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Spacecraft and Orbit Determination
Introduction to Physics-Based Control Methods
Spacecraft control suffers from inter-axis coupling regardless of control methodology due to the physics that dominate their motion. Feedback control is used to robustly reject disturbances, but is complicated by this coupling. Other sources of disturbances include zero-virtual references associated with cascaded control loop topology, back-emf associate with inner loop electronics, poorly modeled or un-modeled dynamics, and external disturbances (e.g. magnetic, aerodynamic, etc.). As pointing requirements have become more stringent to accomplish missions in space, decoupling dynamic disturbance torques is an attractive solution provided by the physics-based control design methodology. Promising approaches include elimination of virtual-zero references, manipulated input decoupling, which can be augmented with disturbance input decoupling supported by sensor replacement. This chapter introduces these methods of physics-based control. Physics based control is a method that seeks to significantly incorporate the dominant physics of the problem to be controlled into the control design. Some components of the methods include…
Introduction to Middle Atmosphere: Discharge Phenomena
The layer between 10 and 100 km altitude in the Earth atmosphere is generally categorized as the middle atmosphere (Brasseur & Solomon, 1986). The boosting development of rocket and satellite technologies during the past 50 years has made it possible to directly probe the middle atmosphere (Brasseur & Solomon, 1986). Recently, transient luminous events (TLEs) open up another window; through observing the discharge phenomena in the middle atmosphere from both the ground and the space, the physical processes in this region can be inferred. Besides the present satellite missions (ISUAL, Tatiana-2, SPRITE-SAT, Chibis-M mission), future orbit missions include JEM-GLIMS, ASIM, TARANIS will soon join the efforts. These space missions provide the unique platforms to explore the plasma chemistry and atmospheric electricity in the middle atmosphere,…
Introduction to Spacecraft Relative Orbital Motion
The relative orbital motion problem may now be considered classic, because of so many scientific papers written on this subject in the last few decades. This problem is also quite important, due to its numerous applications: spacecraft formation flying, rendezvous operations, distributed spacecraft missions. The model of the relative motion consists in two spacecraft flying in Keplerian orbits due to the influence of the same gravitational attraction center (see Fig. 1). The main problem is to determine the position and velocity vectors of the Deputy satellite with respect to a reference frame originated in the Leader satellite center of mass. This non-inertial reference frame, traditionally named LVLH (Local-Vertical-Local-Horizontal) is chosen as follows: the Cx axis has the same orientation as the position vector of the Leader with respect to an inertial reference frame originated in the attraction center; the Cz axis has the same orientation as the Leader orbit angular momentum; the Cy axis completes a right-handed frame. Consider ω = ω(t) the angular velocity of the LVLH reference frame with respect to an inertial frame originated in the attraction center. By denoting rc the Leader position vector with respect to an inertial frame originated in O (the attraction center), fc = fc (t) the true anomaly, ec the eccentricity and pc the semilatus rectum of the Leader orbit, it follows that vector ω has the expression:…
