m long. The fragment stream would be generated at the same speed at which the missile moved through the column. At the same time, the interceptor would position itself for a hit-to-kill attack.
If the missile passed through that fragment stream, the interceptor would carry out a direct engagement 0.003s after the gun engagement. If the interceptor missed in this second opportunity, however, the Metal Storm proposal would include a third engagement option.
Firing a gun in space, O'Dwyer points out, would require that the same weapon allow for an equal and opposite to ensure that the initial engagement did not divert the interceptor from its convergence trajectory for a hit to kill against the enemy missile.
The basic solution, O'Dwyer proposes, is a solution where the barrel is open at both ends, meaning that, for every round fired forwards, an equivalent round is also fired backwards. This means that, from the moment the initial engagement begins, a second stream of rounds forms a 90-150m tail behind the interceptor, through which the missile will pass.
The idea, O'Dwyer admits, sounds odd. He says, however, that detailed evaluation indicates it is feasible - and could offer advantages.
Source: Flight International
