For the highly accurate calculation of orbit and attitude dynamics for dedicated scientific satellite missions a multi-purpose tool is developed. The range of applications given by the modular approach including a diversity of models and tools allows spanning the bridge between multiple engineering and science tasks. Application includes all mission phases such as spacecraft design, system verification, disturbance estimation and science signal modeling. Its high gravitational detail faithfully reflecting Earth¿ gravity anomalies and comprehensive environmental modeling has made the simulator particularly useful for application to science missions aiming to measure very small signals that easily can be falsified by effects that are not quantified with high precision. A strong focus is also laid on highly accurate modeling for the resolution of coupling interaction in a multi-body dynamics system. The current application includes post-mission data analysis of the science mission Gravity Probe B for validation purpose. The verification with science data represents the ultimate test towards simulator reliability and accuracy.