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Spacecraft Actuators
Published in Yaguang Yang, Spacecraft Modeling, Attitude Determination, and Control Quaternion-based Approach, 2019
Thrusters are another type of actuators. They can be used for attitude control for any spacecraft. Fuels have to be loaded to thrusters and fuel budget is a major limitation on the use of thrusters. Thrusters use different propellants, such as cold gas propellant, solid chemical propellant, liquid chemical propellant, and electrical propellant. The same basic equation of propulsion holds for all kinds of propellants. The thrust force F is related to the exhaust velocity Ve relative to the satellite body, the fuel consumption rate dmdt, the gas and ambient pressures Pe and Pa, and the area of the nozzle exit Ae. More specifically (see [181]), () F=Vedmdt+Ae(Pe−Pa)
Satellites
Published in Mohammad Razani, Information, Communication, and Space Technology, 2017
Although each satellite varies in shape, size, and mission, they all have something in common. Each satellite needs a power source, has instrumentation consisting of scientific and engineering sensors that measure changes in the satellite and its surroundings, and has special propulsion systems aboard called thrusters to push the satellite into its desired orbit. Small thrusters provide attitude, altitude, and propulsion control to modify and stabilize the satellite’s position in space. Guidance and control sensors keep the satellite on its proper course, and sensors such as horizon seekers, star trackers, and sun seekers help determine the satellite’s positions. Altitude (Log scale)
Rocket Engines
Published in Ahmed F. El-Sayed, Aircraft Propulsion and Gas Turbine Engines, 2017
Electric propulsion is defined as “the acceleration of gases for spacecraft propulsion by electric heating and/or by electric and magnetic body forces” [13]. Electric thrusters typically use much less propellant than chemical rockets because they have a higher exhaust speed and higher specific impulse over long periods compared with chemical rockets. Thus, electric propulsion can work better than chemical rockets for deep space missions. However, it is not usually suitable for launches from the Earth’s surface, because of its very small thrust.
Energy-efficient control of a thruster-assisted position mooring system using neural Q-learning techniques
Published in Ships and Offshore Structures, 2021
Huacheng He, Lei Wang, Xuefeng Wang, Bo Li, Shengwen Xu
Four control modes of operation for surge, sway and yaw can be defined for a PM system, including manual, damping, setpoint and tracking control (Strand et al. 1998). Setpoint control keeps the position of a marine structure at a specific location, and the thrusters provide both damping and restoring forces to prevent the marine structure from drifting away. In general, the structure of a PM control system can be divided into three levels: decision making level, plant control level and actuator control level, as shown in Figure 1. The high-level decision maker produces the feasible setpoints for the feedback controller at the plant control level to follow, which generates the control forces. The thrust allocation is responsible for distributing the commanded force into each individual thruster, which is controlled by its own actuator control system.