Mars Gravity Bio-Satellite:
6 Degree of Freedom Simulation
An extensible 6 degree of freedom (6 DOF) plant model of the Mars Gravity Biosatellite was created using the MATLab/Simulink version R14. The 6 DOF plant model is to be used as a tool for control algorithm design and optimization, prediction of the on-orbit dynamic performance of the satellite, and overall system design.
The environmental disturbance model includes the gravity gradient torque, the 1976 US standard atmosphere for calculating drag, and the World Geodetic S84 gravity model. The vehicle is modeled as a rigid body with constant mass properties. Variation of projected area in the direction of the spacecraft velocity vector based on orientation is included, along with the location, orientation, and performance specifications of the reaction thrusters.
The 6 DOF is designed in a way that allows users to easily improve the fidelity of the disturbance environment and vehicle model, quickly implement their own modules for parametric design studies, and test potential feedback control functions. In its current state, the simulation outputs the trajectory and orientation of the uncontrolled spacecraft in a variety of coordinate systems based on an initial circular orbit altitude of 370 km and inclination of 41.5 degrees. The simulation predicts an orbit decay of about 5 km over the 35 day mission, and a gravity gradient torque that is within a reasonable range.
The framework provided by the Stevens team will allow a team of summer interns of the Mars Gravity (MG) program to prepare the simulation for detailed system design studies and control design activity based on the needs of the MG Systems Engineering Team.