# State Propagation

In this section, the different stages and options of a typical simulation setup for a numerical state propagation are described. Tudat is organized as shown in the figure below.

## Inputs

There are two distinct input types necessary to create a simulation:

Environment Setup: physical modeling of environment and system properties (for both celestial and artificial bodies)

Propagation Setup: formulation of the differential eq uations representing the problem, and the method to solve them

## Simulation & Output

Once all the settings are in place, the numerical solution to the equations of motion can be generated. All the details about this part, including the interpretation and availability of outputs, are explained in the following pages:

Propagating Dynamics: For simulations in which only the dynamics are propagated

Propagating Variational Equations For simulations in which the dynamics and associated variational equations are propagated