Control dynamics
Somayeh Jamshidi; mehdi mirzaei
Abstract
This paper compares spacecraft attitude control in the presence of disturbance torque using an adaptive backstepping controller and an extended state observer-based backstepping controller. Firstly, the adaptive backstepping controller is designed, in which the unknown parameters in a specific disturbance ...
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This paper compares spacecraft attitude control in the presence of disturbance torque using an adaptive backstepping controller and an extended state observer-based backstepping controller. Firstly, the adaptive backstepping controller is designed, in which the unknown parameters in a specific disturbance model are estimated using an adaptive law so that the closed-loop system is stable. Afterward, the backstepping control based on the extended state observer is designed. In this approach, the standard backstepping controller is initially designed, and then disturbances with a completely unknown model are estimated by the extended state observer, and the disturbance is rejected by applying the feed-forward law. The simulation results for two different disturbance models show that the backstepping controller based on the extended state observer demonstrates very good results compared to the adaptive backstepping controller when no disturbance information is available. This is for the reason that the extended state observer estimates the uncertainties more accurately.
Control dynamics
Ehsan Maani miandoab; Ehsan Zabihian; Hossein Najafi
Abstract
In all types of satellites, communication systems are utilized for data transmission between satellite and ground stations. pointing the communication antennas to the ground is necessary for the correct mission transmission information. The vibration of the satellite antenna leads to deforming antenna ...
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In all types of satellites, communication systems are utilized for data transmission between satellite and ground stations. pointing the communication antennas to the ground is necessary for the correct mission transmission information. The vibration of the satellite antenna leads to deforming antenna pattern, creating noise and reducing connection quality. Moreover, working the attitude control actuators near the antenna's natural frequency leads to its resonance and large amplitude vibration in the antenna and satellite structure. Thus it is necessary to identify the satellite antenna dynamic behavior as natural frequency and damping ratio. In this paper, the satellite antenna is intended as a smart beam, based on the free vibration of clamped-free beam shape of satellite antenna and sensing its vibration by the piezoelectric sensor, its dynamic characteristic as damping and frequency is identified and verified by comparing the results with experimental ones. The considered mathematical model is very accurate and this model can be used to determine the dynamic behavior of the antenna in different satellite secondary structures.
Flight dynamics
Behrooz Raeisy; Fatemeh Ghofrani
Abstract
Various sensors can be used to attitude determination of a satellite, including the Earth Horizon Sensor. These sensors generally divided into two types: static and scanning types. In the static type, two- dimensional array or several linear arrays capture instantly the Earth image information to attitude ...
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Various sensors can be used to attitude determination of a satellite, including the Earth Horizon Sensor. These sensors generally divided into two types: static and scanning types. In the static type, two- dimensional array or several linear arrays capture instantly the Earth image information to attitude determination. In the scanning type sensors, a narrow-band optical beam mechanically sweeps a ring of space to find the crossing point of the beam to the Earth using a single spot detector. In this research, a new algorithm for a static earth horizon sensor with a two-dimensional array is presented. The algorithm does not need elevation of the sensor and this is the main advantage with respect to old ones. To extract the equations, a tangent vectors from the aperture of the pine- hole camera to the Earth is considered and this vector is extracted in two different body coordinates and base coordinates that are connected to the ground. By equating the two, an equation with three unknowns of pitch, roll and elevation is obtained. The equation is satisfied by each pixel on the Earth horizon Thus; the system of equations is formed by the number of the Earth horizon pixels in the camera image and parameters are estimated by numerical solving of the unknown equations.
