Computer simulation, also known as computer simulation, is a mathematical model that describes the physical process of the system on the computer, and quantitative research and experiments are carried out on the system on this model. This simulation method is often used in the scheme design stage of the system and some occasions (including some failure modes) that are not suitable for physical simulation. It has the characteristics of good repeatability, high precision, great flexibility, convenient use and low cost, and can be real-time or non-real-time. The fidelity and accuracy of mathematical simulation depend on the accuracy of simulation computer and the correctness and accuracy of mathematical model. Mathematical simulation can use analog computers, digital computers and mixed digital and analog computers.

Semi-physical simulation

Part of physical model and part of mathematical model simulation. The physical model adopts the physical objects in the control system, and the dynamic process of the system itself adopts the mathematical model. Hardware-in-the-loop simulation system usually consists of simulation computer, motion simulator (generally using three-axis mechanical turntable), target simulator, console and some objects that meet the real-time requirements. Control system electronics and sensors are placed on the turntable. Hardware-in-the-loop simulation has high fidelity, so it is often used to verify the correctness and feasibility of the control system scheme, simulate the fault mode, and conduct closed-circuit dynamic acceptance tests for each development stage of the control system. In addition, training astronauts with space simulators and training pilots with flight simulators also belong to the nature of hardware-in-the-loop simulation, and the latter focuses more on visual simulation and man-machine relationship. It can also be considered as a hardware-in-the-loop simulation in which the system model is realized by a simulation computer and the electronic circuit of the spacecraft computer or control system is taken as the physical object for closed-circuit testing. This simulation focuses on checking the correctness of the control computer software or studying some functions and parameters in the control mode. The fidelity of semi-physical simulation depends on the number of connected physical components, the speed, accuracy and function of the simulation computer, and the performance of the turntable and each target simulator. Usually, the requirements for three-axis mechanical turntable are high precision, large rotation range, fast dynamic response, and the frame arrangement does not hinder the field of view of optical sensors. Hardware-in-the-loop simulation technology is the development focus of modern control system simulation technology.

Full physical simulation

All adopt physical model simulation, also called physical simulation. For example, the motion of air bearing table (single axis or three axes) is used to replace the dynamic process of spacecraft, and the control system adopts physical objects. Because the object is placed on the air-bearing platform, this method is very suitable for studying the three-axis coupling of spacecraft attitude control system with angular momentum storage device and the dynamic relationship between the control system and other subsystems in mechanics. In the full physical simulation of spacecraft attitude control system, the objects installed on the air bearing platform should include attitude sensor (see spacecraft attitude sensor), controller actuator (see spacecraft attitude control actuator), telemetry and remote control device and related subsystems. The target simulator, environment simulator and operation console are all set on the ground. The motion of spacecraft in space is simulated by air bearing platform, so the fidelity and accuracy of all-physical simulation mainly depend on the performance of air bearing platform. The requirements for air bearings are small friction torque and eddy current torque, large vertical bearing capacity and lateral stiffness, and good dynamic and static balance of air bearings. All-physical simulation technology is complex, and it is generally only used when necessary.