# State Propagation

In this section, the different stages of a typical simulation setup are described. TudatPy 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 properties (for both celestial and artificial bodies)

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

## Simulation & Output

Once all the settings are in place, the solution can be generated. All the details about this part, including the interpretation and availability of outputs, are explained in the page about Propagating Dynamics. For simulations in which the dynamics and associated variational equations are propagated, see the page on Propagating Variational Equations.