Radar air-to-air missile semi-physical simulation system scheme

An Fengzeng, Wu Zhaoxin, Wang Haifeng, Ma Huimin, China Academy of Air-to-Air Missile Research

The development of a missile weapon system is an incredibly complex endeavor. It involves numerous specialized fields and the integration of cutting-edge technologies. As a result, the cost of developing a single missile has skyrocketed. Testing the full performance of a missile's guidance system through flight trials is prohibitively expensive and time-consuming. Additionally, certain extreme conditions can only be replicated in a lab setting. This is where simulation technology comes into play, offering a cost-effective way to address these challenges.

With advancements in technology and shifting global defense priorities, the simulation of missile weapon systems has seen significant growth. Semi-physical simulations of missile guidance loops have become particularly vital in modern missile development. Leading countries like the U.S., the UK, and others have established state-of-the-art simulation facilities. For example, the U.S. Army Advanced Simulation Center (ASC) and Raytheon have invested heavily in facilities to simulate advanced missile systems such as the AIM-120. These labs have accelerated the development and testing processes, proving invaluable to the industry.

The design goals for the radar-guided missile semi-physical simulation system are as follows:

a. To support the semi-physical simulation testing during the missile guidance system development phase. This includes providing tools for parameter tuning, model validation, and algorithm coordination checks, while also predicting outcomes for field trials;

b. To enable automatic control of the entire simulation testing process, from initial diagnostics to completion;

c. To ensure real-time data acquisition from the simulation, including telemetry data from the missile, trajectory outputs from the simulation model, and control information from the simulation equipment. This data should be displayed and analyzed both in real-time and post-simulation;

d. To offer real-time monitoring of the simulation process and the capability to handle any anomalies that arise.

After analyzing the system goals and considering the latest developments in simulation and computer technology, we adopted the following concepts:

a. Utilizing a five-axis turntable as the core, supplemented by essential simulation equipment, to create a radar-guided missile semi-physical simulation system;

b. Employing computer-controlled simulation devices to automate the entire testing procedure;

c. Dividing the system into different subsystems based on their functions to simplify design, reduce costs, and expedite development;

d. Implementing a real-time network to form a distributed real-time simulation system.

The aim of the radar-based air-to-air missile simulation system is to provide a highly realistic motion and electromagnetic environment for missile testing. Such systems typically include the following components:

a. A microwave anechoic chamber: This provides a free space for electromagnetic wave propagation. Inside, there is usually a radio frequency target simulator at one end and a flight turntable at the other;

b. A Target Simulator: This emits RF signals to mimic targets and backgrounds;

c. A Target Signal Simulator: This generates the RF signals representing the target and background;

d. A Turntable: This mimics the missile's flight attitude;

e. A Simulation Computer System and Software: This controls the simulation equipment, solves simulation models, and manages the overall test process;

f. For composite long-range missiles, a data link simulator may also be included.

4.1 Structure of the Target Simulator

The choice of target simulator directly impacts the overall system composition. Common types include mechanical target simulators, array target simulators, and compact field target simulators.

a. Mechanical Target Simulator: Uses perpendicular guide rails driven by motors to move the target horn and simulate the target's position;

b. Array Target Simulator: Employs a triad antenna array to control the target position by adjusting the amplitude and phase of the resultant signals;

c. Compact Field Target Simulator: Uses a collimator principle to feed the RF signal of the analog target through a waveguide and coaxial cable to a horn antenna at the focal point of a cut parabolic antenna. The RF signal radiated by the horn antenna is reflected by the parabolic antenna to form a plane wave, meeting far-field conditions.

While mechanical target simulators are less accurate and are rarely used today, array target simulators offer high precision and can simulate multiple targets and interference types. However, they require a large, expensive setup with hundreds of horn antennas. Compact field simulators, on the other hand, have a compact structure and do not require a large microwave chamber or spherical array, reducing costs significantly.

Therefore, the simulation system employs a compact field target simulator.

4.2 Computer Control Methods

With the advancement of computer technology, air-to-air missiles are becoming increasingly intelligent. The missile's control algorithms are now handled by onboard computers. Given the complexity of hardware-in-the-loop simulations, all simulation equipment is controlled by computers to automate operations and facilitate seamless information exchange between devices.

Computer control methods can generally be centralized or distributed. Centralized control is ideal for smaller systems, while distributed control suits more decentralized functionalities. In this radar-guided air-to-air missile simulation system, both extensive mathematical computations and numerous simulation devices require significant I/O capacity. A centralized approach would demand high-end computers, increasing costs substantially. Moreover, due to the strong interdependence of computers and simulation equipment, distributed control proves more suitable. Many international RF simulation labs, such as those at Boeing Aerospace and Raytheon, have adopted distributed control solutions.

4.3 Real-time Network Solution

As the simulation system employs a distributed architecture, computer interconnectivity becomes crucial. The update rate for the missile semi-physical simulation system must be under 1 ms. Each subsystem must complete numerous calculations within this timeframe and transmit data efficiently. Any lag would hinder the system's real-time performance, complicating computer interconnectivity. Thus, high-speed real-time performance is the foremost requirement for the simulation network.

In the past, local area networks were primarily used for resource sharing, making them unsuitable for missile simulations due to their slow and unpredictable response times. Initially, special interface equipment connected external hardware-in-the-loop simulation computers, which was bulky and costly. Later, VME bus products became popular for real-time control applications abroad, leading to technologies like VME bus repeaters, multi-master module repeaters, DMA data transfer, and shared memory interfaces. While these satisfied real-time simulation needs, they were not true networks and had limited scalability and maintenance challenges.

Recently, real-time interconnection technology has made significant strides. Various ring and star topology real-time networks based on shared memory interfaces have emerged, offering excellent scalability for missile simulations. In this system, VMIC's reflective memory network was chosen. It uses a ring topology, supports up to 256 independent nodes, and ensures software-transparent data transmission with minimal overhead. Its node physical delay is less than 1 μs, with high transmission rates, fully meeting the 1 ms update rate requirement for radar-based air-to-air missile simulations.

4.4 Simulation System Configuration

Based on the chosen target simulator format, computer control method, and real-time network solution, the new RF simulation system is centered around a five-axis turntable and a missile guidance control system. The detailed configuration includes:

a. Five-axis turntable: Comprised of a three-axis turntable simulating missile attitude and a two-axis turntable simulating target movement. Its role is to receive missile yaw, pitch, and roll channel information from the simulation computer, replicate missile attitude movements, receive target azimuth and altitude information, and reproduce changes in the missile-target line of sight;

b. Target Signal Simulator: Generates simulated target echo signals to mimic Doppler shifts, power attenuation with distance, distance delays, and various interferences;

c. Data Link Simulator: Simulates data link signals for carrier trajectory corrections;

d. Simulation Computer: Solves kinematic models of the carrier, missile, and target, relative missile-target kinematics, carrier aircraft kinematics, and missile dynamics;

e. Simulation Console: Manages the system's operational status and conducts timing detection and control for simulation tests;

f. Real-time Network: Facilitates real-time communication among the simulation system's internal computers and transmits control information and simulation results from the simulation equipment.

A block diagram of the radar air-to-air missile semi-physical simulation system is shown in Figure 1.

Fig.1 Block diagram of a semi-physical simulation system for radar-based air-to-air missiles

The semi-physical simulation system, using a compact field target simulator and other simulation equipment, provides a highly realistic motion and electromagnetic environment for active radar missiles. It meets the needs of optimizing missile guidance and control system parameters, validating models, and predicting flight test results.

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