Weapons: A Harder, Networked Army? | ADM July 2009

Gregor Ferguson | Sydney

The RAN's new Hobart-class Air Warfare Destroyers (AWDs) will be armed with Raytheon's new Standard Missile (SM) 6 Extended Range Active Missile (ERAM); they will also incorporate the same company's Cooperative Engagement Capability (CEC) to network the sensors and weapons of ships in a task group.

This will give the AWDs the most powerful anti-aircraft armament of any ships in the region as well as unprecedented levels of interoperability with the US Navy and Royal Navy, both above and below the surface.

While the Royal Navy looks set to adopt the CEC, with a so-called ‘Main Gate' decision some time in 2010, the RAN will become the first export customer for the SM-6 and is so far the only customer approved for release of the SM-6/CEC combination.

The SM-6 is based on the proven SM-2 and SM-3 families and can be fired from the same Mk41 Vertical Launch System (VLS) strike-length launchers.

Its airframe is derived from the SM-3, but it uses the Mk104 rocket motor and 21-inch Mk72 booster from the SM-2 Block IV which was designed as an area air defence weapon and adapted to provide an interim antiballistic missile capability.

These bestow a range of more than 370kms to provide a very wide area air defence capability, which is one of the principal roles of the AWDs.

The other critical feature of the SM-6 is its employment of Advanced Medium Range Air-Air Missile (AMRAAM) active radar seeker technology, making it the first active guidance member of the SM family.

The weapon doesn't employ the AIM-120C AMRAAM's active radar seeker, but it employs much of the technology and processing capability - only, instead of being in a seven-inch diameter AMRAAM missile body it is in the 13.7 inch SM-6 missile body which provides a far greater power aperture, with obvious benefits.

Evolutionary differences
It's important to understand the differences between the earlier SM-2/3 and the SM-6; the former, being a semi-active missile, depends on a target illuminator to track the target and provide track data to the missile via a data link.

In the terminal phase of the engagement the missile either continues to use semi-active illumination or switches into ‘Home on Jam' (HOJ) mode to intercept the target.

The SM-6 uses semi-active guidance during the mid-course phase, for reasons discussed below; in the terminal phase, however, control is transferred directly to the missile which completes the engagement under its own active guidance.

The SM-6 can revert to ‘legacy mode' if circumstances require.

The flight profile of the missile is a key part of its capability.

Raytheon says the SM-6 retains full velocity and manoeuvrability right to the edge of its range envelope by following a parabolic flight path - its Mk72 booster lofts the missile to high altitude which help maintain kinetic energy on its downward path towards the target.

This indirect path requires the use of a data link to provide updated track information before the missile starts the active phase of the engagement.

But maintaining that semi-active data link capability also provides the essential channel of fire for the CEC.

Put simply, the CEC is a networked sensor data fusion system which enables a warship to launch and guide a missile accurately towards a target which the ship can't detect on its own radar.

It is now fielded right across the US Navy and Marines and has been retrofitted to the majority of US Navy CGs, DDGs, amphibious landing ships and aircraft carriers and E-2C/D Hawkeye airborne early warning systems.

No modifications to the missile or core Aegis combat system are required.

The CEC consists of a Signal Data Processor within the ship's Combat Information Centre (CIC), which fuses track data from the ship's own radar with that from the radars aboard other CEC-equipped ships in the task group; these are shared using a dedicated C-band tactical data link with its own planar array antenna.

The CEC provides the ship with a composite track created by fusing all of the track data from all of the ships in the group.

If the ship itself hasn't been able to develop its own target track, then the CEC provides the same track data and air picture that's available to all other CEC-equipped ships in the group.

Not only does this provide collective situation awareness, fusing data from multiple sensors provides much higher tracking accuracy and reduces false alarms.

The track data is then fed to the ship's fire control system just like ‘native' Aegis fire control data.

From the missile's point of view it makes no difference where the target was originally detected and tracked - it still gets accurate target track data via the uplink from its mother ship, even if that ship can't see the target itself.

The CEC isn't limited to Aegis-equipped warships - in the UK it will be integrated with the SSDS combat system aboard Royal Navy frigates and destroyers, while the US Marines integrate it into their Composite Tracking Network.

The other services also have a stake through the Joint Land Attack Elevated Network System (JLENS), a tethered aerostat carrying a sensor array to detect threats like incoming cruise missiles.

FMS for CEC
ADM understands the CEC will be ordered for the AWDs under a US FMS arrangement.

The 2009 Defence White Paper also says Defence will examine adding CEC to the RAAF's Wedgetail Airborne Early Warning & Control aircraft; this would be a logical and very sensible next step for the ADF.

The fact that CEC can be integrated economically into as small a platform as the E-2C/D Hawkeye suggests that integration into larger platforms like the Wedgetail is a relatively low-risk activity.

To appreciate the potential importance of CEC, imagine two ships a few kilometres apart: between them they could provide air defence coverage over a strip that's up to 800km long and nearly 400km wide.

Integrate an airborne surveillance platform such as Wedgetail and the resulting area surveillance and air defence capabilities in both open ocean and littoral environments is truly significant.

As for the SM-6, development testing began last year with a number of successful test launches, with more firings planned through 2009.

Ship qualification testing will take place over the next six months or so, ADM was told, with US Navy Operational Test & Evaluation (OTE) firings scheduled for 2010.