The problem of attitude control can be expressed in terms of Euler axis/angle, where a nominal Euler axis rotation directly takes the spacecraft from an initial attitude to a desired final one. When three independent control torques are not available, e.g. when magnetic torquers are the only attitude effectors, the nominal rotation cannot be performed. Nonetheless a feasible rotation around a 'non-nominal' axis allows exact pointing of a given body-fixed axis towards any prescribed target direction. This geometric property results into a control law that enables magnetically actuated spacecraft to align and spin around a desired direction. When, in addition, the activation of a momentum wheel along the spinning axis allows complete alignment with the desired reference, the problem of saturation arises, for example in the presence of drag disturbance torque. A second magnetic law enables the wheel to never saturate, avoiding the classical periodic desaturation manoeuvres.
Magnetic-only spacecraft attitude control: a non-nominal Euler axis approach
AVANZINI, Giulio;
2011-01-01
Abstract
The problem of attitude control can be expressed in terms of Euler axis/angle, where a nominal Euler axis rotation directly takes the spacecraft from an initial attitude to a desired final one. When three independent control torques are not available, e.g. when magnetic torquers are the only attitude effectors, the nominal rotation cannot be performed. Nonetheless a feasible rotation around a 'non-nominal' axis allows exact pointing of a given body-fixed axis towards any prescribed target direction. This geometric property results into a control law that enables magnetically actuated spacecraft to align and spin around a desired direction. When, in addition, the activation of a momentum wheel along the spinning axis allows complete alignment with the desired reference, the problem of saturation arises, for example in the presence of drag disturbance torque. A second magnetic law enables the wheel to never saturate, avoiding the classical periodic desaturation manoeuvres.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
