APC Function and Flowchart

APC is a very complicated numerical integrator with a lot of moving parts. This wiki is intended to maintain a human readable description of APC and how each component functions.

Function: picard_chebyshev_propagator()

This is one of the outerlayers of the numerical integrator proper and runs the main propagation while loop. This loop will continue running until the integrator has passed the final desired time, or the integrator has determined that some condition has occurred to end the integration early (such as the propagated position falling below 0 altitude.)

The initial portion of the function (before the loop) is for the function to access the stored variables from the orbit class object that are necessary for propagation. Next the function accesses the initial state (t=0) and assigns it to the orbit object as z0_seg. From here the main propagation loop begins.

Propagation loop

There are X main segments of the overall propagator loop that are performed on each segment until the propagation loop ends.

A. Calculate Chebyshev Nodes

B. Keplerian Warm Start

C. Picard Iteration

D. ASSIGN NEXT SEGMENT INITIAL CONDITIONS

E. REOSCULATE PERIGEE