No abstract

A potential function approach for attitude manoeuvres in the presence of constraints on admissible attitudes is implemented for a spacecraft controlled by a cluster of control moment gyroscopes. An angular velocity command derived from the potential function defined in the quaternion error vector space is directly implemented by means of a gimbal position command generation algorithm. The manoeuvre is performed by tracking the maximum angular momentum component, corresponding to the commanded angular velocity parallel to the eigenaxis that takes the spacecraft directly onto the desired final attitude. Corrections to the resulting desired angular velocity are implemented if the attitude gets close to one of the forbidden attitudes ('obstacles'), represented by peaks of the Lyapunov function in the attitude space. Numerical simulations are used to demonstrate the validity of the approach and to compare the overall performance with results reported in the literature.

A 35-year-old man, normotensive, nondiabetic, a nonsmoker, and army personnel, presented with swelling on the right side of the neck, which appeared only after exercise or with exertion for the previous 6 months. The swelling was not associated with pain or difficulty with breathing or swallowing. He had no history of foul breath, regurgitation of food, trauma to the neck, or any surgical procedure. On examination, the swelling was not visible; however, it appeared when performing the Valsalva maneuver. It was soft, cystic, nontender, and compressible on palpation and measured approximately 3 × 1.5 cm at maximum expansion ( Figure 1A). There was no bruit on auscultation, and the swelling was not transilluminant.