Intercontinental ballistic missiles are an important defense force of the P5. Previously, the United States, Russia, France, the United Kingdom, and China have all test fired a round of intercontinental ballistic missiles.
The Minuteman missile was launched in 1962 and is an important component of the US nuclear deterrence force. The Minuteman III missile is currently the only land-based intercontinental ballistic missile (ICBM) in the United States, with a total of 400 missiles ready for launch at any time, distributed in five central states. The missile contains a precision guidance system that can launch the warhead to a target 13000 kilometers (8000 miles) away with an accuracy of 200 meters (660 feet).
The following figure shows the guidance system of the Minuteman III missile (1970). The guidance system consists of over 17000 electronic and mechanical components, valued at $510000 (approximately $4.5 million in current US dollars). The core of the guidance system is the gyroscope stabilization platform, which uses gyroscope sensors and accelerometer sensors to measure the direction and acceleration of the missile. The computer uses the measurement values of the platform to determine the position of the missile and guide it along its trajectory towards the target. The other key components are the missile guidance device controller, which includes electronic equipment to support the gyroscope stabilization platform, as well as amplifiers to connect the computer to the rest of the missile. In this article, the components of guidance systems used before the early 2000s were carefully studied.
Fundamentally, the guidance computer will continuously compare the missile's position with the expected trajectory and generate appropriate steering commands to keep the missile in orbit. The following figure shows how to guide the engine nozzle to rotate the missile around its three axes: roll, pitch, and yaw. In the launch well, the roll angle (azimuth) is consistent with the target direction. The missile takes off vertically, and then gradually rotates along the pitch axis to tilt towards the target. During flight, adjustments along all three axes can keep the missile on target. Minuteman III has four rocket stages, so the guidance computer will discard each stage and ignite the next one in sequence.
stabilized platform
The principle of inertial navigation is to track the position of a missile by continuously measuring its acceleration. By integrating the acceleration, the velocity can be obtained. By integrating the speed, the position can be obtained. Inertial navigation is independent, which is a great advantage for missiles because enemies cannot interfere with your navigation. The difficult part is to measure acceleration and angle extremely accurately, as even small errors can multiply during missile flight. More specifically, the inertial guidance of the Minuteman missile is built around a gyro stabilized platform that maintains a fixed orientation and is mounted on two universal joints. The feedback from the gyroscope drives three torque motors to rotate the universal joint, ensuring that the stable platform maintains the same direction regardless of how the missile rotates.
The following figure shows the components of the stable platform, which are oriented roughly in the same direction as the figure above. Three accelerometers are installed on the stable platform to measure acceleration. The accelerometer is oriented along three vertical axes, so each accelerometer measures acceleration along one axis. (The accelerometer axis is not aligned with the platform axis; this will distribute the acceleration (mostly "upward") on the accelerometer, thereby improving accuracy.) Two alignment mirrors enable the stable platform to align with a precision device called an autocollimator, as described below. The gyro compass uses the Earth's rotation to accurately determine the north, providing backup alignment technology. Both the alignment mirror and the gyro compass can be rotated to precise angles, and the report is finally decoded by the parser.
When launching, the missile must be rotated inside the launch well to align with the target, and this angle is called the launch azimuth. This angle must be very precise, as even small angle errors can be greatly amplified during the missile's flight. Targeting missiles is a tedious process that requires the use of the North Star to determine the north. Due to the inability to see the North Star inside the launch shaft, a complex measurement technique was employed, using a surveyor's theodolite to measure the angle between the North Star and three concrete monuments outside the launch shaft. In the launch well, the nearest monument can be seen through the sight tube, allowing for precise angle measurements to be transmitted to the launch well. After multiple measurements in the launch well, a special device called an autocollimator is precisely positioned at 90 ° of the desired launch azimuth. The autocollimator emits a beam of light through the window on the side of the missile, which is reflected back from the mirror on the stable platform and then returns to the autocollimator. If the returned beam is not completely parallel, the auto collimator will send a signal to the guide missile, causing the stable platform to rotate as needed. The result of this process is that the stable platform is perfectly aligned with the target's angle.
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