PHOENIX satellite is a 2kg CubeSat that is being developed as a part of the FP7 international QB50 project. QB50 is an international network of 50 CubeSats for multi-point, in-situ measurements in the largely-unexplored lower thermosphere and for re-entry research. The CubeSat constellation will be launched in the first half of 2015 into a circular orbit at 320 km altitude, inclination 79°. A unique challenge of the QB50/PHOENIX satellite is the attitude control requirements. The satellite is required to align its body long axis along the velocity vector so that the scientific instrument onboard the satellite can measure in-situ data for the analysis of the lower thermosphere. The configuration is less susceptible to aerodynamic drag and torque which may then destabilize the satellite and reduce the mission life. To design the attitude control system, an in-depth understanding and modeling of the aerodynamic density model is essential. The paper outlines the development of the attitude propagator by accounting for environmental forces and torques in a comprehensive and effective manner. The simulation environment then serves as a platform for the verification of attitude control system.