Cooperative Guidance for Shipborne Surface-to-Air Missile Systems

Overview

When multiple platforms cooperate to guide shipborne surface-to-air missiles (SAMs) for beyond-visual-range interception of low-altitude anti-ship missiles, missiles launched beyond line of sight gradually move away from the launch platform and descend in altitude. Once a missile exceeds the guidance range of its launch platform, the platform can no longer transmit guidance commands to the missile. In this case, to complete mid-course guidance the guidance authority must be transferred to a cooperative guidance platform, which then transmits radio guidance commands to the missile. Alternatively, when a fleet-level command center issues a guidance handover order for formation-level requirements, guidance authority must be transferred between guidance platforms. In other words, there is a guidance handover during the mid-course guidance phase of the SAM.

What is guidance handover?

Guidance handover is the process of transferring the right to send mid-course radio guidance commands from one guidance platform to another (a cooperative guidance platform). The mid-course guidance phase for a shipborne SAM is split into two parts: the initial part is guided by the launch platform and the later part by the cooperative platform. The sending of guidance commands shifts from the launch platform to the cooperative guidance platform, which transmits radio commands directly to the missile.

Key systems involved

1. Shipborne SAM weapon system. A modern shipborne SAM system must retain existing SAM functions while adding cross-platform cooperative guidance handover capability.

2. The ship's command and control system. The ship's command and control system manages and decides how to allocate the ship's combat resources, provides a comprehensive situational picture and target strike decision support, and supplies target designation information to weapon systems while supervising their engagement of targets.

The guidance handover process for SAMs involves instruction distribution and target selection, and thus requires information exchange between the ship's command and control system and the SAM weapon system.

3. The ship's multi-platform cooperative engagement system. Guidance handover depends on rapid distribution of target and missile kinematic data across platforms. Current multi-platform cooperative engagement systems installed on modern destroyers and escorts enable platforms to share fire-control-grade situational data.

From a compatibility and extensibility perspective, a cooperative guidance unit (CGU) can be added to the SAM weapon system, making the CGU part of a modern SAM system. The CGU interfaces with existing weapon system equipment (missile fire-control equipment, launch control equipment, guidance antenna equipment), the ship's command and control system, and the multi-platform cooperative engagement system to exchange information and coordinate functions, thereby enabling smooth transfer of guidance authority between platforms.

CGU role and operational flow

Given the CGU role, it is necessary to analyze its command mode and information flow from operational and procedural perspectives, and to propose an overall CGU design that defines its functional composition and the information exchange relationships with the other three major systems: the missile weapon system, the ship's command and control system, and the multi-platform cooperative engagement system.

One CGU-based multi-platform cooperative guidance mode's basic operating principle is as follows:

Cooperative platforms share target and missile tracking data via the multi-platform cooperative engagement system.
Based on the tactical picture, each platform's command and control system exchanges information with the CGU. After multi-platform cooperative decision making, tasks are allocated among platforms, launch and handover platforms are designated, and the timing for guidance handover is determined.
The CGU on the launch platform exchanges information with the SAM weapon system to perform fire-control parameter computation, missile launch, and initial guidance tasks.
The CGU on the cooperative handover platform exchanges handover parameters via the multi-platform cooperative engagement system, carries out the cooperative handover, and controls the SAM until it completes mid- and terminal-phase guidance.

(1) Platforms share target and missile tracking via MCE.
(2) The command and control system performs intercept suitability, threat assessment and prioritization, and weapon assignment, and returns results to the CGU.
(3) The CGU is the core subsystem enabling multi-platform cooperative guidance. Based on command decisions, it performs launch decision-making and platform allocation.
(4) Using target tracking data from the multi-platform cooperative engagement system, the CGU on the launch platform pre-processes fire-control parameters and prepares data for the SAM weapon system's fire-control solution.
(5) The missile weapon system completes the fire-control solution and executes launch control.
(6) The CGU formulates guidance handover plans and completes the guidance transfer.
(7) The CGU pre-processes parameters required to form guidance commands using target and missile tracking data from the multi-platform cooperative engagement system. Depending on platform type, the CGU either directly generates guidance commands or delegates command generation to the SAM weapon system, which produces guidance commands based on the CGU's pre-processed parameters.
(8) The command transmission system transmits guidance commands to the missile at prescribed intervals.

CGU core functions

The CGU is the core unit for beyond-visual-range multi-platform cooperative guidance. Based on a shared fire-control-grade tactical picture provided by the multi-platform cooperative engagement system and in cooperation with the SAM weapon system, the CGU integrates target and missile motion data, generates relay-guidance engagement plans, and implements target assignment, weapon channel organization, fire-control parameter computation, launch control, relay-platform guidance handover, missile control, and target intercept.

1. Cooperative management

Cooperative management handles fire-control management and decision-making for cooperative guidance. Based on threat assessment and target allocation from the command and control system, the CGU computes launch decision parameters, assigns platform tasks, and determines handover timing. Key tasks include:

Determining decision basis parameters, including dynamic handover zones across platforms, launch zones, kill zones, handover success probability, and guidance error estimates.
Feasibility analysis of handover schemes.

This function is implemented by the multi-platform dynamic networking and optimization module. From cooperative detection and guidance requirements, optimization algorithms control platform layouts and operations. The optimization software comprises three parts: detection-platform network optimization, guidance-platform network optimization, and multi-platform integrated optimization.

Detection-platform network optimization: Given the positions, velocities, and sensing capabilities of detection platforms, optimize the detection-platform network to maximize collective detection performance.
Guidance-platform network optimization: Given the positions, velocities, and guidance capabilities of guidance platforms, optimize the guidance-platform network to satisfy cooperative guidance requirements.
Multi-platform integrated optimization: Combine the requirements from detection and guidance network optimization modules to produce a globally optimal dynamic network. Convert the network into concrete optimization commands for detection and guidance platforms and deliver dynamic network control commands via the high-speed data link communication module to each platform's command and control system.

2. Cooperative control

After cooperative management issues a launch decision, the CGU determines the fire-control solution type based on the integrated tactical picture from the multi-platform cooperative engagement system and performs the pre-processing needed for fire-control computation (coordinate transformation, smoothing, etc.). Tasks include:

Cross-platform reference frame matching;
Coordinate transformation and correction of cross-platform target and missile parameter data.

This function is implemented by the cooperative guidance data processing and fire-control solution module. Considering the real-time requirements of cooperative guidance data and the specific needs of cooperative fire-control computation, the module processes data and applies cooperative guidance solution methods to produce required inputs for cooperative fire-control calculations. It comprises three subunits: spatiotemporal consistency transformation, firing solution computation, and cooperative guidance ballistic parameter solution.

Spatiotemporal consistency transformation: Receive cooperative information from other platforms and combine it with local sensing to perform spatiotemporal consistency transformations so that target and guidance data satisfy the platform's time and space requirements for fire-control computation and cooperative guidance.
Cooperative firing solution computation: Using cooperative platform information and target data, compute firing solution parameters for cooperative engagement, including intercept route shortcuts, cooperative kill-zone and launch-zone boundaries, predicted encounter points, and times to enter launch-zone near and far boundaries.
Cooperative guidance ballistic parameter solution: Receive computed target and cooperative platform information from the firing solution unit, compute the initial parameters required for missile launch under cooperative guidance requirements, and load those initial parameters into the missile launcher via the command and control system.

3. Handover guidance

Based on launch and control parameters, the CGU formulates a guidance handover decision plan, performs missile handoff and takeover, and for different platform types either pre-processes guidance command parameters (coordinate transform, smoothing) or directly generates and encodes guidance commands for transmission. Key tasks include:

Missile handover decision;
Missile handover processing;
Guidance command parameter pre-processing;
Generation and transmission of guidance command parameters.

This function is implemented by the cooperative guidance command handover control module. According to cooperative guidance needs, a handover control logic governs the transmission of guidance commands, performs real-time monitoring of handover execution, and ensures successful mid-course guidance handover. The module consists of four functional units: information distribution, handover situation estimation, guidance handover control, and cooperative command generation.

Information distribution: Classify cooperative information from the command and control platform and route it to appropriate functional units. Handover allocation information from cooperative platforms goes to the guidance handover control unit; handover participant information goes to the handover situation estimation unit; guidance-related commands go directly to the platform's guidance command transmit/receive system.
Handover situation estimation: Receive handover-related member information from the information distribution unit, including target state, missile state, and platform state. Compute the handover airspace using mathematical models and assess the handover situation in real time to decide whether to initiate handover and issue control commands.
Guidance handover control: Await the handover initiation command from the handover situation estimation unit. Before handover initiation, this unit accepts commands from the command and control platform and controls the guidance command transmit/receive system accordingly. After handover initiation, it accepts cooperative guidance commands from other platforms and controls the transmit/receive system to perform the handover.
Cooperative command generation: Receive acknowledgements from the guidance command transmit/receive system, estimate handover status from acknowledgement patterns, and based on that status issue further cooperative commands to partner platforms via the command and control system and the high-speed data link communication module.

CGU modular composition

The multi-platform cooperative guidance unit (CGU) is an external extension to the SAM weapon system and works with the platform command and control system and the SAM weapon system to handle engagement command, resource management, missile launch, handover, and guidance control tasks.