The document discusses estimating a satellite's drag coefficient in low Earth orbit using GPS pseudorange measurements and orbit determination. It aims to compare measurements of the drag coefficient Cd for different initial satellite conditions. Dynamics include gravity and drag modeled with a Runge-Kutta integrator. Pseudoranges from GPS satellites are used for navigation. Orbit determination solves variational equations to estimate Cd and other parameters by minimizing the difference between measured and predicted pseudoranges. Testing different initial conditions showed the estimation does not change dramatically.