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  3. Inertial guidance is the name given to those types of systems which guide and keep track of the location of vehicles which are f

Inertial guidance is the name given to those types of systems which guide and keep track of the location of vehicles which are f

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问题      Inertial guidance is the name given to those types of systems which guide and keep track of the location of vehicles which are free to move in three dimensions. Vehicles which move only on a plane surface, such as ships or automobiles, require only an accurate compass, sextant, and clock to keep track of their present position. When a vehicle can travel up or down as well as north or east, it is much more difficult to fix its position. An inertial platform is used in inertial guidance to measure vehicle altitude and acceleration which are then integrated to provide position and velocity. The inertial platform consists of three gyroscopes and three accelerometers mounted in the inner gimbal of the four gimbal platform. The purpose of the inertial platform is to allow the vehicle to move in any direction about the inner gimbal containing the gyros and accelerometers, without disturbing or turning them from their original orientation. Thus the gyros and accelerometers do not mm when the vehicle turns so they sense altitude and acceleration with respect to their original inertial reference frame. If the acceleration is always known with respect to this original inertial reference frame, it can be integrated to provide velocity and then integrated again to provide distance. Thus the distance and velocity of the vehicle with respect to its starting point are known.
     Inertial guidance systems are used today in airplanes, submarines, and spacecraft. They display for the pilot his pitch, roll and yaw angles, his heading, his speed, and his latitude and longitude. These are very important items to have readily available, whether one is in a high speed vehicle with very low visibility due to poor weather, or in a spacecraft traveling in lunar orbit. The main features of inertial systems are that they are automatic and do not require any external information. Thus, the pilot does not have to feed in any information except the original position and altitude. Inertial systems serve a need on fast moving vehicles moving in a three dimensional plane, where position information is required by the pilot almost constantly.
The main purpose of this passage was
选项 A、to provide training information to new pilots and navigators.
B、to motivate people’s interest in space travel.
C、to explain how to use an inertial guidance system.
D、to describe the structure and importance of an inertial guidance system.
答案D
解析 本题考查主旨。文章的第一段和第二段分别描述了惯性制导系统的结构和重要性，故选项D 的内容正是这篇文章的主要目的。文章只是粗略地介绍了这种系统，不能用作训练新飞行员的材料，所以选项A 不正确；选项B 和C 不切题。
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