An inverse-free technique for attitude control of spacecraft using CMGs

Krishnan, S.; Vadali, Srinivas R.

doi:10.1016/s0094-5765(96)00152-x

Cited by 22 publications

(6 citation statements)

References 5 publications

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“…Different control strategies have been proposed to avoid these singularities or, at least, handle them efficiently (Kennel, 1970;Li and Bainum, 1990;Krishnan and Vadali, 1996;Kurokawa, 1997 A few researchers have suggested using double-gimbal CMGs to avoid singularities (Wie, 1998;Ahmed and Bernstein, 2002;Bolandi et al, 2006), a solution that is more costly and complex for the dynamical modeling view point (Wie, 1998). McMahon and Schaub (2010), Richie and Lappas (2007), and Jin and Hwang (2011) have designed variable-speed control moment gyroscopes to produce the exact effective torque required at the cost of increasing the difficulty of dynamical modelling and controller design.…”

Section: Control Moment Gyrosmentioning

confidence: 99%

Attitude Dynamics and Control of Satellites With Fluid Ring Actuators

Nobari

Misra

2012

Journal of Guidance, Control, and Dynamics

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Successful mission of a satellite depends on maintaining a fixed orientation with respect to the Earth. However, the attitude angles of a satellite can be perturbed because of various natural disturbance sources, such as the Earth's gravity gradient, solar radiation pressure, and the Earth's magnetic field. Modeling the attitude dynamics and developing a controller to stabilize the attitude motion are quite important steps in the design of satellites. Although several actuators exist to control the attitude motion, a novel type considered in the thesis, shows promise of producing a high torque to mass ratio. This potential justifies the in-depth study reported. The novel actuator in question consists of a ring containing fluid, whose flow is regulated by a pump. The control torque is produced due to the variation of the angular velocity of the fluid.In this thesis, first, a redundant actuator system composed of four fluid rings in a pyramidal configuration is studied. The dynamical model of the system is developed for a satellite travelling either in a circular or an elliptical orbit. The dynamical analysis of this system leads to an underdetermined system of nonlinear differential equations, whose solution without considering the control input (the torque produced by the pump pressure) shows that the fluid rings can damp out the attitude disturbances of a satellite in a circular orbit and the roll-yaw disturbances in an elliptical orbit. However, this passive damping effect is fairly slow; an active controller is hence designed in the next step. The effect of the failure of one fluid ring on the performance of the attitude control subsystem (ACS) of a satellite is also studied. It is observed that even in the case of failure of one fluid ring, the satellite can be stabilized by slight modification of the active controller.Later, a sliding mode controller is designed to cope with the uncertainties existing in the fluid model and in other parameters of the system. Although the results achieved are quite satisfactory, the chattering that exists in the steady response of the system is not i desirable; hence a switching controller consisting of a sliding mode and a PID control law is designed to eliminate this chattering effect.Next, the theoretical results obtained are validated by conducting several experiments. To this end, first, a setup with one fluid ring is designed and built. Here, a single fluid ring is attached to a disk so as to verify the controllability of the system with a fluid ring and also the validity of the theoretical model. Although the experimental results confirm the theory developed in this thesis, the large torque-to-mass ratio expected is revealed to be only possible at the cost of a quite high input voltage to the pumps regulating the flow. Therefore, two novel applications of fluid rings are proposed: as an actuator for spin stabilized satellites, or as an auxiliary actuator in satellites with magnetic torquers.Using fluid rings in spin stabilized satellites is proposed in the the...

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Section: Control Moment Gyrosmentioning

confidence: 99%

Attitude Dynamics and Control of Satellites With Fluid Ring Actuators

Nobari

Misra

2012

Journal of Guidance, Control, and Dynamics

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“…Angular momentum conservation constraints must be applied directly. It is possible to do this straightforwardly by employing active three-axis attitude stabilization by non-fuel expending wheelsmomentum wheels (MWs), reaction wheels (RWs) or control moment gyroscopes (CMGs) [62]-to compensate for the dynamic attitude reactions based on computations of the reaction forces and moments applied at the base of the robotic manipulators. Such spinning wheels effectively redistribute angular momentum within the spacecraft.…”

Section: Freeflying Robotic Kinematic-dynamic Problem Formulationmentioning

confidence: 99%

An engineering approach to the dynamic control of space robotic on-orbit servicers

Ellery¹

2004

Proceedings of the Institution of Mechanical Engineers, Part G:

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Robotic on-orbit servicing is the key to the commercial development of a space robotics infrastructure. A major technical difficulty has been the problem of control of the robotic manipulators mounted onto a freeflying platform in space. The problem of control is directly related to the fact that manipulator motions exert reaction effects on the mounting spacecraft. A solution to this problem is outlined-one in which no fuel is expended and that demands no excessive computational resources that would otherwise preclude real-time performance.

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“…Singularities are incurred when the gimbal angles lock up and the CMG can no longer generate torque as the CMG Jacobian inversion loses rank. Singularities are avoided through the use of a steering law applied to four single gimbal CMGs in a pyramid configuration (17) . They have seen service in large, manned spacecraft such as Skylab, Mir and ISS by virtue of their large torque capabilities and in the US military Key Hole satellites which has a re-tasking and re-orienting requirement.…”

Section: Attitude Control Systemsmentioning

confidence: 99%

Robotic in-orbit servicers — the need for control moment gyroscopes for attitude control

Ellery¹

2004

Aeronaut. j.

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Robotic in-orbit servicing has yet to be realised due to a number of technical difficulties. One such difficulty is analysed here. The requirement for force control in robotic manipulation imposes significant design requirements on space robots by virtue of the lack of a mounting platform to react against external forces and torques. The spacecraft attitude control system must effectively serve the same role as the ground in terrestrial manipulators. The reaction torques imposed on the spacecraft due to the manipulators is high when force control is used in grappling targets in space, limiting the choice of attititude actuator to control moment gyroscopes. NOMENCLATUREgeneralised external cartesian forces acting on the end effector F T total force acting at manipulator base (x 0 y 0 z 0 ) with respect to base coordinates i link number from 0 to n I i inertia matrix of link imass of each component rigid body i comprising the system m 0 mass of the spacecraft bus m n+1 mass of manipulator target total mass of the system N ci total moment about link i centre of mass N T total moments acting at manipulator base (x 0 y 0 z 0 ) with respect to base coordinates N r total reaction torque about centre of mass of spacecraft bus with respect to inertial co-ordinates n number of serial rigid body links n+1 payload link p i-1 position of link i origin with respect to base coordinates p ci location of centre of mass of link i with respect to base co-ordinates p* position of end effector with respect to inertial coordinates p* ci position of link i centre of mass with respect to inertial co-ordinates p* cm location of centre of mass of total robot/spacecraft system with respect to inertial co-ordinates q=(nsap) T generalised cartesian position of end effector with respect to base co-ordinates q · =(vw) T generalised cartesian velocity of end effector with respect to base co-ordinates q ·· = (v · w · ) T generalised cartesian acceleration of end effector R i =(n i s i a i ) 3×3 direction cosine matrix of each link with respect to base co-ordinates R 0 attitude of spacecraft with respect to inertial co-ordinates r i =(p i-1 -p ci ) vectorial distance from origin of link i to the centre of mass of link i r ci =(p i-1 -p ci+1 ) distance between centres of mass of adjacent links with respect to base co-ordinates r c0 position of spacecraft centre of mass with respect to inertial co-ordinates THE AERONAUTICAL JOURNAL

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An inverse-free technique for attitude control of spacecraft using CMGs

Cited by 22 publications

References 5 publications

Attitude Dynamics and Control of Satellites With Fluid Ring Actuators

Attitude Dynamics and Control of Satellites With Fluid Ring Actuators

An engineering approach to the dynamic control of space robotic on-orbit servicers

Robotic in-orbit servicers — the need for control moment gyroscopes for attitude control

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