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Hypersonic Defence series.  
(Access to other chapters at the end of this article)

Air Raid Warning Red – enemy forces have launched hypersonic missiles that can be expected to reach strategically vital targets within minutes...

The previous episodes in this series explained how Early Warning systems provided the initial alert and how the Command, Control & Communications network then spring into action to activate theatre-wide defence capabilities. 
This issue explains the vital role that Detection, Identification & Tracking sensor systems have in the defence against hypersonic missile threats.
The role of the sensors is to perform Early Warning, persistent tracking, classification and identification (hostile or not, what type of missile) of the threat.

All with the primary aim to enable the next steps in the hypersonic threat defence: the actual engagement of the incoming missiles by priming whatever Engagement modules are available and by supporting the necessary Fire-Control system.

The tasks associated with Detection, Identification & Tracking can be done with one or multiple sensors, of the same or different types, depending on the scale of the defended area and the capability of both the threat and the defensive interceptors. 

... and their performance must be impeccable, because the window(s) available for successful interception will typically be narrow. 

•    There might be an opportunity in the boost phase but this could be outside of range for the interceptor systems.
•    Attempting an intercept in the exo-atmospheric phase could be too far away, as well.
•    It should be possible to intercept the threat during its glide phase: typically after re-entry for a glider or in its final phase for certain hypersonic cruise missiles. 
•    The threat missile will typically slow down before it starts its terminal phase just before impact. 

Furthermore, the intercept hit point must be estimated – which implies that the threat’s trajectory must be determined as accurately as possible. One difficulty here is that hypersonic missiles are manoeuvrable: if interceptor missiles are launched too early the engagement may be unsuccessful.

Also, the time between early detection and identification must be very short (seconds). This identification normally relies on an assessment matrix considering dozens of features, including the threat’s point of origin (launch point), signature characteristics (radar, optronic, …), external shape, velocity and flight trajectory.
At C2 level, all these features are analysed and compared with pre-established models of the different threats, designed to trigger a pre-planned response.

The challenges here are:

-    Detect as early as possible to have the time needed to identify and to react.
-    Horizon-related detection limitations (compared to Ballistic Missiles, that have a similar range/velocity profile, Hypersonic missiles typically fly at far lower altitudes, appearing above the horizon much later).
-    Provide the right type of data (that can be used for classification).
-    Accurately track the object. This includes maintaining the established classification-identification status while the threat traverses very great distances, quite possibly cross-borders requiring a collaborative Track ID; and to know the threat’s trajectory with extreme precision to enable engagement at the exact right point of intercept. 

The process of Detection, Tracking, Classification and Identification*  relies on a network of different types of sensors to … : 

*Identification as defined according to the following categories : Friend, Foe or Neutral

o    Detect the object as soon as possible (radar and infrared signatures) from the surface up to space: SMART-L MM- and GAxxx radar; Stratobus- or (ARTEMIS) infrared search & track (IRST); plus future sensors still in the pipeline. The requirement is to be able to detect the hypersonic missiles as soon as they appear above the radar horizon (typically 600-1200 km away, for targets at cruise altitudes from 20-80 km).

o    Persistently track the objects across the theatre of operation with either dedicated radars, or volunteered radars that are normally tasked for other purposes. Radars used for such a purpose need to combine sufficient range/velocity/elevation coverage with the right update rate to deal with aggressively-manoeuvring target behaviour. Given the geographic distances involved, dynamic orchestration of different types of sensors that may come from multiple different nations will be required. 

o    Classify the object into the correct high-level category such as HCM, HGV, Hybrid, and if possible, detailed classification to type. Supporting sensors for this can be the radars that are used for tracking and if included in the sensor mix, IRST.

o    Identify the object as a threat or not. This is a system task combining the classification assessment (strongly based on sensor data) and intelligence (threat library) for the identification of unknown patterns.

And aims to delivering information to enable:

o    Intelligence (to gather and store information about the object, its signature and its position).
o    Passive defence (alerting population, preparing for impact).
o    Counter action (to take out the launch site, for example).
o    Active defence (to shoot down the incoming threat): target designation to the fire control radar (a process known as TEWA: Threat Evaluation and Weapon Assignment).
 

Networking heterogeneous sensors in a smart grid

Considering all sensors listed above and their vast variety, a sensor grid provides operational capabilities to achieve dynamic and evolving awareness in the battlespace, enhancing overall performance. Multiple sensors operating together will allow persistent tracking over the complete theatre, despite horizon limitations. As stated above, this type of cooperation requires dynamically orchestrated sensor tasking, data fusion, and real-time distribution of services, all across international borders. The resulting grid uses multiple sensors with overlapping coverage, complementing each other and increasing interoperability tempo.

By deploying sensors with overlapping coverage, the grid takes advantage of multiple sensors sharing data to complete the air, ballistic and hypersonic picture. The orchestrator can coordinate active tracking of threats, ensuring continuous tracking even if one radar loses track. The optimiser plays a crucial role in designating available radars for active tracking, locking onto threats, and potentially accelerating tracking for improved accuracy.

In the case of sensor jamming, the optimiser adjusts the multi-frequency coverage of sensors and utilizes unjammed sensors to reduce the jamming effect. Dedicated tracking tasks can be employed to perform classification and/or raid assessment. The jammer position & type can be determined  through multi-frequency triangulation and the use of ESM sensors.

Overall, this tactical approach provides defence systems with an integrated sensor grid that maximizes the utilization of multiple sensors, enhances situational awareness, and enables effective response to dynamic and evolving threats in the battlespace.