This thesis aims to design a reliable CubeSat platform, including the avionic subsystems that can sustain a high radiation environment for a mission having a lifetime of at least six months. The science instruments put stringent requirements on the platform to achieve and maintain the desired spin rate. The simulation background is set up in Systems Tool Kit (STK). A trade-off analysis for the Attitude and Orbit Control System (AOCS) of FORESAIL 2 was done, focusing on the actuators and their ability to offer the right amount of torque to fulfill the tether deployment. Mission design analyses were performed to conclude on the form factor of the CubeSat, its ability to generate power, its compliance with the Space Debris Mitigation (SDM) technical requirements, and the total radiation dose accumulated. It was found that a 6U form factor is preferred to allocate more space for each subsystem, alongside with generating enough power for the satellite to work in all modes wanted. The mission is compliant with European Cooperation for Space Standardization (ECSS) and International Organization for Standardization (ISO) standards if the CubeSat is to be launched in September 2022. To allow a threshold limit of 10 krads on the components of the satellite, a shielding wall of 7 mm should be implemented on the CubeSat’s structure. Major requirements for the designed mission were written to initialize the investigation on the sensors and actuators. The results showed that only a propulsion system provided the necessary angular momentum to deploy the tether. The lack of magnetic field makes magnetorquers almost unusable in the desired orbit, leaving reaction wheels as the only option remaining to assist the propulsion units. The different analyses and simulations led to a final AOCS configuration composed of five various sensors (Sun sensors, magnetometers, a GPS, an IMU, and housekeeping sensors) for the attitude determination. A propulsion system and reaction wheels will provide the necessary control over the satellite.