The Impact of Gravity-Gradient Stabilization on ADCS Efficiency and Design Optimization in CubeSats

From the perspective of attitude dynamics, a rigid body in orbit is subjected to various external torques and disturbances that can significantly impact its orientation and, consequently, a satellite's overall mission performance and sub-systems. Due to its inherent Earth-pointing capability, gravity-gradient stabilization emerges as a valuable passive attitude control method for some missions. A proper mechanical design of a CubeSat can leverage gravity-gradient stabilization, offering notable improvements in control efficiency and indirect benefits, such as reduced weight, simpler design, and lower power consumption. The CubeSat Design Specifications (CDS) allows the body to achieve inertia ratios in all gravity-gradient stability map regions - Lagrange, Debra-Delp, Pitch, Roll-Yaw, and Unstable - which gives the mechanical project freedom to seek a design with better stability features. This paper investigates and compares the effects of gravity-gradient stabilization with two commonly used active control methods: magnetorquers and reaction wheels within the CubeSat standard. The study utilizes Python-based simulations to model the satellite's attitude in a circular Low Earth Orbit (LEO) at 500 km altitude. Scenarios are evaluated for CubeSats equipped with active Attitude Determination and Control Systems (ADCS) - magnetorquers and reaction wheels - independently and in conjunction with gravity-gradient stabilization, across different CubeSat sizes. The analysis focuses on the performance of ADCS, particularly in control action and power consumption, while also discussing implications for weight and design optimization. The findings of this work aim to assess the potential advantages of integrating gravity-gradient stabilization into the CubeSat design, highlighting its impact on control performance and overall satellite efficiency.