Copernicus Imaging Microwave Radiometer (CIMR): System Aspects and Technological Challenges

Modeling and Attitude Control of Spacecraft With an Unbalanced Rotating Device

“…, ∀λ ∈ To finally conclude that the controller (32) solves Problem 1, we need to show that the closed-loop solutions are GUUB for any inertial unbalance d. To this aim, we refer to the Lyapunov function V 1 := 1 2 |R e | 2 K R + 1 2 ω J s (Q)ω and compute its Lie derivative along the closed-loop system (7), (34), (35), which can be bounded as follows:…”

“…We report a numerical example to show the effectiveness of the proposed control design in a mission scenario in which the attitude of the multi-body spacecraft must be stabilized starting from perturbed initial conditions. The simulation data are inspired by the CIMR mission [1]: the spacecraft operates along an almost polar, slightly elliptical orbit (i = 98.7deg, e = 0.0011), with an altitude of 824.6km, a corresponding orbital period of T = 6074.7s and an orbital rate ω o = 0.001rad/s. The payload is rotating at Ω = 1 rad/s.…”

“…In this condition, it is reasonable to neglect τ u for control design purposes. 1 As a byproduct of this assumption, the dynamical system takes a cascade structure, wherein the attitude subsystem ( 6), (25) perturbs the position subsystem (10), (24). The control design for the attitude dynamics, being the upper subsystem in the cascade, can be carried out independently.…”

“…In recent years there has been an increasing interest in space missions that require the use of spacecraft endowed with rotating devices, such as large antenna reflectors, to achieve high Earth observation capabilities [1], [2]. These systems demand a careful design since the presence of unavoidable inertial asymmetries in the rotating devices give rise to internal forces and torques in the spacecraft, leading to a reduction of pointing accuracy and stability, and undermining the outcome of the mission itself.…”

“…The first option is interesting because it would solve the problem just by using suitable control laws. On the other hand, it would be inefficient and risky in case of large unbalances: the attitude control system would waste a lot of power in compensating the unbalance 1 Davide Invernizzi is with Dipartimento di Scienze e Tecnologie Aerospaziali, Politecnico di Milano, Via La Masa 34, 20156 Milano, Italy {davide.invernizzi}@polimi.it torque and the prolonged application of interface loads could damage the bearings of the motor sustaining the payload rotation. The second option would require carrying additional mass onboard the spacecraft.…”