Innovative Structural and Mechanical Satellite Systems

Abstract

This thesis covers two topics within the field of satellite mechanical engineering. The first topic covered is the structural and thermal design and validation BeaverCube 2 Earth-imaging CubeSat. The second topic covered is the electromagnetics modeling and simulation of inductive spin drive for a novel magnetically levitated spherical control moment gyroscope for satellite attutide control.

For the first topic on BeaverCube 2, the key tasks were to design and assemble the structure of the CubeSat, ensure that subsystems maintain their operating temperatures on orbit, and validate the structural integrity of the CubeSat structure during launch. We design and manufacture 24 components that integrate all subsystems of BeaverCube 2 and meet the size requirements of a 3U (3 x (100cm3)) CubeSat, including a chassis, panels, payload structure and connectors for the stack of boards. Next, we ensure that all subsystems of the satellite do not exceed their temperature limits through analytical and simulated thermal analysis, showing that during worst case hot (70∘ beta angle) and worst case cold (70∘ beta angle) orbits, no subsystem reaches within 5 ∘C of its operating temperature limits. Finally, we analyze the structure of BeaverCube 2 to validate that the components can structurally withstand the 4-7 G linear accelerations, 13.5 rad/s radial accelerations, 1200 N side rail loads, and random vibration environment that may be experienced during launch [1]. The design is shown to be robust in these conditions, with margins of safety of stress ranging from 19.97 to 37.56 and deformation of the stack of circuit boards not exceeding 0.05 mm. The minimum frequencies of modes of vibration throughout the structure occur at 623 Hz, which is well above the allowed minimum mode of 100 Hz.

For the second topic of modeling the spherical control moment gyroscope, the key tasks were to design an actuation method using inductive drive and to experimentally validate a closed-loop controller for suspension of a prototype. For the actuation method, we present the electromagnetics modeling of an inductive spin drive, including analytical derivations of a bulk conductivity model and a skin current model. The analytical skin model shows that inductive drive with a rotating dipole magnetic field can generate a peak value 130 𝜇Nm of torque. We simulate both models with a rotating dipole and a rotating quadrupole stator drive configuration. Next, we successfully magnetically levitate a permanent magnet rotor prototype. We develop an analytical plant model for the system and a controller for closed-loop suspension with 40 Hz crossover and 20∘ phase margin, then we present preliminary experimental results.