Dear Colleagues,

I am working on a simulation to propagate uncertainties of a spacecraft/ orbit due to imperfect knowledge of its initial state vector **and** disturbance force parameters. I am doing this in OREKIT 11.0

So far i have reproduced the FieldPropagation available in the GitLab tutorials but I changed it from a Keplerian orbit to a Cartesian orbit.

First of all, I would like to include the effect of uncertainties in the acceleration due to drag through the drag coefficient. My understanding, from a post of 2018 vintage from @luc is that I have to do the following:

- Define a custom acceleration method that “
*takes a FieldSpacecraftState and an array of Field elements that correspond to the current value of the force model parameters*.” - “
*Before propagation start you will have to set up the parameters for the force model…*” as shown by @Luc in the reply.

I am stuck because I don’t know how to implement step 1 in general and in particular for the acceleration due to drag. The IsotropicDrag class has methods that calculate both regular acceleration and a field one. Should I start by rewriting it?

Thank you for your help.

Bogdan