This thesis documents the design of an Attitude Determination and Control (ADC) subsystem for a 50 kg, low Earth orbiting space weather probe. The work emphasizes three major tasks: an architecture trade study, an analysis of the spinup maneuver, and a demonstration of the attitude determination method.
This document follows the systems engineering process used to design the ADC subsystem in the context of the Drag and Atmospheric Neutral Density Explorer (DANDE) mission. A number of missions relevant to the design of the DANDE spacecraft are reviewed. Some missions are similar to DANDE in their design constraints (e.g., student satellites), others serve as examples of successfully implemented design decisions.
A subsystem architecture trade study is then performed, leading to the key design decisions in the ADC subsystem: DANDE is a major-axis spinning spacecraft, spinning at 10 RMP about the orbit normal vector. DANDE attains its required spin rate in a closed loop algorithm and is aligned open loop. DANDE determines partial attitude using a magnetometer during spinup, then full spin axis determination is accomplished using Horizon Crossing Indicators. Active control is performed using magnetic torque rods, and nutation is passively damped with a fluid-filled ring.
Lower level requirements are then derived from the subsystem level requirements, and each actuator is designed according to these requirements.
An attitude simulation program is designed and implemented in MATLAB. This model is used to perform an analysis of the spinup maneuver, demonstrating that the subsystem is capable of spinning up the spacecraft from an unknown initial state within the time required. A baseline algorithm is tested, then refined to mitigate conditions that could prevent spinup from completing within the budgeted time.
To validate requirements on the attitude determination hardware, a spin axis determination scheme is presented, and a worst-case analysis performed. The study generates a reference attitude profile in software, models the sensor response to the environment, and calculates the determined attitude. This is compared against the reference attitude and used to find the minimum quantity of sensor data needed to meet the attitude determination requirements.